Introduction to Instrumentation and Measurements 2nd Edition By Robert B Northrop

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Introduction to Instrumentation and Measurements 2nd Edition By Robert B Northrop

Preface

Purpose: This text is intended to be used in a classroom course for engineers that covers
the theory and art of modern instrumentation and measurements (I&M). There is more
than enough material to support two semesters’ work. Thus, the instructor has the
option of choosing those topics and the depth of coverage that suit his or her interests
and curriculum. Due to its breadth, Introduction to Instrumentation and Measurements,
2nd edition will also be useful as a reference for the practicing engineer and scientist
interested in I&M.
Why have a classroom course in I&M? Over the past decade or so, in the U.S, many
EE departments have discontinued classroom courses on the theory and practice of
instrumentation and measurements. In this period, we have also seen the swift
development of new and exciting means of measurement using new technologies, the
adoption of new standards and, concurrently, the lack of development of a coherent
educational base to support their understanding and use. Using an instrument in
the laboratory is not the same as understanding the physical and electronic principles
underlying its design and functional limitations. Clearly, there is now more than ever
a need for classroom experience in the new I&M that will give students the necessary
technical background to use and design sensors, signal conditioning systems and I&M
systems. We feel that this text supports that need.
This text was written based on the author’s 40 years of experience in teaching
a classroom course (EE 230), Electrical Instrumentation, to juniors and seniors in the
Electrical and Computer Engineering Department at the University of Connecticut,
Storrs.
Obviously, in 40 years we have seen the field of instrumentation and measurements
evolve with the rest of electrical engineering technology. Due to the rapid pace of
technical development, it has generally been difficult to find an up-to-date text for our
Electrical Instrumentation course. After years of frustration trying to match a text to
course content, I decided to write one that would not only encompass the ‘‘traditional’’
aspects of I&M, but also include material on modern IC and photonic sensors,
microsensors, signal conditioning, noise, data interfaces and DSP.
Reader Background: Readers are assumed to have taken core EE curriculum courses,
or their equivalents. The reader should be skilled in basic linear circuit theory (i.e., the
reader has mastered Thevenin’s and Norton’s theorems, Kirchoff’s Laws, superposition,
dependent sources, and ideal op-amps, and should know how to describe DC and AC
steady-state circuits in terms of loop and node equations). An introductory systems
course should have given him/her familiarity with both time and frequency domain
methods of describing linear dynamic systems characterized by ordinary, linear, differential
or difference equations, including state space, Fourier, Laplace and z-transforms,
transfer functions, steady-state frequency response of systems, and Bode plots. From
physics or an EE course in electromagnetics, the reader should have a basic knowledge
of electric and magnetic fields, inductance, capacitance, reluctance, etc. There should also
be some familiarity with electromagnetic waves, Maxwell’s equations, transmission lines
and polarization. From a first course in electronics, there should be basic knowledge of
BJTs, JFETs, diodes, photodiodes and their simple linear circuit models.
Scope of the Text: A major feature of Introduction to Instrumentation and Measurements,
2nd edition is its breadth of coverage. Throughout the text, a high level of mathematical
analytical detail is maintained. It is not a ‘‘picture book’’; we assume that readers have
already had contact with basic electrical instruments, including oscilloscopes and meters
in their introductory EE and physics labs.
In the following paragraphs, we give an overview of the contents.
Chapter 1, ‘‘Measurement Systems,’’ is introductory in nature. In it, we illustrate
measurement system architecture and describe sensor dynamics, signal conditioning,
data display and storage. Errors in measurements are discussed, including the meaning
of accuracy and precision, limiting error, etc. The recent (1990) quantum standards
adopted for the volt and the ohm are described, as well as other modern electrical and
physical standards.
In Chapter 2, ‘‘Analog Signal Conditioning,’’ we describe, largely at the systems level,
the means of conditioning the analog outputs of various sensors. Op-amps, differential,
instrumentation, auto-zero and isolation amplifiers are covered. Applications of op-amps
in active filters, differential instrumentation amplifiers, charge amplifiers, phase sensitive
rectifiers, etc. are shown. We also give practical considerations of errors caused by offset
voltage, bias currents, input impedance, slew rate and gain bandwidth product etc. There
is also a section on nonlinear signal processing with op-amps.
Noise and coherent interference in measurements are treated in depth in Chapter 3.
A heuristic yet rigorous approach is used in which we define and use one-sided, noise
voltage and current power density spectra to describe the effect of noise in instruments
and measurement systems. Noise factor and figure are covered, and output signal-tonoise
ratios are used to evaluate system noise performance. Examples are given of
calculations of the noise-limited resolution of the quantity under measurement (QUM).
