Chapter 5 Special Application Test Equipment
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5-1 UNCLASSIFIED 5 SPECIAL-APPLICATION TEST EQUIPMENT LEARNING OBJECTIVES
Upon completing this chapter, you should be able to:
1. Explain the theory of operation of two types of power meters. 2. Describe the purpose of the controls and indicators found on power meters. 3. Describe the proper procedure for taking power measurements for incident and reflected energy. 4. Describe the uses and purposes of the controls and indicators found on the signal generator. 5. Explain the theory of operation of a typical frequency counter. 6. Describe the uses and purposes of the controls and indicators found on the frequency counter. 7. Explain the uses and purposes of the controls and indicators found on the Huntron Tracker 2000. 8. Describe the proper procedures for troubleshooting with a logic probe. 9. Describe the proper procedures for troubleshooting using the Huntron Tracker 2000.
5.1 INTRODUCTION In chapters 3 and 4, you studied the more common pieces of test equipment. As a technician, you will routinely use this test equipment to troubleshoot and perform maintenance on electronic equipment. However, the equipments you will study in this chapter may or may not be found in your shop. This is because these equipments have specific or specialized uses. Unless your rating is involved with the equipment with which they are used, you may not have reason to use them. They are presented here so that you will be familiar with their overall function should the need arise. The equipments you will study in this chapter are power meters, signal generators, frequency counters, and integrated circuit-testing devices.
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5-2 UNCLASSIFIED 5.2 POWER METERS As a technician, you will use a POWER METER to measure power. There are various types of power meters, some of which are called WATTMETERS. Figure 5-1 shows the AN/URM-120 wattmeter, which is one type of power meter commonly used in the Navy. This particular power meter measures power directly; that is, you connect it directly between the transmitter output (rf source) and the load, most likely an antenna.
Other types of power meters measure power indirectly; that is, they sample power in other ways - but not by being placed directly between the output of the transmitter and the load. Let's discuss the direct-measuring power meter first; then we'll talk about an indirect-measuring power meter.
Figure 5-1 Wattmeter (AN/URM-120)
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5-3 UNCLASSIFIED 5.2.1 Direct-Measuring Power Meters The direct-measuring power meter is designed to measure incident (forward) and reflected (reverse) rf power from 50 to 1,000 watts at 2 MHz to 30 MHz and 10 to 500 watts at 30 MHz to 1,000 MHz. Three separate COUPLER-DETECTORS (sometimes called ATTENUATORS), each rated to cover a portion of the frequency and power ranges, are provided with the wattmeter. These devices couple the rf signal into the wattmeter and detect the signal. The coupler-detector knob projects through the top of the wattmeter case, as shown on the AN/URM-120 wattmeter in figure 5-1.
A nameplate on the top of the POWER RANGE knob indicates the power range. The POWER RANGE knob can be rotated 360º to the desired power range. The coupler- detector rotates 180º inside the metal case for either forward or reverse power measurements. Also located inside the metal case are the indicating meter and cable for interconnecting the meter to the coupler-detector. The LOCKING knob locks the coupler- detector and POWER RANGE knobs in place.
Two N-TYPE connectors (one male and one female) are located on either side of the wattmeter case to connect the instrument between the power source and the load. The upper and lower parts of the wattmeter are held together with quick-action fasteners, which permit easy access to the inside of the wattmeter.
Power measurements are made by inserting the proper coupler-detector and connecting the wattmeter in the transmission line between the load and the rf power source. To measure incident power with the wattmeter, rotate the arrow on the COUPLER- DETECTOR knob toward the load, and position the POWER RANGE knob for peak meter reading. To measure reflected power, position the arrow toward the rf power source.
In effect, rotating the coupler-detector causes the coupler to respond only to a wave traveling in a particular direction, either to (incident) or from (reflected) the load. It will be unaffected by a wave traveling in the opposite direction. A diode rectifier in the coupler rectifies the energy detected by the coupler. This detected rf energy is measured across a known impedance to obtain either incident or reflected power.
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5-4 UNCLASSIFIED 5.2.1.1 Operating the Wattmeter Always de-energize and tag the rf power source before measuring incident power. Insert the proper coupler-detector for the rf power being measured into the wattmeter case. Remove the wire shunt (not shown in figure 5-1) from the meter terminals, then connect the wattmeter into the transmission line, either at the load or the rf source. Ensure that all connections are tight.
Position the POWER RANGE knob to a value higher than the rated power of the rf source.
CAUTION
If the rated power to be measured is not known, place the POWER RANGE knob in the highest power position before turning on the power source.
Q-1. To measure incident power, you must rotate the coupler-detector of the wattmeter so that the arrow indicating power flow points toward which end of the transmission line? Reflected power is measured in the same manner as described for incident power, except that the coupler-detector is rotated so that the arrow points toward the rf source.
After completing power measurements, de-energize the rf source, disconnect the wattmeter from the transmission line, and place the wire shunt on the meter terminals.
