MCP617 op amp problem

Thread Starter

mah

Joined Mar 15, 2010
393
i used MCP617 to amplify 0-8 millivolt signal from sensor the non inverting amplifier is working well with a signal larger that 1.5 mv but for less that that value the output is bigger that expected i tried 0.8 mv but the output using total gain 106V/V was 129 mv , i don't know if my op amp is not sensitive with this value or it need enhancements .
 

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BobTPH

Joined Jun 5, 2013
8,765
What is the input offset voltage of the opamp? I suspect that is is comparable to the 1.5mV you have as input.

Bob
 

BobTPH

Joined Jun 5, 2013
8,765
Not very small compared to your signal of 800uV. The offset is definitely going to cause inaccuracy at that level.

Bob
 

LvW

Joined Jun 13, 2013
1,749
I have already done this step and the output was zero:)
I do not believe that it wa really "zero" - however, perhaps you couldn`t measure with more accuracy.
What about resistor tolreances?
Perhaps you should give us some real values rather than simply stating "bigger than expected"?
 

Thread Starter

mah

Joined Mar 15, 2010
393
I do not believe that it wa really "zero" - however, perhaps you couldn`t measure with more accuracy.
What about resistor tolreances?
Perhaps you should give us some real values rather than simply stating "bigger than expected"?
sorry there was disconnected wire the output is alternating between 9mv and 10.5 mv for zero input , now iam measuring .4 mv input signal with gain 441 the output is 0.51 v . what is the solution now ? i need accurate measurement.
 
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LvW

Joined Jun 13, 2013
1,749
"...output alternating" ?
What does this mean? Oscillating? Slowly changing?

How did you measure 400µV at the input? Opamp connected yes/no?
What are thr resistor values?
What is the internal source resistance?

You should show us the COMPLETE circuit with parts values and power supply. Otherwise no help possible.
 
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