the dim state and must be driven to one of the other three states by voltage levels at the probe tip. The
threshold. The LED is usually dim for voltages between the logic "1" and logic "0" thresholds and for
open circuits.
Q-7. The LED lamps of a typical logic probe are normally in what state?
Another logic circuit analysis technique is useful with the logic probe. This technique is to run the
RESET, START, STOP, SHIFT, TRANSFER, or CLOCK. Questions such as "Is the counter operating?"
activity is present.
This ends our discussion on logic probes. Now, we'll study another piece of electronics test
equipment that is used in evaluating integrated circuits, the HUNTRON TRACKER 2000.
5-22
component level. Another device you can use is the Huntron Tracker 2000. It is a very versatile electronic
de-energized circuit cards quickly and safely without requiring the removal of component leads. The unit
provides a built-in display that allows you to visually analyze the component under test conditions.
Before connecting the Huntron Tracker 2000, you must first secure all power, then discharge all high-voltage capacitors.
within this chapter. We will therefore concentrate our discussion only to the externally accessible
features. To find information on internal controls and indicators, you should review the most current
technical manual with up-to-date changes entered for the unit being used.
The front-panel (figure 5-18) design allows you to easily select the desired function. All the push
to show the functions that are active, by lighting up when active. A detailed description of each item on
the front panel is provided in table 5-3.
5-23
Table 5-3.—Front-Panel Controls and Connectors
NO. NAME DESCRIPTION
1 HORIZ control When adjusted this controls the horizontal position of the CRT display.
2 VERT control When adjusted, this controls the vertical position of the CRT display.
When this is rotated clockwise, the power is turned on. Further adjustment
of the switch controls the intensity of the CRT display. When it is rotated
fully counterclockwise, the power is turned off.
4 TRACE ROTATE control When adjusted, this controls the trace rotation of the CRT.
5 CRT display This displays the signatures produced by the unit.
ranges: LOW, MEDIUM 1, MEDIUM 2, and HIGH.
ranges from low to high. The speed of the scanning is determined by the
CRT.
9 CHANNEL A test plug This is a fused test lead connector that is active when channel A is selected.
All test lead connectors accept standard banana plugs.
channel A and channel B. The speed of this is determined by the RATE
control (item 14).
reference point for channel A and channel B.
CRT.
13 CHANNEL B test plug This is a fused test lead connector that is active when channel B is selected.
14 RATE control This controls the channel alteration and/or the range scanning.
15 G1 and G2 plugs These are used for the pulse generator output test leads.
16 WIDTH control This controls the duty cycle of the pulse generator.
17 LEVEL control This controls the amplitude of the internal pulse generator.
generator: positive (+), negative () or PULSE/DC.
frequencies: 50/60 Hz, 400 Hz, 2000 Hz.
The CRT display (figure 5-19) is used to view the signature of the component under test. The display
has a graticule consisting of a horizontal and vertical axes. The horizontal axis is used to represent voltage
with the vertical axis being used to represent current. The axes divide the display into four quadrants.
Each quadrant displays a different portion of the signature for the component under test.
5-24
• Quadrant 1 displays positive voltage and positive current.
• Quadrant 2 displays negative voltage and positive current.
• Quadrant 3 displays negative voltage and negative current.
• Quadrant 4 displays positive voltage and negative current.
Q-8. On the CRT display, what information is displayed in Quadrant 4?
estimate the voltage at which changes occur in the signature for the component being tested. The
associated approximate horizontal sensitivities for each range are:
• High = 15.0 Volts/Div.
• Medium 2 = 5.0 Volts/Div.
• Medium 1 = 3.75 Volts/Div.
• Low = 2.5 Volts/Div.
The back panel (figure 5-20) provides three additional controls and connectors. One is the accessory
HSR410. Next, is the power cord connector used to provide the required ac line voltage used to power the
unit. The last item found on the back panel is the FOCUS control; this controls the focus for the front-
panel CRT display.
5-25
The following sections explain how to use most of the front- and back-panel controls and connectors.
Each control and connector has already been briefly described. To review this information, refer to figure
5-18 and table 5-3.
First, turn the POWER/INTENSITY knob located on the front panel to the clockwise, on, position.
50/60 Hz, low range, and pulse/DC.
displayed. This is done by first turning the INTENSITY control to a level comfortable for the eye, and
then adjusting the FOCUS control (back panel) for the narrowest possible trace.
signature is in during a change. With a short circuit applied to channel A (connect a cable between jack A
vertical axis. Then, adjust the HORIZ (horizontal) control until the vertical trace is as close to even with
the vertical axis as possible.
Q-9. When aligning the trace with a short applied to channel A, which control should be adjusted to bring the trace parallel to the vertical axis?
(vertical) control until the horizontal trace is as close to even with the horizontal axis as possible. Once
set, these adjustments should not need readjusting during the unit's operation. However, remember that
each time the unit is used, this process will need to be repeated.
Four impedance ranges (LOW, MED 1, MED 2, and HIGH) can be selected on the Tracker 2000.
These ranges will become active when the appropriate front-panel button is pressed. To obtain the most
the two medium ranges (medium 1 or medium 2). If the display appears to be an open (horizontal trace),
then the next higher range should be selected to get a more accurate signature for analysis. If the display
appears to be a short (vertical trace), then the next lower range should be selected.
5-26
at a speed set by the technician using the RATE control knob. This allows the user to keep his or her
analysis. The HIGH LOCKOUT, when selected by the technician, prevents the unit from functioning in
the HIGH range in either the manual or AUTO mode.
or channel B (test probes connected to B and COM jacks) push button on the front panel. When using a
test lead into the common test jack. When testing a component, you should connect the red probe to the
positive terminal and the black probe to the negative terminal of the component under test. Following this
correct quadrants of the CRT display.
channel B. This allows you to easily compare two components or the same test points on two circuit
boards. You select the ALT mode by pressing the ALT push button on the front panel. The rate of
panel. You will find that the ALT mode feature is very useful for comparing a known good component
with the same type of component that is of unknown quality.
under test. This test mode uses the supplied common test leads to connect two equivalent points on the
boards to the common test jack. Note that the black probe is now being used in the channel B jack rather
than the COM jack. When the technician uses the ALT and AUTO features together, each channel is
displayed before the range selection will change. Figure 5-22 shows the sequence of these changes.
5-27
provided by pressing the appropriate front-panel push button. During most troubleshooting evolutions, the
50/60 Hz test signal is the best to start with. The 400 Hz and 2000 hz frequencies are generally used to
view small amounts of capacitance or large amounts of inductance.
A built-in pulse generator is also provided with the Tracker 2000. It allows the technician to do
dynamic, in-circuit testing of certain devices in their active mode. In addition to using the red and black
with one of the blue micro clips provided with the unit. The pulse generator has two outputs (G1 and G2
jacks) so that three devices can also be tested in the ALT (alternate) mode. Figure 5-23 shows a way of
connecting the unit in the ALT mode using the pulse generator.
shown in figure 5-24. First, the technician must select the PULSE mode or DC mode using the
PULSE/DC button located on the front panel. In the PULSE mode, the PULSE/DC LED flashes at a slow
rate. While in the DC mode, this LED will be continuously on.
5-28
negative (−) push buttons. All three buttons only function in a push-on/push-off mode and will only
interact with each other to avoid the NOT ALLOWED state found in figure 5-24.
LEVEL and WIDTH controls. The LEVEL control is used to vary the magnitude of the output amplitude
from zero to 5 volts (peak or DC). During the PULSE mode, the WIDTH control will adjust the cycle of
the pulse output from low to 50 percent maximum (square wave).
in the pulse frequency being equal to the selected test signal frequency.
The end of the pulse is determined by the WIDTH control setting, which determines the cycle length.
The WIDTH control, however, has no effect when the DC mode is selected.
There are six major sections in the Tracker 2000, as shown in the block diagram in figure 5-25. The
generator mode according to the front-panel buttons pushed by the technician. The oscillator provides the
test signal that is used by the signal and pulse generator sections. In the signal section, the test jacks are
vertical signals used by the CRT section to produce a component signature on the display. The pulse
generator provides an added source for testing three additional terminal devices. The power supply
produces all the required voltages needed to operate the Tracker 2000.
5-29
The control logic senses which button is pushed on the front panel. Since the buttons are the
sections.
the power is secured. The HIGH LOCKOUT and PULSE GENERATOR push buttons are the only ones
that require repetitive pressing to be turned on or off.
The channel relay is controlled by CHANNEL buttons A, ALT, and B. The relay is a single-pole,
double-throw type and is de-energized for channel A and energized for channel B. If CHANNEL A is
B selected. When the ALT button is pressed, another control line is set, which enables an internal clock to
toggle the channel relay on and off, causing the unit to alternate between channels A and B.
The internal clock is controlled by the RATE control knob on the front panel. When the ALT mode
is active, the LEDs within the A and B buttons flash alternately, and the ALT LED is on continuously.
become active.
and the pulse generator. The RANGE buttons (LOW, MED 1, MED 2, and HIGH) control four relays in
the signal section that select the appropriate terminal characteristics for each impedance range (table 5-4).
5-30
Table 5-4.—Terminal Characteristics for Impedance ranges
High 60 0.57
Medium 2 20 0.53
Medium 1 15 8.5
automatically by using the AUTO function. When AUTO is activated, the control logic will follow the
sequence LOW, MED 1, MED 2, and HIGH over and over if HIGH LOCKOUT is off. The current active
range is always indicated by the LED for the range selected. The AUTO mode will stay active until you
select a particular range by pressing its associated button. While AUTO is active, the AUTO LED is
continuously on.
The speed at which the ranges are scanned is controlled by the front-panel RATE control knob. This
allows you to adjust the time each range is displayed for signature analysis on the CRT display. If AUTO
with ALT having priority. This is done so that the two channels can be compared to each other within one
range before the next range is selected (figure 5-26).
volts peak vice 60 volts peak. When you select the manual mode (AUTO off), activating the HIGH
LOCKOUT prevents the HIGH range from being selected. If the HIGH range is active when the HIGH
and become active. When you select the AUTO mode, the RANGE sequence with the HIGH LOCKOUT
AUTO mode is stopped.
that change the polarity and output type of the pulse generator.
5-31
The oscillator produces a constant amplitude, low distortion sine wave test signal. The frequency of
(400 Hz and 2000 Hz). The variable frequency depends on the input power line used for the Tracker
2000; a 50-Hz line produces a 50-Hz test signal, and a 60-Hz line produces a 60-Hz test signal. If a 400-
Hz power line is used, an 80-Hz test signal is provided. This versatility is built in to ensure you will
always have low, medium, and high frequencies to work with.
The signal section is considered to be the heart of the Tracker 2000. In this section, the signal from
the oscillator is applied across two terminals of a device being tested via the front-panel jacks.
terminals. The current flow causes a vertical deflection of the trace on the CRT display, while the voltage
drop across the device causes a horizontal deflection of the trace on the CRT display. By combining
these, the current-voltage signature of the device being tested is displayed on the CRT.
source (Vs) with a series output impedance (Zs). An equivalent circuit of the signal section is shown in
figure 5-27. As you can see, the figure also shows how the terminal voltage affects the horizontal
plates through current sensing point I.
terminals. In all ranges, this is represented by a straight horizontal trace from left to right on the CRT
display, as seen in figure 5-28 view A. When a short occurs, maximum current flows through the
terminals, and the voltage drop is considered to be zero. This occurs in all ranges and is represented by a
straight vertical trace from top to bottom of the CRT display, as seen in figure 5-28 view B.
5-32
of the device under test. The normal two-terminal mode of testing can be considered a static test, since
devices with three or more terminals are not tested in their active mode. However, with the pulse
generator, an in-circuit active test is possible.
pulse. When positive (+) is enabled, a positive-going zero crossing triggers a positive pulse. When
negative (−) is enabled, a negative-going zero crossing triggers a negative pulse. If both are enabled, then
both positive and negative pulses are produced on alternate crossings (composite pulses). Once a pulse is
triggered, its duration is set by the WIDTH control knob. Figure 5-29 shows the waveforms for three
pulse polarity types at various settings of the WIDTH control.
on the pulse polarity selected. When an open circuit is present, a maximum output of 5 volts peak-to-peak
5-33
active.
Q-10. What minimum/maximum voltage level can be attained in the pulse generator section by adjusting the LEVEL control?
In the DC mode, a zero-to-5-volts DC level is produced at G1 and G2 on the front panel. The
polarity of the level is controlled by the positive and negative buttons. By pressing the positive button,
you enable a positive DC output and disable the negative button. By pressing the negative button, you
enable a negative DC voltage only if the positive button is in the off position. The WIDTH control knob
has no effect in the DC mode of operation.
levels needed by the deflection plates in the CRT. The HORIZ (horizontal) and VERT (vertical) controls
on the front panel adjust the position of the CRT trace. The TRACE ROTATE control on the front panel
is used to adjust the short circuit vertical trace to be parallel with the vertical axis on the CRT graticule.
brightness and clarity of the trace. The front-panel INTENSITY control is the primary way to adjust the
visual quality of the trace. FOCUS is located on the back panel and is used as your trimming adjustment.
Astigmatism is an internal adjustment and is set at the factory.
POWER/INTENSITY knob located on the front panel. Once power is turned on, the power supply
provides 12 V dc (nominal) and ±5 V dc (regulated) for normal circuit operational use in the oscillator, pulse generator, signal, and control logic sections of the Tracker 2000.
The other outputs from the power supply are provided to the CRT display section. The CRT is
provided with a filament voltage of 6.3 Vrms, +180 V dc for the deflection driver circuits, and a regulated
−1320 V dc for the CRT acceleration voltage.
examples of different components with values and their associated displays. Because of the large number
of different values that can be given to any component, this section will present only a few.
counterclockwise direction around its center axis from an open circuit position. The degree of rotation is
directly related to the resistance value. The higher the value, the less rotation will be observed.