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5-5 UNCLASSIFIED 5.2.1.2 Interpreting Power Measurements Made by the Wattmeter The rf power measurements made by the wattmeter are used to determine the voltage standing wave ratio (VSWR) of the load and the power absorbed by the load. (VSWR is covered in NEETS, Module 10, Introduction to Wave Propagation, Transmission Lines, and Antennas.) The VSWR can be determined from a chart provided in the wattmeter technical manual, or it can be calculated (as shown in the following example for a UHF transmitter) by the formula below (Pi is the incident power, and Pr is the reflected power as measured by the wattmeter):
Where:
Pi = 30 watts
Pr = 0.5 watts
VSWR = �Pi + �Pr �Pi − �Pr
VSWR = √30 + √0.5 √30 – √0.5
= 5.47 + 0.71 5.47 − 0.71
= 6.18 4.76
= 1.30
The example above results in a standing wave ratio expressed as 1.3 to 1. In a perfectly matched transmission line where there is no reflected power (P r = 0), the standing wave ratio would be 1 to 1. A standing wave ratio of 1.5 to 1 indicates a 5-percent reflection of energy (loss) and is considered to be the maximum allowable loss. So, our example is within allowable limits.
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5-6 UNCLASSIFIED If the standing wave ratio is greater than 1.5 to 1, then the transmission line efficiency has decreased and troubleshooting is necessary. An excellent discussion of the reasons for standing wave ratio increases is presented in EIMB, Test Methods and Practices, NAVSEA 0967-LP-000-0130.
You can determine the rf power absorbed by the load simply by subtracting the reflected power reading from the incident power reading made by the wattmeter (30 watts - 0.5 watts = 29.5 watts).
The power meter just discussed is often described as an IN-LINE POWER METER because readings are taken while the power meter is connected in series with the transmission line. Another type of power meter used by the Navy measures power indirectly. An example of an indirect-measuring power meter is described in the next section.
5.2.2 Indirect-Measuring Power Meters An example of an indirect-measuring power meter is the HP-431C, shown in figure 5-2. The controls, connectors, and indicators for the power meter are illustrated in figure 5-3. This power meter can be operated from either an ac or dc primary power source. The ac source can be either 115 or 230 volts at 50 to 400 hertz. The dc source is a 24-volt rechargeable battery. Overall circuit operation of the power meter is shown in the block diagram in figure 5-4.
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Figure 5-2 Power meter (HP 431C)
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Figure 5-3 Power meter controls, indicators, and connectors
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The HP-431C power meter indirectly measures microwave frequency power by using two bridge circuits - the detection bridge and the compensation and metering bridge. The detection bridge incorporates a 10-kilohertz (kHz) oscillator in which the amplitude is determined by the amount of heating of the thermistors in that bridge caused by microwave power. (Thermistors were covered in chapter 2 of this module.) The compensation and metering bridge contains thermistors that are affected by the same microwave power heating as those of the detection bridge.
An unbalance in the metering bridge produces a 10-kHz error signal. This error signal, plus the 10-kHz bias that is taken directly from the 10-kHz OSCILLATOR-AMPLIFIER, is mixed in the SYNCHRONOUS DETECTOR. The synchronous detector produces a dc current (I dc) that is proportional to the 10-kHz error signal. The Idc error signal is fed back to the compensation and metering bridge, where it substitutes for the 10-kHz power in heating the thermistor and drives the bridge toward a state of balance. The dc output of the synchronous detector also operates the meter circuit for a visual indication of power.
Figure 5-4 Power meter block diagram
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5-10 UNCLASSIFIED Q-2. What condition produces the 10-kHz error signal generated by the metering bridge in the HP-431C power meter? The HP-431C power meter measures rf power from 10 microwatts (−20 dBm) to 10 milliwatts (+10 dBm) full scale in the 10 MHz to 18 GHz for a 50-ohm coaxial system and 2.6 GHz to 40 GHz for a waveguide system.
5.3 SIGNAL GENERATORS Standard sources of ac energy, both audio frequency (af) and radio frequency (rf), are often used in the maintenance of electronic equipment. These sources, called SIGNAL GENERATORS, are used to test and align all types of transmitters and receivers. They are also used to troubleshoot various electronic devices and to measure frequency.
The function of a signal generator is to produce alternating current (ac) of the desired frequencies and amplitudes with the necessary modulation for testing or measuring circuits. (Modulation was discussed in NEETS Module 12, Modulation Principles.) It is important that the amplitude of the signal generated by the signal generator be correct. In many signal generators, output meters are included in the equipment to adjust and maintain the output at standard levels over wide ranges of frequencies.
When using the signal generator, you connect the output test signal into the circuit being tested. You can then trace the progress of the test signal through the equipment by using electronic voltmeters or oscilloscopes. In many signal generators, calibrated networks of resistors, called ATTENUATORS, are provided. You use attenuators in signal generators to regulate the voltage of the output signal. Only accurately calibrated attenuators can be used because the signal strength of the generators must be regulated to avoid overloading the circuit receiving the signal.
Q-3. In signal generators, what device is used to regulate the voltage of the output signal? There are many types of signal generators. They are classified by use and the frequency range covered as AUDIO-FREQUENCY (AF) GENERATORS, VIDEO SIGNAL GENERATORS, RADIO-FREQUENCY (RF) GENERATORS, FREQUENCY- MODULATED RF GENERATORS, and other special types, which combine frequency ranges.
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5-11 UNCLASSIFIED 5.3.1 Audio and Video Signal Generators AUDIO SIGNAL GENERATORS produce stable af signals used for testing audio equipment. VIDEO SIGNAL GENERATORS produce signals that include the audio range and extend into the rf range. These signal generators are used to test video amplifiers and other wideband circuits. In both audio and video signal generators (figure 5-5), major components include a POWER SUPPLY, an OSCILLATOR (or oscillators), one or more AMPLIFIERS, and an OUTPUT CONTROL.
