I'm working with a dsPIC that measures the output of a variable 20V power supply. I'm experiencing errors on the ADC measurements and they are not constant errors, they vary according to the output voltage. I measured the output voltage of the power supply and the voltage at the ADC input of the microcontroller with a
UNI-T IT61E multimeter:
Output Voltage is the measured voltage at the output of the power supply, the
Voltage in ADC is the voltage measured in the ADC pin relative to the AVSS pin and the
Division Factor is calculated as
Voltage in ADC/Output Voltage. As you can see, this factor is not constant, so my multimeter is not that accurate (I think it should be precise and accurate enough) or the ADC input stage is not that linear. Here's the input stage:
Is it due to the OPAMP or the low pass filters? Or is it really my multimeter giving wrong readings?