Forum Post: RE: ADS1247 Output

Hello Bob,

I tried all the things you've suggested, but I am unable to remove this 20 deg C offset.Is there anything wrong with my circuit or the way I am connecting PT100 or is it a software issue ?

Formula I currently using for resistance calculation is,

R_PT100 = R_COMP + ((LSB/I_EXC) x ADC) where, LSB = (Vref/PGA)/(2^23-1) & Vref =  (2 x I_EXC x R_BIAS)

This reduced to-> R_PT100 = R_COMP + ((2 x R_BIAS x ADC) / (PGA x (2^23-1))

Further reduced to-> R_PT100 = ((2 x R_BIAS x ADC) / (PGA x (2^23-1)), where R_COMP = 0

I think only source of error here is tolerance of R_BIAS value. I guess I will have to do the external calibration. How do you suggest to calibrate out this R_BIAS error ?

Thanks,

Saumitra A Deshpande