• Strain Gages • - - - When a fine wire (25 μm)is strained within its elastic limit, the wire's resistance changes because of changes in the diameter, length, and resistivity. measure extremely small displacements on the order of nanometers Equations: R = PL length L (meters). A p (ohms meter) pdL dR = - PA-2L dA + L dp A A A (meters squared) • ΔΑ Δρ AR AL AA Ap = - A + ρ Dr. Shamekhi, Sahand University of Technology Displacement Meas. - Resistive Sensors - p3 Equation: Poisson's ratio u relates the change in diameter μ AD to the change in length, Substituting this: AD/D ======== -μAL/L AR AL Δρ === = (1 + 2μ)· + R L P Dimensional effect Piezoresistive effect Gage Factor: G= ARIR ALIL Aplp (1 + 2μ) + ALIL Changes in the lattice structure of the material, 6

Electricity for Refrigeration, Heating, and Air Conditioning (MindTap Course List)
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Author:Russell E. Smith
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Chapter12: Electronic Control Devices
Section: Chapter Questions
Problem 14RQ
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Question
Derive the equations in the picture using the Poisson ratio method.
• Strain Gages
•
-
-
- When a fine wire (25 μm)is strained within its elastic limit,
the wire's resistance changes because of changes in the
diameter, length, and resistivity.
measure extremely small displacements on the order of
nanometers
Equations: R =
PL
length L (meters).
A
p (ohms meter)
pdL
dR =
- PA-2L dA + L
dp
A
A
A (meters squared)
•
ΔΑ
Δρ
AR AL AA Ap
=
-
A
+
ρ
Dr. Shamekhi, Sahand University of Technology
Displacement Meas. - Resistive Sensors - p3
Equation: Poisson's ratio u relates the change in diameter
μ
AD to the change in length,
Substituting this:
AD/D
========
-μAL/L
AR
AL
Δρ
===
= (1 + 2μ)·
+
R
L
P
Dimensional
effect
Piezoresistive
effect
Gage Factor:
G=
ARIR
ALIL
Aplp
(1 + 2μ) +
ALIL
Changes in the
lattice structure
of the material,
6
Transcribed Image Text:• Strain Gages • - - - When a fine wire (25 μm)is strained within its elastic limit, the wire's resistance changes because of changes in the diameter, length, and resistivity. measure extremely small displacements on the order of nanometers Equations: R = PL length L (meters). A p (ohms meter) pdL dR = - PA-2L dA + L dp A A A (meters squared) • ΔΑ Δρ AR AL AA Ap = - A + ρ Dr. Shamekhi, Sahand University of Technology Displacement Meas. - Resistive Sensors - p3 Equation: Poisson's ratio u relates the change in diameter μ AD to the change in length, Substituting this: AD/D ======== -μAL/L AR AL Δρ === = (1 + 2μ)· + R L P Dimensional effect Piezoresistive effect Gage Factor: G= ARIR ALIL Aplp (1 + 2μ) + ALIL Changes in the lattice structure of the material, 6
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