Exercise 8. Troubleshooting a Radar Target Tracker EXERCISE OBJECTIVE

Transcription

1 Exercise 8 Troubleshooting a Radar Target Tracker EXERCISE OBJECTIVE When you have completed this exercise, you will be able to apply an efficient troubleshooting procedure in order to locate instructor-inserted faults in the Radar Target Tracker of the Lab-Volt Tracking Radar. DISCUSSION Introduction Troubleshooting the target tracker of a tracking radar is basically the same as troubleshooting any electrical, electronic, or mechanical device. Individual initiative and imagination, coupled with efficient and effective techniques are important elements in successful troubleshooting. Good troubleshooting techniques depend on a sound understanding of the equipment and the way it normally operates, as well as a procedure that limits the number of signals which are tested. Troubleshooting Techniques Troubleshooting can be structured according to four levels of activity designed to identify, locate, and correct a problem. Each level brings us closer to the solution of the problem. The levels of activity, listed in the order in which they should normally be performed, are: 1. Observation of the operation of the system (in order to find the symptoms of the problem) 2. Location of the defective part of circuitry 3. Component checking 4. Substitution or replacement of the defective component(s) In this exercise, you will concentrate on the first two levels of activity, with special emphasis being placed on locating the defective part of circuitry. To successfully troubleshoot the target tracker of a tracking radar, it is necessary to understand the equipment and its operation. The best way to start the troubleshooting job is to read through the instruction manual, which will tell you how the equipment should operate. Often, the manual will have lists of typical faults and probable causes. This manual may also include a list of normal operating parameters, functional block diagrams, electrical schematics, timing diagrams showing typical waveforms of the signals at various points in the circuit, etc. Once the problem and its symptoms have been observed, each successive test should reduce the portion of the circuitry suspected to be defective in order to locate 8-1

2 the source of the problem. Signal flow tracing is commonly used as a troubleshooting technique once enough information concerning the problem has been accumulated. Signal flow tracing consists in analyzing signals at different points along their path. Obviously, the equipment should be operated in the situation where defective operation was discovered, while signal flow tracing is performed. The choice of the signal to analyze, and where to analyze it, should never be done on a random basis. A straightforward, logical approach leads to quicker identification and correction of a problem. Signal flow tracing can be approached in two ways. They are basically the same, except for the direction followed in analysis: 1. Signal flow tracing from input to output 2. Signal flow tracing from output to input Depending on the ability and training of the troubleshooter, and on the functional complexity of the equipment, one of the two approaches will be preferred. Extensive knowledge of the equipment operating principles is necessary to trace signals from output to input. Troubleshooting equipment with only one output and multiple inputs can, however, usually be better performed with the output-to-input method. In this exercise, signal flow tracing from input to output will be used because it is the easiest one to carry out. Once a defective part of circuitry has been located, you must be cautious before drawing any conclusions. In certain unusual cases, the problem may be caused by more than one defective part of circuitry. Therefore, you must make sure that the discovered malfunction plausibly explains the problem. If not, there is most likely another defective part of circuitry which would complete the explanation of the problem. A systematic troubleshooting procedure is summarized in the following steps: 1. Observe the problem and note the symptoms. Using various tests, identify the module(s) or operating mode(s) which may be defective. 2. Check the power supplied to each suspected module. On the Radar Training System modules, a green POWER ON LED lights up to indicate that power is supplied to the module. 3. Use signal flow tracing within the module(s) suspected to be defective in order to locate a defective part of circuitry. 4. Verify if there are other branches of circuitry meeting at the point where defective operation has been discovered. If so, verify that these branches are operating normally before concluding that the part of circuitry located in the previous steps is really defective. 5. Once a defective part of circuitry has been located, make sure that its malfunction plausibly explains the problem. If not, there is probably another defective part of circuitry which would complete the explanation of the problem. Return to step 3 of this procedure. 6. Diagnose the problem. 8-2

