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INA125: Not getting expected gain

Shruti Sagar
Prodigy 10 points
Part Number: INA125


Hi,

I am a newly joined member. I am trying to use INA125p to amplify the load cell output from CZL601 and then using Launchpad TMS320F2802x, to get a digital output from ADCINA7 (J5.3) on board.

The problem I am facing is that I am not getting any digital output. I checked the output of INA125 which was in millivolts. To check the gain of the amplifier, I gave 3.3 V as input and got 4.18 V output, although I used a 310 ohm resistor as Rg (gain = 200 from data sheet). So,I am not getting expected gain. Please suggest me something on why this is happening and how do I get the desired gain. This is the schematic I am using.

  • 0
    TI__Mastermind 23050 points

    Hi Shruti,

    The INA125, and any op amp for that matter, cannot output signals outside of the range of your power supply. With a 3.3V input and a gain of 200, you would expect to see 660V, which is more than 100 times your power supply. Because the device is unable to source this voltage, it saturates and you see a constant 4.18V. You have to make sure you stay within the linear operating region for the input and the output.

    Looking at the datasheet for the CZL601, it requires an excitation voltage of 9-12Vdc, so you may not be getting a useful output from the sensor with a 5V excitation.

    Regards,

    Zak Kaye