Grunff wrote:
Hi all,

This would probably fit better in another NG, but I know quite a few
people on here who will be able to provide some good ideas, so here goes.

I have an experiment where a voltage of ~250 VDC is applied across a
load, resulting in a current consumption of around 2A. The experiment
runs for around 5 minutes.

The nature of the load is such that the current consumption is very
spiky - it may average to around 2A, but you get very short, sharp
spikes, probably of 10-15A.

I need to be able to measure, with 1% or better accuracy, the total
energy dissipated in the load over the duration of the experimental run.

I don't need instantaneous V or I values - all I need to know is the
total energy consumption over the run.

The only sensible way I can think of doing this is to use a data logger,
and sample V and I at a high rate thoughout the experimental run, then
calculate average power over the run, then multiply by run time.

However, this seems like a very round-about way of achieving my goal.
Anyone have any thoughts on other ways of doing this? I must stress that
it is the electrical energy input to the system that I'm interested in,
so measuring temperature rise of the load etc. is out of the question.


TIA



If you want super accurate, you'll need to sample the instantaneous
voltage and current rapidly and record the results for the length
of your experiment.

From that you can work out the power consumption by computing the
instantaneous power, and then integrating that over the period of
the experiment.

For less accuracy, you could:

1. Assume a constant mains supply voltage & frequency
2. Using a True RMS meter with peak avg/min/max record
facility, measure the current.
3. Compute the avg/min/max power from the meter readings
and assumed supply voltage.

For example, a Fluke 87 meter would do this quite happily.

Cheers,
Mark.