LOW RANGE.The low range is designed to test for resistance values between 1Ω and 1K. Figure 5-30 shows the effect of resistance on the angle of rotation in low range. A 1Ω resistor causes almost 90º of rotation, and a 50Ω resistor produces a 45º rotation. A 400Ω resistor causes a very small rotation angle. Resistors lower than 1Ω will appear as a short circuit (vertical trace), and resistance values above 400Ω will look like an open circuit (horizontal trace).
5-34
MEDIUM 1 RANGE.The medium 1 range is designed to test for resistance values between 50Ω and 10KΩ. Figure 5-31 shows the signatures for a 50Ω resistor, a 1KΩ resistor, and a 10KΩ resistor using the medium 1 range. Resistors that are smaller than 50Ω display a signature that is almost a vertical line. A 1KΩ resistor causes a change in the angle of rotation of 45º, whereas the display of a 10KΩ resistor shows only a slight rotation. Resistance values under test higher than 10KΩ produce a signature with such a small rotation angle that it almost appears to be a horizontal line.
Q-11. Medium 1 range is designed to check what resistance values?
MEDIUM 2 RANGE.The medium 2 range is designed to test for resistance values between 1KΩ and 200KΩ Figure 5-32 shows the signatures for a 1KΩ resistor, a 15KΩ resistor, and a 200KΩ resistor in the medium 2 range. Resistance values that are smaller than 1KΩ will appear to be almost a vertical line. A 15KΩ resistor causes a change in the angle of rotation of 45º, whereas the display for a 200KΩ resistor shows only a slight rotation. When resistance values being tested are higher than 200KΩ, the displayed signature that they produce will have such a small rotation that it appears to be almost a
horizontal line.
5-35
HIGH RANGE.The high range is designed to test resistance values between 3KΩ and 1MΩ. Figure 5-33 shows the signatures that would be displayed for a 3KΩ resistor, a 50KΩ resistor, and a 1MΩ resistor using the high range. Resistors that are smaller than 3KΩ will appear to be almost a vertical line. A 50KΩ resistor will cause a change in the angle of rotation of 45º, whereas the display for a 1MΩ resistor shows only a slight rotation that is very close to a horizontal line. Resistance values higher than
1MΩ will produce such a small rotation that it appears to be a horizontal line.
When you test capacitors, the signature will be displayed as an ellipse. The size and shape of the
ellipse depend on the capacitor value, test signal frequency, and the selected impedance range. Figure 5-
34 shows the signature of a 0.22µF capacitor in each of the 12 combinations of range and frequency. As you review this figure, you will notice that the signature appears to be an open circuit in the low range at
60 Hz; while in the high range at 2000 Hz, the signature appears to be a short. Between these, the
combinations are better than others for examining a capacitor.
5-36
for the Tracker 2000. The lowest value of capacitance in each combination will produce a signature of a
very narrow horizontal ellipsoid. Capacitors with less of a value than these will appear to be an open. The
signature. Capacitors of greater value than these will appear as a vertical line signature of a short circuit.
5-37
Table 5-5.—Min/Max Capacitance Values
HIGH .001µF-1µF 500pF-.1µF 100pF-.02µF
MEDIUM 1 .01µF-2µF .001µ-.5µF 200pF-.05µF
MEDIUM 2 .2µF-50µF .02µF-5µF .005µ-1µF
LOW 5µF-2000µF .5mF-100µF .2mF-25µF
Inductors, like capacitors, produce an elliptical signature on the Tracker 2000. Figure 5-35 shows
you the signatures produced in each of the 12 range and frequency combinations by a 250mH inductor.
different. Ferrite inductors operate well at high frequencies, but saturate at low frequencies. Figure 5-36
shows the signature of a 490mH ferrite inductor tested at 60 Hz. In low and medium 1, you can see that
5-38
the signature shows distortion. However, in medium 2 and high ranges, the impedance of the inductor is
low compared with the internal impedance of the Tracker 2000, so the signatures are a split vertical trace.
Figures 5-37 and 5-38 show the same 490mH inductor being tested at 400 Hz and 2000 Hz.
5-39
Now that we have completed this chapter, let's review the more important points.
The type of meter used to measure power is the POWER METER.
One type of wattmeter is the AN/URM-120. It is an IN-LINE TYPE WATTMETER.
concerned.
There are basically two types of signal generators: AF and RF FREQUENCY GENERATORS.
The instrument used to determine the frequency of a signal is the FREQUENCY COUNTER.
LOGIC PROBE.
is disconnected to the device under test.
5-40
ANSWERS TO QUESTIONS Q1. THROUGH Q11.
A-1. Load.
A-2. An unbalance in the metering bridge.
A-3. Attenuator.
A-4. Oscillator circuit, modulator, and output control circuit.
A-5. To produce an af (or video) signal that can be superimposed on the rf signal produced by the oscillator.
A-6. 1 MHz and 10 MHz.
A-7. DIM.
A-8. Positive voltage (+V) and negative current (−I).
A-9. TRACE ROTATE control.
A-10. 0 to 5 volts.
A-11. 50Ω to 10KΩ.
6-1
Upon completing this chapter, you should be able to:
1. Describe the purpose of the CRT used in the oscilloscope.
2. Explain the operation of an oscilloscope.
3. Describe the purpose of the controls and indicators found on an oscilloscope.
4. Describe the proper procedure for using a dual-trace oscilloscope.
5. Describe the accessory probes available for use with a dual-trace oscilloscope.
6. Explain the operation of the spectrum analyzer.
7. Describe the purpose of the controls and indicators found on the spectrum analyzer.
One of the most widely used pieces of electronic test equipment is the OSCILLOSCOPE. An oscilloscope is used to show the shape of a video pulse appearing at a selected equipment test point. Although some oscilloscopes are better than others in accurately showing video pulses, all function in fundamentally the same way. If you learn how one oscilloscope operates, you will be able to learn others.
As you will learn in this chapter, there are many different types of oscilloscopes—varying in complexity from the simple to the complex. Before we get into our discussion of the dual-trace oscilloscope, we will first present a general overview of basic single-trace oscilloscope operation. Shortly, we will see how oscilloscopes use a CATHODE-RAY TUBE (CRT) in which controlled electron beams are used to present a visible pattern of graphical data on a fluorescent screen.
Another piece of test equipment used is the SPECTRUM ANALYZER. This test equipment is used to sweep over a band of frequencies to determine what frequencies are being produced by a specific circuit under test, and then the amplitude of each frequency component. An accurate interpretation of the display will allow you to determine the efficiency of the equipment being tested.
A detailed discussion of CATHODE-RAY TUBES (CRTs) is presented in NEETS, Module 6, Electronic Emission, Tubes, and Power Supplies. Before continuing with your study of CRTs in this section, you may want to review chapter 2 of that module.
Cathode-ray tubes used in oscilloscopes consist of an ELECTRON GUN, a DEFLECTION SYSTEM, and a FLUORESCENT SCREEN. All of these elements are enclosed in the evacuated space
6-2
inside the glass CRT. The electron gun generates electrons and focuses them into a narrow beam. The deflection system moves the beam horizontally and vertically across the screen. The screen is coated with a phosphorous material that glows when struck by the electrons. Figure 6-1 shows the construction of a CRT.
The ELECTRON GUN consists of a HEATER and a CATHODE to generate electrons, a CONTROL GRID to control brightness by controlling electron flow, and two ANODES (FIRST and SECOND). The main purpose of the first (FOCUSING) anode is to focus the electrons into a narrow beam on the screen. The second (ACCELERATING) anode accelerates the electrons as they pass. The control grid is cylindrical and has a small opening in a baffle at one end. The anodes consist of two cylinders that contain baffles (or plates) with small holes in their centers.
Q-1. What element controls the number of electrons striking the screen? Q-2. What element is controlled to focus the beam?
As in most conventional electron tubes, the cathode is indirectly heated and emits a cloud of electrons. The control grid is a hollow metal tube placed over the cathode. A small opening is located in the center of a baffle at the end opposite the cathode. The control grid is maintained at a negative potential with respect to the cathode to keep the electrons bunched together.
A high positive potential on the anodes pulls electrons through the hole in the grid. Because the grid is near the cathode, it can control the number of electrons that are emitted. As in an ordinary electron tube, the negative voltage of the grid can be varied either to control electron flow or stop it completely. The brightness (intensity) of the image on the fluorescent screen is determined by the number of electrons striking the screen. This is controlled by the voltage on the control grid.
The electron beam is focused by two ELECTROSTATIC FIELDS that exist between the control grid and first anode and between the first and second anodes.
Figure 6-2 shows you how electrons move through the electron gun. The electrostatic field areas are often referred to as LENSES because the fields bend electron streams in the same manner that optical
6-3
lenses bend light rays. The first electrostatic lens cause the electrons to cross at the first focal point within the field. The second lens bend the spreading streams and return them to a new, second focal point at the CRT.
Q-3. Why are the electrostatic fields between the electron gun elements called lenses?
Figure 6-2 also shows the relative voltage relationships on the electron-gun elements. The cathode (K) is at a fixed positive voltage with respect to ground. The grid is at a variable negative voltage with respect to the cathode. A fixed positive voltage of several thousand volts is connected to the second (accelerating) anode. The potential of the first (focusing) anode is less positive than the potential of the second anode. The first anode can be varied to place the focal point of the electron beam on the screen of the tube. Control-grid potential is established at the proper level to allow the correct number of electrons through the gun for the desired image intensity.
Q-4. What is the function of the second anode? ELECTRON BEAM-DEFLECTION SYSTEM
The electron beam is developed, focused, and accelerated by the electron gun. The beam appears on the screen of the CRT as a small, bright dot. If the beam is left in one position, the electrons will soon burn away the illuminating coating in that one area. To be of any use, the beam must be able to move. As you have studied, an electrostatic field can bend the path of a moving electron.
As you have seen in the previous illustrations, the beam of electrons passes through an electrostatic field between two plates. You should remember that electrons are negatively charged and that they will be deflected in the direction of the electric force (from negative to positive). This deflection causes the electrons to follow a curved path while in the electrostatic field.
6-4
When the electrons leave the electrostatic field, they will take a straight path to the screen at the angle at which they left the field. Because they were all deflected equally, the electrons will be traveling toward the same spot. Of course, the proper voltages must exist on the anodes to produce the electrostatic field. Changing these voltages changes the focal point of the beam and causes the electron beam to strike the CRT at a different point.
The ANGLE OF DEFLECTION (the angle the outgoing electron beam makes with the CRT center line axis between the plates) depends on the following factors:
• The accelerating voltage on the second anode.
LENGTH OF DEFLECTION FIELD.—As shown in figure 6-3, a long field (long deflection plates) has more time to exert its deflecting forces on an electron beam than does a shorter field (short deflection plates). Therefore, the longer deflection plates can bend the beam to a greater deflection angle.
Q-5. What effect do longer deflection plates have on the electron beam? SPACING BETWEEN PLATES.—As shown in figure 6-4, the closer together the plates, the more
effect the electric force has on the deflection angle of the electron beam.
6-5
Q-6. What effect does closer spacing of plates have on the electron beam? DIFFERENCE OF POTENTIAL.— The potential on the plates (figure 6-5) can be varied to cause
a wider or narrower deflection angle. The greater the potential, the wider the deflection angle.
Q-7. Is the deflection angle greater with higher or lower potential on the plates? BEAM ACCELERATION.—The faster the electrons are moving, the smaller their deflection angle
will be, as shown in figure 6-6.
Q-8. Is the deflection angle greater when the beam is moving faster or slower?
6-6
If two sets of deflection plates are placed at right angles to each other inside a CRT (figure 6-7), the electron beam can be controlled in any direction. By varying the potential of the vertical-deflection plates, you can make the spot (beam) on the face of the tube move vertically. The distance the beam moves will be proportional to the change in potential difference between the plates. Changing the potential difference between the horizontal-deflection plates will cause the beam to move a given distance from one side to the other. Directions other than up-down and left-right are achieved by a combination of horizontal and vertical movement.
As shown in figure 6-8, position X of the beam is in the center. It can be moved to position Y by going up 2 units and then right 2 units. Movement of the beam is the result of the simultaneous action of both sets of deflection plates. The electrostatic field between the vertical plates moves the electrons up an amount proportional to 2 units on the screen. As the beam passes between the horizontal plates, it moves to the right an amount proportional to 2 units on the screen.
6-7
If the amount of deflection from the left and down occurred so that each set of plates acted at the same time, the picture would be like the one in view A of figure 6-9. For example, if the vertical plates moved the beam downward (starting from point X) at the rate of 3 units per second and the horizontal plates moved it to the left at the rate of 1 unit per second, both movements would have been completed in 1 second at point Y. The result would be a straight line.
In view B, the potentials on the vertical and horizontal plates change at the same rate. In the same time period, say 1 second, both plates move the beam 1 unit. The horizontal plates have completed their task at the end of 1 second, but the vertical plates have moved the beam only one-third of the required distance. In this case, the picture in view B would appear on the screen.
Recall from your study of chapter 2 of this module that waveforms are described in terms of amplitude versus time. You have just seen how the movement of the CRT beam depends on both potential (amplitude) and time.
Q-9. Waveforms are described in terms of what two functions? VERTICAL-DEFLECTION PLATES.—We will use figure 6-10 to explain the action of the
vertical-deflection plates in signal amplitude measurements. As this discussion begins, remember that vertical-deflection plates are used to show amplitude of a signal, and horizontal-deflection plates are used to show time and/or frequency relationships.
6-8
1. From T0 to T1, the vertical plates maintain their static difference in potential and the beam stays at 0 units; the T0 to T1 change causes an increasing potential difference in the horizontal plates, and the beam moves 1 unit to the right.
2. At T1, a positive potential difference change in the vertical plates occurs, which causes the beam to move up (instantaneously) 2 units. This vertical (amplitude) beam location is maintained from T1 to T4; horizontal beam movement continues moving to the right as 3 units of time pass.
3. At T4, an instantaneous negative change in potential of 4 units in amplitude occurs, and the beam moves from +2 to - 2 units.
