## PHYS345 Electricity and Electronics

Special Problem 12.1

You may wish to refer to a brief discussion of the Wheatstone bridge.

A motor with an eccentric load is turning at 1200 rpm. A strain gauge is used to monitor the vibration in the motor mounting. The Wheatstone bridge and amplifier produce an output voltage proportional to the strain in the mounting. The capacitor blocks the dc component from the bridge, ac-coupling the amplifier.

1. Assuming that the strain gauge resistance, Rsg, is nominally 1k, find the value of the capacitance that will set the characteristic frequency of the coupling to one-third of the frequency of vibration.

2. Choose Av so that a 1.0% change in the strain gauge resistance produces a 5 V change in the output of the amplifier.

HINT: Find the Thévenin equivalent for the Wheatstone bridge!

This problem is from Roadstrum and Wolaver Ch. 8, Problem 9.

"http://www.physics.udel.edu/~watson/phys345/problems/12-1.html"
Last updated Nov. 16, 1999.
Copyright George Watson, Univ. of Delaware, 1999.