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INA125: Output drifting over time

Alon Goldstein
Prodigy 10 points
Part Number: INA125

I'm using INA125 to read a 350 Ohm Load Cell. This is the circuit I'm using.
I assembled 10 circuits, and while 8 of them are working fine, 2 of them seem to have a value drift that accumulates to few Volts within 2 hours.
I tried connecting to unloaded Load Cell, to make sure it's not caused by load cell creepage. I also tried lowering the LC driving voltage from 10V to 5V, to decrease self heating by the current through the LC.

I measured the output at point A, so I know it's not caused by the second stage. I Also made sure with 0.1mV accuracy voltmeter, that the supply voltages, the LC drive voltage and the zeroing voltage, are all stable.

Made some exchanges between the good and bad circuits, also replaced the chips with new ones, and still the issue was not resolved.

Any other suggestions?

  • 0
    TI__Guru 54986 points

    Hi Alon,

    1) Have you measured the voltages at the inputs of the instrumentation amplifier with a high-impedance, high-resolution precision voltage meter with micro-volt resolution to ensure that the load-cells are not drifting?

    2) What is the % tolerance and drift specification for the RG resistor? 

    3) Is there a bypass capacitor on the negative supply?

    4) Another factor to consider when performing high precision measurements is to ensure that the PCB board is completely clean and free of flux residue and contaminants after the soldering process.  On our evaluation boards we use a we use a deionized water, ultrasonic bath clean for 15 minutes to ensure complete removal of the flux underneath the devices. However, in your PCB, the appropriate flux removal process may vary depending on the type of flux used. The PCB boards must be submitted to the bath clean every time devices are replaced.

    Thank you and Best Regards,

    Luis