Re: True RMS and averaging.

Jerry Avins <jya@xxxxxxxx> wrote:
(snip)

You need to get the decrement just right with an exponential averager,
and even then it's only approximate. By squaring each reading, adding it
to the sum of squares, stuffing it into the circular buffer, and
subtracting what comes out the end from the sum of squares, there is an
exact result at all times. The cost is one squaring, one add, one
subtract, one store, one read, and two pointer updates for each phase.
That is probably acceptable. (Don't try this with floating point.
Fixed-point arithmetic makes the boxcar from winding up.)

But how do you know how long to make it?

Well, I suppose with the decaying average you also need a constant.

If you know the period, then yes you can do that and average over
one period. If you don't know the period, as most True RMS DVM's
don't, then what do you do?

-- glen
.

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