Figure 5-9.Constant Current Ripple and Noise
Test Setup
of a regulated power supply. AC ripple and noise current is usually specified and measured in terms of its RMS value.
s -49 Most of the instructions pertaining to the ground loop and pickup problem-s associated with constant voltage ripple and noise measurement
TM 11-6625-2958-14&P
also apply to the measurement of constant current ripple and noise. Figure 5-9illustrates the most important precautions to be observed when measuring the ripple and noise of a constant current sup- ply. The presence of a 120Hz waveform on the oscilloscope is normally indicative of a correct measurement method. A waveshape having 60Hz as its fundamental component is typically associated with an incorrect measurement setup.
5-50 Ripple and Noise Measurement. To check the ripple and noise, proceed as follows:
a. Connect oscilloscope or RMS voltmeter as shown in Figures 5-9Aor 5-9B.
b. Turn VOLTAGE controls fully clockwise.
c.Adjust CURRENT controls until front pan- e 1 ammeter reads exactly maximum rated output cur- rent.
d.The observed ripple and noise should be less than:
6259B 250µVrms
6260B 250µVrms
6261B 250µVrms
6268B 334µVrms
6269B 250µVrms
5-51TROUBLESHOOTING
5-52 Before attempting to troubleshoot this instru- ment, ensure that the fault is with the instrument and not with an associated circuit. The performance test (Paragraph 5-5) enables this to be determined without having to remove the instrument from the cabinet.
5-53 A good understanding of the principles of operation is a helpful aid in troubleshooting, and it is recommended that the reader review Section IV of the manual before attempting to troubleshoot the unit in detail. Once the principles of operation are understood, refer to the overall troubleshooting procedures in Paragraph S-S 6 to locate the symptom and probable cause.
5-54 The schematic diagram at the rear of the manual (Figure 7-11) contains normal voltage readings taken at various points within the circuits. These voltages are positioned adjacent to the applicable test points (identified by encircled num- bers). The component location diagrams (Figures
7-1through 7-8,and Figure 7-10) at the rear of the manual should be consulted to determine the location of components and test points.
5-55 If a defective component is located, replace it and re-conduct the performance test. When a component is replaced, refer to the repair and replacements (Paragraph 5-71)and adjustment and calibration (Paragraph 5-73)sections of this man- u a l
