On Tue, 11 Nov 1997 18:04:58 -0400, you wrote:

>Dave Celsnak wrote:
>.....
>> Not sure what a load cell is....
>.....
>
>A load cell is a piece of steel with strain gauges in wheatstone-bridge
>configuration in it, normally used for weighting purposes....
>
>As the steel (and the strain gauges glued on it) deforms, the resistance
>values of the bridge change, and there develops an output voltage between
>two of the legs of the bridge, normally a very small voltage (in the order
>of some mV), not so easy to measure and process in an industrial
>environment with lots of noise, induction on cables, sometimes very high
>temperature fluctuations, and the like. Also the input voltage to the
>bridge must be held very constant, or there must be some means to measure
>that voltage too and compensate (software !!!) for fluctuations in it I
>think.......
Not necessarily - if you link the ADC reference to the bridge supply
(e.g. connect both to a stable supply rail), the errors cancel out.
You do need to be careful, though if there are significant offsets &
tempcos to deal with.  
     ____                                                           ____
   _/ L_/  Mike Harrison / White Wing Logic / wwl@netcomuk.co.uk  _/ L_/
 _/ W_/  Hardware & Software design / PCB Design / Consultancy  _/ W_/
/_W_/  Industrial / Computer Peripherals / Hazardous Area      /_W_/