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Figure 72. Measurement of PARD (Ripple and Noise) for a CV Supply
Either a twisted pair or preferably a shielded two-wire cable should be used to connect the output terminals of
the power supply to the vertical input terminals of the scope. When using shielded two wire, it is essential for
the shield to be connected to ground at one end only so that no ground current will flow through this shield
preventing induced noise signals in the shielded leads.
To verify that the oscilloscope is not displaying ripple that is induced in the leads or picked up from the
grounds, the (+) scope lead should be shorted to the (-) scope lead at the power supply terminals. If the ripple
magnitude of the "shorted" test approaches the actual ripple measurement, then the measurement results are
unreliable.
In most cases, the single-ended scope method of Figure 72B will be adequate to eliminate non-real components
of ripple and noise so that a satisfactory measurement may be obtained. However, in more critical cases, or in