# 3441 Industrial Instruments 1 Chapter 5 Mechanical Sensors

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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

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Princess Sumaya University Industrial Instruments 1 Mechanical Sensors Objective Understand how mechanical sensors work and how to interface them.

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

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

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Princess Sumaya University Industrial Instruments 1 Mechanical Sensors Displacement, Location, or Position Sensors LVDT

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

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

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

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Princess Sumaya University 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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Princess Sumaya University 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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Princess Sumaya University Industrial Instruments 1 Mechanical Sensors Strain Sensors Construction

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

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Princess Sumaya University Industrial Instruments 1 Mechanical Sensors Strain Sensors Load Cells

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

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

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Princess Sumaya University Industrial Instruments 1 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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Princess Sumaya University Industrial Instruments 1 Mechanical Sensors Pressure Sensors p > 1 atmosphere Diaphragm

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Princess Sumaya University Industrial Instruments 1 Mechanical Sensors Pressure Sensors p > 1 atmosphere Bourdon Tube

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

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

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Princess Sumaya University 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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Princess Sumaya University 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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Princess Sumaya University 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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Princess Sumaya University Industrial Instruments 1 Mechanical Sensors Flow Sensors Liquid-Flow Obstruction Type

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

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Princess Sumaya University Industrial Instruments 1 Mechanical Sensors End of Chapter 5