Engineering Strain Gauge Project Circuit Question

[kacollie]

Design a circuit that uses a stain gauge to create a voltage related to the strain experienced by the gauge. The strain gauge should remain electrically isolated from the ground. The DC common mode voltage should be minimized. Only stain-related signal to be measured does not have any significant energy components with frequencies above 10hz. Random voltage fluctuations unrelated to strain with frequency components above 100hz should be reduced, relative to strain related voltage fluctuations, by a factor of at least 10 without significantly affecting the stain-related voltage measured. Do not use more then 2 op-amps in your circuit. Assume the unloaded resistance of the strain gauge is 120ohms.

This seems really difficult, I would be really impressed if someone had any insight into how to build such a circuit.

 

[larny]

I suggest that you have 2 power rails, say +15V & -15V.

Connect a resistor to each rail (equal resistors) and connect the strain gauge between them.

Then connect the ends of the strain gauge to the inputs of a differential amp (use an Op Amp configured as a diff amp).

Use capacitors to limit the bandwidth and design the amp to provide a suitable gain.

eg. a 1 Volt change at the output of the amp would represent a suitable value of strain.

 

[kacollie]

Hey Larry,

Thanks for the prompt response, do you know how I would setup the equations to design such a circuit?

Thanks

 

[kacollie]

I also forgot to put the part about it being amplified by 1000.

Design a circuit that uses a stain gauge to create a voltage related to the strain experienced by the gauge. The strain gauge should remain electrically isolated from the ground. The DC common mode voltage should be minimized. Only stain-related voltage fluctuations caused by the gauge should be amplified by 1000. Assume that the stain-related signal to be measured does not have any significant energy components with frequencies above 10hz. Random voltage fluctuations unrelated to strain with frequency components above 100hz should be reduced, relative to strain related voltage fluctuations, by a factor of at least 10 without significantly affecting the stain-related voltage measured. Do not use more then 2 op-amps in your circuit. Assume the unloaded resistance of the strain gauge is 120ohms.

 

[larny]

Have you seen these threads?

https://www.physicsforums.com/showthread.php?t=383720

https://www.physicsforums.com/showthread.php?t=314265

https://www.physicsforums.com/showthread.php?t=314265

https://www.physicsforums.com/showthread.php?t=230313

https://www.physicsforums.com/showthread.php?t=230313

I have attached a .pdf that shows a number of Op Amp configurations including a difference amp (page 1).

This should give you a starting point.

There is plently of info available on the internet & electronics forums (eg. www.electro-tech-online.com[/url] & [url]www.edaboard.com[/URL]) that can help you.

You may need 2 Op Amps in tandem for gain of 1000. eg. one (a differential amp) with a gain of say 10 & the other (non differential) with a gain of 100.

You can taper the frequency response in both amps.

You will need to carefully consider off set and common mode gain