Techniques are shown for the minimization of coherent interference.
The traditional topics of DC null measurements and AC null measurements are
presented in Chapter 4 and Chapter 5, respectively. Wheatstone and Kelvin bridges, and
potentiometers are described in Chapter 4, and the major AC bridges used to measure the
inductance, Q, and capacitance, D, are treated in Chapter 5. New material added to this
chapter includes a description and analysis of the Anderson Current Loop method of
reading sensor outputs.
A survey of sensor mechanisms is presented in Chapter 6. This is a large and
substantive chapter covering a broad range of sensor mechanisms and types. Of special
note is the introduction of certain fiber optic and electro-optic sensors, as well as selected
chemical and ionizing radiation sensors. The Sagnac effect is introduced and the basic
fiber optic gyro is described.
New material in Chapter 6 includes a description and analysis of sensors based on the
giant magnetoresistive effect and the anisotropic magnetoresistive effect. Pyroelectric IR
sensors are also introduced. The various means of measuring the rotation of linearly
polarized light is presented, as well as a substantive section on photomultiplier tubes and
channel-plate photomultipliers. Finally, a new section has been added on electronic noses
which are used to sense volatile organic compounds.
In Chapter 7, ‘‘Applications of Sensors to Physical Measurements,’’ a detailed analysis
of mechanical gyroscopes, clinometers and accelerometers is given, including new
material on micromachined accelerometers and gyros. The Doppler effect in ultrasonic
velocimetry and laser Doppler velocimetry are covered. Also new in Chapter 7 is large
section on the global positioning (GPS) system, a section on optical interferometry, and
an extensive introduction to spectrophotometry, sonoluminescence and surface plasmon
resonance which are used for substance detection.
In Chapter 8, ‘‘Basic Electrical Measurements,’’ the classic means of measuring
electrical quantities are presented, as well as newer methods such as Faraday magnetooptic
ammeters and Hall effect gaussmeters and wattmeters. Electronic means of
measuring stored charge and static electric fields are described.
Digital interfaces on measurement systems are covered in Chapter 9. This chapter
begins with a description of the sampling theorem, aliasing and quantization. The
traditional topics of hold circuits, DACs and many types of ADC are covered. Also
covered in Chapter 9 are data buses. New material includes a section on dithering as a
means of reducing quantization noise, a section on delta-sigma ADCs and a section on
the new USB. Virtual instruments and PXI systems are also introduced.
Since digitized, measured data is processed and stored on computers in modern
instrumentation practice, Chapter 10, ‘‘Introduction to Digital Signal Conditioning,’’ was
written to acquaint the reader to this specialized field. The z-transform and its use in
describing filtering operations on discrete, digitized data in the frequency domain is
introduced. Examples of FIR and IIR digital filters are given, including numerical
integration and differentiation routines, viewed both in the time and frequency domains.
The discrete and fast Fourier transforms are covered and the effect of data windows
on spectral resolution is discussed. Finally, the use of splines in interpolating discrete
data sequences and estimating missing data points is described.
In Chapter 11, ‘‘Examples of the Design of Measurement Systems,’’ four examples of
complex measurement systems developed by the author and his students are given to
illustrate design philosophy:
1. A self-nulling microdergree polarimeter to measure glucose concentration
2. A system to detect and locate partial discharges on underground, high-voltage
power cables
3. Design of a laser velocity and distance measuring system
4. Design of capacitance sensors to detect hidden objects
Problems: Chapters 1 through 10 are followed by problems taken from the author’s
extensive classroom experience in teaching courses in instrumentation and measurement
at the University of Connecticut. The problems are solvable; they are student-tested.
References and Bibliography: The references cited encompass a wide time span; from
the 1950s to the present. There are many recent entries of review articles and specialized
texts that should lead the reader interested in pursuing a specialized area of I&M further
into that particular field.
Index: A complete index allows the reader to access topics, both featured and not
featured in the Contents.
