# Homework Help: Calibrating a strain gauge/thermistor

1. May 11, 2010

### Robbie-Eng

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

Hey guys,

Im abit confused on the method of calibrating a strain gauge/thermistor, i know they both use a wheatstone bridge (resistance). At the moment i have gathered this information,

Transducers and sensors which produce a change in resistance are typically used in a bridge circuit. This consists of an arrangement of resistances supplied from a stable voltage source. For the bridge to be balanced, the ratio of resistances in each branch must be balanced. Any change in resistance will produce a potential difference between the two junctions. The values of resistance are designed so that the small change in resistance from the sensor will result in an improvement in resolution of the measurement.

Equations i have gathered:

VA=R3/(R3+R1)*Vin

VB=R2/(R4+R2)*Vin

Once i have found the two node voltages am i to substract them from each other to find the difference between them?

and from that answer can i then say for example i got a voltage output of 1v, can i say that 1v is equal to 1m in displacement for the strain gauge?

ive read that R4 is used to compensate for temperature variations and it is not subjected to stress, R3 is used to balance the bridge, R2 is replaced from the transducer and i am not sure what R1 is used for?

2. Relevant equations

V_A=R3/(R3+R1)*Vin

V_B=R2/(R4+R2)*Vin

R2/R4=R1/R3

3. The attempt at a solution