I have a scenario that implies measuring 2 inputs: - voltage through a resistive divider - current through a hall sensor followed by opamp for offset, direction and scaling
In my software, each channel has it's own average factor. I plan to use a simple 2 points (MIN/MAX) calibration technique on each channel.
The problem is slightly more complicated since my sensor use a opamp that (may) have it's own gain offset errors. Moreover, the sensor itself vary with Vdd and for this effect I use ratiometric measurement: ADC and sensor share the same Vref.
For voltage measurement I use a simple resistive divider which isn't perfect (measured ratio it's quite different from calculated) mostly due to un-precise resistors used. But even when I'll use 1% will be some errors which I compensate with 2 point method above.
The question is where should I measure / apply the calibration data?
Calibrate once raw ADC data (offset and gain) and use for all channels
Use separate 2 points for each channel on entire paths:
- hall sensor -> opamp -> adc -> average for this channel -> apply calibration
- voltage -> divider -> adc -> average for this channel -> apply calibration