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ELECTRICAL MEASUREMENTS & INSTRUMENTATION
Contents
Part 1 Principles of measurement
1 Introduction to measurement
Measurement units
Measurement system applications
Elements of a measurement system
Choosing appropriate measuring instruments
2 Instrument types and performance characteristics
Review of instrument types
Active and passive instruments
Null-type and deflection-type instruments
Analogue and digital instruments
Indicating instruments and instruments with a signal output
Smart and non-smart instruments
Static characteristics of instruments
Accuracy and inaccuracy
Precision/repeatability/reproducibility
Tolerance
Range or span
Linearity
Sensitivity of disturbance
Hysteresis effects
Dead space
Dynamic characteristics of instruments
Zero order instrument
First order instrument
Second order instrument
Necessity for calibration
Self-test questions
3 Errors during the measurement process
Introduction
Sources of systematic error
Errors due to environmental inputs
Wear in instrument components
Connecting leads
Reduction of systematic errors
Careful instrument design
Method of opposing inputs
High-gain feedback
Calibration
Manual correction of output reading
Intelligent instruments
Quantification of systematic errors
Random errors
Statistical analysis of measurements subject to random errors
Graphical data analysis techniques-frequency
Distributions
Aggregation of measurement system errors
Combined effect of systematic and random errors
Aggregation of errors from separate measurement
System components
Total error when combining multiple measurements
Self-test questions
References and further reading
4 Calibration of measuring sensors and instruments
Principles of calibration
Control of calibration environment
Calibration chain and traceability
Calibration records
References and further reading
5 Measurement noise and signal processing
Sources of measurement noise
Inductive coupling
Capacitive coupling
Noise due to multiple earths
Noise in the form of voltage transient
Thermoelectric potentials
Shot noise
Electrochemical potentials
Techniques for reducing measurement noise
Location and design of signal wires
Earthling
Shielding
Other techniques
Introduction to signal processing
Analogue signal filtering
Passive analogue filters
Active analogue filters
Other analogue signal processing operations
Signal amplification
Signal attenuation
Differential amplification
Signal linearization
Bias removal
Signal integration
Voltage follower
Voltage comparator
Phase-sensitive detector
Lock-in amplifier
Signal addition
Signal multiplication
Digital signal processing
Signal sampling
Sample and hold circuit
Analogue-to-do-digital converters
Digital-to-analogue conversion
Digital filtering
Autocorrelation
Other digital signal processing operations
References and further reading
6 Electrical indicating and test instruments
Digital meters
Voltage-to-time conversion digital voltmeter
Potentiometric digital voltmeter
Dual-slope integration digital voltmeter
Voltage-to-frequency conversion digital voltmeter
Digital millimeter
Analogue meters
Moving-coil meters
Moving –iron meter
Electrodynamics meters
Clamp-on meters
Analogue multimeter
Measuring high-frequency signals
Thermocouple meter
Electronic analogue voltmeters
Calculation of meter outputs for non-standard
Waveforms
Cathode ray oscilloscope
Cathode ray tube
Channel
Single-ended input
Differential input
Differential input
Timebase circuit
Vertical sensitivity control
Display position control
Digital storage oscilloscopes
References and further reading
7 Variable conversion elements
Bridge circuits
Null-type, d.c. bridge
Deflection-type d.c. bridge
Error analysis
A.c bridges
Resistance measurement
D.c bridge circuit
Voltmeter-ammeter method
Resistance-substitution method
Use of the digital voltmeter to measure resistance
The ohmmeter
Codes for resistor values
Inductance measurement
Capacitance measurement
Alphanumeric codes for capacitor values
Current measurement
Frequency measurement
Digital counter-timers
Phase-locked loop
Cathode ray oscilloscope
The wien bridge
Phase measurement
Electronic counter-timer
X-Y plotter
Oscilloscope
Phase-sensitive detector
Self-test questions
References and further reading
8 Signal transmission
Electrical transmission
Transmission as varying voltages
Current loop transmission
Transmission using an a.c. carrier
Pneumatic transmission
Fibre-optic transmission
Principles of fibre optics
Transmission characteristics
Multiplexing schemes
Optical wireless telemetry
Radio telemetry
Digital transmission protocols
References and further reading
9 Digital computation and intelligent devices
Principles of digital computation
Computer operation
Interfacing
Practical considerations in adding computers to
Measurement systems
Intelligent devices
Intelligent instruments
Smart sensors
Smart transmitters
Communication with intelligent devices
Computation in intelligent devices
Future trends in intelligent devices
Self-test questions
References and further reading
10 Instrumentation/computer networks
Introduction
Serial communication lines
Asynchronous transmission
Parallel data bus
Local area networks
Star networks
Ring and bus networks
Gateways
Hart
Digital fieldbuses
Communication protocols for very large systems
Protocol standardization
Future development of networks
References and further reading
11 Display, recording and presentation of measurement data
Display of measurement signals
Electronic output displays
Computer monitor displays
Recording of measurement data
Mechanical chart recorders
Ultra-violet recorders
Fibre-optic recorders
Hybrid chart recorders
Magnetic tape recorders
Digital recorders
Storage oscilloscopes
Presentation of data