In the audio and video generators that produce a beat-frequency, the output frequency is produced by mixing the signals of two separate rf oscillators. One is fixed in frequency, and the other is variable. The difference between the frequencies of the two oscillators is equal to the desired audio or video frequency.
Audio signal generators often include resistance-capacitance (rc) oscillators in which the af is directly produced. In these signal generators, a resistance-capacitance circuit is the frequency-determining part of the oscillator. The frequency varies when either the resistance or the capacitance is changed in value.
Figure 5-5 Af and video signal generator block diagram
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5-12 UNCLASSIFIED In other signal generators, however, the capacitance alone is often chosen as the only variable element. The change in frequency that can be produced by this method is limited, and it is usually necessary to cover the entire range of the generator in frequency steps. This is usually accomplished by providing several rc circuits, each corresponding to a specific portion of the entire range of frequency values. The circuits in the oscillator are switched one at a time to provide the desired portion of the af range.
The amplifier section of the block diagram (figure 5-5) usually consists of a voltage amplifier and one or two power amplifiers, which are coupled by means of rc networks. The output of the final power amplifier is often coupled to the output control (attenuator) by means of an output transformer.
The output control section regulates the amplitude of the signal. A commonly used af signal generator is the model SPN audio oscillator shown in figure 5-6. The model SPN is a programmable synthesized signal generator designed to provide a stable, low-distortion, wide-amplitude range signal over a 1-Hz to 1.3-MHz frequency range. Additionally, the equipment provides a square wave output and means for swept operation with an external signal and can be remotely controlled via an IEEE-488 bus. For the proper operation of any test equipment, you should always refer to the specific technical manual that describes its use.
Figure 5-6 Model SPN audio oscillator
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5-13 UNCLASSIFIED 5.3.2 Radio-Frequency (Rf) Signal Generators In addition to the necessary power supply, a typical rf signal generator contains three other main sections: an OSCILLATOR CIRCUIT, a MODULATOR, and an OUTPUT CONTROL CIRCUIT. The modulator modulates the rf signal of the oscillator. In addition, most rf generators are provided with connections through which an external source of modulation of any desired waveform can be applied to the generated signal. Metal shielding surrounds the unit to prevent signals from the oscillator from affecting the circuit under test.
Q-4. Name the three main sections of a typical rf signal generator. A block diagram of a representative rf signal generator is shown in figure 5-7. The function of the oscillator stage is to produce a signal that can be accurately set in frequency at any point within the range of the generator. The type of oscillator circuit used depends on the range of frequencies for which the generator is designed. In lower frequency rf signal generators, the oscillating circuit consists of one of a group of coils combined with a variable capacitor. One of the coils is selected by the position of a range selector switch that connects the coil to a capacitor to provide an inductance-capacitance circuit. The inductive-capacitance circuit then has the correct range of resonant frequencies.
Figure 5-7 Rf signal generator block diagram
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5-14 UNCLASSIFIED The function of the modulator is to produce an audio (or video) modulating signal that can be superimposed on the rf signal produced by the oscillator. The modulating signal may be provided by an audio oscillator within the generator. This is termed INTERNAL MODULATION. It may also be derived from an external source. This is termed EXTERNAL MODULATION. In some signal generators, either of these two methods of modulation can be employed. In addition, a means of disabling the modulator section is available so that the pure, unmodulated signal from the oscillator can be used when desired.
Q-5. What is the function of the modulating circuit? The type of modulation selected depends on the application of the particular signal generator. The modulating signal may be a sine wave, a square wave, or pulses of varying duration. In some special generators, provision is made for pulses over a wide range of repetition rates and widths.
The output circuit of the rf signal generator usually contains a calibrated attenuator and an output level meter. The output level meter provides an indication and permits control of the output voltage of the generator. The attenuator allows you to select the amount of this output. The attenuator is made up of a group of resistors that form a voltage-dropping circuit.
It is controlled by a control calibrated in microvolts. When the control is adjusted so that the output meter reads unity (1.0), the reading on the attenuator control gives the exact value (no multiplication factor) of the output in microvolts. If an output voltage at a lower value is desired, the attenuator control is varied until the meter indicates some decimal value less than 1. This decimal is multiplied by the attenuator reading to give the actual output in microvolts.
An rf signal generator currently in wide use by the Navy is the HP 8640B (figure 5-8). The HP 8640B signal generator covers the frequency range of 500 kilohertz to 512 megahertz, and can be extended to 1,024 MHz by using adapters.
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This completes our discussion of signal generators. The following section deals with an instrument that measures frequency - the FREQUENCY COUNTER.
Figure 5-8 Rf signal generator (HP-model 8640B)
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5-16 UNCLASSIFIED 5.4 FREQUENCY COUNTERS The signal generators you studied in the previous section provide signals for use in testing, aligning, and troubleshooting electronic equipment. Now, we will study the FREQUENCY COUNTER, an instrument that measures frequencies. Frequency counters are used to measure frequencies already in existence. An example of a typical frequency counter, the model 5328A, is shown in figure 5-9.
5.4.1 General Description of the Frequency Counter The following description is for the model 5328A counter only. Other counters use different techniques to derive the displayed frequency. The outputs available vary from counter to counter. For further information on other types of counters and their uses, refer to EIMB, Test Equipment, NAVSEA 0967-LP-000-0040.