Features: Every chapter in the second edition of Introduction to Instrumentation and
Measurements has been revised to reflect modern technology. In addition, many chapters
contain all-new material which expands the scope of the text to include geophysical,
chemical and photonic instrumentation. Some of this unique new material includes:

1. The Anderson Current Loop technology for conditioning the outputs of remote
resistive and capacitive sensors (Chapter 4)
2. The design of optical polarimeters and their application to polarization
responding sensors (Chapter 6)
3. Photonic measurements with photomultipliers and channel plate photon sensors
(Chapter 6)
4. Introduction of the sensing of gas phase analytes; the vertebrate olfactory
system is described, as well as various chemical sensors, and feature extraction of
complex odorants (Chapter 6)
5. The Sagnac effect as a means of measuring vehicle angular velocity (Chapter 6)
6. Micromachined, vibrating mass and vibrating disk rate gyros. The Humphrey air
jet gyro is also analyzed. Traditional pendulum, as well as fluid-filled clinometers,
is described. Micromachined, IC accelerometers are also covered (Chapter 7)
7. Global Positioning System (GPS) and its various modifications to improve its
accuracy (Chapter 7)
8. Substance detection using photons (Chapter 7); dispersive, non-dispersive, and
Fourier transform spectroscopy are described, as well as sonoluminescence and
surface plasmon resonance
9. Dithering, delta-sigma ADCs, data acquisition cards, the USB, and virtual
instruments and PXI systems (Chapter 9)

Contents

Preface……………………………………………………………………………………………………………………….. vii
The Author………………………………………………………………………………………………………………… xi
Chapter 1 Measurement Systems
1.1 Introduction ………………………………………………………………………………………………………. 1
1.2 Measurement System Architecture …………………………………………………………………… 1
1.2.1 Sensor Dynamics ……………………………………………………………………………………. 3
1.2.2 Overview of Signal Conditioning…………………………………………………………… 6
1.3 Errors in Measurements ……………………………………………………………………………………. 7
1.3.1 Gross Errors……………………………………………………………………………………………. 7
1.3.2 System Errors …………………………………………………………………………………………. 7
1.4 Standards Used in Measurements…………………………………………………………………….. 13
1.4.1 Electrical Standards………………………………………………………………………………… 13
1.4.1.1 Potential Difference…………………………………………………………………… 14
1.4.1.2 Resistance………………………………………………………………………………….. 18
1.4.1.3 Current and Charge………………………………………………………………….. 23
1.4.1.4 Capacitance……………………………………………………………………………….. 26
1.4.1.5 Inductance ………………………………………………………………………………… 28
1.4.2 Time and Frequency ………………………………………………………………………………. 30
1.4.3 Physical Standards …………………………………………………………………………………. 31
1.4.3.1 Mass………………………………………………………………………………………….. 31
1.4.3.2 Length……………………………………………………………………………………….. 32
1.4.3.3 Temperature ……………………………………………………………………………… 33
1.4.3.4 The SI Base Units ……………………………………………………………………… 33
1.5 Chapter Summary …………………………………………………………………………………………….. 34
Problems……………………………………………………………………………………………………………………. 34
Chapter 2 Analog Signal Conditioning
2.1 Introduction ………………………………………………………………………………………………………. 39
2.2 Differential Amplifiers………………………………………………………………………………………. 39
2.2.1 Analysis of Differential Amplifiers………………………………………………………… 40
2.2.2 Common-Mode Rejection Ratio……………………………………………………………… 41
2.2.3 Measurement of CMRR, AD and AC………………………………………………………. 41
2.2.4 Effect of Source Resistance Asymmetry on CMRR………………………………… 42
2.3 Operational Amplifiers……………………………………………………………………………………… 44
2.3.1 Types of Op-amps ………………………………………………………………………………….. 45
2.3.2 Basic Broadband Amplifier Design Using Op-amps……………………………… 47
2.3.2.1 Non-Inverting Amplifier…………………………………………………………… 48
2.3.2.2 The Inverting Amplifier and Summer ……………………………………… 49
2.3.3 Current Feedback Op-amps …………………………………………………………………… 50
2.4 Analog Active Filter Applications Using Conventional Op-amps……………………. 54
2.4.1 Introduction……………………………………………………………………………………………. 54
2.4.2 Analog Active Filter Architectures ………………………………………………………… 55
