full bridge strain gage measurement

Discussion in 'Homework Help' started by 0001T, Oct 11, 2007.

1. 0001T Thread Starter Member

Feb 28, 2007
15
0
Hi,

i am doing a project on wheatstone bridge (full bridge strain gage measurement). How do I convert the data to stress?

I have the following information.

gage factor, G = 2.08, Kt = 0.9/0.2 resistance, Ro = 120ohm
output from bridge is in voltage

eg. at a load of 1300N, i have an output (Vo) of 3.495V (gain of 640 used).

the strain e was calculated to be 0.000525 using the equation (Vo/gain)=Vi*G*e

I managed to find out the changes in R1 to R4 as follows:

R1=R3 = Ro(1+Ge) = 120.131ohm
R2=R4 = Ro(1-Ge) = 119.869ohm

however, how do i go further from here to obtain the stress result?

2. beenthere Retired Moderator

Apr 20, 2004
15,808
295
The change in resistance in the strain gauge should relate to the compressional/tensional change in length. That should give you your stress.

3. recca02 Senior Member

Apr 2, 2007
1,211
1
stress is proportional to strain
if u know the young's modulus for the material then
stress=young's modulus*strain.

4. 0001T Thread Starter Member

Feb 28, 2007
15
0
thanks for the replies.

i understand that the strain gauges will measure both tension and compressive strains. and using stress-strain equation, i can calculate the stress.

question is - is this strain (or stress) value an average strain(or stress) of the four gauge results? or is it an total strain (stress) result?

5. beenthere Retired Moderator

Apr 20, 2004
15,808
295
I should think the process speaks for itself, but the result is total strain - assuming proper placement of the strain gauges.