ETME360 Spring 2014
Eproblem 5 Solution

A stainless steel cube instrumented with a single strain gage is to be used as a robust pressure transducer for investigating injection mold cavity pressures. A prototype unit is fabricated, waterproofed with a polymer coating and hydrostatically tested. Gage resistance is monitored via voltage output of the Wheatstone bridge circuit shown. Ignoring temperature considerations and lead wire resistance,


a.    Determine the sensitivity deo/dP of the system.

b.    The device is suspended in an injection mold cavity during a calibrated 30,000 psi test run. What electrical output eo will result at this 30,000 psi hydrostatic pressure?

The common length dimension of the solid cube is 1.00 inches.
E stainless = 28 x 106 psi,
ν=0.29.  Gage factor F = 2.0. Ei=12 Volts.
Nominal Gage Resistance R=1000
Ω, Fixed resistance Ro=1000 Ω.