2.4.2.1 Controlled Source Active Filters……………………………………………….. 56
2.4.2.2 Biquad Active Filters ………………………………………………………………… 58
2.4.2.3 Generalized Impedance Converter Active Filters …………………….. 62
2.4.2.4 High-Order Active Filters …………………………………………………………. 64
2.4.3 Operational Amplifier Integrators and Differentiators ………………………….. 66
2.4.4 Summary………………………………………………………………………………………………… 67
2.5 Instrumentation Amplifiers ………………………………………………………………………………. 68
2.5.1 Instrumentation Amplifiers Made from Op-amps…………………………………. 68
2.5.2 Isolation Amplifiers ……………………………………………………………………………….. 71
2.5.3 AutoZero Amplifiers ……………………………………………………………………………… 73
2.5.4 Absolute Isolation ………………………………………………………………………………….. 74
2.5.5 Summary………………………………………………………………………………………………… 74
2.6 Nonlinear Analog Signal Processing by Op-amps and by Special
Function Modules……………………………………………………………………………………………… 77
2.6.1 Introduction……………………………………………………………………………………………. 77
2.6.2 Precision Absolute Value (Absval) Circuits……………………………………………. 78
2.6.3 Multifuntion Converters ………………………………………………………………………… 80
2.6.4 True RMS to DC Converters ………………………………………………………………….. 81
2.6.5 Square Root Circuits and Dividers ………………………………………………………… 83
2.6.6 Peak Detectors and Track and Hold (T&H) Circuits……………………………… 85
2.6.7 Log Ratio and Trigonometric ICs …………………………………………………………… 88
2.6.8 Summary………………………………………………………………………………………………… 90
2.7 Charge Amplifiers …………………………………………………………………………………………….. 90
2.7.1 Charge Amplifiers Used with Piezoelectric Transducers ………………………. 90
2.7.2 Charge Amplifier as Integrating Coulombmeter …………………………………… 93
2.7.3 Summary………………………………………………………………………………………………… 94
2.8 Phase Sensitive Rectifiers ………………………………………………………………………………….. 94
2.8.1 Double-Sideband, Suppressed Carrier Modulation ……………………………….. 94
2.8.2 Demodulation of DSBSCM Signals by Analog Multiplier …………………….. 95
2.8.3 Other PSR Designs…………………………………………………………………………………. 96
2.8.4 The Lock-In Amplifier……………………………………………………………………………. 96
2.8.4.1 Introduction………………………………………………………………………………. 96
2.8.4.2 Calculation of the SNR Improvement Using
a Lock-In Amplifier ………………………………………………………………….. 100
2.8.5 Summary………………………………………………………………………………………………… 104
2.9 Chapter Summary …………………………………………………………………………………………….. 104
Problems……………………………………………………………………………………………………………………. 105
Chapter 3 Noise and Coherent Interference in Measurements
3.1 Introduction ………………………………………………………………………………………………………. 113
3.2 Random Noise in Circuits ………………………………………………………………………………… 113
3.2.1 Probability Density Functions………………………………………………………………… 114
3.2.2 The Power Density Spectrum ………………………………………………………………… 115
3.2.3 Sources of Noise in Signal Conditioning Systems …………………………………. 118
3.2.3.1 Noise from Resistors…………………………………………………………………. 118
3.2.3.2 The Two Source Noise Model for Active Devices ……………………. 120
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3.2.3.3 Noise in JFETs…………………………………………………………………………… 121
3.2.3.4 Noise in BJTs …………………………………………………………………………….. 122
3.3 Propagation of Gaussian Noise through Linear Filters…………………………………….. 124
3.4 Broadband Noise Factor and Noise Figure of Amplifiers………………………………… 125
3.5 Spot Noise Factor and Figure …………………………………………………………………………… 127
3.6 Transformer Optimization of Amplifier Fspot and Output SNR………………………… 129
3.7 Cascaded Noisy Amplifiers………………………………………………………………………………. 130
3.8 Calculation of the Noise Limited Resolution of Certain
Signal Conditioning Systems…………………………………………………………………………….. 131
3.8.1 Calculation of the Minimum Resolvable AC Input Voltage
to a Noisy, Inverting Op-amp Amplifier ……………………………………………….. 131
3.8.2 Calculation of the Minimum Resolvable DC Current in
White and 1/f Noise………………………………………………………………………………. 133
3.8.3 Calculation of the Minimum Resolvable AC Input Signal to Obtain a
Specified Output SNR in a Transformer Coupled, Tuned Amplifier…….. 134
3.8.4 Calculation of the Smallest R=R in a Wheatstone
Bridge to Give a Specified SNRo……………………………………………………………. 135
3.8.5 Determination of the Conditions for Maximum Output
SNR Given a Simple Inverting Op-Amp Amplifier
