Hi Rick:
> On the surface it seemed like a simple exercise of putting a DC current
> meter in series with each of the outputs. Given that the current demand
> for each of these outputs is dynamic, corresponding with the processing
> activity, does it make sense to measure this output current with a True
> RMS meter?
Since you said you wanted to "baseline output power,"
then you would want to use a true-rms meter.
Power is a measure of the electric energy that could
be converted to thermal energy. Consequently, you
must measure any ac component with a true-rms meter.
A true-rms meter will measure both dc and ac.
However, this may not give you what you want if the
dynamic periods of current change are longer than the
period of the meter measurement. However, if you get
a constant current reading, then you are getting an
accurate measure.
> If this is the case, I would assume that the True RMS meter takes the
> measurement based on some type of a time weighted average or sample
> time. Do any of you have a feel for how this is calculated?
There are basically two kinds of true-rms meters.
The first kind essentially converts the energy to
thermal energy, and measures the temperature.
The second kind does an analog-to-digital conversion,
and then calculates, point-by-point, the rms value
of the waveform.
If you have access to an electronic instrument museum,
you can use any analog meter that has an iron-vane
meter movement.
RMS = Root of the Mean of the Squares of each
increment of the waveform.
> How do manufacturers of these PC supplies address the maximum output
> current ratings for each voltage. Does this rating take into account
> PEAK demands for current (or over current)?
Most power supplies are rated according to the maximum
continuous load. The ratings for multiple-output
supplies is when all outputs are loaded to their
maximum continuous load.
(Typically, if any one output is loaded and all others
are not loaded, then that one output can be quite a bit
higher than its rating. But, this is taken as a fault
condition in the load.)
Peak ratings are specific to the power supply and its
application. Essentially, the peak rating (and its
repetition) are determined by the output storage
capacitor, both discharge time and charge time.
Best regards,
Rich
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