4. From T4 to T7, the beam remains at - 2 units. During this time period, the beam continues moving horizontally to the right, indicating the passage of time.
5. At T7, a positive increase of amplitude occurs, and the beam moves vertically from - 2 to 0 units. From T7 to T8, no change occurs in vertical beam movement; however, horizontal movement continues with time.
The vertical-plate potential difference follows the voltage of the waveform. The horizontal-plate potential follows the passage of time. Together, they produce the image (trace) produced on the screen by the moving beam.
Q-10. The vertical-deflection plates are used to reproduce what function? Q-11. The horizontal-deflection plates are used to produce what function?
HORIZONTAL-DEFLECTION PLATES.—Now let's look at horizontal-deflection action. Assume that the resistance of the potentiometer shown in figure 6-11 is spread evenly along its length. When the arm of the potentiometer is at the middle position, the same potential exists on each plate. Since there is zero potential difference between the plates, an electrostatic field is not moved downward at a uniform rate; the right plate will become more positive than the left (you are looking down through the top of the CRT). The electron beam will move to the right from screen point 0 through points 1, 2, 3, and 4 in equal time intervals.
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If the potentiometer arm is moved at the same rate in the opposite direction, the right plate will decrease in positive potential until the beam returns to the 0 position. At that point, the potential difference between the plates is again zero. Moving the arm toward the other end of the resistance causes the left plate to become more positive than the right, and the beam moves from screen points 0 through 4. If the movement of the potentiometer arm is at a uniform (linear) rate, the beam moves at a uniform rate.
Notice that the ends of the deflection plates are bent outward to permit wide-angle deflection of the beam. The vertical plates are bent up and down in the same manner.
Q-12. Why are the ends of the deflection plates bent outward? For ease of explanation, the manual movement of the potentiometer arm is satisfactory to introduce
you to horizontal beam movement. However, in the oscilloscope this is not how horizontal deflection is accomplished. Beam movement voltages are produced much faster by sawtooth circuitry. You may want to review the sawtooth generation section in NEETS, Module 9, Introduction to Wave-Generation and Wave-Shaping Circuitry before continuing. Nearly all oscilloscopes with electrostatic deflection apply a sawtooth voltage to the horizontal plates to produce horizontal deflection of the beam, as shown in figure 6-12.
In the figure, the sawtooth generator replaces the potentiometer and is connected to both horizontal plates of the CRT. At the reference line, the potential on both plates is equal. Below the line, the left plate is more positive and the right plate is less positive. This causes the beam to move left. Above the line, the right plate is made more positive than the left and the beam moves to the right. The waveform amplitude causes a uniform movement of the beam across the screen (called TRACE). RETRACE time, shown at the trailing edge of the waveform, quickly deflects the beam back to the starting point.
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A GRATICULE was used in our previous discussion in figure 6-10. It is simply a calibrated scale (made of clear plastic) of amplitude versus time that is placed on the face of the CRT.
The graticule can be used to determine the voltage of waveforms because the DEFLECTION SENSITIVITY of a CRT is uniform throughout the vertical plane of the screen. Deflection sensitivity states the number of inches, centimeters, or millimeters a beam will be deflected for each volt of potential difference applied to the deflection plates. It is directly proportional to the physical length of the deflection plates and their distance from the screen and inversely proportional to the distance between the plates and to the second-anode voltage. Deflection sensitivity is a constant that is dependent on the construction of the tube.
Deflection sensitivity for a given CRT might typically be 0.2 millimeters per volt. This means the spot on the screen will be deflected 0.2 millimeters (about 0.008 inch) when a difference of 1 volt exists between the plates. Sometimes the reciprocal of deflection sensitivity (called DEFLECTION FACTOR) is given. The deflection factor for the example given would be 125 volts per inch (1/0.008).
Q-13. What term is used to describe the reciprocal of deflection sensitivity of a scope? In the above example, 125 volts applied between one set of plates would deflect the beam 1 inch on
the screen. This means that the deflection caused by small signals would likely not be observed. For this reason, the deflection plates are connected to amplifiers that magnify the signals applied to the vertical input of the scope.
Assume, for example, that a peak-to-peak value of a known voltage applied to the oscilloscope indicates that each inch marking on the graticule is equal to 60 volts. Each of the 10 subdivisions will, therefore, equal a value of 6 volts. Most oscilloscopes have ATTENUATOR controls to decrease or GAIN controls to increase the strength of a signal before it is placed on the deflection plates. Attenuator and gain settings must not be disturbed after the calibration has been made. For maximum accuracy, you should recalibrate the graticule each time a voltage is to be measured.
Cathode-ray tubes are identified by a tube number, such as 2AP1, 2BP4, or 5AP1A. The first number identifies the diameter of the tube face. Typical diameters are 2 inches, 5 inches, and 7 inches. The first letter designates the order in which a tube of a given diameter was registered. The letter-digit combination indicates the type of phosphor (glowing material) used on the inside of the screen. Phosphor P1, which is used in most oscilloscopes, produces a green light at medium PERSISTENCE. Persistence refers to the length of time the phosphor glows after the electron beam is removed. P4 provides a white light and has a short persistence. If a letter appears at the end, it signifies the number of the modification after the original design.
Although the CRT is a highly versatile device, it cannot operate without control circuits. The type of control circuits required depends on the purpose of the equipment in which the CRT is used.
There are many different types of oscilloscopes. They vary from relatively simple test instruments to highly accurate laboratory models. Although oscilloscopes have different types of circuits, most can be
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divided into the basic sections shown in figure 6-13: (1) a CRT, (2) a group of control circuits that control the waveform fed to the CRT, (3) a power supply, (4) sweep circuitry, and (5) deflection circuitry.
Q-14. List the circuits that all oscilloscopes have in common. Figure 6-14 is a drawing of the front panel of a dual-trace, general-purpose oscilloscope.
Oscilloscopes vary greatly in the number of controls and connectors. Usually, the more controls and connectors, the more versatile the instrument. Regardless of the number, all oscilloscopes have similar controls and connectors. Once you learn the fundamental operation of these common controls, you can move with relative ease from one model of oscilloscope to another. Occasionally, controls that serve similar functions will be labeled differently from one model to another. However, you will find that most controls are logically grouped and that their names usually indicate their function.
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The oscilloscope in figure 6-14 is called DUAL-TRACE because it can accept and display two vertical signal inputs at the same time—usually for comparison of the two signals or one signal and a reference signal. This scope can also accept just one input. In this case, it is used as a SINGLE-TRACE OSCILLOSCOPE. For the following discussion, we will consider this to be a single-trace oscilloscope. The oscilloscope in the figure is commonly used in the fleet. You are likely to use this one (model AN/USM-425) or one very similar to it. Let's now look at the front panel controls. COMPONENTS USED TO DISPLAY THE WAVEFORM
The CRT DISPLAY SCREEN is used to display the signal (figure 6-15). It allows you to make accurate measurements using the vertical and horizontal graticules, as discussed earlier.
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COMPONENTS USED TO ADJUST CRT DISPLAY QUALITY The controls in figure 6-16 allow you to adjust for a clear signal display. They also allow you to
adjust the display position and magnify the horizontal trace by a factor of 10 (X10). Keep in mind that the controls may be labeled differently from one model to another, depending on the manufacturer. Refer to figure 6-16 as you study the control descriptions in the next paragraphs.
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on the CRT. The control is rotated in a clockwise direction to increase the intensity of the beam and should be adjusted to a minimum brightness level that is comfortable for viewing. FOCUS and ASTIG (Astigmatism) Controls
The FOCUS control adjusts the beam size. The ASTIG (astigmatism) control adjusts the beam shape. The FOCUS and ASTIG controls are adjusted together to produce a small, clearly defined circular dot. When displaying a line trace, you will use these same controls to produce a well-defined line. Figure 6-17, view A, shows an out-of-focus beam dot. View B shows the beam in focus. Views C and D show out-of-focus and in-focus traces, respectively.
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The TRACE ROTATION control (figure 6-16) allows for minor adjustments of the horizontal portion of the trace so that you can align it with the horizontal lines on the graticule.
Occasionally, the trace will actually be located off the CRT (up or down or to the left or right) because of the orientation of the deflection plates. When pushed, the BEAM FINDER (figure 6-16) pulls the beam onto the screen so that you can use the horizontal and vertical POSITION controls to center the spot.
The horizontal and vertical POSITION controls (figure 6-16) are used to position the trace. Because the graticule is often drawn to represent a graph, some oscilloscopes have the positioning controls labeled to correspond to the X and Y axes of the graph. The X axis represents horizontal movement; the Y axis represents the vertical movement. Figure 6-18 shows the effects of positioning controls on the trace.
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In view A, the horizontal control has been adjusted to move the trace too far to the right; in view B, the trace has been moved too far to the left. In view C, the vertical POSITION control (discussed later) has been adjusted to move the trace too close to the top; in view D, the trace has been moved too close to the bottom. View E (figure 6-18) shows the trace properly positioned. 10X MAG (Magnifier) Switch
The 10X MAG (magnifier) switch (figure 6-16) allows you to magnify the displayed signal by a factor of 10 in the horizontal direction. This ability is important when you need to expand the signal to evaluate it carefully.
We will now discuss the dual-trace components of the scope. You will use these components to determine the amplitude of a signal. Notice in figure 6-19 that the highlighted section at the upper left of the scope looks just the same as the section at the lower left of the scope. This reveals the dual-trace capability section of the scope. The upper left section is the CH (channel) 1 input and is the same as the CH 2 input at the lower left. An input to both inputs at the same time will produce two independent traces on the CRT and use the dual-trace capability of the scope.
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For purposes of this introductory discussion, we will present only CH (channel) 1. You should realize that the information presented also applies to CH 2.
The vertical POSITION control allows you to move the beam position up or down, as discussed earlier.
The vertical input (or signal input) jack connects the signal to be examined to the vertical-deflection amplifier. Some oscilloscopes may have two input jacks, one labeled AC and the other labeled DC. Other models may have a single input jack with an associated switch, such as the AC GRD DC switch in figure 6-19. This switch is used to select the ac or dc connection. In the DC position, the signal is connected directly to the vertical-deflection amplifier; in the AC position, the signal is first fed through a capacitor. Figure 6-20 shows the schematic of one arrangement.
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The VERTICAL-DEFLECTION AMPLIFIER increases the amplitude of the input signal level required for the deflection of the CRT beam. The deflection amplifier must not have any other effect on the signal, such as changing the shape (called DISTORTION). Figure 6-21 shows the results of distortion occurring in a deflection amplifier.
An amplifier can handle only a limited range of input amplitudes before it begins to distort the signal. Signal distortion is prevented in oscilloscopes by the incorporation of circuitry that permits adjustment of the input signal amplitude to a level that prevents distortion from occurring. This adjustment is called the ATTENUATOR control in some scopes (VOLTS/DIV and VAR in figure 6-19). This control extends the usefulness of the oscilloscope by enabling it to handle a wide range of signal amplitudes.
The attenuator usually consists of two controls. One is a multiposition (VOLTS/DIV) control, and the other is a variable (VAR) potentiometer. Each position of the control may be marked either as to the amount of voltage required to deflect the beam a unit distance, such as VOLTS/DIV, or as to the amount of attenuation (called the DEFLECTION FACTOR) given to the signal, such as 100, 10, or 1.
Suppose the .5 VOLTS/DIV position were selected. In this position, the beam would deflect vertically 1 division for every 0.5 volts of applied signal. If a sine wave occupied 4 divisions peak-to- peak, its amplitude would be 2 volts peak-to-peak (4 · 0.5), as shown in figure 6-22.
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The vertical attenuator control (VOLTS/DIV in figure 6-19) provides a means of adjusting the input signal level to the amplifiers by steps. These steps are sequenced from low to high deflection factors. The potentiometer control (VAR in figure 6-19) provides a means of fine, or variable, control between steps. This control may be mounted separately, or it may be mounted on the attenuator control. When the control is mounted separately, it is often marked as FINE GAIN or simply GAIN. When mounted on the attenuator control, it is usually marked VARIABLE or VAR.
The variable control adds attenuation to the step that is selected. Since accurately calibrating a potentiometer is difficult, the variable control is either left unmarked or the front panel is marked off in some convenient units, such as 1-10 and 1-100. The attenuator control, however, can be accurately calibrated. To do this, you turn off the variable control to remove it from the attenuator circuit. This position is usually marked CAL (calibrate) on the panel, or an associated light indicates if the VAR control is on or off. In figure 6-19, the light called UNCAL indicates the VAR control is in the uncalibrated position.
As we discussed earlier, channel 1 is being used to discuss basic operating procedures for the oscilloscope. Figure 6-23 shows how the vertical mode of operation is selected. The VERT MODE section contains push-button switches that enable you to select channel 1, channel 2, and several other vertical modes of operation. For the present discussion, note only that CH 1 is selected by these switches.
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The TIME/DIV (figure 6-24) controls on the scope determine the period time of the displayed waveform. As we discussed earlier, the sweep generator develops the sawtooth waveform that is applied to the horizontal-deflection plates of the CRT. This sawtooth voltage causes the beam to move across the screen. This trace (sometimes called SWEEP) sets the frequency of the TIME BASE of the oscilloscope. The frequency of the time base is variable, which enables the oscilloscope to accept a wide range of input frequencies. Again, two controls are used (figure 6-24). One is a multiposition switch (TIME/DIV) that changes the frequency of the sweep generator in steps. The second control is a potentiometer (VAR) that varies the frequency between steps. Each step on the TIME/DIV control is calibrated. The front panel has markings that group the numbers into microseconds and milliseconds.
