Strain Gauge Quiz: Oct 19, 2011
See the image below of a horizontal cantilever beam.
The beam is 20 cm long = L, 1 cm thick and 4.9 cm wide = W, fixed by one end to the left wall.
Say that on top of the beam are TWO longitudinal strain gages (serpentine patterns point from left to right...) and on the bottom of the beam are TWO transverse gages (serpentine patterns along the "W" width axis).

The gauge factor of each strain gauge is 2.0.

Let Young's modulus E of the beam material be 5x10^8 N/m^2, and its Poisson ratio nu = ν = 0.25.

Hung by a tray from the end of the beam is a 10 Kg mass (not shown).

Assume that as the beam is loaded and bends, the top surface strains longer exactly as much as the lower surface strains shorter. Assume also that the area of interest for calculating stress is width X thickness, and that the mass of interest is 10Kg.

The strain gauges are all of unloaded value 350 Ohms and are wired into a Wheatstone bridge as shown to the right, below.
Vex = 10 volts. If there is no load on the bar, Vout is zero volts.

Your question: What should GAIN = G be to have Vout = +1.00 volts for the 10Kg load?