Differential amplifier drift at output

Hi,

In our design we are using differential amplifier( AD629BRZ) but it is behaving some what different.

my application is measuring current,for your reference i am adding schematics

<>ez.analog.com/.../pastedImage_5.png

my current is 48mA

I have measured voltage across the resistor is 4.8mV,but output of differential amplifier is 4.4mV,there is a drift of 0.4mV

why this much of variation in input and output?

I want exact  input voltage in output what i will do ,can you please guide how to resolve this issue

Thanks in advance..

Thanks,

Siva Nageswara Rao

Mobile: +91 9030346190

Parents
    •  Analog Employees 
    on May 6, 2018 6:26 PM

    Hi Siva,

    Can you tell me what is the part number of the shunt resistor that you used? If the value of the shunt resistor change due to temperature, it will reflect as gain error on the measurements.

    How did you expose the parts on 60°C? May I know if all your circuit was exposed to this temperature or only the AD629? I just want to check all variable that could contributes on the error of your measurements.

    May I also know what is the common mode voltage across the shunt resistor? I have experience that CMRR also drift with respect to temperature but since the AD629 is almost 20 years old part, this information is not available on its TPC. But we have the newer version of the AD629 which is the AD8479, it has better overall accuracy specs than the AD629 which you might also consider.

    Are you working with a new development design? May I know why you chose the AD629 on your applications?

    Best regards,

    Emman

Reply
    •  Analog Employees 
    on May 6, 2018 6:26 PM

    Hi Siva,

    Can you tell me what is the part number of the shunt resistor that you used? If the value of the shunt resistor change due to temperature, it will reflect as gain error on the measurements.

    How did you expose the parts on 60°C? May I know if all your circuit was exposed to this temperature or only the AD629? I just want to check all variable that could contributes on the error of your measurements.

    May I also know what is the common mode voltage across the shunt resistor? I have experience that CMRR also drift with respect to temperature but since the AD629 is almost 20 years old part, this information is not available on its TPC. But we have the newer version of the AD629 which is the AD8479, it has better overall accuracy specs than the AD629 which you might also consider.

    Are you working with a new development design? May I know why you chose the AD629 on your applications?

    Best regards,

    Emman

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