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The potentiometer is labeled VAR, and the panel has an UNCAL indicator that lights when the VAR control is in the variable position. When you desire to accurately measure the time of one cycle of an input signal, turn the VAR control to the CAL position and turn the TIME/DIV switch to select an appropriate time base. Suppose you choose the 10-microsecond position to display two cycles of an input signal, as shown in figure 6-25. One cycle occupies 3 centimeters (small divisions) along the horizontal axis. Each cm has a value of 10 microseconds. Therefore, the time for one cycle equals 30 microseconds (3 · 10). Recall that the frequency for a signal may be found by using the following procedure:
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In selecting a time base, you should select one that is lower in frequency than the input signal. If the input signal requires 5 milliseconds to complete one cycle and the sawtooth is set for 0.5 milliseconds per centimeter with a 10-centimeter-wide graticule, then approximately one cycle will be displayed. If the time base is set for 1 millisecond per centimeter, approximately two cycles will be displayed. If the time base is set at a frequency higher than the input frequency, only a portion of the input signal will be displayed.
In the basic oscilloscope, the sweep generator runs continuously (FREE-RUNNING); in more elaborate oscilloscopes, it is normally turned off. In the oscilloscope we’re using as an example, the sweep generator can be triggered by the input signal or by a signal from some other source. (Triggering will be discussed later in this chapter.) This type of oscilloscope is called a triggered oscilloscope. The triggered oscilloscope permits more accurate time measurements to be made and provides a more stable presentation than the nontriggered-type oscilloscope.
On some oscilloscopes, you will find a 10 times (10X) magnification control. As previously mentioned, this allows the displayed sweep to be magnified by a factor of 10.
Q-15. When you select the time base to display a signal, should the time base be the same, higher, or lower than the input signal?
The triggering and level controls are used to synchronize the sweep generator with the input signal. This provides a stationary waveform display. If the input signal and horizontal sweep generator are unsynchronized, the pattern tends to jitter, making observations difficult.
The A TRIGGER controls at the lower right of the scope (figure 6-26) are used to control the stability of the oscilloscope CRT display. They are provided to permit you to select the source, polarity, and amplitude of the trigger signal. These controls, labeled A TRIGGER, LEVEL, SOURCE, and SLOPE, are described in the following paragraphs.
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The SOURCE control allows you to select the appropriate source of triggering. You can select input signals from channel 1 or 2, the line (60 hertz), or an external input. TRIGGER LEVEL/SLOPE Controls
The LEVEL control allows you to select the amplitude point of the trigger signal at which the sweep is triggered. The SLOPE lets you select the negative or positive slope of the trigger signal at which the sweep is triggered.
The TRIGGER LEVEL (mounted with the TRIGGER SLOPE on some scopes) determines the voltage level required to trigger the sweep. For example, in the TRIGGER modes, the trigger is obtained from the signal to be displayed. The setting of the LEVEL control determines the amplitude point of the input waveform that will be displayed at the start of the sweep.
Figure 6-27 shows some of the displays for a channel that can be obtained for different TRIGGER LEVEL and TRIGGER SLOPE settings. The level is zero and the slope is positive in view A; view B also shows a zero level but a negative slope selection. View C shows the effects of a positive trigger level setting and positive trigger slope setting; view D displays a negative trigger level setting with a positive trigger slope setting. Views E and F have negative slope settings. The difference is that view E has a positive trigger level setting, whereas F has a negative trigger level setting.
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In most scopes, an automatic function of the trigger circuitry allows a free-running trace without a trigger signal. However, when a trigger signal is applied, the circuit reverts to the triggered mode of operation and the sweep is no longer free running. This action provides a trace when no signal is applied.
Synchronization is also used to cause a free-running condition without a trigger signal. Synchronization is not the same as triggering. TRIGGERING refers to a specific action or event that initiates an operation. Without this event, the operation would not occur. In the case of the triggered sweep, the sweep will not be started until a trigger is applied. Each succeeding sweep must have a trigger before a sweep commences. SYNCHRONIZATION, however, means that an operation or event is brought into step with a second operation.
A sweep circuit that uses synchronization instead of triggering will cause a previously free-running sweep to be locked in step with the synchronizing signal. The TRIGGER LEVEL control setting can be increased until synchronization occurs; but, until that time, an unstable pattern will appear on the CRT face.
The COUPLING section allows you to select from four positions: AC, LF REJ, HF REJ, and DC. The AC position incorporates a coupling capacitor to block any dc component. The LF and HF REJ positions reject low- and high-frequency components, respectively. The DC position provides direct
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coupling to the trigger circuits. This is useful when you wish to view only the LF or HF component of a signal.
The TRIG MODE section in figure 6-28 allows for automatic triggering or normal triggering. In AUTO (automatic), the triggering will be free-running in the absence of a proper trigger input or will trigger on the input signal at frequencies above 20 hertz. In NORM (normal), the vertical channel input will trigger the sweep.
For the present, notice only that the HORIZ DISPLAY (horizontal display) in figure 6-29 can be controlled by the TIME/DIV switch. Other switches in this section will be explained later in this chapter.
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In figure 6-30, you can see the components used to calibrate the test probe on the scope. A 1-volt, 2-kilohertz square wave signal is provided for you to adjust the probe for an accurate square wave and to check the vertical gain of the scope. You adjust the probe with a screwdriver, as shown in the figure.
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The oscilloscope you use may differ in some respects from the one just covered. Controls and circuits may be identified by different names. Many of the circuits will be designed differently. However, all the functions will be fundamentally the same. Before using an oscilloscope, you should carefully study the operator’s manual that comes with it.
An oscilloscope can be used for several different types of measurements, such as time, phase, frequency, and amplitude of observed waveforms. Earlier in this chapter, you learned that the oscilloscope is most often used to study the shapes of waveforms when the performance of equipment is being checked. The patterns on the scope are compared with the signals that should appear at test points (according to the technical manual for the equipment under test). You can then determine if the equipment is operating according to peak performance standards.
Q-16. Oscilloscopes are used to measure what quantities?
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Before turning on the scope, make sure it is plugged into the proper power source. This may seem obvious, but many technicians have turned all knobs on the front panel out of adjustment before they noticed that the power cord was not plugged in. On some scopes, the POWER switch is part of the INTEN (intensity) control. Turn or pull the knob until you hear a click or a panel light comes on (figure 6-31). Let the scope warm up for a few minutes so that voltages in all of the circuits become stabilized.
When adjusting a pattern onto the screen, adjust the INTEN (intensity) and FOCUS controls for a bright, sharp line. If other control settings are such that a dot instead of a line appears, turn down the intensity to prevent burning a hole in the screen coating. Because of the different speeds at which the beam travels across the screen, brightness and sharpness will vary at various frequency settings. For this reason, you may have to adjust the INTEN and FOCUS controls occasionally while taking readings. NUMBER OF CYCLES ON THE SCREEN
Because distortion may exist at the beginning and end of a sweep, it is better to place two or three cycles of the waveform on the screen instead of just one, as shown in figure 6-32.
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The center cycle of three cycles provides you with an undistorted waveform in its correct phase. The center of a two-cycle presentation will appear inverted, but will be undistorted. To place waveforms on the CRT in this manner, you must understand the relationship between horizontal and vertical frequencies. The relationship between the frequencies of the waveform on the vertical plates and the sawtooth on the horizontal plates determines the number of cycles on the screen, as shown in figure 6-33.
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The horizontal sweep frequency of the scope should always be kept lower than, or equal to, the waveform frequency; it should never be higher. If the sweep frequency were higher, only a portion of the waveform would be presented on the screen.
If, for example, three cycles of the waveform were to be displayed on the screen, the sweep frequency would be set to one-third the frequency of the input signal. If the input frequency were 12,000 hertz, the sweep frequency would be set at 4,000 hertz for a three-cycle scope presentation. For two cycles, the sweep frequency would be set at 6,000 hertz. If a single cycle were desired, the setting would be the same as the input frequency, 12,000 hertz.
The information presented in the previous sections served as a general overview of basic single-trace oscilloscope operation using one channel and operating controls. Now, you will be introduced to DUAL- TRACE operation.
Dual-trace operation allows you to view two independent signal sources as a dual display on a single CRT. This operation allows an accurate means of making amplitude, phase, time displacement, or frequency comparisons and measurements between two signals.
A dual-trace oscilloscope should not be confused with a dual-beam oscilloscope. Dual-beam oscilloscopes produce two separate electron beams on a single scope, which can be individually or jointly controlled. Dual-trace refers to a single beam in a CRT that is shared by two channels.
Q-17. Scopes that produce two channels on a single CRT with a single beam are referred to as what types of scopes?
The VERT MODE controls (figure 6-34) allow you to select the operating mode of the scope for vertical deflection.
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CH 1 AND CH 2.—These controls allow you to display signals applied to either channel 1 or channel 2, as discussed earlier.
TRIGGER VIEW.—The TRIG VIEW allows you to display the signal that is actually used to trigger the display. (Triggering was discussed earlier.)
ALT.—The ALT (alternate) mode (figure 6-35) of obtaining a dual trace uses the techniques of GATING between sweeps. This control allows the signal applied to channel 1 to be displayed in its entirety; then, channel 2 is displayed in its entirety. This method of display is continued alternately between the two channels. At slow speeds, one trace begins to fade while the other channel is being gated. Consequently, the ALT mode is not used for slow sweep speeds. The CHOP mode, shown in figure 6-36 (explained next), will not produce a satisfactory dual sweep at high speeds. The ALT mode is deficient at low speeds. Therefore, both are used on dual-trace oscilloscopes to complement each other and give the scope a more dynamic range of operation.
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The output dc voltage references on each of the amplifiers are independently adjustable. Therefore, the beam will be deflected by different amounts on each channel if the voltage reference is different at each amplifier output. The output voltage from each amplifier is applied to the deflection plates through the gate. The gate is actually an electronic switch. In this application, it is commonly referred to as a BEAM SWITCH.
Switching is controlled by a high-frequency multivibrator in the CHOP mode. That is, the gate selects the output of one channel and then the other at a high-frequency rate (1200 kilohertz in most oscilloscopes). Because the switching time is very short in a good-quality oscilloscope, the resultant display is two sets of horizontally dashed lines, as shown in figure 6-37, view A.
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Dashed line CH 1 is the output of one channel, while line CH 2 is the output of the other. The trace moves from left to right because of the sawtooth waveform applied to the horizontal plates. A more detailed analysis shows that the beam moves from CH 1 to CH 2 while the gate is connected to the output from one channel. Then, when the gate samples the output of the CH 2 during time 3 to 4, the beam is at a different vertical LOCATION. (This is assuming that CH 2 is at a different voltage reference.) The beam continues in the sequence 5 to 6, 7 to 8, 9 to 10, and 11 to 12 through the rest of one horizontal sweep.
When the chopping frequency is much higher than the horizontal sweep frequency, the number of dashes will be very large. For example, if the chopping occurs at 100 kilohertz and the sweep frequency is 1 kilohertz, each horizontal line would then appear as a series of closely spaced dots, as shown in figure 6-37 view B. As the sweep frequency becomes lower compared to the chopping frequency, the display will show apparently continuous traces; therefore, the CHOP mode is used at low sweep rates.
When signals are applied to the channel amplifiers (view A of figure 6-38), the outputs are changed according to the triggering signal (view B). The resultant pattern (view C) on the screen provides a time- base presentation of the signals of each channel.
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ADD.—The ADD switch (shown earlier in figure 6-34) algebraically adds the two signals of channels 1 and 2 together for display.
Most dual-trace oscilloscopes have both an A and B time base for horizontal sweep control. Notice in the upper right corner on our example scope (figure 6-34) the COUPLING, SOURCE LEVEL, and SLOPE controls. These serve the same function as did those same controls in the A time-base section of the scope. The B time base is selected using the same A and B TIME/DIV control (pull out outer knob).
The use of the B time base is controlled by the HORIZ DISPLAY section discussed earlier in the A time-base section. However, inexperienced technicians generally do not use A and B time bases together in the MIXED, A INTEN (intensified), and B D'LYD (delayed) settings. These controls are fully explained in the applicable technical manuals; therefore, we will not discuss the controls in this chapter. Figure 6-39 is a block diagram of a basic dual-trace oscilloscope without the power supplies.
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The basic dual-trace oscilloscope has one gun assembly and two vertical channels. However, there are many variations. The horizontal sweep channels vary somewhat from equipment to equipment. Some have one time-base circuit and others have two. These two are interdependent in some oscilloscopes and in others they are independently controlled. Also, most modern general-purpose oscilloscopes are constructed of modules. That is, most of the vertical circuitry is contained in a removable plug-in unit, and most of the horizontal circuitry is contained in another plug-in unit.
The main frame of the oscilloscope is often adapted for many other special applications by the design of a variety of plug-in assemblies. This modular feature provides much greater versatility than in a single-trace oscilloscope. For instance, to analyze the characteristics of a transistor, you can replace the dual-trace, plug-in module with a semiconductor curve-tracer plug-in module.
Other plug-in modules available with some oscilloscopes are high-gain, wide-bandwidth amplifiers; differential amplifiers; spectrum analyzers; physiological monitors; and other specialized units. Therefore, the dual-trace capability is a function of the type of plug-in unit that is used with some oscilloscopes.
To get maximum usefulness from an oscilloscope, you must have a means of connecting the desired signal to the oscilloscope input. Aside from cable connections between any equipment output and the oscilloscope input, a variety of probes are available to assist in monitoring signals at almost any point in a circuit. The more common types include 1-TO-1 PROBES, ATTENUATION PROBES, and CURRENT PROBES. Each of these probes may be supplied with several different tips to allow measurement of signals on any type of test point. Figure 6-40 shows some of the more common probe tips.
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In choosing the probe to use for a particular measurement, you must consider such factors as circuit loading, signal amplitude, and scope sensitivity.
The 1-to-1 probe offers little or no attenuation of the signal under test and is, therefore, useful for measuring low-level signals. However, circuit loading with the 1-to-1 probe may be a problem. The impedance at the probe tip is the same as the input impedance of the oscilloscope.