3 Note: This procedure is also summarized on the Troubleshooting Worksheet at the end of this exercise. Troubleshooting the Target Tracker of a Tracking Radar A common difficulty that arises when troubleshooting the target tracker of a tracking radar is determining whether range or angle tracking prevents normal tracking of a target. This is because range tracking cannot be achieved when the antenna is not properly aligned with the target to be tracked, and angle tracking requires target range information which is usually provided by the range tracker. In other words, tracking a target in both range and angle is no longer possible as soon as either the range tracker or the angle tracker is defective, since the range and angle tracking functions are intimately linked. Therefore, a means for isolating range tracking from angle tracking must be found to help in determining whether the range tracker or the angle tracker is defective. To do so, a target that moves either along or perpendicular to the antenna axis direction can be used. A target moving along the antenna axis direction allows one to determine whether or not the range tracker is defective since angle tracking is not required. On the other hand, a target moving perpendicular to the antenna axis direction allows one to determine whether or not the angle tracker is defective since range tracking is not required. In practice, however, it may not be possible or practical to have a target moving either along or perpendicular to the antenna axis direction for the purpose of troubleshooting the target tracker of a radar. In this case, special test equipment capable of simulating a video signal corresponding to a target moving either along or perpendicular to the antenna axis direction is often used, the video signal being injected into the video input of the target tracker. In the Radar Target Tracker, there are twelve faults which can be activated. Before continuing this exercise, it would be helpful to review Exercises 1 to 5 of this manual. Procedure Summary In the first part of the exercise, Equipment Setup, you will set up the Tracking Radar, position the target table with respect to the Tracking Radar, and calibrate the Tracking Radar. In the second part of the exercise, Guided Troubleshooting of a Fault in the Radar Target Tracker, you will be guided through the Troubleshooting Procedure described in the Discussion, to locate a fault in the Radar Target Tracker. You will fill in the Troubleshooting Worksheet provided at the end of the exercise. This sheet contains a summary of the Troubleshooting Procedure and provides grids to sketch any useful waveforms observed. It is recommended that the steps of the Troubleshooting Procedure be completed in order. In the third part of the exercise, Troubleshooting a Second Fault in the Radar Target Tracker, you will carry out the Troubleshooting Procedure yourself in order to locate another fault in the Radar Target Tracker. 8-3

4 PROCEDURE Equipment Setup G 1. Before beginning this exercise, the main elements of the Tracking Radar Training System (i.e., the antenna and its pedestal, the target table, the RTM and its power supply, the training modules, and the host computer) must be set up as shown in Appendix A. On the Radar Transmitter, make sure that the RF POWER switch is set to the STANDBY position. On the Antenna Controller, make sure that the MANual ANTENNA ROTATION MODE is selected and the SPEED control is set to the 0 position. Turn on all modules and make sure the POWER ON LED's are lit. G 2. Turn on the host computer, start the LVRTS software, select Tracking Radar, and click OK. This begins a new session with all settings set to their default values and with all faults deactivated. If the software is already running, click Exit in the File menu and then restart the LVRTS software to begin a new session. G 3. Connect the modules as shown on the Tracking Radar tab of the LVRTS software. For details of connections to the Reconfigurable Training Module, refer to the RTM Connections tab of the software. Note: Make the connections to the Analog/Digital Output Interface (plug-in module 9632) only if you wish to connect a conventional radar PPI display to the system or obtain an O-scope display on a conventional oscilloscope. Note: The SYNC. TRIGGER INPUT of the Dual-Channel Sampler and the PULSE GENERATOR TRIGGER INPUT of the Radar Transmitter must be connected directly to OUTPUT B of the Radar Synchronizer without passing through BNC T-connectors. Connect the hand control to a USB port of the host computer. G 4. Make the following settings: On the Radar Transmitter RF OSCILLATOR FREQUENCY CAL. PULSE GENERATOR PULSE WIDTH... 1 ns 8-4

