I have a circuit which utilises 2 ADS1243's to read the output differential from load cells.
I am struggling to understand how the SELFGCAL and SELFOCAL commands modify the readings from the ADS1243 and how to get repeatable results using the same input signal (weight on a load cell) with different ADS1243's on different PCB's.
The Vdd is 3.3V, VREF+ is 1.19V, VREF- is 0V, each circuit has 2 ADS1243 chips on it so up to 8 load cells and there are multiple of the PCBs/circuits in a system.
My setup procedure after a reset is to do the following:
1. RESET Command.
2. SELFGCAL Command.
3. Set gain to 64.
4. SELFOCAL Command.
5. Set the Unipolar setting.
(Anything else not mentioned is left at default values).
After doing the SELFGCAL and SELFOCAL commands my FSR registers will typically be between 21829 <> 21850 and my Offset value will be between 172 <> 202 across approx 4 different ADS1243 chips that I have tested with.
When I connect the same load cell with the same weight into each of the 4 ADS1243 chips I am unable to get out the same output from them. I have accounted for the slight VRef variations and slight excitation voltage variations.
So my questions are:
After the self calibrations should each ADS1243 output the same result given the same VREF and Input voltage?
Do we have to do any sort of further calculation using the offset and full-scale values after calibrating to get consistent results between different ADS1243 chips?