The model 5328A is a portable, solid-state electronic frequency counter. It is used to precisely measure and display, using a nine-digit LED readout, frequency, period, period average, time interval, time interval average, and ratio of electronic frequency signals. This frequency counter can also provide a 1-MHz and 10-MHz output signal through the back-panel BNC.
Q-6. What frequencies are provided through the back-panel BNC?
Figure 5-9 Model 5328A 500 MHz universal frequency counter
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5-17 UNCLASSIFIED The model 5328A frequency counter can be divided into four major internal subsections: the main counter section, input section, power supply, and interface bus section. Additionally, two separate (front panel) input channels provide for time interval measurements. Each channel has an attenuator, trigger slope selector, level control, ac or dc coupling, and an oscilloscope marker output. A third input channel is provided to allow the measurement of 30 MHz to 500 MHz with a maximum input of 5 volts rms with a fused-protected connection.
Front-panel controls are provided for you to do the function selection, frequency resolution, sample rate, and reset display. Also, a push-button control on the front panel allows the unit to be used in the operational or standby mode (power applied to the crystal oven to eliminate warm-up). Rear-panel connectors provide the gated output frequencies and an input for an external frequency standard. A detachable front cover is used to store accessory cables and connectors.
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5-18 UNCLASSIFIED 5.4.1.1 Controls and Indicators Figures 5-10 and 5-11 show all the front- and rear-panel operating controls and indicators. Refer to tables 5-1 and 5-2 for a description of each of the numbered controls and connectors shown in figures 5-10 and 5-11, respectively.
Figure 5-10 Front-panel controls and indicators Figure 5-11 Rear-panel controls and connectors
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5-19 UNCLASSIFIED Table 5-1 Front Panel Controls and Connectors NO. NAME DESCRIPTION 1 LINE switch This is a two-position switch that can be selected for STBY or OPER. When in STBY, the power supply provides power to the oven of the high stability time base to maintain a constant temperature for the crystal. When in OPER, the power supplies normal power to the unit for operation. 2 RESET This button, when pressed, resets the display and internal count to zero. When pressed continuously, this button lights all segments of the LED display and all annunciator LEDs for a LED test. 3 FUNCTION This is a 10-position selector used to select the mode of operation. FREQ A This position, when selected, allows the counter to measure frequency at channel A. FREQ C This position, when selected, allows the counter to measure the frequency at channel C. PER A This position, when selected, allows the counter to measure the period at channel A. PER AVG A This position, when selected, allows the counter to make a period average measurement of the signal at channel A. The number of periods over which the average is made is determined by the RESOLUTION switch selection. T. I. AVG A!B This position, when selected, allows the counter to make a time interval measurement of a signal applied to channel A. The number of time intervals over which the average will be made is determined by the RESOLUTION switch selection made. T. I. A!B This position, when selected, allows the counter to make a time interval measurement. The start signal would be applied to channel A and the stop signal applied to channel B. CHECK This position, when selected, applies a 10-MHz signal to the decade counting assemblies, verifying operation of the SAMPLE RATE control, RESOLUTION switch, and RESET. 3 Continued RATIO C/A This position, when selected, allows the counter to measure the ratio of the frequency at channel C to the frequency at channel A. RATIO B/A This position, when selected, allows the counter to measure the ratio of the frequency at channel B to the frequency at channel A. Top This position is blank and has no function. 4 FREQ RESOLUTION, N This is an eight-position switch that is used to select the resolution in frequency measurements and N for totalizing and averaging measurements. This also determines how long the main gate is open for frequency measurements.
N GATE TIME (seconds) RESOLUTION (Hz) 1 1 X 10-6 1M 10 10 X 10-6 100k 102 100 X 10-6 10k 103 1 X 10-3 1k 104 .01 100 105 .1 10 106 1 1 107 10 .1
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5-20 UNCLASSIFIED NO. NAME DESCRIPTION 5 SAMPLE RATE control This is used to vary the time between measurements continuously from approximately 2 milliseconds to an indefinite hold of the display. 6 500 MHz, 50 Ω This is the channel C input connector. 7, 14 OUTPUT MARKER These are the channel A and B Schmidt trigger outputs used to indicate when a channel is triggered by 0 to 300 mV levels with less than 20 nanoseconds delay. 8, 13 AC/DC These control the selection of ac or dc coupling for the input signal. When the input amplifier control switch (No. 18) is in COM A, channel B coupling is determined by setting of channel A coupling switch. 9, 12 ATTEN switches These select the attenuation of the input signal. The signal amplitude is reduced by 10 in ×10 and by 100 in ×100. When the input amplifier control switch (No. 18) is in COM A, the channel B attenuation is determined by the channel A attenuation switch. 10, 11 INPUT A and B These are the input BNC connectors for channels A and B. 15, 20 LEVEL A/B These controls are used in conjunction with the ATTEN (Nos. 9, 12) to select the voltage at which triggering will occur. With X1 attenuator selected, the level is variable at ±2.5 volts, and ×100 at ±250 volts. 16, 21 Channel A and B triggering lights The light will blink for the associated channel when triggering is occurring. When the light is off, the input signal is below triggering level and on when the signal is above triggering level. 17, 19 Channel A and B SLOPE switch These switches control the selection of triggering on either the positive or negative slope of the input signal. 18 COM A/SEP This is the input amplifier control switch that selects independent operation of channels A and B in SEP (separate) position. When in COM A (common A) position, the signal at A is also applied to channel B; this disconnects the channel B input circuitry. Channel B coupling and attenuation are then determined by the channel A setting. 22 OVERLOAD This indicator will flash on and off if more than 5 volts is applied to channel C input. 23 K, S, M, n, and Hz These will light up to show the appropriate units multiplier of the measurement being taken. 24 LED display This is a nine-digit LED display that shows the numerical measurement taken. 25 OVFL This indicates an overflow of one or more of the most significant digits (leftmost from the decimal point) are not displayed. 26 RMT Lights when the unit is in remote operation. 27 GATE Lights when the counter's main gate is open and a measurement is in progress.