An attenuator probe has an internal high-value resistor in series with the probe tip. This gives the probe a higher input impedance than that of the oscilloscope. Because of the higher input impedance, the probe can measure high-amplitude signals that would overdrive the vertical amplifier if connected directly to the oscilloscope. Figure 6-41 shows a schematic representation of a basic attenuation probe. The 9-megohm resistor in the probe and the 1-megohm input resistor of the oscilloscope form a 10-to-1 voltage divider.
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Since the probe resistor is in series, the oscilloscope input resistance is 10 megohms when the probe is used. Thus, using the attenuator probe with the oscilloscope causes less circuit loading than using a 1- to-1 probe.
Before using an attenuator probe for measurement of high-frequency signals or for fast-rising waveforms, you must adjust the probe compensating capacitor (C1) according to instructions in the applicable technical manual. Some probes will have an IMPEDANCE EQUALIZER in the end of the cable that attaches to the oscilloscope. The impedance equalizer, when adjusted according to manufacturer’s instructions, assures proper impedance matching between the probe and oscilloscope. An improperly adjusted impedance equalizer will result in erroneous measurements, especially when you are measuring high frequencies or fast-rising signals.
More information on oscilloscope hook-ups can be found in Electronics Information Maintenance Books (EIMB), Test Methods and Practices.
Special current probes have been designed to use the electromagnetic fields produced by a current as it travels through a conductor. This type of probe is clamped around a conductor without disconnecting it from the circuit. The current probe is electrically insulated from the conductor, but the magnetic fields about the conductor induce a potential in the current probe that is proportional to the current through the conductor. Thus, the vertical deflection of the oscilloscope display will be directly proportional to the current through the conductor.
The spectrum analyzer is used to examine the frequency spectrum of radar transmissions, local oscillators, test sets, and any other equipment operating within its testable frequency range. With experience, you will be able to determine definite areas of malfunctioning components within equipment. Successful spectrum analysis depends on the proper operation of a spectrum analyzer and your ability to correctly interpret the displayed frequencies. Although there are many types of spectrum analyzers, we will use the Tektronix, Model 492 for our discussion.
The spectrum analyzer accepts an electrical input signal and displays the frequency and amplitude of the signal on a CRT. On the vertical, or Y, axis, the amplitude is plotted. The frequency would then be found on the horizontal, or X, axis. The overall pattern of this display (figure 6-42) indicates the proportion of power present at the various frequencies within the spectrum (fundamental frequency with sideband frequencies).
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The model 492 analyzer can be divided into six basic sections, as follows:
• Power and cooling section.
The converter section actually consists of three frequency converters, made up of a mixer, local oscillator (LO), and required filters. Only one frequency can be converted at a time and pass through the filters to reach the next converter. The analysis frequency can, however, be changed by altering the frequency of the LO and adjusting the FREQUENCY control knob.
FIRST CONVERTER.—The first (front end) converter changes the input signal to a usable IF signal that will either be 829 MHz or 2072 MHz. The IF signal to be produced is dependent on which measurement band selection is currently being used. The 829 MHz IF signal will be selected for bands 2 through 4, while the 2072 MHz IF signal is selected for bands 1 and 5 through 11.
Q-18. The first converter is also known by what other name?
6-39
SECOND CONVERTER.—The second converter actually contains two converters. Only one of these two converters in this section is ever operational, and selected as a result of the measurement band currently being used. The selected converter will convert the frequency received from the first converter to a usable (110 MHz) IF signal, which is then provided to the third converter.
THIRD CONVERTER.—This converter takes the 110 MHz IF signal, amplifies it, and then converts it to the final IF of 10 MHz. This signal, in turn, is then passed on to the IF section.
The IF section receives the final IF signal and uses it to establish the system resolution by using selective filtering. System resolution is selected under microcomputer control among five bandwidths (1 MHz, 100 kHz, 10 kHz, 1 kHz, and 100 Hz). The gain for all bands are then leveled and logarithmically amplified. This is done so that each division of signal change on the CRT display remains equal in change to every other division on the CRT. For example, in the 10-dB-per-division mode, each division of change is equal to a 10 dB difference, regardless of whether the signal appears at the top or bottom of the CRT. The signal needed to produce the video output to the display section is then detected and provided.
The display section provides a representative display of the input signal on the CRT. It accomplishes this by performing the following functions:
• Receives control levels from the front panel beam controls and generates unblanking signals to control display presence, brightness, and focus.
The vertical deflection of the beam is increased as the output of the amplitude detector increases. The horizontal position is controlled by the frequency control section and is the frequency analyzed at that instant. The beam sweeps from left to right, low to high frequencies during its analysis. During this analysis, any time a signal is discovered, a vertical deflection will show the strength of the signal at the horizontal position that is the frequency. This results in a display of amplitude as a function of frequency.
The frequency control section accomplishes the tuning of the first and second LOs within the converter section. The frequency immediately being analyzed is controlled by the current frequencies of the LOs. To analyze another frequency, you must change an LO frequency to allow the new frequency to be converted to a 10 MHz signal by the converter section. Periodically, the unit sweeps and analyzes a frequency range centered on the frequency set by the FREQUENCY knob. Adjusting the FREQUENCY knob will cause the LOs to be tuned to the new frequency. Only the LOs of the first two converters can be changed to vary the frequency being analyzed.
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All the internal functions are controlled from the front panel through the use of a built-in microcomputer. The microcomputer uses an internal bus to receive or produce all communication or control to any section of the analyzer.
The main power supply provides almost all the regulated voltages required to operate the unit. The display section provides the high voltage necessary for CRT operation.
The cooling system allows fresh cool air to be routed to all sections of the unit in proportion to the heat that is generated by each section.
This section will describe the function of the front panel controls, indicators, and connectors. For a complete description of each function, refer to table 6-1 while reviewing the front panel in figure 6-43. The numbers located in column 1 of table 6-1 equate to the same numbers found on the front panel of figure 6-43. Because most operational functions of this spectrum analyzer are microprocessor-controlled, they are switch-selected rather than adjusted.
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Table 6-1.—Description of Front Panel Controls, Indicators, and Connectors
ITEM FUNCTION DESCRIPTION 1 INTENSITY This knob controls the brightness of the CRT trace and the CRT readout display.
The focus is electronically adjusted. 2 READOUT This push button switches the readout display on and off. All spectrum analyzer
parameters are displayed except TIME/DIV. The brightness for this display is proportional to the trace brightness and can be readjusted on internal controls only by a qualified technician.
3 GRATILLUM This push button switches the graticule light on and off. 4 BASELINE CLIP This push button, when activated, clips (subdues) the intensity at the baseline. 5 TRIGGERING This area allows one of four triggering modes to be selected by push buttons that
illuminate when active. When any of these four are selected, the others are canceled.
5a FREE RUN When activated, the sweep is free-running without regard to trigger signals. 5b INT When activated, the sweep is triggered by any signal at the left edge of the display
with an amplitude of 1.0 divisions of the graticule or more. 5c LINE When activated, a sample of the ac power line voltage is used to trigger the sweep. 5d EXT When selected, the sweep is triggered by an external signal (applied through the
back panel IN HORZ/TRIG connector) between a minimum and maximum of 0.5 and 50 volt peak.
6 SINGLE SWEEP This push button, plus a ready indicator (No. 7), provides the single sweep operation. When this operation is selected, one sweep is initiated after the sweep circuit has been triggered. Pushing this button does not cancel the other trigger modes. When single sweep is first selected, the present sweep is aborted, but the sweep circuit is not yet armed. An additional push is required to initially arm the sweep. The button must be pushed again to rearm the sweep circuit each time the sweep has run. To cancel single sweep, you must select one of the four trigger mode selections.
7 READY When single sweep is selected, this indicator lights while the sweep circuit is armed and ready for a trigger signal. The indicator stays lit until the sweep is complete.
8 MANUAL SCAN When the TIME/DIV (No. 9c) selector is in the MNL position, this control will manually vary the CRT beam across the full horizontal axis of the display.
9 TIME/DIV Is used to select sweep rates from 5 VHF�GLY�WR���� VHF�GLY��7KLV�VZLWFK�DOVR selects AUTO, EXT, and MNL modes.
9a AUTO In this position, the sweep rate is selected by the microcomputer to maintain a calibrated display for any FREQ SPAN/DIV, RESOLUTION, and VIDEO FILTER combination.
9b EXT When selected, this control allows an external input source to be used with the sweep rates.
9c MNL When selected, this control is used in conjunction with No. 8 (see MANUAL SCAN, No. 8).
10 FREQUENCY This control is manually turned to allow you to tune to the center frequency. 11 FREQUENCY
RANGE (band) These two push buttons are used to shift the center frequency up or down. Frequency range on the band is displayed on the CRT readout.
12 F This control is used for measuring the frequency difference between signals. When selected, the frequency readout goes to zero. It will then read out the deviation from this reference to the next frequency desired as the FREQUENCY knob is adjusted.
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Table 6-1.—Description of Front Panel Controls, Indicators, and Connectors—Continued
frequency by adjusting the FREQUENCY control for the correct reading. When accomplished, you should deactivate the CAL mode.
14 DEGAUSS When this button is pressed, current through the local oscillator system is reduced to zero in order to minimize magnetism build-up around the LOs. This is done to enhance the center frequency display and amplitude accuracy. You should do this after every significant frequency change and before calibrating the center frequency.
The signal identify feature can become functional only when the FREQ SPAN/DIV is set to 500 kHz. When activated (button lit), true signals will change in amplitude on every sweep. Images and spurious response signals will shift horizontally or go completely off the CRT display. To ensure that the signal is changing amplitude every sweep, you should decrease the sweep rate so that each sweep can be analyzed.
16 PHASE LOCK When this control is activated (button lit), it will reduce residual FM when narrow spans are selected. In narrow spans, the phase lock can be turned off or back on by pressing the button. Switching the PHASE LOCK off may cause the signal to shift position. In narrow spans, the signal could shift off the display; however, it will usually return to its phase locked position after a few moments. The microcomputer automatically selects PHASE LOCK for a span/division of 50 kHz or below in bands 1 through 3, 100 kHz or below for band 3, and 200 kHz for bands 5 and above.
This push button, when activated, will automatically select the bandwidth for FREQ SPAN/DIV, TIME/DIV, and VIDEO FILTER. The internal microcomputer selects the bandwidth to maintain a calibrated display. This can be checked by changing the FREQ SPAN/DIV and observing the bandwidth change on the display.
This is a continuous detent control that selects the frequency span/div. The span/div currently selected is displayed on the CRT. The range of the span/div selection is dependent on the frequency band selected:
1-3 (0-7.1GHz) 4-5 (5.4-21GHz) 6 (18-26GHz) 7-8 (26-60GHz) 9 (60-90GHz)
Two additional bands are provided: full band (max span) and 0 Hz span. When max span is selected, the span displayed is the full band. When zero span is selected, time/div is read out instead of span/div.
This is also a continuous detent control that selects the resolution bandwidth. The bandwidth is shown on the CRT display. The range of adjustment is from 1 kHz to 1 MHz in decade steps. When you change the resolution bandwidth with this control, it will deactivate the AUTO RESOLUTION.
These four push buttons select the display mode. The scale factor can be seen on the CRT display.
20a 10dB/DIV When this is activated, the dynamic range of the display is calibrated to 80 dB, with each major graticule representing 10 dB.
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Table 6-1.—Description of Front Panel Controls, Indicators, and Connectors—Continued
division represents 2 dB. 20c LIN When activated, this selects a linear display between zero volts (bottom graticule
line) and the reference level (top graticule line) scaled in volts/division (see REFERENCE LEVEL, No. 23a).
When selected, this increases the fall time of the pulse signals so that very narrow pulses in a line spectrum display can be observed.
21 VIDEO FILTER One of two (NARROW OR WIDE) filters can be activated to reduce video bandwidth and high-frequency components for display noise averaging. The narrow filter is approximately 1/300th of the selected resolution bandwidth with the wide filter being 1/30th the bandwidth. Activating either one will cancel the other. To disable, completely switch filter off.
Five push buttons and ON control operate the digital storage functions. With none of the push buttons activated, the display will not be stored.
22a VIEW A, VIEW B When either or both of these push buttons are selected, the push button illuminates, and the contents of memory A and/or memory B are displayed. With Save A mode off, data in a memory is interlaced with data from B memory.
22b B-SAVE A When activated, the differential (arithmetic difference) of data in B memory and the saved data in memory A are displayed. SAVE A mode is activated and SAVE A button will be lit.
22c MAX HOLD When activated, the digital storage memory retains the maximum signal amplitude at each memory location. This permits visual monitoring of signal frequency and amplitude at each memory location over an indefinite period of time. This feature is used to measure drift, stability, and record peak amplitude.
22d PEAK/AVERAGE This control selects the amplitude at which the vertical display is either peak detected or averaged. Video signals above the level set by the control (shown by a horizontal line or cursor) are peak detected and stored while video signals below the cursor are digitally averaged and stored.
23 MIN RF ATTEN This control is used to set the minimum amount of RF attenuation. Changing RF LEVEL will not decrease RF attenuation below that set by the MIN RF ATTEN selector.
This is a continuous control that requests the microcomputer to change the reference level one step for each detent. In the 10 dB/DIV vertical-display mode, the steps are 1 dB or 0.25 dB if the FINE mode (No. 26) is selected.
23b MIN RF ATTEN DB This selects the lowest value of attenuation allowed: Actual RF attenuation is set by the microcomputer according to the logarithm selected by the MIN NOISE/MIN DISTORTION (No. 27) button. If RF attenuation is increased by changing MIN RF ATTEN, the microcomputer automatically changes IF gain to maintain the current reference level.
24 UNCAL This indicator lights when the display amplitude is no longer calibrated (selecting a sweep rate that is not compatible with the frequency span/div and resolution bandwidth).
These adjustments calibrate the dynamic range of the display. The LOG calibrates any logarithm gain dB/Div, and the AMPL calibrates the reference level of the top graticule line at the top of the display.
26 FINE When activated, the REFERENCE LEVEL (No. 23a) switches in 1 dB increments for 10 dB/Div display mode, 0.25 dB for 2 dB/Div, and volts 1 dB for LIN display mode.
