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INA122

Cynthia Leung
Prodigy 40 points

Other Parts Discussed in Thread: INA122

Hi,  we're currently working on a design using the INA122 and have a couple questions.

1) For the spec on the INA122 web page that says

Output Offset (+/-)(Max)(uV)

100/G 

How should that be interpreted? 100uV of offset for every unit of gain (therefore if I set my gain at 500, I can expect up to 50mV of offset?) or 100uV divided by your gain (100uV / 500 = 0.2uV offset?)

2) We're also using a small Vref to offset the output of a loadcell. Mainly we are measuring compression (under compression the difference between S+ and S- are roughly 2mV) but also would like to measure a small range on tension (so the S+ and S- would be -0.1mV) which is why we want to use a small offset rather than tie Vref to GND.

It's working fine, but we are wondering what the Vout gain and offset accuracy is now? Can we still assume the 1% gain error as declared in the datasheet? And % Vout offset?

Thanks in advance

cynthia

  • 0
    TI__Intellectual 2770 points

    Hello Cynthia,

    The offset voltage referred to input is specified in the datasheet in the "INPUT" section. The typical value is +/-100uV. To calculate the offset voltage at the output you have to include the gain. The higher the gain the higher your offset voltage at the output will be.

    Using a a different voltage other than GND at the Vref shouldn't be an issue: Page 7 in the datasheet shows an example circuit. I don't see any reasons why the the INA122 could have a bigger gain error in this configuration. Since the output voltage is referred to Vref you will directly add the max offset error of your offset correction circuit to your output voltage.

    I hope this helps

    Thomas