AnsweredAssumed Answered

Instrumentation amplifier with unexpected higher gain

Question asked by Sparkles! on Aug 31, 2014
Latest reply on Sep 3, 2014 by Georgy

Hello,

 

I've set up the instrumentation amplifier AD8226 as shown in the attached file to measure the current flowing through RLOAD.

Using RG=100R it must achieve a gain of 495 according to table 7 in the datasheet; however I'm obtaining a gain of approximately 6.3 times higher than that (tested with RLOAD=33R, 66R and 150R).

 

Strangely enough, I've measured the gain to be indeed 495 V/V, introducing 20mV at the input I obtain around 10V at the output. I've tried using RG=1000R with similar results.

 

Then, why am I not obtaining the expected gain? I cannot measure the voltage drop at the 0R005 resistor because it's too low and I can only see noise with the oscilloscope. Could it be that I'm trying to amplify too weak signals?

 

Thank you in advance!

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