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Table 6-1.—Description of Front Panel Controls, Indicators, and Connectors—Continued
This selects one of two logarithms used to control attenuator and IF gain. MIN NOISE (button illuminated) reduces the noise level by reducing attenuation and IF gain 10 dB. MIN DISTORTION (button not illuminated) reduces distortion to its minimum. To observe any changes, the RF attenuation displayed on the CRT readout must be 10 dB higher than that set by the MIN RF ATTEN selector.
28 POWER This is a pull switch that turns power on when extended. 29 RF INPUT This is a 50 ohm coaxial input jack used to input signals of 21GHz or below. The
maximum nondestructive input signal level that can be applied to this input is +13 dBm or 30 mW. Signals above 10 dB may cause signal compression.
30 POSITION These controls are used to position the display on the horizontal and vertical axes. 31 CAL OUT This is an output jack that has a calibrated 20 dBm 100 MHz signal, with frequency
markers spaced 100 MHz apart. The calibrated 100 MHz marker is used as a reference for calibrating the reference level and log scale. The combination of 100 MHz markers is used to check span and frequency readout accuracy.
These jacks provide access to the output of the respective LOs. The jacks must have 50 ohm terminators installed when not connected to an external device.
33 EXTERNAL MIXER When the EXTERNAL MIXER button is activated, bias is provided out the EXTERNAL MIXER port for external waveguide mixers. The IF output from the EXTERNAL MIXER is then applied through the EXTERNAL MIXER port to the second converter for use.
34 PEAKING This control varies the mixer bias for external mixers in the EXTERNAL MIXER mode. This control should be adjusted for maximum signal amplitude.
With power applied (power knob pulled out), the spectrum analyzer will automatically (upon microcomputer control) go into the following conditions. If you do not find these indications, there is a probably a problem with the unit.
• Frequency: 0.00 MHz;
• Frequency range: 0.0 to 1.8 GHz;
6-45
• All other indicators off or inactive.
Now that we have completed this chapter, we will briefly review the more important points covered.
A CATHODE-RAY TUBE (CRT) is used in an oscilloscope to display the waveforms. The CRT used in oscilloscopes consists of an ELECTRON GUN, a DEFLECTION SYSTEM,
and a FLUORESCENT SCREEN.
The ELECTRON BEAM in an oscilloscope is allowed to be controlled in any direction by means of HORIZONTAL- and VERTICAL-DEFLECTION PLATES.
VERTICAL-DEFLECTION PLATES are used to show AMPLITUDE of a signal.
HORIZONTAL-DEFLECTION PLATES are used to show TIME and/or FREQUENCY relationship.
A GRATICULE is a calibrated scale of AMPLITUDE VERSUS TIME that is placed on the face of the CRT.
A DUAL-TRACE OSCILLOSCOPE is designed to accept two vertical inputs at the same time. It uses a single beam of electrons shared by two channels.
The SPECTRUM ANALYZER accepts an electrical input signal and displays the signal’s frequency and amplitude on a CRT display.
ANSWERS TO QUESTIONS Q1. THROUGH Q18. A-1. Control grid.
A-2. The first anode. A-3. Because they bend electron streams in much the same manner that optical lenses bend light rays.
A-4. It accelerates the electrons emerging from the first anode. A-5. A greater deflection angle. A-6. A greater deflection angle. A-7. Higher potential.
A-8. Slower beam.
A-9. Amplitude and time.
A-10. Amplitude.
A-11. Time and/or frequency relationships.
6-46
A-12. To permit wide-angle deflection of the beam. A-13. Deflection factor. A-14. A CRT, a group of control circuits, power supply, sweep circuitry, and deflection circuitry. A-15. Lower.
A-16. Amplitude, phase, time, and frequency. A-17. Dual-trace oscilloscopes.
A-18. Front end.
AI-1
ABSORPTION WAVEMETER—An instrument used to measure audio frequencies.
AMMETER—A meter used to measure current.
BACK RESISTANCE—The larger resistance value observed when you are checking the forward resistance of a semiconductor.
BAND PASS FILTER—A tuned circuit that passes only a specific frequency.
BAND REJECT FILTER—A tuned circuit that does not pass a specified band of frequencies.
BARRETTER—A type of bolometer characterized by an increase in resistance as the dissipated power rises.
BEAT FREQUENCY—The difference between the oscillator frequency and the unknown audio frequency.
BEL—The unit that expresses the logarithmic ratio between the input and output of any given component, circuit, or system.
BOLOMETER—A loading device that undergoes changes in resistance as changes in dissipated power occur.
CAVITY WAVEMETER—An instrument used to measure microwave frequencies.
CONTINUITY—An uninterrupted, complete path for current flow.
CORRECTIVE MAINTENANCE—Used to isolate equipment failures. Includes replacement of defective parts to return equipment to proper performance.
DAMPING—The process of smoothing oscillations of the meter pointer.
D’ARSONVAL METER MOVEMENT—The permanent-magnet moving coil movement used in most meters.
dBm—An abbreviation used to represent power levels above or below a 1-milliwatt reference.
DUMMY ANTENNA—See DUMMY LOAD.
DUMMY LOAD—A resistor used to replace the normal load, which is specifically designed to have low reactance and possess the ability to dissipate required amounts of power.
ELECTRODYNOMETER METER MOVEMENT—A meter movement using fixed field coils and a moving coil; usually used in wattmeters.
EXTERNALLY EXCITED METER—A term used to describe meters that get their power from the circuit to which they are connected.
AI-2
FORWARD RESISTANCE—The smaller resistance value observed when you are checking the forward resistance of a semiconductor.
FREQUENCY METER—An instrument used to measure the rate at which ac voltages are generated. GALVANOMETER—A meter used to measure small values of current by electromagnetic or
electrodynamic means.
GENERAL PURPOSE ELECTRONIC TEST EQUIPMENT (GPETE)—Test equipment that has the capability, without modification, to generate, modify, or measure a range of electronic functions required to test two or more equipments or systems of basically different designs.
INDUCTANCE BRIDGE—An ac bridge circuit used to measure an unknown value of inductance.
MAINTENANCE—Work done to correct, reduce, or counteract wear, failure, and damage to equipment.
MEASURE (Metrology Automated System for Uniform Recall and Reporting)—A Navy standardized system designed to provide the recall, scheduling, and documenting of test equipment into calibration facilities.
MECHANICAL-ROTATION FREQUENCY—The speed in revolutions per minute of armatures in electric motors and engine-driven generators; blade speed in turbines.
MEGGER—A meter used to measure insulation resistance.
METER MOVEMENT—The part of the meter that moves to indicate some electrical value.
METER SHUNT—A resistor placed in parallel with the meter terminals; used to provide increased range capability.
OHMMETER—A meter used to measure resistance.
POWER FACTOR—An indication of the various losses of a capacitor, such as current leakage and dielectric absorption.
PREVENTIVE MAINTENANCE—Consists of mechanical, electrical, and electronic checks; used to determine whether or not equipment is operating properly.
SCAT CODES—A four-digit subcategory code used to identify the functional measurement parameters that can be satisfied by any one of many pieces of test equipment.
SELF-EXCITED METER—A term used to describe meters that operate from their own power sources.
SENSITIVITY—(1) For an ammeter, the amount of current that will cause full-scale deflection of the meter. (2) For a voltmeter, the ratio of the voltmeter resistance divided by the full-scale reading of the meter; expressed in ohms per volt.
SCLSIS (Ship Configuration and Logistics Support Information System)—This encompasses the automated data processing system and all practices and procedures used for identification and status accounting of ship's configuration, logistics, technical data reviews, and equipment configuration audits.
SHORT CIRCUIT—An unintentional current path between two components in a circuit or between a component and ground; usually caused by a circuit malfunction.
AI-3
SPECIAL PURPOSE ELECTRONIC TEST EQUIPMENT (SPETE)—Test equipment that is specifically designed to generate, modify, or measure a range of electronic functions of a specific or peculiar nature on a single system or equipment.
STROBOSCOPE—An instrument that allows viewing of rotating or reciprocating objects by producing the optical effect of a slowing down or stopping motion.
SYMPTOM ELABORATION—Using built-in indicating instruments or other aids to define an equipment malfunction.
SYMPTOM RECOGNITION—Recognition of a situation in equipment operation that is not normal.
TACHOMETER—An instrument that measures the rate at which a shaft is turning.
TEST EQUIPMENT INDEX—The Navy guide used to assist in identifying portable electrical/electronic test equipment required for support of prime electrical/electronic, IC, weapons, and reactor instrumentation systems.
TEST POINTS—Locations in equipment that are accessible to the technician's probes where operating voltages or signals can be monitored.
THERMISTOR—A type of bolometer characterized by a decrease in resistance as the dissipated power increases.
TROUBLESHOOTING—A procedure used to evaluate equipment performance and repair equipment when it fails to operate properly.
TUNED CIRCUIT—A circuit that is used as a filter which passes or rejects specific frequencies. VOLTMETER—A meter that is used to measure voltage.
WATT—The unit of electrical power that is the product of voltage and current.
WATTMETER—An electrodynamometer type meter used to measure electrical power.
WAVEFORM ANALYSIS—Observation of displays of voltage and current variations with respect to time or by harmonic analysis of complex signals.
WAVEMETER—Calibrated resonant circuits that are used to measure frequency.
WHEATSTONE BRIDGE—An ac bridge circuit used to measure unknown values of resistance, inductance, or capacitance.
AII-1
NOTE: Although the following references were current when this TRAMAN was published, their continued currency cannot be assured. Therefore, you need to ensure that you are studying the latest revision.
EIMB, Test Equipment, NAVSEA 0967-LP-000-0040, Naval Sea Systems Command, Washington, DC, 1981.
EIMB, Test Methods and Practices, NAVSEA 0967-LP-000-0130, Naval Sea Systems Command, Washington, DC, 1980.
Electronic Test Equipment Calibration Program Indoctrination Handbook, NAVMAT P-9491, Naval Material Command, Washington, DC, 1979.
Metrology Automated System for Uniform Recall and Reporting (MEASURE) Users Manual, OP 43P6A, Chief of Naval Operations, Washington, DC, 1984.
Navy Electricity and Electronics Training Series, Module 3, Introduction to Circuit Protection, Control, and Measurement, NAVEDTRA B72-03-00-93, Naval Education and Training Professional Development and Technology Center, Pensacola, FL, 1993.
Portable Electrical/Electronic Test Equipment (PEETE) Index NAVSEA ST-AA-IDX-010- PEETE, Naval Sea Systems Command, Washington, DC, 1986.
Ships Configuration and Logistics Support Information System (SCLSIS), S0752-AA-SPN- 010/SCLSIS, Naval Sea Systems Command, Washington, DC, 1988.
Standard General Purpose Electronic Test Equipment, MIL-STD 1364(Series) (NAVY), Naval Sea Systems Command, Washington, DC, 1991.
Stowage Guide for Portable Electrical/Electronic Test Equipment (PEETE) NAVSEA ST000- AB-GYD-010/PEETE, Naval Sea Systems Command, Washington, DC, 1987.
Electronics Technician 3 and 2, NAVEDTRA 80197-1, Naval Education and Training Professional Development and Technology Center, Pensacola, FL, 1987.
Fire Controlman Third Class, NAVEDTRA 10276-1, Naval Education and Training Professional Development and Technology Center, Pensacola, FL, 1988.
Navy Electricity and Electronics Training Series, Module 9, Introduction to Wave-Generation and Wave-Shaping Circuits, NAVEDTRA 172-09-00-83, Naval Education and Training Professional Development and Technology Center, Pensacola, FL, 1983.*
AII-2
Navy Electricity and Electronics Training Series, Module 7, Introduction to Solid-State Devices and Power Supplies, NAVEDTRA B72-07-00-92, Naval Education and Training Professional Development and Technology Center, Pensacola, FL, 1992.
Navy Electricity and Electronics Training Series, Module 21, Test Methods and Practices, NAVEDTRA B72-21-00-87, Naval Education and Training Professional Development and Technology Center, Pensacola, FL, 1987.
Navy Electricity and Electronics Training Series, Module 2, Introduction to Alternating Current and Transformers, NAVEDTRA 172-02-00-91, Naval Education and Training Professional Development and Technology Center, Pensacola, FL, 1991.
Radioman 3 & 2, NAVEDTRA 10228-H1, Naval Education and Training Professional Development and Technology Center, Pensacola, FL, 1991.
Navy Electricity and Electronics Training Series, Module 5, Introduction to Generators and Motors, NAVEDTRA B72-05-00-94, Naval Education and Training Professional Development and Technology Center, Pensacola, FL, 1994.
Navy Electricity and Electronics Training Series, Module 1, Introduction to Matter, Energy, and Direct Current, NAVEDTRA B72-01-00-92, Naval Education and Training Professional Development and Technology Center, Pensacola, FL, 1992.
Navy Electricity and Electronics Training Series, Module 3, Introduction to Circuit Protection, Control, and Measurement, NAVEDTRA B72-03-00-93, Naval Education and Training Professional Development and Technology Center, Pensacola, FL, 1993.
8000A Digital Multimeter, NAVSEA 0969-LP-279-9010, Naval Sea Systems Command, Washington, DC.
Navy Electricity and Electronics Training Series, Module 7, Introduction to Solid-State Devices and Power Supplies, NAVEDTRA B72-07-00-92, Naval Education and Training Professional Development and Technology Center, Pensacola, FL, 1992.
Navy Electricity and Electronics Training Series, Module 13, Introduction to Number Systems and Logic Circuits, NAVEDTRA B72-13-00-86, Naval Education and Training Professional Development and Technology Center, Pensacola, FL, 1986.*
Operation and Maintenance Instructions, Volt-Ohm-Milliammeter 260 Series, NAVSEA 0969- LP-286-1010, Naval Sea Systems Command, Washington, DC, 1977.
EIMB, Test Methods and Practices, NAVSEA 0967-LP-000-0130, Naval Sea Systems Command, Washington, DC, 1980.
