Minimum microstrains that a wheatstone bridge or strain gauges will pick up?

[Vale-46]

I'm wanting to measure the torque output of a cyclist by measuring the shear force induced in the crank arms.

I've done some calculations for the minimum amount of strain that I'll want to pick up and it is around 6e-6 m/m. I'll be using a full wheatstone bridge with a constant voltage supply (I'm not sure what is a decent voltage to use) which will be plugged into an amplifier of some sort I guess.

Signal noise and temperature changes will be an issue I guess, but I'm just wondering what sort of accuracy I ought to be able to get at this sort of strain level.

The equation for the constant velocity circuit is of no use to me as all I can end up with is a relationship between the change in current and the change in resistance, plus I don't know what sort of resolution for resistance change measurement I can get.

 

[conway]

I worked with strain gauges some years ago and with a voltmeter that read accurately down to microvolts, we could detect changes of one or two microstrain. It all depended on having a very good voltmeter.