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
    15,815
    282
    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
    0
    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
    15,815
    282
    I should think the process speaks for itself, but the result is total strain - assuming proper placement of the strain gauges.
     
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