Huntron Tracker 2000 Operation and Maintenance Manual, Mill Creek, WA, 1985.
AII-3
Navy Electricity and Electronics Training Series, Module 10, Introduction to Wave Propagation, Transmission Lines, and Antennas, NAVEDTRA 172-10-00-83, Naval Education and Training Professional Development and Technology Center, Pensacola, FL, 1983.*
Navy Electricity and Electronics Training Series, Module 12, Modulation Principles, NAVEDTRA 172-12-00-83, Naval Education and Training Professional Development and Technology Center, Pensacola, FL, 1983.*
EIMB, Test Methods and Practices, NAVSEA 0967-LP-000-0130, Naval Sea Systems Command, Washington, DC, 1980.
EW Technician AN/SLQ-32A(V)3 ECM Maintenance Trainee Guide, A-102-0216 (Vol 1), Chief of Naval Technical Training, Pensacola, FL, 1992.
Navy Electricity and Electronics Training Series, Module 9, Introduction to Wave-Generation and Wave-Shaping Circuits, NAVEDTRA 172-09-00-83, Naval Education and Training Professional Development and Technology Center, Pensacola, FL, 1983.*
Navy Electricity and Electronics Training Series, Module 6, Introduction to Electronic Emission, Tubes, and Power Supplies, NAVEDTRA B72-06-00-92, Naval Education and Training Professional Development and Technology Center, Pensacola, FL, 1992.
Tektronix 492/492P Spectrum Analyzer Instruction Manual, Beaverton, OR, 1981.
*Effective 1 September 1986, the Naval Education and Training Program Development Center became the Naval Education and Training Program Management Support Activity. Effective 1 October 1996, the name was changed to Naval Education and Training Professional Development and Technology Center.
INDEX-1
INDEX-2
INDEX-3
INDEX-4
INDEX-5
Information: The text pages that you are to study are provided at the beginning of the assignment questions.
1
Textbook assignment: Chapter 1, “Test Equipment Administration and USE,” pages 1-1 through 1-33. Chapter 2, “Miscellaneous Measurements,” pages 2-1 through 2-27.
1-1. What system is currently used by U.S. military services to identify electronic equipment with standardized nomenclature?
1. Joint Electronic Type Designation
System (JETDS) 2. Joint Electronics Type Category
System (JETCS) 3. Army-Navy (AN) System 4. Navy Tactical Data Systems (NTDS)
1-2. Which of the following categories of test equipment is/are designed to test, without modification, a range of electronic parameters needed for two or more systems that are different in design?
1. GPETE 2. SPETE 3. Both 1 and 2 above 4. Installed
1-3. For what purpose was the ETE classification board established?
1. To control inventory limits 2. To control the increase of
nonstandard GPETE 3. To control the increase of
nonstandard SPETE 4. To become final approval authority
1-4. Which of the following systems provides an inventory of test equipment actually located in the fleet? 1. 3M 2. SCLSIS 3. STEED 4. SPETREL
1-5. You can determine if a piece of test equipment has been calibrated by checking which of the following documents?
1. The test equipment logbook 2. A directive from the EMO 3. The completed maintenance action
form for the instrument 4. A tag or label attached to the
1-6. What label is used to identify a test instrument that is within tolerance on all parameters?
1. INACTIVE 2. CALIBRATED 3. CALIBRATED—Refer to report 4. ORGANIZATION LEVEL
1-7. Which of the following conditions warrants the use of one of the SPECIAL CALIBRATION labels and/or tags?
1. Calibration deviates from the usual
tolerances 2. The instrument has more than one
calibration interval 3. The instrument is too large to move
and requires in-place calibration 4. Each of the above
2
1-8. Under what circumstances should the USER CALIBRATION label be affixed to a piece of test equipment?
1. When a certain calibration schedule is
assigned 2. When user calibration is required
before, during, or after use 3. When the equipment is out for
calibration 4. Each of the above
1-9. Which of the following statements must appear on the CALIBRATION NOT REQUIRED label affixed to an instrument?
1. By what authority the label was
affixed 2. The reason no calibration is required 3. The date the label was affixed 4. The METRL page number
1-10. Which of the following labels is attached to an unusable instrument, and may have an additional tag attached?
1. INACTIVE 2. REJECTED 3. CALIBRATED 4. SPECIAL CALIBRATION
1-11. A test instrument that has plug-in modules and/or easily accessible potentiometer or controls which affect the calibration of the instrument should have which of the following labels attached?
1. CALIBRATED 2. CALIBRATION NOT REQUIRED 3. CALIBRATED—REFER TO
REPORT 4. CALIBRATION VOID IF SEAL
1-12. A replacement part needed by an IMA to repair a piece of test equipment should be ordered by the activity sending the inoperative equipment for repair and calibration. For which of the following reasons is this a good practice?
1. IMAs are not allowed to order repair
parts 2. The ship has more repair funds than
the IMA 3. The ship is usually able to obtain the
parts more quickly 4. It is more likely the technician on the
1-13. When maintenance personnel are not authorized to make repairs to a piece of test equipment, what items, if any, must be sent to the calibration repair facility with the equipment?
1. The unit and its power cord 2. All the accessories 3. Standards used to calibrate 4. None
1-14. In what type of environment should test equipment be stowed?
1. Dry 2. Dark and damp 3. High humidity and low temperature 4. High temperature and high humidity
1-15. In a stowage space aboard ship, what device(s) should be used to hold the test equipment in place?
1. Set clasp springs 2. Tie down cord 3. Steel straps 4. Stretch seat-belt-type straps
3
1-16. What system is used to provide for a standardized recall and scheduling of test equipment into calibration facilities?
1. MDCC 2. SCLSIS 3. METER 4. MEASURE
1-17. The meter card is used to provide what information concerning test equipment?
1. Changes 2. Additions 3. Deletions 4. All of the above
1-18. Which of the following actions would be classified as preventive maintenance?
1. Purchasing a new piece of test
equipment 2. Isolating an equipment failure to the
component level 3. Aligning a servo assembly after a
repair 4. Replacing a defective transistor
1-19. Which of the following actions would be regarded as part of corrective maintenance?
1. Routine lubrication of a radar pedestal 2. Mechanical inspection of a bearing
assembly in a motor housing 3. Alignment of a servo assembly after a
repair 4. Cleaning a filter in accordance with a
1-20. Troubleshooting electrical and electronic equipment includes which of the following actions?
1. Fault isolation 2. Equipment repair 3. Equipment performance evaluation 4. Each of the above
1-21. The initial operating conditions of newly installed equipment are referred to as
1. alignment data 2. manufacturer's specifications 3. baseline operating characteristics 4. expected operation characteristics
1-22. When working on energized equipment, you should follow which of the following practices?
1. Work alone 2. Work with both hands 3. Insulate yourself from ground 4. Wear rubber gloves at all times
1-23. When measuring 300 volts or more, you should first take what step?
1. Turn off equipment power 2. Ground all components capable of
retaining an electrical charge 3. Short-circuit all components capable
of retaining an electrical charge 4. Connect the meter leads to the points
1-24. Which of the following insulating materials is suitable for covering a grounded metal work bench?
1. Dry insulating material that contains
no holes or conductors 2. Dry canvas that has holes in it 3. Dry phenolic material that has
conductors embedded in it 4. Damp plywood
1-25. Prior to working on a circuit, you use a shorting probe discharge which of the following types of components?
1. Capacitors only 2. Cathode-ray tubes only 3. Capacitors and cathode-ray tubes 4. Inductors
4
1-26. If a 28 volt 6 ampere fuse blows, the proper procedure is to replace it with which of the following devices?
1. A larger fuse until the cause of the
overload has been determined 2. A fuse of the same voltage and
current rating 3. A fuse rated 20 percent lower than the
blown fuse 4. A copper strap until the cause of the
1-27. Before electrical equipment is overhauled or repaired, what general safety precaution, if any, should be followed?
1. The fuse for the associated circuits
2. The main supply switches should temporarily be shorted out
3. The power switches should be secured open and tagged out of service
4. None
1-28. After work on equipment is complete, who should remove any attached tags?
1. The job inspector 2. The repair crew leader 3. Any member of the repair crew 4. The person who signed and attached
1-29. What is the purpose of the grounding cable attached to the frame of a generator aboard ship?
1. Create a potential difference between
the frame and the ship 2. Conduct power to the generator under
emergency conditions 3. Ensure equipment is at same ground
potential as the ship 4. Break the circuit between the frame
1-30. Which of the following steps should you take to help ensure that metal-case test equipments are safe to use?
1. Energize the instrument to test the
ground 2. Ensure the equipment is grounded 3. Insulate the metal case from ground 4. Connect all metal cases to a common
1-31. Which of the following precautions should you observe when using measuring instruments?
1. Avoid strong magnetic fields 2. Avoid excessive current 3. Avoid mechanical shock 4. Each of the above
1-32. The meter movement in a voltmeter can be easily damaged by excessive current if you do not follow certain procedures. When setting up the meter to read voltage, the RANGE SWITCH should first be set to (a) what relative range and then changed to (b) what relative range?
1. (a) Highest
(b) Closest to the voltage to be read 2. (a) Highest
(b) Lower than the voltage to be read 3. (a) Lowest
(b) Lower than the voltage to be read 4. (a) Lowest
5
A. Place one hand in your pocket or behind your back.
B. Turn on the power. C. Connect the meter ground to the
equipment ground. D. Place the positive meter lead on the
test point; select for positive or negative polarity.
IN ANSWERING QUESTION 1-33, REFER TO THE PROCEDURES IN FIGURE 1A. 1-33. When you measure voltages less than
300 volts, in what order should you complete the task?
1. A B C D 2. B C D A 3. C A D B 4. D C B A
_________________________________ IN ANSWERING QUESTIONS 1-34 THROUGH 1-37, SELECT FROM THE MEASUREMENT COLUMN BELOW THE ANSWER THAT MATCHES THE SITUATION BEING DESCRIBED.
MEASUREMENT 1. Current 2. Inductance 3. Resistance 4. Capacitance
_________________________________ 1-34. This measurement is rarely taken in
preventive or corrective maintenance or testing because unsoldering is usually required. Ohm's law is normally applied to determine this value.
1-35. This is a valuable aid in locating faults
during corrective maintenance, but cannot be made with power applied. Many technical manuals contain charts that indicate the test points for this measurement.
1-36. This measurement provides an indication of dielectric strength and is used to determine the power factor.
1-37. This measurement is seldom taken during
troubleshooting. It can be taken using a bridge or another instrument that is primarily designed to measure another quantity; however, a conversion chart is required.
1-38. The power factor is an indication of the
losses caused by which of the following conditions?
1. Excessive voltage 2. Dielectric absorption 3. Current leakage 4. Both 2 and 3 above
1-39. The Wheatstone bridge can be used for precision measurements of which of the following quantities?
1. Voltage 2. Current 3. Impedance 4. Resistance
6
Figure 1B.—Dc resistance bridge.
IN ANSWERING QUESTION 1-40, REFER TO FIGURE 1B. 1-40. In the dc resistance bridge, what is the
value of Rx?
1. 42 ohms 2. 400 ohms 3. 420 ohms 4. 4,200 ohms
Figure 1C.—Ac resistance bridge.
IN ANSWERING QUESTION 1-41, REFER TO FIGURE 1C. 1-41. In the ac resistance bridge, what is the
value of Rx?
1. 25 ohms 2. 250 ohms 3. 2,500 ohms 4. 25,000 ohms
Figure 1D.—Capacitance bridge.
IN ANSWERING QUESTION 1-42, REFER TO FIGURE 1D. 1-42. In the capacitance bridge, what is the
value of Cx?
1. 25 microfarads 2. 117 microfarads 3. 256 microfarads 4. 1,178 microfarads
1-43. Dc power is stated in which of the following units?
1. Watts 2. Farads 3. Amperes 4. Henries
7
1-44. Power in an audio-frequency circuit is stated in which of the following units?
1. Decibels (dB) only 2. Decibels referenced to 1 milliwatt
(dBm) only 3. Both dB and dBm 4. Volt units (Vu)
1-45. The bel is a unit of measurement used with voltage, current, or power that compares which of the following circuit values?
1. The input to the output 2. The output to a reference 3. The voltage to power 4. The current to power
1-46. What is the relationship between the values of the bel and the decibel?
1. The bel is twice the decibel 2. The decibel is twice the bel 3. The bel is 1/10 the decibel 4. The decibel is 1/10 the bel
1-47. What is the corresponding increase in dBm each time power is doubled?
1. +1 dB 2. +2 dB 3. +3 dB 4. +10 dB
1-48. A thermocouple ammeter is used to measure which of the following quantities?
1. Rf current 2. Af current 3. Motor current 4. Generator current
1-49. A bolometer is a power meter that measures power in certain frequency ranges. Which of the following methods is/are used by the bolometer to measure power values?
1. A barretter detects increases in power
when its resistance increases 2. A thermistor detects increases in
power when its resistance decreases 3. Both 1 and 2 above 4. Power is measured directly
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Figure 1E.—Thermistor bridge.
IN ANSWERING QUESTION 1-50, REFER TO FIGURE 1E. 1-50. In the thermistor bridge, what is the
purpose of RT-1 and RT-3?
1. To compensate for power used by RT-2
2. To compensate for temperature changes outside the waveguide
3. To control the amount of rf energy applied to RT-2
4. To control the temperature of the waveguide
1-51. To measure shaft rotation rate on an
engine, you should use, which, if any, of the following instruments?
1. An ammeter 2. A bolometer 3. A tachometer 4. None of the above
1-52. In the centrifugal tachometer, what
component restricts the action on the lower collar that is produced by centrifugal force?
1. The spring 2. The pointer 3. The upper collar 4. The lower collar
1-53. What is the usual speed range (in feet per minute) of a chronometric tachometer?