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5-21 UNCLASSIFIED Table 5-2 Rear-Panel Controls and Connectors NO. NAME FUNCTION 1 VOLTAGE SELECTOR Used to select 115 or 230 volt operation. 2 LINE FUSE This requires the insertion of a 2.0 amp fuse for 115 volt or 1.0 amp fuse for 230 volt operation. 3 Input ac connector Used to connect the input ac to the unit. 4 ARM When this switch is in the OFF position, the counter is armed by the signal that is selected for measurement. In the ON position, the measurement is armed by an input other than the input being measured. 5 EXT OSC This input connector allows a separate outside signal to be used for the time base. 6 1 MHz OUT and 10 MHz OUT These connectors allow an internal oscillator signal to be used externally when connected. 7 GATE/MARKER OUT Applies a high to the output when the main gate is open. 8 HP-IB This is an interface bus connector that allows the unit to receive programming instructions.
5.4.1.2 Frequency Measurement As discussed previously, the model 5328A frequency counter is capable of measuring frequency, time period (inverse of frequency), ratio, and time interval. We will start with frequency. When the FUNCTION selector is in the FREQ A or FREQ C position, the counter measures the frequency, f, by accumulating the number of cycles, n, of the input signal that occurs over the time period, t. This is expressed by:
f = n t
The basic counter elements necessary to perform this measurement are shown in figure 5- 12. The INPUT AMPLIFIER/TRIGGER essentially conditions the input signal to a format that is compatible with the internal circuitry of the counter. As figure 5-12 indicates, the output of the amplifier/trigger corresponds directly to the input signal.
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The TIME BASE OSCILLATOR is a 10-MHz temperature-controlled (oven-regulated) precision, crystal oscillator used for the time base element from which time, t, is derived. DECADE DIVIDERS take the time base oscillator signal as the input and provide a pulse train, whose frequency is variable in decade steps. This frequency can be controlled by the FREQ RESOLUTION, N switch. The time, t, is determined by the period of this pulse train.
The heart of the counter is the MAIN GATE. When the gate is opened, pulses from the amplifier/trigger are allowed to pass through. The opening and closing of the main gate is controlled by the decade divider output to the main gate flip-flop. The output of the MAIN GATE is then sent to the DECADE COUNTING ASSEMBLIES (DCAs), where the pulses are combined and displayed after the gate is closed.
If the FREQUENCY RESOLUTION, N selection switch, is set for 10 6, the main gate is open for 1 second, and the decade counting assemblies display the frequency of the input signal in hertz (refer to figure 5-10, FREQUENCY RESOLUTION, N selection switch).
Figure 5-12 Basic elements of the frequency counter
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5-23 UNCLASSIFIED 5.4.1.3 Period Measurement Period, the inverse of frequency, can be measured with the counter by reversing the inputs to the main gate. With the FUNCTION selector switch in the PER A position, the input signal controls the duration over which the main gate is open and the decade divider output is counted by the DCAs (see figure 5-13). The duration of the count is one cycle or period of the input signal. When the FUNCTION selector is in the PER AVG A position, the unused decades in the decade divider chain are used to divide the amplifier/trigger output so that the gate remains open for decade steps of each input period rather than a single period. This is the basis for multiple period averaging. Period and period averaging techniques are used to increase measurement accuracy on low-frequency measurements.
5.4.1.4 Ratio Measurement Placing the FUNCTION selector switch to RATIO C/A OR B/A sets the counter to measure the ratio of the signal frequency at channel C or B to the signal frequency at channel A. Using the same configuration as in figure 5-13 and replacing the time base with a second input frequency, f 2, you can measure the ratio of f 2/f. The signal at frequency f can be divided into decade steps in the same manner as multiple period averaging for higher resolution.
Figure 5-13 Measuring period
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5-24 UNCLASSIFIED 5.4.1.5 Time Interval Measurement Figure 5-14 illustrates the configuration for the measurement of time between two events or time interval. This is done by placing the FUNCTION selector in the T.I.AVG AB position. The START input opens the main gate, and the STOP input closes it. The START input is applied to channel A, and the STOP input is applied to channel B. The decade divider output (clock pulses) is counted, and the display shows the elapsed time between START and STOP signals, as shown in figure 5-15.
Figure 5-14 Basic elements of a time interval counter
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5.4.1.6 Resolution The resolution of the measurement is determined by the frequency of the counted clock (for example, a 10-MHz clock provides 100 ns resolution [see figure 5-10, FREQUENCY RESOLUTION, N selection switch]). The input amplifier, main gate, and DCAs (elements of the time interval counter) must operate at speeds consistent with the clock frequency; otherwise the instrument's resolution would be meaningless. Clock frequencies of 1, 10, and 100 MHz, and other 10n frequencies, are preferred, since the accumulated count, with the appropriate placement of the decimal point, gives a direct readout of the time interval. This explains why the conventional time interval counter is presently limited to 10 nanoseconds, a clock frequency of 100 MHz. One GHz is beyond reach, and a clock frequency of 200 MHz would require some arithmetic processing of the accumulated count in the DCAs to enable time to be displayed directly.
