MECH 182 Experimental Methods

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MECH 182Experimental Methods
Dr. S-W. Ricky Lee Department of Mechanical
Engineering Hong Kong University of Science and
Technology Clear Water Bay, Kowloon, Hong Kong
Lecture 3
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Basic Electrical Instrumentation for
Measurements (I)
1. Introduction 2. Review on Electricity 3.
Sensors Transducers 4. Basic Conditioning
Circuits
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Introduction
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Flow Chart of Measurements
Quantities to be measured
Sensors Transducers
Signal Conditioning Circuits
Data Recording Processing
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Typical Physical Quantities
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Typical Measuring Devices
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Other Instrumentation
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Review on Electricity
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Basic Terminology
-
-
Charge (C)
Voltage (V)

Electric Field (V/mm)
Current (A)
-
-
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Fundamental Laws
(?)
E
)
(pF)
(nH)
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Piezoelectric Effects
Piezo Effect
Converse Piezo Effect
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Sensors Transducers
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What are Transducers?
Transducers are electromechanical devices which
convert a mechanical quantity change into a
change in an electrical signal which can be
monitored as a voltage/current/charge after
conditioning.
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Linear Variable Differential Transformer(LVDT)
E
V
(Inductive Transducer)
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Proximity Sensor
To AC Power Supply

d
Target
(Capacitive Transducer)
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Strain Gauge
a
a
--- Gauge Factor
(Resistive Transducer)
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Piezoelectric Sensors
M
M
Pressure Sensors
Accelerometer
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Thermo Couple
Material B
Material B
V
Material A
T1
T2
Seebeck Effect
VSA/B(T1-T2)
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Basic Conditioning Circuits
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Potentiometer
if ?R2/R1gtgt1
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Wheastone Bridge
R1
R2
E

V
let ?R2/R1 linear
R4
R3