with Known ena and ina …………………………………………………………………………. 137
3.9 Modern, Low Noise Amplifiers for Use in Instrumentation
Signal Conditioning Systems…………………………………………………………………………….. 137
3.10 Coherent Interference and its Minimization …………………………………………………….. 139
3.10.1 Sources of Coherent Interference …………………………………………………………… 139
3.10.1.1 Direct Electrostatic Coupling of Coherent
Interference ……………………………………………………………………………… 140
3.10.1.2 Direct Magnetic Induction of Coherent
Interference ……………………………………………………………………………… 141
3.10.1.3 Ground Loops…………………………………………………………………………. 142
3.10.2 Cures for Coherent Interference …………………………………………………………….. 144
3.10.2.1 Power Line Low Pass Filters…………………………………………………… 144
3.10.2.2 Transient Voltage Suppressors ………………………………………………… 145
3.10.2.3 Coherent Interference Induced in Coaxial Cables
by Magnetic Coupling…………………………………………………………….. 147
3.10.2.4 Single Grounding of Coax Shields to Prevent
Ground Loop Interference ………………………………………………………. 150
3.10.2.5 Use of a Longitudinal Choke or Neutralizing Transformer
to Attenuate Common-Mode Coherent Interference ………………. 150
3.10.2.6 Experimental Verification of Cabling and Grounding
Schemes to Achieve Minimum Noise Pickup…………………………. 152
3.10.2.7 Circuit Grounding…………………………………………………………………… 154
3.10.2.8 Ferrite Beads and Feed Through Capacitors…………………………… 155
3.10.2.9 Interruption of Ground Loops by the Use
of Isolation Transformers and Photo-Optic
Couplers ………………………………………………………………………………….. 155
3.10.2.10 Photo-Optic Couplers ……………………………………………………………… 155
3.10.2.11 The Use of Guarding and Shielding to Reduce
Common-Mode, Coherent Interference…………………………………… 157
3.10.3 Summary of Techniques for Coherent Noise Reduction ……………………….. 163
3.11 Chapter Summary …………………………………………………………………………………………….. 163
Problems……………………………………………………………………………………………………………………. 164
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Chapter 4 DC Null Measurement
4.1 Introduction ………………………………………………………………………………………………………. 171
4.2 Wheatstone Bridge Analysis …………………………………………………………………………….. 172
4.3 The Kelvin Bridge …………………………………………………………………………………………….. 174
4.4 The Anderson Constant Current Loop……………………………………………………………… 176
4.4.1 Introduction……………………………………………………………………………………………. 176
4.4.2 The Anderson Loop Applied to Groups of Sensors………………………………. 178
4.4.3 Conclusion……………………………………………………………………………………………… 183
4.5 Potentiometers…………………………………………………………………………………………………… 183
4.6 Chapter Summary …………………………………………………………………………………………….. 185
Problems……………………………………………………………………………………………………………………. 185
Chapter 5 AC Null Measurements
5.1 Introduction ………………………………………………………………………………………………………. 191
5.2 Inductor Equivalent Circuits …………………………………………………………………………….. 191
5.3 Capacitor Equivalent Circuits …………………………………………………………………………… 193
5.4 AC Operation of Wheatstone Bridges. ……………………………………………………………… 195
5.5 AC bridges………………………………………………………………………………………………………… 195
5.5.1 Bridges Used to Measure Capacitance…………………………………………………… 196
5.5.1.1 The Resistance Ratio Bridge……………………………………………………… 196
5.5.1.2 The Schering Bridge………………………………………………………………….. 197
5.5.1.3 The Parallel C Bridge ……………………………………………………………….. 198
5.5.1.4 The De Sauty Bridge…………………………………………………………………. 199
5.5.1.5 The Wien Bridge……………………………………………………………………….. 200
5.5.1.6 The Commutated Capacitor Bridge………………………………………….. 202
5.5.2 Bridges Used to Measure Inductance and Mutual
Inductance ……………………………………………………………………………………………… 203
5.5.2.1 The Maxwell Bridge………………………………………………………………….. 203
5.5.2.2 Parallel Inductance Bridge………………………………………………………… 204
5.5.2.3 The Hay Bridge ………………………………………………………………………… 205
5.5.2.4 The Owen Bridge ……………………………………………………………………… 205
5.5.2.5 The Anderson Bridge ……………………………………………………………….. 206
5.5.2.6 The Heaviside Mutual Inductance Bridge………………………………… 207
5.5.2.7 The Heydweiller Mutual Inductance Bridge ……………………………. 208
5.5.3 Null Method of Measuring Transistor Small Signal
Transconductance and Feedback Capacitance ……………………………………….. 209
5.6 Chapter Summary …………………………………………………………………………………………….. 211
