Since you have a processor, you can compute the true RMS.

Basically, RMS is mathematically the same thing as standard deviation.  You
collect samples over a period of time long enough to span several samples.
As you collect the samples, compute the sum of the samples, the sum of the
samples squared, and make sure you know how many samples you've collected.
Then a few more computations (look it up in a statistics textbook, and you
may need to do a little algebra), and you have it.  The usual algorithms in
most textbooks assume you have the samples stored in an array, so they make
two passes at the samples computing the sum and sum of squares, but with a
little algebra, it can be done in one pass without storing any of the
samples, so you don't need 10 times the RAM of a PIC.

> -----Original Message-----
> From: Friedel Bruening [mailto:bolinst@COTAS.COM.BO]
> Sent: Monday, November 12, 2001 12:38 PM
> To: PICLIST@MITVMA.MIT.EDU
> Subject: Re: [EE]:Measuring AC currents
>
>
> At 07:15 a.m. 12/11/01 -0700, you wrote:
> >I am looking at 60 Hz, 120VAC.  Basically to monitor the
> loads on each of
> >the circuit breakers.  So accuracy is not high, but I would
> like it as best
>
> You  may start off with a current transformer for isolation
> and in order to
> make the thing overload proof, very important.
> You can make that yourself if you need just some, or you may buy them
> BTW, what will be the range you are looking at, mA, A, 1000A,
> then you need a circuit to sense the current transformer, I
> can help you
> with that if you need the circuit.
> Then you need the rectifier circuit in order to a DC voltage which is
> proportional to you AC currrent, the AD536 (get yourself a datasheet)
> solution is kind expensive but TRUE RMS measurment, the other
> solution using
> an OP and diode will give avarage measurement.
> If you need I can help you with the circuit again
>
> Friedel
>
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