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INA12* Large Offset Problem

Other Parts Discussed in Thread: INA128, INA129, INA333

Hi all.

 

I have been working on an instrumentational amplifier circuit to amplify a 0-10mv differential voltage (Loadcell) up to 0-2.5V to be read by and Arduino ADC

Currently I have tried using an INA129 and an INA128. Both of these amplifiers are giving me about a 80mV offset voltage at the output even when the inputs are tied together. I decided to build a circuit on a bread board to test the amplifiers incase my PCB design was wrong. Even using a gain of 1 and and connecting the the inputs together I still get the 80mV offset. The offset its self is not a problem except it you mathematically subtract it from the output the linearity is out by about 25% (not good for accurately measuring force). Below is the circuit any comments would be much appreciated.

P.S. I have a few amplifiers and it seams to be the same with all of them

  • Matthew;

    The INA128 & INA129 are nice devices but they are not universal-- they are not rail-to-rail amplifiers. In the data sheet they are specified down to +/-2.25V power supplies, not +5V.

    In your application an INA333 might be a better choice.

     

  • Hello, I have the same problem, im using a pressure sensor MPX2010DP with differential output (SPAN 0 - 25mv), INA129 is the amplifier, sourced with +15v, and the negative pin grounded, im having a 100mv offset, if i change the gain resistor value, this offset doesnt change, if i shorting +Vsignal - -Vsignal offset doesnt change too, so the problem here is the negative pin to the ground?? its not easy to buy another Amplifier to me couse the city and country im leaving they dont use to have stock, thats why im trying to figer out how could i minimize this offset..


    Thanks

    Guille Hernan