Strain Gauge circuits

[Tricky Dicky]

I am looking for a circuit that uses a strain gauge as a sensor and came across one using a standard Wheatstone bridge and differential amp whose output was fed into a picaxe. Unfortunetly I forgot to bookmark the website which I think was either an Aussie or NZ site. I would be grateful if anyone could point me in the right direction or better still if anyone has any suggestions.

The circuit is to measure the weight of a gas cylinder mounted on a cantilever platform by measuring the changes in strain as the cylinder empties. The Picaxe will be used to display a series of LEDs indicating how full the cylinder is.

Richard

 

 

[evanh]

The bridge arrangement was the loadcell itself and the differential op-amp is your typical precision instrumentation op-amp.

To make use of the dynamic range of these things you either need to have a precise and stable offset control or something like a 24 bit ADC and a power supply to match.


Evan

 

[evanh]

A quick search ... <A href='http://en.wikipedia.org/wiki/Load_cell' Target=_Blank>External Web Link</a>
<A href='http://www.analog.com/library/analogDialogue/archives/39-12/weigh_scale.html' Target=_Blank>External Web Link</a>

 

[Michael 2727]

Try the data sheet on the INA122 OP Amp.

 

[Tricky Dicky]

Thanks guys a great help. Since this is a GCSE project some of the stuff is going to go over the head of my student, but we should be able to get something up and running.

Thanks again and please post anything else on the subject you come across.
Richard

 

 

[womai]

As for the opamp, you should look for a type called &quot;instrumentation opamp&quot;. Basically those are opamps with very high common mode rejection ratio, meaning they really only amplify the difference between their inputs regardless of the absolute levels. You can get such opamps from a variety of vendors, e.g. Maxim (www.maxim-ic.com) and Texas Instruments.

Wolfgang