Figure 5-15 Clock pulses
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5-26 UNCLASSIFIED 5.4.1.7 Time Interval Averaging The time interval averaging technique is based on the fact that if the ±1 count error is truly random, it can be reduced by averaging a number of measurements. The words "truly random" are significant. For time interval averaging to work, the time interval must (1) be repetitive and (2) have a repetition frequency that is asynchronous to the instrument's clock. Under these conditions, the resolution of the measurement is:
resolution = ±1 count √N
where N = number of time intervals averaged
With averaging, resolution of a time interval measurement is limited only by the noise inherent in the instrument. The 5328A can obtain 10-picoseconds resolution. Most time interval averaging has one severe limitation: The clock period limits the minimum measurable time interval. With the FUNCTION selector switch in the T.I. AVG AB position, synchronizers are used to remove this limitation. These synchronizers enable the 5328A to measure intervals as short as 100 picoseconds.
Referring to figure 5-16, note that the input waveshape shows a repetitive time interval, which is asynchronous to the square wave clock. When these signals are applied to the main gate, with no synchronizers, an output similar to the third waveform results. Since the DCAs are designed to count at the clock frequency and are unable to accept pulses of shorter duration than the clock, the resulting counts accumulated in the DCAs will be in error, as shown in the fourth waveform. This problem is alleviated by the synchronizers, which are designed to detect leading edges of the clock pulses that occur while the gate is open. They detect and reconstruct the leading edges, making the pulses applied to the DCAs the same duration as the clock, as shown in the fifth waveform. Occasionally, when the input time interval repetition is synchronous with the internal clock, time interval averaging cannot be performed.
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This ends our discussion on electronic frequency counters. Now, we'll study an area of electronics test equipment that is becoming more widespread and important each day - the testing of electronic logic components. A test instrument of value for any technician who works on digital equipment is the LOGIC PROBE, which is an integrated circuit- testing device.
Figure 5-16 Synchronizer operation with time interval averaging
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5-28 UNCLASSIFIED 5.5 INTEGRATED CIRCUIT-TESTING DEVICES Digital integrated circuits are relatively easy to troubleshoot and test because of the limited numbers of input and output combinations involved in circuits. The two-state conditions in logic circuits are often referred to as (1) low or high, (2) on or off, or (3) one or zero (1 or 0).
Other terminology may also be used. Any particular integrated circuit (IC) can be tested by simply comparing it to a known good one. The LOGIC PROBE is a device that can be of great value in troubleshooting digital integrated logic circuits.
The ideal logic probe has the following characteristics:
• It will detect a steady logic level. • It will detect a train of logic levels. • It will detect an open circuit. • It will detect a high-speed transient pulse. • It will have over-voltage protection. • It will be small, light, and easy to handle.
The use of a suitable logic probe can greatly simplify your troubleshooting of logic levels through digital integrated logic circuitry. It can immediately show you whether a specific point in the circuit is low, high, open, or pulsing. Some probes have a feature that detects and displays high-speed transient pulses as small as 10 nanoseconds wide. These probes are usually connected directly to the power supply of the device being tested, although a few have internal batteries.
Most IC failures show up in a circuit as a constant high or low level. Because of this, logic probes provide a quick, inexpensive way of locating the fault. They can also display the single, short-duration pulse that is hard to detect on an oscilloscope. Figure 5-17 shows a basic logic probe.
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The logic probe can be powered from the supply of the circuit under test or from a regulated dc power supply. If a separate power supply is used, the ground points of the power supply and circuit under test should be connected together.
The display LED (light-emitting diode) near the probe tip provides an immediate indication of the logic state existing in the circuit under test. The LED will provide any of four indications: (1) off, (2) dim (about one-half brilliance), (3) bright (full brilliance), and (4) flashing on and off. The LED is normally in the dim state and must be driven to one of the other three states by voltage levels at the probe tip. The LED is usually bright for inputs above the logic "1" threshold and off for inputs below the logic "0" threshold. The LED is usually dim for voltages between the logic "1" and logic "0" thresholds and for open circuits.
Figure 5-17 Basic logic probe
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5-30 UNCLASSIFIED 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 circuit under test at its normal clock (timing) rate while monitoring for various control signals, such as RESET, START, STOP, SHIFT, TRANSFER, or CLOCK. Questions such as "Is the counter operating?" are quickly resolved by noting if the probe indicator is flashing on and off, indicating that pulse train 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.
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5-31 UNCLASSIFIED 5.6 HUNTRON TRACKER 2000 The logic probe we just discussed is but one specialized tool used to isolate problems to the component level. Another device you can use is the Huntron Tracker 2000. It is a very versatile electronic troubleshooting tool that is used to evaluate suspect components and/or locate defective components on 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.
CAUTION Before connecting the Huntron Tracker 2000, you must first secure all power, then discharge all high-voltage capacitors.
5.6.1 Physical Features Because the Tracker 2000 has so many controls and indicators, it would impractical to cover each 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.
5.6.1.1 Front Panel The front-panel (figure 5-18) design allows you to easily select the desired function. All the push buttons are the momentary action type and have light-emitting diode (LED) indicators embedded in them 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.