1. 0 to 30 2. 0 to 300 3. 0 to 3,000 4. 0 to 30,000
9
1-54. You are measuring the speed of a fan blade by using a stroboscopic tachometer. Setting the flash at a rate 5 rpm SLOWER than the fan speed will cause the blades to appear to move (a) in what relative direction and (b) at what speed?
1. (a) Forward (b) 5 rpm 2. (a) Forward (b) 10 rpm 3. (a) Backward (b) 10 rpm 4. (a) Backward (b) 5 rpm
1-55. The flashing rate of a strobotac is
controlled by which of the following circuits?
1. An electronic pulse generator 2. A frequency divider 3. A power supply 4. An amplifier
1-56. The flashing rate of the strobotron tube affects its life expectancy. What is the range (in hours) of life expectancy of the strobotron tube?
1. 15 to 24 2. 25 to 49 3. 50 to 99 4. 100 to 250
1-57. The vibrating-reed frequency meter is a delicate instrument and should not be subjected to vibrations, such as those associated with motor-generators or their associated control panels.
1. True 2. False
1-58. When using the vibrating-reed frequency meter, you take the reading in which of the following ways?
1. Read the digital readout 2. Read the dial indication 3. Read the mechanical setting 4. Read the reed that vibrates the most
1-59. Bandpass filters and band reject filters are tuned circuits that either pass or reject specific frequencies. In these filters, (a) what type offers very high impedance to currents at its resonant frequency, and (b) what type offers a very low impedance to currents at its resonant frequency?
1. (a) Parallel-tuned (b) series-tuned 2. (a) Parallel-tuned (b) parallel-tuned 3. (a) Series-tuned (b) parallel-tuned 4. (a) Series-tuned (b) series-tuned
1-60. When you are zero beating an unknown frequency with a frequency provided by a calibrated, high-precision oscillator within a heterodyne frequency meter, what will be the indication when the two frequencies are matched?
1. One dot of light on the screen will be
superimposed on the other 2. One vertical line on the screen will be
superimposed on the other 3. The two tones in the headset will
4. The tone in the headset will decrease in pitch and be replaced by clicks that will become slow or nonexistent
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Figure 1F.—Absorption wavemeter circuit.
IN ANSWERING QUESTION 1-61, REFER TO FIGURE 1F. 1-61. When you are using an absorption
wavemeter to measure frequency, the greatest accuracy may be obtained by loosely coupling the pickup coil so that the indicator lamp burns (a) with what degree of brilliance (b) under what resonance condition?
1. (a) Maximum brilliance
2. (a) Maximum brilliance (b) when not tuned to the resonant frequency
3. (a) Dimly (b) when not tuned to the resonant frequency
4. (a) Dimly (b) when tuned to the resonant frequency
1-62. Which of the following instruments
should be used to accurately measure a frequency in the shf range?
1. Absorption wavemeter 2. Resonant, cavity-type wavemeter 3. Resonant, coaxial-line-type
wavemeter 4. Both 2 and 3 above
1-63. In a cavity wavemeter, moving the plunger farther into the cavity space causes which of the following changes to (a) the cavity size and (b) the resonant frequency of the cavity?
1. (a) Decrease (b) increase 2. (a) Decrease (b) decrease 3. (a) Increase (b) decrease 4. (a) Increase (b) increase
1-64. For which of the following purposes is a cathode-ray oscilloscope used?
1. To measure microwave energy 2. To visually analyze waveforms 3. To provide frequency modulation 4. To locate stray radio interference
1-65. The synchroscope contains which of the following circuits?
1. Retrace blanking circuit 2. A wide band amplifier 3. A trigger sweep 4. All of the above
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11
Figure 1G.—Waveform display.
IN ANSWERING QUESTION 1-66, REFER TO FIGURE 1G. MEASUREMENT X REPRESENTS THE HORIZONTAL DISTANCE OF THE WAVEFORM; MEASUREMENT Y REPRESENTS THE VERTICAL DISTANCE OF THE WAVEFORM. 1-66. In the figure, (a) time is represented by
what measurement, and (b) amplitude is represented by what measurement?
1. (a) X (b) X 2. (a) X (b) Y 3. (a) Y (b) Y 4. (a) Y (b) X
1-67. An oscilloscope measures voltage and displays waveforms. It can be used to measure currents, temperatures, speeds, and accelerations if they are first converted to
1. heat 2. light 3. voltages 4. pressures
1-68. The spectrum analyzer is used to display which of the following quantities?
1. Amplitude within each frequency
component in a circuit 2. Proportions of power within each
frequency component in the spectrum 3. Frequencies produced in a circuit 4. Each of the above
1-69. While testing a semiconductor diode, you determine that the forward resistance value is 60 ohms. You should consider the diode good if the backward resistance is at least which of the following values?
1. 6 ohms 2. 60 ohms 3. 600 ohms 4. 6,000 ohms
1-70. When you are using an oscilloscope to test a crystal diode, what is shown by (a) the vertical deflection and (b) the horizontal deflection?
1. (a) Crystal current
(b) voltage applied to the diode 2. (a) Crystal current
(b) power developed in the diode 3. (a) Crystal voltage
(b) power developed in the diode 4. (a) Crystal voltage
1-71. When you are using the oscilloscope to test the Zener diode, what is represented by (a) vertical deflection and (b) horizontal deflection?
1. (a) Zener current
(b) Zener power 2. (a) Zener current
(b) applied voltage 3. (a) Applied voltage
(b) Zener power 4. (a) Applied voltage
12
1-72. When troubleshooting transistorized circuits, you should first check the condition of which of the following circuits?
1. Counters 2. Amplifiers 3. Oscillators 4. Power supplies
1-73. Which of the following instruments is used to check transistors for collector leakage current and current gain?
1. Ohmmeter 2. Voltmeter 3. Wheatstone bridge 4. Semiconductor test set
1-74. When making base-to-emitter bias voltage checks on a transistor, you should read which of the following voltage ranges?
1. 5 to 20 microvolts 2. 50 to 200 millivolts 3. 5 to 20 volts 4. 50 to 200 volts
1-75. When making resistance measurements on a transistor with an ohmmeter, you should allow what maximum current in the transistor?
1. milliampere 2. milliampere 3. microampere 4. microampere
13
Textbook assignment: Chapter 3, “Basic Meters,” pages 3-1 through 3-34. Chapter 4, “Common Test Equipment,” pages 4-1 through 4-10.
2-1. What are the two basic components of a galvanometer?
1. A movable permanent magnet and a
movable coil 2. A stationary permanent magnet and a
stationary coil 3. A stationary permanent magnet and a
movable coil 4. A stationary coil and a movable coil
2-2. The coil in a galvanometer rotates to allow measurement of current. Which of the following actions causes this reaction?
1. Current flowing in opposite
directions through two coils 2. Tension of the hairspring and the
3. Magnetism produced by current flowing in the movable coil and the tension of the hairspring
4. Magnetism of the permanent magnet and magnetism produced by current in the movable coil
2-3. In a galvanometer, the phosphor bronze
ribbon serves which of the following functions?
1. Provides a conduction path from the
circuit being tested to the coil 2. Restores the coil to its original
position 3. Allows the coil to twist 4. Each of the above
2-4. In galvanometers, which of the following components is/are used to indicate the value of the current being measured?
1. Pointer 2. Light and mirror 3. Both 1 and 2 above 4. Digital readout
2-5. The phosphor bronze ribbon in the
galvanometer serves the same purpose as what component in the D'Arsonval meter?
1. Hairspring 2. Movable coil 3. Fixed iron core 4. Permanent magnet
2-6. The direction in which the D'Arsonval meter pointer deflects depends on what characteristic of the current applied to the coil?
1. Phase 2. Polarity 3. Frequency 4. Amplitude
2-7. The D'Arsonval meter movement is damped to prevent which of the following conditions?
1. Oscillating readings 2. Inconsistent readings 3. Consistently low readings 4. Consistently high readings
14
2-8. The weight of the rotating coil assembly and the type of bearings used in the D'Arsonval meter are factors that affect which of the following characteristics of the meter?
1. The accuracy and the linearity of the
meter scales 2. The amount of restraining force
required of the hairspring 3. The maximum current that can be
measured 4. The sensitivity
2-9. For a meter to read linearly, its face is divided into equal segments. What meter feature makes this possible?
1. The curved poles of the permanent
magnet 2. The jeweled bearings in the meter
movement 3. An additional coil placed in the
meter circuit 4. A long, lightweight meter pointer
2-10. What is the purpose of a shunt in a dc ammeter?
1. To decrease the sensitivity of the
meter 2. To increase the linearity of the meter
movement 3. To increase the current range of the
meter 4. To decrease meter damping
2-11. A particular D'Arsonval meter has a full- scale current reading of 1 milliampere. A full-scale reading of 100 milliamperes may be achieved by using which of the following components?
1. A low-value resistance placed in
series with the meter terminals 2. A high-value resistance placed in
series with the meter terminals 3. A movable coil composed of large-
diameter wire 4. A resistance of proper value placed
2-12. To measure 10 milliamperes on a 1- milliampere D'Arsonval meter movement, a shunt resistance is added that will carry 9 milliamperes. What maximum value of current will pass through the meter movement?
1. 1 milliampere 2. 3 milliamperes 3. 6 milliamperes 4. 9 milliamperes
2-13. In a meter movement, shunt strips with a
zero temperature coefficient are used instead of regular carbon resistance for which of the following reasons?
1. Because regular carbon resistances
cause interfering magnetic fields 2.  Because regular carbon resistances
4. Because regular carbon resistances are affected by heat due to current and cause readings to vary
2-14. One consideration in choosing the value
of a meter shunt resistance is that the meter readings should be in the midscale range. Which of the following factors is another consideration?
1. Meter switching is easier for
midscale deflection 2. Meter shielding against magnetic
interference is greatest near midscale 3. Minimum loading effect will be
experienced near midscale 4. The meter is protected from
2-15. For which of the following current ranges would you likely use a meter that contains internal shunt?
1. 1 to 10 amperes 2. 11 to 30 amperes 3. 31 to 50 amperes 4. All of the above
15
Figure 2A.—Shunt ammeter.
IN ANSWERING QUESTIONS 2-16 THROUGH 2-19, REFER TO FIGURE 2A. THE METER IN THE CIRCUIT IS DESIGNED FOR MAXIMUM OF .001 AMPERE AND HAS AN INTERNAL RESISTANCE OF 10 OHMS. YOU ARE FIGURING THE SHUNT RESISTANCE NECESSARY TO MEASURE 5 AMPERES. 2-16. What is the voltage drop across the meter
coil?
1. .01 volt 2. .005 volt 3. .0001 volt 4. .0005 volt
2-17. What is the voltage drop across the shunt resistance? 1. .01 volt 2. .005 volt 3. .0001 volt 4. .0005 volt
2-18. When the meter is deflected full scale and is measuring 5 amperes, what is the maximum value of current flow through the shunt resistance?
1. 0.010 ampere 2. 0.490 ampere 3. 4.999 ampere 4. 5 amperes
2-19. What is the approximate value of the shunt resistance?
1. .001 ohm 2. .002 ohm 3. .003 ohm 4. .004 ohm
2-20. Simple range-switching arrangements for current meters are less satisfactory than other methods of range switching for which of the following reasons?
1. Meter damage can occur when line
2. Resistance in the contacts may cause inaccurate readings
3. Both 1 and 2 above 4. Resistor damage may occur
Figure 2B.—Ammeter connections.
IN ANSWERING QUESTION 2-21, REFER TO FIGURE 2B. 2-21. In the figure, five ammeters are
connected to the circuit resistors. Of those five, which one(s) is/are connected correctly?
1. E only 2. A and E 3. A and C 4. A, B, and D
16
2-22. What will be the probable result of connecting an ammeter (or milliammeter) in PARALLEL with a source of voltage or a circuit component?
1. A burned-out meter that will provide
no useful readings 2. A higher than normal meter reading 3. A lower than normal meter reading 4. A normal meter reading
Figure 2C.—Series-parallel circuit.
IN ANSWERING QUESTIONS 2-23 AND 2-24, REFER TO FIGURE 2C. 2-23. To measure total circuit current, you
should break the circuit to connect an ammeter at which of the following points?
1. A only 2. B or C 3. C, D, or E 4. A, B, or F
2-24. To measure the current flow through resistor R2 only, you should break which of the following points to connect the ammeter?
1. A 2. B 3. C 4. F
2-25. Meter sensitivity is determined by the amount of current required by the ammeter coil to provide full-scale deflection of the pointer. An ammeter coil requiring which of the following current values provides the greatest sensitivity?
1. 1 milliampere 2. 10 milliamperes 3. 100 microamperes 4. 500 microamperes
2-26. Circuits in which low-sensitivity ammeters are used are said to be "loaded." Which of the following statements describes the cause of circuit loading?
1. The ammeter circuit draws NO
current from the circuit being tested 2. The ammeter circuit draws
3. The ammeter circuit draws EXCESSIVE current from the circuit being tested
4. The ammeter circuit INDUCES current into the circuit being tested
2-27. In which of the following electronic
circuits does the use of a meter with low sensitivity have the greatest loading effect?
1. High-power circuits 2. Low-current circuits 3. High-current circuits 4. High-voltage circuits
17
2-28. A basic D'Arsonval meter is used to measure voltage by connecting its meter coil to (a) what type of component in (b) what circuit arrangement?
1. (a) Multiplier resistor
(b) series 2. (a) Multiplier resistor
(b) parallel 3. (a) Capacitor
(b) parallel 4. (a) Capacitor
2-29. In a voltmeter, the D'Arsonval meter movement is caused to move by what electrical action?
1. Power 2. Voltage 3. Current 4. Conductance
2-30. In a voltmeter, the meter scale is calibrated in which of the following categories?
1. Power 2. Voltage 3. Current 4. Conductance
2-31. To figure the total value of series resistance needed to extend the range of a voltmeter, you need to know the value of current to cause full-scale deflection of the meter and what other value?
1. Minimum applied voltage 2. Maximum applied voltage 3. Maximum applied current 4. Minimum applied current