"Grunff" wrote in message
...
John wrote:

you need a digital data logger connected to a PC. eg Maplin sell
multimeters with RS232 output which give a serial data o/p. so if the
load has no phase problems you just need to measure the current. I don't
have detailed knowledge of the specs.


If I'm going to go down the data logger route, I will probably go for one
of these:
http://www.audon.co.uk/labjack.html

I used one before in a previous project, and found it to be a very nice
piece of kit.

But that wasn't my question really - I can see how to get the measurement
I want by sampling V and I with a data logger - but I can't help wondering
if there isn't a cleverer, simpler way, given that all I want is total
energy.

Another way of asking the question - I can see how to integrate the data
electronically, after collecting a huge number of data points. But I'm
wondering if there isn't another way of doing the integration. If that
makes sense.


Right, ideally you need to multiply I and V and integrate the product.
Easy if you had an 1960's analogue computer, but these are all in museums
now. The only analogue route I can think of is to use an analogue
multiplier (search in Google) to get the product of V and I. Then construct
an integrator using an OP amp.
http://www.st-andrews.ac.uk/~www_pa/...rt8/Page3.html
You still need to sample the integrator's output, so the integration may as
well be done in the PC rather than in an IC..