Dear reader,

I have a weighing scale board with AD623 and AD7708 as an ADC. After instrumentaion amplifier, I have RC filter. Initially I used 1K and 0.uF. But because of fluctuations, I kept on increeasing RC valuse until I reach 100k and 0.33uF. With this fluctuations seems to be less without ham[ering responce. Now when I kept 1Kg. weight, it drifts by 20 gms in 20 mins .

I suspected capacitor discharge votage, so I checked waveforms on CRO. To my surprise, DC line was pretty clear before RC filter. So I opened ADC pin and knew that noice was introduced by ADC itself. Now stuck up since I have al;ready taken all the care including bypass capacitor, grounding plane, ripple in poer supply, stable refernce volateg etc.

Need a direction!

Could anybody send link for filter calculation for various sensors?

Thanks in advance.

 

Is the buffer enabled in the AD7708? Also, how stable is your Vref?

 

Is CHOP\ = 0?

What's the gain of your instrumentation amp?

 

Thanks for your replies.

But my reference is pretty constant. The gain is around 110 an chop is enabled.