Tabular data presentation
Graphical presentation of data
Self-test questions
References and further reading
12 Measurement reliability and safety systems
Reliability
Principles of reliability
Laws of reliability in complex systems
Improving measurement system reliability
Software systems
Introduction to safety systems
Operation of safety systems
Design of a safety system
Self-test questions
References and further reading
Part-2 Measurement sensors and instruments
13 Sensor technologies
Capacitive and resistive sensors
Magnetic sensors
Half –effect sensors
Piezoelectric transducers
Strain gauges
Piezoresistive sensors
Strain gauges
Piezoresistive sensors
Optical sensors
Optical sensors
Intrinsic sensors
Extrinsic sensors
Distributed sensors
Ultrasonic transducers
Transmission speed
Direction of travel of ultrasound waves
Directionality of ultrasound waves
Relationship between wavelength, frequency and
Directionality of ultrasound waves
Attenuation of ultrasound waves
Ultrasound as a range sensor
Use of ultrasound in tracking 3D object motion
Effect of noise in ultrasonic measurement systems
Exploiting Doppler shift in ultrasound transmission
Ultrasonic imaging
Nuclear sensors
Micro sensors
References and further reading
14 Temperature measurement
Principles of temperature measurement
Thermoelectric effect sensors
Thermocouple tables
Non-zero reference junction temperature
Thermocouple protection
Thermocouple manufacture
The thermopile
Digital thermometer
The continuous thermocouple
Varying resistance devices
Resistance thermometers
Thermistors
Semiconductor devices
Radiation thermometers
Optical pyrometers
Radiation pyrometers
Thermography
Thermal expansion methods
Liquid-in-glass thermometers
Bimetallic thermometer
Pressure thermometers
Quartz thermometers
Fibre-optic temperature sensors
Acoustic thermometers
Colour indicators
Change of state of materials
Intelligent temperature-measuring instruments
Choice between temperature transducers
Self-test questions
References and further reading
15 Pressure measurement
Diaphragms
Capacitive pressure sensor
Fibre-optic pressure sensors
Bellows
Bourdon tube
Manometers
Resonant-wire devices
Dead-weight gauge
Special measurement devices for low pressures
High-pressure measurement
Intelligent pressure transducers
Selection of pressure sensors
16 Flow measurements
Mass flow rate
Conveyor-based methods
Coriolis flow meter
Thermal mass flow measurement
Joint measurement of volume flow rate and fluid
Density
Volume flow rate
Differential pressure meters
Variable area flow meters
Positive displacement flowmeters
Turbine meters
Electromagnetic flowmeters
Vortex-shedding flowmeters
Ultrasonic flow meters
Other types of flow meter for measuring volume
Flow rate
Intelligent flow meters
Choice between flow meters for particular applications
References and further reading
17 Level measurement
Dipsticks
Float systems
Pressure-measuring devices
Capacitive devices
Ultrasonic level gauge
Radar methods
Radiation methods
Other techniques
Vibrating level sensor
Hot-wire elements/carbon resistor elements
Laser methods
Fibre-optic level sensors
Thermography
Intelligent level-measuring instruments
Choice between different level sensors
References and further reading
18 Mass force and torque measurement
Mass measurement
Electronic load cell
Pneumatic/hydraulic load cells
Intelligent load cells
Mass-balance instruments
Spring balance
Force measurement
Use of accelerometers
Vibrating wire sensor
Torque measurement
Reaction forces in shaft bearings
Prony brake
Measurement of induced strain
Optical torque measurement
19 Translational motion transducers
Displacement
The resistive potentiometer
Linear variable differential transformer
Variable capacitance transducers
Variable inductance transducers
Strain gauge
Piezoelectric transducers
Nozzle flapper
Other methods of measuring small displacements
Measurement of large displacements
Proximity sensors
Selection of translational measurement transducers
Velocity
Differentiation of displacement measurements
Integration of the output of an accelerometer
Conversion to rotational velocity
Acceleration
Selection of accelerometers
Vibration
Nature of vibration
Vibration measurement
Shock
20
20 Rotational motion transducers
Rotational displacement
Circular and helical potentiometers
Rotational differential transformer
Incremental shaft encoders
Coded-disc shaft encoders
The resolver
The synchro
The induction potentiometer
The rotary inductosyn
Gyroscopes
Choice between rotational displacement transducers
Rotational velocity
Digital tachometers
Stroboscopic methods
Analogue tachometers
Mechanical flyball
The rate gyroscope
Differentiation of angular displacement measurements
Integration of the output from an accelerometer
Choice between rotational velocity transducers
Measurement of rotational velocity transducers
Measurement of rotational acceleration
References and further reading
21 Summary of other measurements
Dimensions measurement
Rules and tapes
Calipers
Micrometers
Gauge blocks and length bars
Height and depth measurement
Angle measurement
Flatness measurement
Volume measurement
Viscosity measurement
Capillary and tube viscometers
Falling body viscometer
Rotational viscometers
Moisture measurement
Industrial moisture measurement techniques
Laboratory techniques for moisture measurement
Humidity measurement
Sound measurement
pH measurement
The glass electrode
Other methods of pH measurement
Gas sensing and analysis
Catalytic sensors
Paper tape sensors
Liquid electrolyte electrochemical cells
Solid –state electrochemical cells
Catalytic gate FETs
Semiconductor sensors
Organic sensors
Piezoelectric devices
Infra-red absorption
Mass spectrometers
Gas chromatography
References and further reading