Problems……………………………………………………………………………………………………………………. 211
Chapter 6 Survey of Sensor Input Mechanisms
6.1 Introduction ………………………………………………………………………………………………………. 215
6.2 Categories of Sensor Input Mechanisms…………………………………………………………… 215
6.3 Resistive Sensors……………………………………………………………………………………………….. 215
6.3.1 Resistive Temperature Sensors……………………………………………………………….. 216
6.3.2 Resistive Strain Gauges………………………………………………………………………….. 218
6.3.3 Photoconductors …………………………………………………………………………………….. 220
6.3.4 Conductive Relative Humidity Sensors …………………………………………………. 223
6.3.5 Use of Resistance Change to Sense Position or Angle…………………………… 226
6.3.6 Giant Magnetoresistive Effect-Based Sensors ………………………………………… 227
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6.3.7 Anisotropic Magnetoresistance (AMR) ………………………………………………….. 230
6.4 Voltage Generating Sensors ………………………………………………………………………………. 236
6.4.1 Thermocouples and Thermopiles…………………………………………………………… 236
6.4.2 Photovoltaic Cells…………………………………………………………………………………… 239
6.4.3 Piezoelectric Transducers……………………………………………………………………….. 241
6.4.4 Pyroelectric Sensors ……………………………………………………………………………….. 245
6.4.5 Sensors Whose Voltage Output is Proportional to d=dt………………………. 249
6.4.5.1 The Variable Reluctance Phonograph Pickup…………………………… 249
6.4.5.2 Electrodynamic Accelerometer …………………………………………………. 251
6.4.5.3 Linear Velocity Sensors …………………………………………………………….. 252
6.4.6 Sensors whose Output EMF Depends on the Interaction
of a Magnetic Field with Moving Charges…………………………………………….. 252
6.4.6.1 Faraday Effect Flowmeters ……………………………………………………….. 252
6.4.6.2 Hall Effect Sensors ……………………………………………………………………. 255
6.5 Sensors Based on Variable Magnetic Coupling ………………………………………………… 257
6.5.1 The LVDT……………………………………………………………………………………………….. 257
6.5.2 Synchros and Resolvers …………………………………………………………………………. 259
6.6 Variable Capacitance Sensors ……………………………………………………………………………. 262
6.7 Fiber Optic Sensors …………………………………………………………………………………………… 264
6.7.1 Magneto-Optic Current Sensors …………………………………………………………….. 265
6.7.2 Measurement of the Optical Rotation of the Linearly
Polarized Light Output of Certain Optical Sensors……………………………….. 268
6.7.3 Fiber Optic (FO) Mechanosensors………………………………………………………….. 278
6.8 Photomultiplier Tubes and Related Electron Multiplication
Devices ……………………………………………………………………………………………………………… 283
6.8.1 Introduction……………………………………………………………………………………………. 283
6.8.2 Operation of PMTs …………………………………………………………………………………. 285
6.8.3 The Single-Channel Photomultiplier ……………………………………………………… 288
6.8.4 Microchannel-Plate Photomultipliers …………………………………………………….. 289
6.8.5 Summary………………………………………………………………………………………………… 290
6.9 Ionizing Radiation Sensors ……………………………………………………………………………….. 291
6.9.1 Geiger-Muller Tube………………………………………………………………………………… 292
6.9.2 Solid State Crystal Radiation Sensors…………………………………………………….. 295
6.9.3 Scintillation Counters …………………………………………………………………………….. 296
6.10 Electro-Chemical Sensors ………………………………………………………………………………….. 298
6.10.1 pH and Specific Ion Electrodes ……………………………………………………………… 298
6.10.2 Polarographic Electrodes ……………………………………………………………………….. 300
6.10.3 Fuel Cell Electrodes ……………………………………………………………………………….. 302
6.11 Electronic ‘Noses’ ……………………………………………………………………………………………… 302
6.11.1 The Rationale for Artificial Noses………………………………………………………….. 302
6.11.2 Olfactory Anatomy and Physiology ………………………………………………………. 303
6.11.3 The Vertebrate Olfactory Chemoreceptor System ………………………………….. 304
6.11.4 Sensors for Gas-Phase Analytes……………………………………………………………… 307
6.11.5 Feature Extraction in E-Noses………………………………………………………………… 318
6.11.6 Summary………………………………………………………………………………………………… 318
6.12 Mechano-Optical Sensors………………………………………………………………………………….. 318
6.12.1 Optical Coding Disks …………………………………………………………………………….. 319
6.12.2 Sagnac Effect Sensing of Angular Velocity…………………………………………….. 320
6.12.3 Laser Doppler Velocimetry…………………………………………………………………….. 323
6.13 Chapter Summary …………………………………………………………………………………………….. 329
Problems……………………………………………………………………………………………………………………. 329
