Wayne Kerr AP10030, Руководство пользователя и обслуживания

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40 Wayne Kerr AP 1kW Power Supplies • Issue 2
8.3.7 Reassembly and Inspection
Check that the earth conductor is secure and undamaged.
Replace the covers ensuring that there is not physical damage to the chassis or the covers
themselves that could reduce safety gaps. Ensure all screws are properly tightened and
trim replaced.
Perform an isulation check @ 500V: input to earth, output to earth and input to output
(In all cases have output shorted and live/neutral shorted together).
8.3 Output Noise And Ripple Measurements
8.3.1 Low Frequency (Mains) Hum And Ripple On Output
This can be observed with an oscilloscope connected to the output in conventional single
channel manner with the timebase locked to mains (line) frequency with a 5-10ms/div.
timebase setting. The waveform will be fairly blurred due to high frequency spikes being
picked up and superimposed on the low frequency ripple waveform. The peak-peak
ripple figure is measured as the voltage between the peaks of the brightest part of the
waveform:
Higher frequency noise
(may not be visible)
10mSec
Ripple
measurement
Fig.8.3. Ripple Measurement
8.3.2 Higher Frequency ‘Spikes’ Measurement
The higher frequency (up to 20MHz) spikes on the output are difficult to measure
accurately with a high impedance single-ended measurement (e.g. standard oscilloscope
probe and single channel). Additional signals are easily picked up and any common-
mode signals (output with respect to ground) register as a differential signal due to the
probe earth impedance at high frequencies.
The recommended measuring system is to use the oscilloscope in a differential mode,
using two channels. This reduces common mode errors. The connections to the
oscilloscope are made via 50
Ω
co-axial leads with a 50
Ω
termination to ground at each
channel input. The connection to the power supply terminals must be capacitively
coupled to prevent damage to the 50
Ω
terminations. See Fig.8.4 .