strain gage signal amplification

[Cetico]

I've made some research on strain gages and nearly all sources state that one needs a full amplifier in order to make the typically 10mV/V signal usable. Now, I'm an engineer but a newbie in electronics, so I went in search of amplifier circuits. Load cell and transducer vendors alike tell me that they cost tens or hundreds of dollars. Now, why can't I simply use an op-amp, which costs only a few cents?

[Buechsenschuetz]

Of course there are two ways to get a suitable amplifier: a) buy a costly ready-made unit, set up some parameters and use it, b) buy a few cheap components, get involved in amplifier and filter design, and try to get it to work.

Anyone designing and manufacturing devices wants to get paid for it (hey, I assume that's why you are doing your job), so of course a ready-made unit costs more than the sum of component prices.

A simple op-amp circuit MAY work but typically a strain-gauge amplifier needs a circuit for a (very stable) excitation voltage, and a true differential input. You probably want to add some analog filtering to avoid overdrive and aliasing of the ADC. Well, if you find someone to pay you for all that work to do maybe building your own amplifier will be cheaper...

[Henrik_Volkers]

Yes, you can sometimes use a simple op-amp...

However, more often you need 3 of them (instrument amp)  and you need a PCB and housing and and

You just stated you are not that familar with electronics, so if you get an ready made amp for tens of bugs that fulfill your needs buy it!

And the reason why companies continuously can sell amplifier for hundreds of bugs is simply because they are worth it.

 (No, I don't talk about audio amplifier and even there you can say: If someone is proud of owning a special brand the name plate is worth it)

You can always get it cheaper (especially in material) , but better/faster/...?

If you really want to build you own amp: the application notes from AD and linear are a good starting point.

[Buechsenschuetz]

To give you an idea what it means to design a strain gauge amplifier you can check this link:

http://www.acfr.usyd.edu.au/teaching/3rd-year/mech3701-Mx3/labs/index.html

This basic circuit does not include analog filtering.