How do I use full-bridge strain gauge circuit to measure F?

[APUGYael]

Hey all,

I am using a Wheatstone bridge with 4 strain gauges as resistors. I have a formula for the output voltage (Vout). My questions is how do I make it so instead of voltage I measure force?

Do I simply apply a set max. force (let's say 140N), see what voltage I get (Vout,max) and then use that information?

Example (bogus numbers):
140 N --> 0,5 V, so 70N --> 0,25V, etc.

Or is there a less practical and slightly more theoretical way?

 

[LURCH]

I suppose that if you know the tensile strength of he material in which your Wheatstone is embedded, you could calculate the force necessary to deform that material enough to give you a certain Vout.

 

[jrmichler]

The hard way is to do the relevant calculations by hand, with this being a good place to start: https://www.omega.com/literature/transactions/volume3/strain.html.

The easy way is to do what you suggested in your OP - measure the bridge voltage for a known load. This is called calibration, and should be done even if you have done all the calculations. The calculations allow you to design a gage installation to get a predetermined sensitivity and accuracy, but do not take into account certain practical realities, such as the exact effect of nearby stress concentrations.