5 On the Radar Synchronizer / Antenna Controller PRF Hz PRF MODE SINGLE ANTENNA ROTATION MODE... PRF LOCK. DISPLAY MODE POSITION On the Dual-Channel Sampler RANGE SPAN m In the LVRTS software System Settings: Log./Lin. Mode Lin. Gain as required Radar Display Settings: Range m G 5. Connect the cable of the target table to the connector located on the rear panel of the Target Controller. Make sure that the surface of the target table is free of any objects and then set its POWER switch to the I (on) position. Place the target table so that its grid is located approximately 1.2 m from the Rotating-Antenna Pedestal, as shown in Figure 8-1. Make sure that the metal rail of the target table is correctly aligned with the shaft of the Rotating-Antenna Pedestal. Figure 8-1. Position of the Rotating-Antenna Pedestal and target table. 8-5

6 G 6. Calibrate the Tracking Radar Training System according to the instructions in sections I to V of Appendix B. Guided Troubleshooting of a Fault in the Radar Target Tracker G 7. Ask your instructor to activate fault (FLT) 4 in the Radar Target Tracker while completing the upper section of the Troubleshooting Worksheet. G 8. The first step of the Troubleshooting Procedure is to observe the problem and its symptoms. The next steps of this exercise will allow you to gather information on the problem and its symptoms. Use the hand control to make the antenna rotate in both directions and vary the range gate distance. Does the hand control allow manual control of the antenna position and range gate distance? G Yes G No G 9. On the Radar Transmitter, set the RF POWER switch to the STANDBY position. The RF POWER STANDBY LED should be lit. Remove the small metal plate target from the mast of the target table. Place a semi-cylinder target on the mast of the target table (convex side oriented toward the radar antenna), then tighten the screw to secure the target to the mast. Make the following settings on the Target Controller: MODE TRAJECTORY TRAJECTORY circle TRAJECTORY SPEED mid position DISPLAY MODE SPEED G 10. On the Radar Transmitter, depress the RF POWER push button. The RF POWER ON LED should start to flash on and off. Align the radar antenna with the target and position the range gate marker on the target echo pulse on the O-Scope Display then press the trigger button on the hand control to lock the Tracking Radar onto the target. Try locking onto the target a few times. 8-6

7 Describe what happens. G 11. On the Target Controller, select the POSITION MODE. Use the hand control to align the radar antenna axis with the target. In LVRTS, set the Azimuth Lock Disable to On. This disables automatic angle tracking. On the Target Controller, make sure that the X- and Y-axis SPEED controls are in the MINimum position, then make the following settings: MODESPEED DISPLAY MODE SPEED Set the Y-axis SPEED control so that the target speed is equal to approximately 10 cm/s. Use the hand control to align the range gate marker with the target echo pulse on the O-Scope Display then press the trigger button on the hand control to lock the Tracking Radar onto the target. Does the range tracker seem to operate normally? Briefly explain. G 12. Make the following settings in LVRTS: Azimuth Lock Disable O Range Lock Disable I This enables automatic angle tracking and disables automatic range tracking. On the Target Controller, select the POSITION MODE then use the Y-axis position control to set the range of the semi-cylinder target so that its echo pulse is aligned with the range gate marker on the O-Scope Display. Note: You can also use the throttle control of the hand control to set the range gate distance so that the target echo pulse is aligned with the range gate marker on the O-Scope Display. 8-7

8 On the Target Controller, make sure that the X- and Y-axis SPEED controls are in the MINimum position, then make the following settings: MODE DISPLAY MODE SPEED SPEED Set the X-axis SPEED control so that the target speed is equal to approximately 5 cm/s. Use the hand control to align the radar antenna with the semi-cylinder target then press the trigger button on the hand control to lock the Tracking Radar onto the target. Does the angle tracker seem to operate normally? Briefly explain. Write a description of the problem and its symptoms in the space provided for this purpose on the Troubleshooting Worksheet. G 13. Carry out step 2 of the Troubleshooting Procedure. What can you conclude? Step 3 of the Troubleshooting Procedure consists in signal flow tracing the Radar Target Tracker to locate a defective part of circuitry. Which portion of the Radar Target Tracker should be tested using signal flow tracing? G 14. In LVRTS, set the Range Lock Disable to off. On the Target Controller, select the POSITION MODE. Use the hand control to align the radar antenna axis with the target. On the Target Controller, use the Y-axis position control to set the range of the semi-cylinder target so that its echo pulse is aligned with the range gate marker on the O-Scope Display. Note: You can also use the throttle control of the hand control to set the range gate distance so that the target echo pulse is aligned with the range gate marker on the O-Scope Display. 8-8

