Re: integrating true RMS wattmeter

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: dest <dest@xxxxxxxxxxxxx>

Hallo Dave.

> Original poster: Sparktron01@xxxxxxxxxxx

>  > c) why did this thing was so nonlinear: -12.66% error at the begin of
>  > scale and +2.69% error at the end? what was the reason of
>  > _nonlinearity_ at all - optocoupler or op amp?
> ----------------------------------------------------
> Reason for non-linearity and inaccuracy is op-amp (741 was used) and
> optocoupler.
>  You are using the optocoupler at the lower end of its operating
> range, so some low range nonlinearity  shoulc be expected).
> -----------------------------------------------------


look - you need +-15v supply for oa, so probably you already have
a small 220/15v stepdown transformer for this purpose, then you can
wind one more secondary on it (even with 5kv insulation, but i think
we don`t need this at all), get, say, +15v (well regulated - small
current) from it and use this galvanic decoupled source to bias
optocoupler diodes, so they would feel just fine even at 1v in mains.
can this improve linearity without any further complicating of ckt
significantly? am i totally stupid here or only partially? : )

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I don't doubt that my logic is flawed, could somebody tell me where?
08-08-97 (c) Gary Lau