ADS1235EVM: How to Offset and Span Calibration

Hi Nimit,

Welcome to the E2E forum!  You can issue the appropriate commands for offset and gain calibration.  Offset calibration should always be done prior to gain calibration.  The commands are discussed in the ADS1235 datasheet in section 8.4.7.

Even though the calibration commands can be issued by command in the GUI, calibrating connected equipment using the GUI is a bit difficult.  The EVM platform cannot be designed to cover the multitudes of sensors that can be connected.  So even though you can issue a offset or gain calibration it is a manual operation of collecting data and determining characteristics of the load cell.

I would start by just issuing the self-offset calibration.  The ADC is factory trimmed for the PGA settings for gain.  So for simplicity and limiting of error on the part of calibration just start with the self-offset calibration.

The measurement should be ratiometric where the excitation voltage of the load cell is the same as the reference.  Let's assume 5V is used.  I would suggest using the maximum gain of 128.  In most cases the span of the load cell will be much less than the full-scale range of the ADC.  So for scale calibration you would use a two point calibration technique.  Use no load as the zero point and save the result.  Then apply a calibrated weight near or at full-scale to determine the slope.  You would use these two points to calibrate the span.  Use the method below to calculate the weight applied to the load cell.

Best regards,

Bob B