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INA122P - Gain Errors

Javier Solis
Prodigy 20 points


Hi I am pretty new at this kind of stuff but get the basics of it. I am working on a project that requires using an instrumentation amplifier but I cant seem to get a correct value for the gain I set. Currently I am inputting 100mv with a 5k resistor to set a gain of 45. I should be getting a value of 4.5 V but cant seem to get anything above 1V. I tried using a 500mv resistor as well and the same happens nothing above 1V. Im not getting something in my head that I should probably be considering but can you all help? I've used multiple breadboards, wires, and I have 10 INA122P's and its basically the same thing. Also with small inputs I get waves but all I get is square looking output waves if that helps any

  • 0
    TI__Mastermind 25825 points

    Hello Javier,

    For some reason I cannot see the figures in your post. Can you please attach them in a zip file?

    In addition, please use an o-scope to measure the voltages at pins 2, 3, 5, 6, and 7. I assume pin 4 is ground. This will ensure that the NI ELVIS II board is working properly. Please update this post with those voltages/screen captures.

  • 0
    Prodigy 20 points

    I'm fairly new to doing this and need some help on a project. I am trying to figure out how the ina122p works and used the equation provided to determine the resistance and placed everything else right I think. I have used multiple breadboards and currently using an NI ElVIS II board to test out the chip. My problem is that for an input of 100mv the gain with a 5k resistance should be around 45 so I should get a reading of about 4.5V. I cant get anything above 1V. There should be a hump not a straight square right? With really low inputs I get hump/waves for the output but nothing that exceeds 1V. I also tried a 500 ohm resister and the output was the same.

    Channel AI0 = input

    Channel AI1 = output

  • 0
    TI__Mastermind 25825 points

    Hello Javier,

    It appears as though you also posted this question in another forum.  I will try to merge the two together.  If that doesn't work, here is the link to your other post:

    http://e2e.ti.com/support/amplifiers/etc_amplifiers__other_linear/f/18/p/355967/1249804.aspx#1249804

    In addition to my response in the other forum, please provide a complete schematic of your circuit.