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Chapter 7 Applications of Sensors to Physical Measurements
7.1 Introduction ………………………………………………………………………………………………………. 343
7.2 Measurement of Angular Acceleration, Velocity and Displacement ………………… 343
7.2.1 Angular Acceleration Measurement………………………………………………………. 343
7.2.1.1 Angular Acceleration Measurement with a Constrained
Mechanical Gyro……………………………………………………………………….. 344
7.2.1.2 Simple Inertia Wheel-Spring-Dashpot Angular
Accelerometer …………………………………………………………………………… 345
7.2.1.3 A Servo Angular Accelerometer……………………………………………….. 346
7.2.2 Angular Velocity Measurement with Mechanical Gyroscopes ………………. 347
7.2.2.1 The Mechanical Rate Gyro ……………………………………………………….. 350
7.2.2.2 Sagnac Effect Fiber Optic Gyroscopes………………………………………. 353
7.2.2.3 The Vibrating Mass Rate Gyro …………………………………………………. 354
7.2.2.4 The Humphrey Air Jet Gyro…………………………………………………….. 357
7.2.2.5 Oscillating Disk Rate Gyro……………………………………………………….. 361
7.2.3 Angular Velocity Measurement with Tachometers ………………………………… 365
7.2.4 Angular Position Measurement with Gyroscopes …………………………………. 371
7.2.5 Angular Position Measurement with Clinometers ………………………………… 373
7.2.6 Angular Position Measurement of Shafts ………………………………………………. 377
7.3 Measurement of Linear Acceleration, Velocity, Displacement
and Position………………………………………………………………………………………………………. 378
7.3.1 Linear Accelerometers ……………………………………………………………………………. 378
7.3.1.1 A Basic Newtonian Accelerometer …………………………………………… 378
7.3.1.2 Servo Accelerometer Design …………………………………………………….. 379
7.3.1.3 Piezoelectric Sensor Accelerometers …………………………………………. 380
7.3.1.4 Micromachined, IC Accelerometers ………………………………………….. 382
7.3.2 Linear Velocity Measurement ………………………………………………………………… 384
7.3.2.1 Measurement of Fluid Velocity…………………………………………………. 384
7.3.2.1.1 Hot Wire and Hot Film Anemometers …………………….. 384
7.3.2.2 Measuring Fluid Velocity and Flow—Other Methods ……………… 388
7.3.3 Measurement of Linear Position ……………………………………………………………. 397
7.3.3.1 Use of the Global Positioning System to Locate
Objects ………………………………………………………………………………………. 401
7.3.3.2 The Use of Optical Interferometry to Measure x…………………… 409
7.3.3.2.1 Measurement of Tympanal Membrane
Displacement by Fiber Optic Fizeau
Interferometer …………………………………………………………… 415
7.3.3.2.2 Measurement of Skin Vibration by
Optical Interferometry………………………………………………. 416
7.3.3.2.3 Two Frequency, Heterodyne
Interferometry…………………………………………………………… 419
7.3.3.2.4 The Fabry-Perot Interferometer………………………………… 421
7.3.3.3 Phase Lock Velocity and Range Sensing with
Ultrasound and EM Radiation………………………………………………….. 423
7.4 Measurement of Force and Torque …………………………………………………………………… 430
7.4.1 Load Cells for Force Measurement………………………………………………………… 430
7.4.2 Torque Measurements ……………………………………………………………………………. 434
7.5 Pressure Measurements…………………………………………………………………………………….. 437
7.5.1 High Pressure Sensors……………………………………………………………………………. 438
7.5.2 Low Pressure Sensors…………………………………………………………………………….. 445
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7.6 Introduction to Substance Detection and Measurement Using
Photons……………………………………………………………………………………………………………… 451
7.6.1 Introduction……………………………………………………………………………………………. 451
7.6.2 Dispersive Spectrophotometry……………………………………………………………….. 454
7.6.3 Non-Dispersive Spectroscopy ………………………………………………………………… 460
7.6.4 Fourier Transform IR Spectroscopy ……………………………………………………….. 464
7.6.5 Single and Multiple Bubble Sonoluminescence……………………………………… 470
7.6.5.1 Single Bubble Sonoluminescence ……………………………………………… 470
7.6.5.2 Multiple Bubble Sonoluminescence ………………………………………….. 473
7.6.5.3 Summary…………………………………………………………………………………… 474
7.6.6 Surface Plasmon Resonance …………………………………………………………………… 474
7.7 Temperature Measurements ……………………………………………………………………………… 479
7.7.1 Temperature Standards ………………………………………………………………………….. 479
7.7.2 Some Common Means of Temperature Measurement…………………………… 481
7.7.2.1 Mechanical Temperature Sensors ……………………………………………… 481
7.7.2.2 Electrical and Electronic Temperature Sensors…………………………. 483
