# Force measurement system - relating output voltage to Force - strain gauges

1. Jan 3, 2013

### mh1985

1. The problem statement, all variables and given/known data

I'm struggling with this, I have series of data for the deflection of a cantilever beam and the corresponding output voltages from a strain gauge, wheatstone bridge and amplifier circuit.

I'm trying to find the relation between voltage output and force, i.e. Force = K x voltage (K = constant) but I don't have the force.

2. Relevant equations

Also I've been given the equation for

Bending moment M = F * Length at gauge

Stress on top surface of beam σ= d/2 * M/1

Output voltage = R2/R* Vs* Kg *ε

Where Kg = guage factor

3. The attempt at a solution

I think Force can be found from 3EId /L^3 , where d = deflection, E= youngs modulus, I = 2nd moment of area. But still think I'm missing something.

I've already found another constant for output voltage = K x deflection, if that is relevant.

Using 3EI/L^3, I get 5171.3 which can then be multiplied by deflection to give the Force - not sure if this is correct?

Hoping someone has done a similar experiment before and can help in some way please?