Question

Question 2 Figure Q2 shows a strain gauge bonded to a piece of steel under a tensile force. The direction of strain measurement is at 90° to the direction of the force. The gauge has been selected to be self-compensating for temperature but the leads to and from the gauge are subject to temperature variations of 130 °C. The strain gauge and the metal have the following properties: Steel specification Gauge specification Gauge factor-2.00 Young's modulus -210 GN/m2 Poisson's ratio 0.3 Resistance -120+ 0.5 Maximum current 30 mA (a) Draw a circuit diagram showing how the strain gauge can be connected into a bridge to measure the strain in the steel. Your circuit should show the gauge, the leads to and from the bridge, the bridge power supply, and a means of balancing the bridge. (b) Calculate the permissible maximum bridge output voltage, V2, for the bridge when the force, F, is 2.5 kN F 30 mm 3 mm 80 mm Figure Q2

Answer 1

a)

Re Vix Strain Geauge www

b)

Stress = F/A =

(2 2.5 10%)/(80 1030 10 )2083333.33Pa

Youngs Modulus = Stress/Strain

Strain ,
AL/L
= Stress/Young's Modulus =
2.083333 10/(210 10) 9.92 10

Gauge Factor =

AR/R/AL/L

AR/R AL/L Gauge Factor

AR 9.92 105 2* 120 0.00238

R 120.002389