1. 3441 Industrial Instruments 1 Chapter 5 Mechanical Sensors
Princess Sumaya University
Industrial Instruments 1
Princess Sumaya Univ. Electronic Engineering Dept.
3441 Industrial Instruments 1 Chapter 5 Mechanical Sensors
Dr. Bassam Kahhaleh
Dr. Bassam Kahhaleh

2. 3441 - Industrial Instruments 1
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Industrial Instruments 1
Mechanical Sensors
Objective
Understand how mechanical sensors work and how to interface them.

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Industrial Instruments 1
Mechanical Sensors
Displacement, Location, or Position Sensors
Potentiometric
V S
R D
R 1
R 3 − + VR
V out
R 2
R3 loading effect!!

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Industrial Instruments 1
Mechanical Sensors
Displacement, Location, or Position Sensors
Capacitive
K = the dielectric constant
ε0 = permittivity = 8.85 pF/m
A = plate common area
D = plate separation

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Industrial Instruments 1
Mechanical Sensors
Displacement, Location, or Position Sensors
Inductive
Permeable core

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Industrial Instruments 1
Mechanical Sensors
Displacement, Location, or Position Sensors
Variable Reluctance
Linear Variable Differential Transformer (LVDT)

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Industrial Instruments 1
Mechanical Sensors
Displacement, Location, or Position Sensors
LVDT

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Industrial Instruments 1
Mechanical Sensors
Displacement, Location, or Position Sensors
Level Sensors
Mechanical
Electrical
Ultrasonic
Pressure

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Industrial Instruments 1
Mechanical Sensors
Strain Sensors
Stress: Forces applied to an object
Strain: the result (deformation) of stress
Tensile Stress-Strain
Compressional Stress-Strain A F l A F l
F = applied force in N
A = cross-sectional area in m2
Δl = change in length in m
l = original length in m

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Industrial Instruments 1
Mechanical Sensors
Strain Sensors
Shear Stress-Strain F l A Δx F l F

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Industrial Instruments 1
Mechanical Sensors
Strain Sensors
Stress-Strain Curve
Modulus of elasticity (Young’s modulus):
Strain
Breaks
Necking
Linear
region
Stress

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Industrial Instruments 1
Mechanical Sensors
Strain Sensors
Strain Gauge (SG)
Resistance in metals:
Constant volume:

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Industrial Instruments 1
Mechanical Sensors
Strain Sensors
Strain Gauge - Temperature effect
Example:
R0 = 120 Ω
Strain = 1000 μm / m
0 = / °C
Strain ΔR = 0.24 Ω
Temp. ΔR = 0.48 Ω / °C

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Industrial Instruments 1
Mechanical Sensors
Strain Sensors
Metal Strain Gauges (SGs)
Gauge Factor:
Typically, GF ~ 2
Special alloys and carbon: GF = 10

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Industrial Instruments 1
Mechanical Sensors
Strain Sensors
Construction

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Industrial Instruments 1
Mechanical Sensors
Strain Sensors
Signal Conditioning
R 1
R 2 D VS a b
R D
R A

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Industrial Instruments 1
Mechanical Sensors
Strain Sensors
Two-arm Bridge
D 1
D 2 D VS a b
A 1
A 2

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Industrial Instruments 1
Mechanical Sensors
Strain Sensors
Semiconductor Strain Gauges (SGs)
Typically, GF: −50 ~ −200

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Industrial Instruments 1
Mechanical Sensors
Strain Sensors
Load Cells

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Industrial Instruments 1
Mechanical Sensors
Motion Sensors
Types of Motion
Rectilinear
Angular
Vibration
Shock

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Industrial Instruments 1
Mechanical Sensors
Motion Sensors
Accelerometer
Spring-Mass System
k = spring constant in N/m
There is a natural frequency at which the system oscillates without acceleration.
Use it with frequency < 1 / (2.5 fN)

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Industrial Instruments 1
Mechanical Sensors
Motion Sensors
Types of Accelerometers
Potentiometric
LVDT
Variable Reluctance
(small magnet / inductor)
Piezoelectric

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Mechanical Sensors
Motion Sensors
Steady-State Acceleration
Example
sensor: 14 mV / g
Design: Vout = 0.25 V / (m/s)
R = 1 MΩ, C = 1 μF
VIntegral = −1.43 mV / (m/s)
GainInverter = −175 R
V in − + C
V out
R 1
R 2

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Industrial Instruments 1
Mechanical Sensors
Pressure Sensors
p > 1 atmosphere
Diaphragm

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Industrial Instruments 1
Mechanical Sensors
Pressure Sensors
p > 1 atmosphere
Bourdon Tube

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Industrial Instruments 1
Mechanical Sensors
Pressure Sensors
p > 1 atmosphere
Solid-State Pressure Sensors

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Industrial Instruments 1
Mechanical Sensors
Pressure Sensors
p > 1 atmosphere
Solid-State Pressure Sensors

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Industrial Instruments 1
Mechanical Sensors
Pressure Sensors
p < 1 atmosphere
In low-pressure environment, the heat loss is proportional
to the number of gas molecules per unit volume.
Pirani Gauge
Measure filament resistance (RTD)
Thermocouple
Ionization Gauge

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Industrial Instruments 1
Mechanical Sensors
Flow Sensors
Solid-Flow Measurement
Where:
Q = flow (kg /min)
W = weight of material on section of length L
R = conveyor speed (m/min)
L = length of weighing platform (m)

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Industrial Instruments 1
Mechanical Sensors
Flow Sensors
Liquid-Flow
Restriction Type
Where:
Q = Volume flow rate
K = constant (for the pipe & liquid type)
Δp = drop in pressure across the restriction

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Industrial Instruments 1
Mechanical Sensors
Flow Sensors
Liquid-Flow
Obstruction Type

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Industrial Instruments 1
Mechanical Sensors
Flow Sensors
Liquid-Flow
Magnetic Type
Conducting
liquids

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Industrial Instruments 1
Mechanical Sensors
End of Chapter 5