9 G 15. In LVRTS, disconnect the Oscilloscope probes 1 and 2 from TP1 and TP2 of the MTI Processor. Leave Probe E connected to TP8 of the Radar Target Tracker. Connect the Oscilloscope probe 1 to TP21 (RANGE GATE output) of the Radar Target Tracker. Make the following settings on the Oscilloscope: Channel V/div Channel Off Time Base ms/div Set the Oscilloscope to Continuous Refresh. Observe the RANGE GATE output signal on the Oscilloscope. Is this signal normal? G Yes G No Note: You can sketch the waveforms of this signal in the grids on the Troubleshooting Worksheet. Can you conclude that the RANGE GATE is defective? Briefly explain. G 16. In LVRTS, disconnect probe 1 connected to TP21 of the Radar Target Tracker then connect it to TP18 of the same module. On the Oscilloscope, set the sensitivity of channel 1 to 2 V/div. Observe the RANGE GATE control signal. Is this signal normal? G Yes G No Can you conclude that the RANGE GATE is defective? G Yes G No Does the malfunction of the defective part of circuitry plausibly explain the observed problem? Briefly explain. 8-9

10 On the Radar Transmitter, set the RF POWER switch to the STANDBY position. The RF POWER STANDBY LED should be lit. Write your diagnosis in the space provided for this purpose on the Troubleshooting Worksheet. Troubleshooting a Second Fault in the Radar Target Tracker G 17. Ask your instructor to return fault 4 in the Radar Target Tracker to its inactive state (O). Ask your instructor to activate another fault in the Radar Target Tracker. G 18. Carry out the Troubleshooting Procedure in order to locate the fault and diagnose the problem. Write your results on the second Troubleshooting Worksheet provided at the end of this exercise. G 19. When the Troubleshooting Procedure is completed, return the fault switch on the Radar Target Tracker to its inactive (O) position. G 20. On the Radar Transmitter, set the RF POWER switch to the STANDBY position. The RF POWER STANDBY LED should be lit. Turn off all equipment. CONCLUSION In the first part of this exercise, guided manipulations helped you to carry out the Troubleshooting Procedure and locate a fault in the Radar Target Tracker. In the second part of the exercise, you gained further experience with this method by locating a second fault in the Radar Target Tracker. You saw that it is important to carefully observe the problem and its symptoms to determine whether range or angle tracking is the source of the problem. 8-10

11 TROUBLESHOOTING WORKSHEET TRACKING RADAR Student's Name: Instructor's Name: Fault:* Troubleshooting Procedure: G 1. Observe the problem and note its symptoms to determine which module(s) may be defective. G 2. Check the power of each suspected module (see that the POWER ON LED is lit). G 3. Use signal flow tracing to locate a defective part of circuitry. G 4. Verify any other branches of circuitry if necessary. G 5. Make sure that the malfunction of the defective part of circuitry plausibly explains the problem observed. If not, return to step 3 of this procedure. G 6. Diagnose the problem. Problem Description and Symptoms**: Suspected Defective Module(s): Diagnosis: Instructor's Comments: Notes: * At instructor's discretion ** If necessary, sketch waveforms in grids provided 8-11

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13 TROUBLESHOOTING WORKSHEET TRACKING RADAR Student's Name: Instructor's Name: Fault:* Troubleshooting Procedure: G 1. Observe the problem and note its symptoms to determine which module(s) may be defective. G 2. Check the power of each suspected module (see that the POWER ON LED is lit). G 3. Use signal flow tracing to locate a defective part of circuitry. G 4. Verify any other branches of circuitry if necessary. G 5. Make sure that the malfunction of the defective part of circuitry plausibly explains the problem observed. If not, return to step 3 of this procedure. G 6. Diagnose the problem. Problem Description and Symptoms**: Suspected Defective Module(s): Diagnosis: Instructor's Comments: Notes: * At instructor's discretion ** If necessary, sketch waveforms in grids provided 8-13

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