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Need some help determining reference value for bridge amplification circuit.

Kevin Mason
Prodigy 35 points

Other Parts Discussed in Thread: INA122

I am using the INA122 to amplify a mV signal from a strain gauge.  My basic circuit works, but it appears that I am falling below the 100 mV minimum input which is causing linearity errors.  This is my spec's.

 

Vcc = 2.5V single supply

Gain R = 425 ohm

The strain gauge is a 350 ohm 2 mV/V output(0 - 5mV).  My a/d has a range of agnd to 2.5V.  I am probably going to have to bias this as well.

 

So what I am looking for is how to calculate the appropriate ref voltage to give me a 150mV to 2.3V output.

 

Thanks in advance.

  • 0
    TI__Genius 14890 points

    Kevin,

     

    I would recommend reducing the gain and then placing a voltage on the Ref terminal to offset the output signal. Maybe a 500mV reference? The datasheet mentions that the voltage applied to the Ref terminal is added to the output signal. Refer to Figure 2 (page 7) of the datasheet for a circuit to help trim the offset voltage. Hope this helps!

     

    Sincerely,

    Alex