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INA122 Stability Issue

Bryden Smith
Prodigy 50 points

Other Parts Discussed in Thread: INA122

Hi

I just recently posted about this amplifier about a week ago (http://e2e.ti.com/support/amplifiers/precision_amplifiers/f/14/t/245154.aspx) The circuit is working perfect .  I am get a linear output.  My problem that I am having Vo is not stable the output is jumping around.   My inputs to Vin+ and Vin- from wheatstone bridge are stable, my V+ in 5.012V which is stable and my ground is also stable.  I have my gain set to 625 and I get my min, and max value.  Just not a stable output from Vo into my ADC.

 

Thanks

Bryden Smith

  • 0
    Guru 21975 points

    Bryden,

    The internal noise of the INA122 would produce an output noise of approximately 8mV peak-to-peak. What is LSB size of your a/d converter (in mV)? When you say "jumping around," how many LSB bits are changing? What is the magnitude of the change in mV?

    Have you looked at the output of the INA122 on an oscilloscope? Please describe the nature of the noise you see. (This may require a high gain oscilloscope.)

    Regards, Bruce

  • 0 in reply to Bruce Trump
    Prodigy 50 points

    Hi Bruce

    The variations in my output are in the 8mV range or less.  I think there is nothing wrong with it.  It is always its jumping around in that range. (Which I now know is normal.)  I am also using a poteniometer for my gain until I find my correct gain which causes a little bit also I have read on other forum questions.  Once I find that I will be going to a exact resistor value. 

    Thanks for answering my question

    Bryden Smith