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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. 3 POWER on/off and INTENSITY control switch 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. 6 RANGE selectors These are push buttons that are used to select one of four impedance ranges: LOW, MEDIUM 1, MEDIUM 2, and HIGH. 7 AUTO selector This push button, when selected, initiates automatic scanning of the four ranges from low to high. The speed of the scanning is determined by the RATE control (item 14) 8 CHANNEL A selector This push button, when selected, causes channel A to be displayed on 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. 10 ALT selector When selected, this push button causes the unit to alternate between channel A and channel B. The speed of this is determined by the RATE control (item 14). Figure 5-18 Front Panel
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5-33 UNCLASSIFIED NO. NAME DESCRIPTION 11 COM test plug This test lead connector is the instrument common to and the common reference point for channel A and channel B. 12 CHANNEL B selector This push button, when selected, causes channel B to be displayed on the 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. 18 PULSE GENERATOR selectors These push buttons are used to select the output modes of the pulse generator: positive (+), negative (-) or PULSE/DC. 19 FREQUENCY selectors These push buttons are used to select one of the three test signal frequencies: 50/60 Hz, 400 Hz, 2000 Hz.
5.6.1.2 Cathode-Ray Tube (CRT) Display The CRT display (figure 5-19) is used to view the signature of the component under test. The display has a graticule consisting of 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.
Figure 5-19 CRT display
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5-34 UNCLASSIFIED • 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? The horizontal axis (see figure 5-19) is divided into eight equal divisions, allowing the technician to 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.
5.6.1.3 Back Panel The back panel (figure 5-20) provides three additional controls and connectors. One is the accessory output connector (ACC), which provides a clock signal and power for the Huntron Switcher Model 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.
Figure 5-20 Back panel
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5-35 UNCLASSIFIED 5.6.2 Operation 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.
5.6.2.1 Initial Setup First, turn the POWER/INTENSITY knob located on the front panel to the clockwise, on, position. Under normal conditions, the unit will come on with the following LEDs illuminated: power, channel A, 50/60 Hz, low range, and pulse/DC.
Focusing the CRT is very critical for the technician to be able to properly analyze the signature being 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.
Aligning the trace will help determine, during troubleshooting, which quadrant the portion of the signature is in during a change. With a short circuit applied to channel A (connect a cable between jack A and COM), adjust the TRACE ROTATE control until the trace is as close to parallel as possible to the 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? With an Open applied to channel A (nothing connected to A and COM test plug), adjust the VERT (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.
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5-36 UNCLASSIFIED 5.6.2.2 Range Selection 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 useful signature display when troubleshooting a component, you should always start by selecting one of 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.
The AUTO feature, when selected, will allow the unit to automatically scan through the four ranges at a speed set by the technician using the RATE control knob. This allows the user to keep his or her hands free to hold test leads while still being able to observe the component under test signature for 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.
5.6.2.3 Channel Selection You can select two channels by pressing the channel A (test probes connected to A jack and COM) or channel B (test probes connected to B and COM jacks) push button on the front panel. When using a single channel, you should plug the red probe into the corresponding channel test jack, and plug the black 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 procedure every time will ensure that the signature for the component under test will be displayed in the correct quadrants of the CRT display.
The ALT (alternate) mode provides automatic switching back and forth between channel A and 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 switching between channels A and B can be varied by adjusting the RATE control knob on the front 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.
Figure 5-21 shows a typical way of connecting the unit to a known good circuit board and a board 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.
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Figure 5-21 ALT (alternate) mode setup Figure 5-22 AUTO/ALT sequence
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5-38 UNCLASSIFIED 5.6.2.4 Frequency Selection There are three test signal frequencies (50/60 Hz, 400 Hz, and 2000 Hz) that can be selected and then 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.
5.6.2.5 Pulse Generator 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 probes, you can connect the output of the pulse generator to the control input of the device to be tested 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.
There are a variety of output waveforms available using the pulse generator selection buttons, as 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.
Figure 5-23 Pulse generator comparison mode
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Next, the technician needs to select the polarity of the output desired by using the positive (+) and/or 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.
Once the specific output type has been selected, the output desired by the technician is set using the 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).
The start of a pulse will be triggered by the appropriate zero crossing of the test signal, which results 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.
Figure 5-24 Pulse generator selector chart
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5-40 UNCLASSIFIED 5.6.3 Functional Overview There are six major sections in the Tracker 2000, as shown in the block diagram in figure 5-25. The control logic section controls the selection of the channel, frequency, impedance range, and pulse 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 driven by the test signal, while signal conditioners monitor the jacks and produce the horizontal and 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.
Figure 5-25 Tracker 2000 block diagram
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5-41 UNCLASSIFIED 5.6.3.1 Control Logic The control logic senses which button is pushed on the front panel. Since the buttons are the momentary action type, the logic must remember what button was pushed, turn on the LED indicator within the button, and activate the appropriate configuration of the oscillator, signal, and pulse generator sections.
After a button is pushed, the unit will remain in that configuration until another selection is made or 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 already selected and the CHANNEL B button is pressed, CHANNEL A will be canceled and CHANNEL 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. Pressing either of the channel buttons will cancel the ALT mode, and the selected channel will then become active.
The FREQUENCY buttons (50/60, 400, and 2000 Hz) directly control the operation of the oscillator 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).
