> > Russell, this is indeed a good introductory issue ! However, I have seen
> > an 1Kg kitchen scale, with 8 pF full delta-C variation for the whole 1Kg
> > range, and the sensor was connected directly to the microcontroller !.
> > The resolution was about 1g and precision about 10g. How they did this ?
>
> Double slope converter and/or balance detector. I have an italian kitchen
> scale with 2kg fs and 1g resolution *and* precision (yes, I checked with
> many individual small weights). No big deal. The sensor is connected
> directly to a micro as far as I can tell. Jeweller's scales work the same
> and are even more accurate (50 grams f.s. and resolve 0.01 grams). I
> suppose that there is temperature compensation and spring non-linearity
> compensation built into the micro somewhere. My scale takes quite a while
> to tare. It is very accurate afterwards.


Peter -

Would you be willing to provide a closeup picture of your sensor or describe
how it works. I'm not trying to build scales per se. I would be happy to buy
such a sensor if it was cost effective although, if we go capacitive, we
will probably end up building our own..

I suspect it is full differential symmetric with tracking (synchronous)
detector. Accuracies far better than that are reported for this type of
sensor.


        Russell McMahon

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