"Grunff" wrote in message
...
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


--
Grunff

I may remember incorrectly, but old rms power meters used to work on the
temperature rise
reated by the power passing through, didn't they? The time constant of such
a meter may be long enough to integrate the spikes out. However, the output
will be analogue which isn't convenient
for data analysis if the rmspower varies significantly on a timescale longer
than the thermal time constant of the meter. You could run theoutput to a
pen plotter ( if available ) and integrate visually
the area nder the curve. All very laborious of course. Perhaps apparatus
that is essentially a calorimeter would work ( i.e. pick off some of the
load power with a series resistor which sits inside a calorimeter: wait five
minutes and measure the temperature rise ).

Andy.