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Logging DC Ripple Voltages

The following describes a method for using the Power Recorder to monitor and log the ripple voltage on a direct rectified DC power rail.

  1. Set the Recorder to "Split Single Phase"
  2. Connect N & G to the DC rail negative
  3. Connect A to any mains input phase
  4. Connect B to the DC rail positive

Phase A is used by the Recorder to phase-lock to the 50/60Hz and, depending on the rectification methods used, could read anywhere from half to almost full Line-Line voltage.

Phase B is the ripple voltage. The harmonics will clearly indicate the number of "rectification pulses". At 50Hz - single phase full wave should show a high 100Hz i.e. 2-pulse, 3-phase showing 300Hz i.e. 6-pulse. Any lower order harmonics will indicate the magnitude of rectification imbalance, or even a blown rectifier.

Note: Input G is not the instrument earth and therefore there is no need for concern about inadvertently grounding the negative DC power rail.


This is usable to a maximum Line-Line voltage of 450VACrms, and 650VDC.

High speed capture must be turned off. Depending on the effectiveness of the diodes in the rectification portion, there are likely to be many switching occurrences that could be construed as high speed events and could flood the recorder.

A Recorder that has been fairly well calibrated (as opposed to verified) must be used. Any imbalance on the inputs will lead to high fundamental voltage readings adding to the ripple voltage.

Although the harmonics are useful for determining the extent of any rectification imbalances, they cannot be used as absolute values for harmonic analysis of the ripple voltage.

If there are any questions please ask.

Note: This web page does not form part of any official documentation.
Any information contained herein is used at own risk.

©  M.T.P. - 24.12.02