IN-AMP(AD8426) gives me huge error at 1 gain

[palpurul]

I was trying to design a very simple in-amp circuit with a gain of 1. As it's spesified in its datasheet that AD8429 defaults to G=1 when no resistor is used between its gain terminal, so I connected 2mv to one of the inputs and expected to get the same voltage at the output but I got 0.5mv of error instead. Isn't it a huge error?.It is also spesified in the datasheet that maximum accuracy is 0.02% when G = 1. I am very new at multisim apologies if it is a dumb question. I attached my circuit and oscilloscope results below.

channel A is connected to the input and channel B is connected to the output pin in oscilloscope.

thanks in advance.

[johnsold]

My guess is that you are seeing offset voltage, not gain error. The specified offsets are 150 uV input offset and 1000 uV output offset.

Try running your simulation with larger values of the input.  The gain error will be related to the slope of the output versus input curve over a range of input values. The offset should just move that curve up or down.

I recently ran simuations of the AD8421 which is very similar to the AD8429 and saw no significant gain errors or other problems with the simulation.

Lynn

[palpurul]

Thank you for your help john I was not aware of offsetvoltage.As I said I am pretty new at electronics, but thanks to you Now I knpw that all opamp(or inamp in this case) inheretly have some offset voltage. Another question regarding this is according to your reply and my observation offset voltage changes dependent upon gain(I hope i am right on this) and I dont know how to calculate it. I read the whole datasheet , but I have not found any information about it. Is there any way to calculate it other than running the simulation accordingly? Thanks in advance