Strain-Guage

Thread Starter

Richi Nixon

Joined Dec 8, 2015
17
Hi,

Simple strain guage measurement circuit has been designed using wheatstone bridge and instrumentation amplifier is used to increase the gain of the bridge output.
with the help of LTspice IV tool, the circuit was simulated and accordingly results were tabulated.
The question is deviation is observed from theoretically calculated output voltage value and measured value (i.e simulated). Please do give your insights on reason for this deviation.
For further details about the circuit design please refer the attachment.

Kind Regards,
Richi Nixon V
 

GopherT

Joined Nov 23, 2012
8,012
View attachment 98891


Hi,
Please find the screenshot.

Ha, in theory, there is no difference between theory and practice. In practice, there is.

If making an instrumentation amp were that easy, the manufacturers would not be able to charge what they do for a good instrumentation amp. Once you try to put this together with three real 741 op amps, you will get much worse results than your simulation. The difference between resistors, the input off-set voltage of the 741s and all else that goes with it. Also, you only have gain of two (I believe) on your in amp. You will need more than that on a load cell.
 

Thread Starter

Richi Nixon

Joined Dec 8, 2015
17
Ha, in theory, there is no difference between theory and practice. In practice, there is.

If making an instrumentation amp were that easy, the manufacturers would not be able to charge what they do for a good instrumentation amp. Once you try to put this together with three real 741 op amps, you will get much worse results than your simulation. The difference between resistors, the input off-set voltage of the 741s and all else that goes with it. Also, you only have gain of two (I believe) on your in amp. You will need more than that on a load cell.
Yes I agree that there will be difference in real time implementation but my concern is i think simulators do work closely to ideol conditions ! If yes what could be the reason for such deviation ..
 
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