5-1 INTRODUCTION
5-2 Upon receipt of the power supply, the performance check (Paragraph 5-10)should be made.
This check is suitable | for | incoming inspection. If |
a fault is detected in | the | power supply while mak- |
ing the performance check or during normal opera- tion, proceed to the troubleshooting procedures (Paragraph 5-48). After troubleshooting and repair (Paragraph 5-58), perform any necessary adjustments and calibrations (Paragraph 5-60). Before returning the power supply to normal operation, repeat the performance check to ensure that the fault has been properly corrected and that no other faults exist. Before doing any maintenance checks, turn-on power supply, allow a ha if-hour warm-up, and read the general information regarding measurement techniques (Paragraph 5-3).
5-3 GENERAL MEASUREMENT TECHNIQUES
5-4 The | measuring device must be connected |
across | the | sensing leads of the supply or as close |
to the | output terminals as possible when measur- |
ing the output impedance, transient response, reg- ulation, or ripple of the power supply in order to achieve valid measurements. A measurement made acress the load includes the impedance of the leads to the load and such lead lengths can easily have an impedance several orders of magnitude greater than the supply impedance, thus invalidating the measurement.
5-5 The monitoring device should be connected to the +S and -S terminals (see Figure 3-2)or as shown in Figure 5-1. The performance characteristics should never be measured on the front terminals if the load is connected across the rear termi- nals. Note that when measurements are made at the front terminals, the monitoring leads are connected at A, not B, as shown in Figure 5-1. Failure to connect the measuring device at A will result in a measurement that includes the resistance of the leads between the output terminals and the point of connection.
Figure 5-1. Front Pane1 Terminal Connections
Figure 5-2. Output Current Measurement Technique
5-6 For output current measurements, the current sampling resistor should be a four-terminal resis- tor. The four terminals are connected as shown in Figure 5-2. In addition, the resistor should be of the low noise, low temperature coefficient (less than 30ppm/°C) type and should be used at no more than 5% of its rated power so that its temperature rise will be minimized.
5-7 When using an oscilloscope, ground one terminal of the power supply and then ground the case of the oscilloscope to this same point. Make certain that the case is not also grounded by some other means (power line). Connect both oscilloscope input leads to the power supply ground terminal and check that the oscilloscope is not exhibiting a ripple or transient due to ground loops, pick-up, or other means.
