Strain Gauge Take-Home Quiz: Oct 23, 2006
Study the strain gauge placements given below and calculate an answer to the
question asked.
This quiz is a take-home; return it to JD or put it under the door of 355 B&H
by noon Tues 10/24.
Regarding this quiz, you are not allowed to seek help from anyone, but you can use
any notes you like.
name________________________________ answer__________________________volts
Consider a rectanguloid bar of "rigid" material, 0.4 inches thick, 2
inches wide and L0 = 44 inches long:
The bar rests on a heavy granite table top and from above a weight of 120 pounds
presses down.
There are two TRANSVERSE strain gauges and one Longitudinal gaugeon the front
face
of the bar (the wide part). The gauges are 120 Ohms, unloaded.
The two transverse strain gauges find their way to opposite sides of a Wheatstone
bridge,
and the longitudnial SG is below RT2, as diagrammed below.
The other resistor R0 in the bridge has a 120 Ohm resistance.
An instrumentation amplifier has an output of Vout = 200*(VL - VR). Vex is 10 volts.
If there is no load on the bar, Vout is zero volts. The gauge factor of each
strain gauge is 2.0.
for longitudinal strain.
The material of the bar has Young's modulus E of 100,000 psi and Poisson's ratio
ν of 0.25.
Your question: What is Vout?
Your quiz will be graded by the next class meeting.
If you figure out the correct answer, you're finished and your scorecard will
be signed.
If not, then at your next GAT you will taken aside for an oral SG quiz.
Show your intermediate calculations and formulas on this test page.
In case you did everything right expect for ONE trivial calculation
mistake, you can still receive credit.
IF YOUR WRONG ANSWER IS EXACTLY THE SAME AS SOMEONE ELSE'S
WRONG ANSWER YOUR SHOWN WORK WILL BE CHECKED AGAINST YOUR ANSWER...
if you understand what I'm saying...