Transcribed Text
Problem 1:
A quarterbridge resistance strain gauge circuit is going to be used for measuring the
deflection of an Aluminum beam. The strain gauge has a nominal resistance of 12092, and a
gauge factor of 3.8. All other resistors in the circuit are 12092. If the maximum allowable
current through the strain gauge is 0.03A, what is the maximum excitation voltage?
Problem 2:
A beam is deflected is measured using a full bridge as shown below. All strain gauges are
identical, with a nominal resistance of 12092 and a gauge factor of 2.5. The gauges are
oriented such that the gauges on top (R1 & R3) measure the tensile strain, and the bottom
gauges (R2 & R4) measure the equal and opposite compression strain. If the excitation
voltage is 6V, and gauges R1 & R3 measure a tensile strain 50s, and gauges R2 & R4
measure a compressive strain of 50e, what is the change in bridge deflection voltage
(Vout)?
F
R1
R4
+
V
O
V

out

in
?
R2
+deflection
Problem 3:
a)
If the manufacturer wired the bridge incorrectly such that compression was
measured on R1 & R2, and tension is measured on R3 & R4, would the circuit still
work? What would the change in bridge deflection voltage be for the same
deflection as Problem 2?
b) If R1 & R3 are on top of the beam (positive strain), and R2 & R4 are on the bottom
(negative strain), what is the output voltage (same as problem #2)? If the beam was
instead axially loaded, would the sensor/transducer still function properly?
Problem #4
Given the following information, estimate the modulus of elasticity of the beam material
and the uncertainty in your estimate. You must use propagation of uncertainty (partials
or relative uncertainty equation) to estimate the uncertainty. Note: the beam is fixed
on the left hand side.
Load

Distance from load to center of strain gauge: 9.6 + 0.2 cm

Applied load: 16.2 0.25 N

Nominal resistance of gauge and resistors: 350 Ohms
R4

Input Voltage: 5V 0.0

Beam width: 2.5 +1 0.05 cm

Beam thickness: 0.5 0.05 cm

Amplification gain (from AD623): 834 0.0

Measured Voltage (assume no bias): 0.481V + 0.05V

Gage factor: 2.1 0.0
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