Table 5-4 Terminal Characteristics for Impedance ranges RANGE OPEN CIRCUIT VOLTAGE (Vp) SHORT CIRCUIT CURRENT (mAr) High 60 0.57 Medium 2 20 0.53 Medium 1 15 8.5 Low 10 132
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5-42 UNCLASSIFIED You can select the four ranges manually by pressing the RANGE button, or you can scan them 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 and ALT (alternate) are active at the same time, the RATE control affects the speed of both functions 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).
The HIGH LOCKOUT function disables the HIGH range and limits the maximum test signal to 20 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 LOCKOUT is pressed, the HIGH range is canceled and the next lower range (MED 2) will be selected and become active. When you select the AUTO mode, the RANGE sequence with the HIGH LOCKOUT active will start with LOW, and sequence through MED 1, MED 2, back to LOW, and continue until the AUTO mode is stopped.
The PULSE GENERATOR buttons (positive [+], negative [−], and PULSE/DC) toggle control lines that change the polarity and output type of the pulse generator.
Figure 5-26 Range scanning sequence with AUTO and ALT active
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5-43 UNCLASSIFIED 5.6.3.2 Oscillator The oscillator produces a constant amplitude, low distortion sine wave test signal. The frequency of the test signal is programmable between one variable frequency (50/60 Hz), and two fixed frequencies (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.
5.6.3.3 Signal Section 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.
The test signal causes a current to flow through the device and a voltage drop to occur across its 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.
The test signal appears at the front-panel test jacks as though it is being originated by a voltage source (V s) 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 deflection plates of the CRT, and how the current through the terminals affects the vertical deflection plates through current sensing point I.
Figure 5-27 Signal section equivalent circuit
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5-44 UNCLASSIFIED An open circuit has zero current flowing through the terminals and maximum voltage drop across the 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.
5.6.3.4 Pulse Generator The pulse generator provides dynamic testing for certain types of devices by driving the control input 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.
In the PULSE mode, this circuit uses the zero crossing of the test signal to trigger the start of the 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.
Figure 5-28 Open and short circuit display
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The LEVEL control adjusts the peak of each pulse from zero to 5 volts with the polarity dependent on the pulse polarity selected. When an open circuit is present, a maximum output of 5 volts peak-to-peak is present with either positive or negative selected, and 10 volts peak-to-peak when the composite pulse is 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.
Figure 5-29 Pulse generator waveforms
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5-46 UNCLASSIFIED 5.6.3.5 CRT Display The CRT deflection drivers boost the low-level outputs from the signal section to the higher voltage 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.
Three other controls (INTENSITY, FOCUS, and astigmatism) are used to adjust the proper 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.
5.6.3.6 Power Supply The power supply is an ac-line-operated power supply that is turned on and off by the 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 V rms, +180 V dc for the deflection driver circuits, and a regulated −1320 V dc for the CRT acceleration voltage.
5.6.4 Component Testing Now that you have a basic understanding of how the Tracker 2000 works, we will show you a few 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.
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5-47 UNCLASSIFIED 5.6.4.1 Testing Resistors A resistance across the test probes will cause the trace of the Tracker 2000 to rotate in a counter-clockwise 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).
Figure 5-30 Effects of resistance on the rotation angle in low range
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5-48 UNCLASSIFIED 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?
Figure 5-31 Effects of resistance on the rotation angle in medium 1 range
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5-49 UNCLASSIFIED 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.
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 3K_ 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.
Figure 5-32 Effects of resistance on the rotation angle in medium 2 range Figure 5-33 Effects of resistance on the rotation angle in high range
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5-50 UNCLASSIFIED 5.6.4.2 Testing Capacitors 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 0.22F 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 signatures displayed are a variety of ellipsoids, which demonstrates that certain range and frequency combinations are better than others for examining a capacitor.
Figure 5-34 Signature of a 0.22μF capacitor
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5-51 UNCLASSIFIED Table 5-5 lists the range of capacitance covered by each of the 12 range and frequency combinations 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 uppermost value of capacitance in each combination will produce a very narrow vertical ellipsoid signature. Capacitors of greater value than these will appear as a vertical line signature of a short circuit.
Table 5-5 Min/Max Capacitance Values RANGE TEST FREQUENCY 50/60 Hz 400 Hz 2000 Hz 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
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5-52 UNCLASSIFIED 5.6.4.3 Testing Inductors 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.
Figure 5-35 Signatures of a 250mH inductor
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5-53 UNCLASSIFIED Ferrite inductors can also be checked using this unit; however, the signature produced will be 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 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.
Figure 5-36 Signatures of a 490mH ferrite inductor tested at 60 Hz.
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Figure 5-37 Signature of a 490mH ferrite inductor at 400 Hz. Figure 5-38 Signature of a 490mH ferrite inductor at 2000 Hz.
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5-55 UNCLASSIFIED 5.7 SUMMARY 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.
The principal function of a SIGNAL GENERATOR is to produce an alternating voltage of the desired frequency and amplitude, which has the necessary modulation for the test or measurement 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.
An instrument of great value to a technician in troubleshooting digital integrated logic circuits is the LOGIC PROBE.
The HUNTRON TRACKER 2000 is a versatile piece of test equipment that is used to compare known good devices against those of unknown quality or troubleshoot to the component level after power is disconnected to the device under test.
NEETS Module 16, NAVEDTRA 14188A UNCLASSIFIED
5-56 UNCLASSIFIED 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. 50 Ω to 10KΩ.