7.7.2.2.1 The Resistance Noise Thermometer …………………………. 483
7.7.2.2.2 The Resistance Thermometer……………………………………. 484
7.7.2.2.3 Electronic IC Temperature Sensors…………………………… 486
7.7.2.2.4 Optical Pyrometers …………………………………………………… 486
7.8 Chapter Summary …………………………………………………………………………………………….. 493
Problems……………………………………………………………………………………………………………………. 494
Chapter 8 Basic Electrical Measurements
8.1 Introduction ………………………………………………………………………………………………………. 501
8.2 DC Voltage Measurements ……………………………………………………………………………….. 501
8.2.1 Electromechanical DC Voltmeters ………………………………………………………….. 502
8.2.1.1 D’Arsonval DC Voltmeters ……………………………………………………….. 503
8.2.1.2 The Capacitor, or Electrostatic Voltmeter …………………………………. 507
8.2.1.3 The Electrodynamometer Meter ……………………………………………….. 508
8.2.2 Electronic DC Voltmeters……………………………………………………………………….. 510
8.3 Static Electric Fields and the Potential of Charged Surfaces
Measurement…………………………………………………………………………………………………….. 513
8.4 DC Current Measurements……………………………………………………………………………….. 522
8.4.1 Electromechanical DC Ammeters…………………………………………………………… 522
8.4.2 Electronic DC Ammeters ……………………………………………………………………….. 524
8.4.2.1 Error Analysis of the Shunt Picoammeter………………………………… 525
8.4.2.2 Error Analysis of the Feedback Picoammeter…………………………… 526
8.4.3 Magneto-Optic Current Sensors …………………………………………………………….. 528
8.5 AC Voltage Measurements ……………………………………………………………………………….. 528
8.5.1 Electromechanical AC Voltmeters ………………………………………………………….. 529
8.5.1.1 The Dynamometer AC Voltmeter……………………………………………… 529
8.5.1.2 Iron Vane Voltmeters ………………………………………………………………… 529
8.5.1.3 Rectifier/D’Arsonval AC Voltmeters………………………………………… 530
8.5.1.4 Vacuum Thermocouple/D’Arsonval AC Voltmeters………………… 532
8.5.2 Analog Electronic AC Voltmeters…………………………………………………………… 533
8.5.2.1 AC Amplifier-Rectifier AC Voltmeters……………………………………… 533
8.5.2.2 Peak Reading Electronic AC Voltmeters …………………………………… 534
8.5.2.3 True RMS AC Voltmeter of the Feedback Type………………………… 535
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8.5.2.4 True RMS AC Voltmeters Using the Direct
Conversion Approach……………………………………………………………….. 539
8.5.3 Measurements of Amplifier Noise Voltages, Noise
Factor and Figure …………………………………………………………………………………… 540
8.6 AC Current Measurements……………………………………………………………………………….. 547
8.6.1 Electromechanical (Analog) AC Ammeters……………………………………………. 547
8.6.2 Electronic and Magneto-Optical AC Ammeters…………………………………….. 549
8.7 Magnetic Field Measurements ………………………………………………………………………….. 550
8.8 Phase Measurements…………………………………………………………………………………………. 559
8.8.1 Analog Phase Measurements…………………………………………………………………. 561
8.8.2 Digital Phase Detectors ………………………………………………………………………….. 564
8.9 Frequency and Period (Time) Measurements …………………………………………………… 566
8.10 Resistance, Capacitance and Inductance Measurement ……………………………………. 571
8.10.1 Resistance Measurements ………………………………………………………………………. 571
8.10.2 Capacitance Measurements ……………………………………………………………………. 576
8.10.2.1 The Use of Q-Meter for Capacitance Measurement ……………….. 576
8.10.2.2 Capacitance Measurement by Q/V ………………………………………… 580
8.10.3 Inductance Measurements ……………………………………………………………………… 584
8.10.3.1 Voltmeter Method of Estimating Inductance ………………………….. 585
8.10.3.2 The Use of Q-Meter for Inductance and
Q Measurement ………………………………………………………………………. 586
8.11 Vector Impedance Meters………………………………………………………………………………….. 586
8.12 Chapter Summary …………………………………………………………………………………………….. 588
Problems……………………………………………………………………………………………………………………. 589
Chapter 9 Digital Interfaces in Measurement Systems
9.1 Introduction ………………………………………………………………………………………………………. 597
9.2 The Sampling Theorem …………………………………………………………………………………….. 597
9.3 Quantization Noise …………………………………………………………………………………………… 601
9.4 Dithering …………………………………………………………………………………………………………… 603
9.5 Digital-to-Analog Converters ……………………………………………………………………………. 606
9.6 The Hold Operation………………………………………………………………………………………….. 611
9.7 Analog-to-Digital Converters ……………………………………………………………………………. 612
9.7.1 Successive-Approximation (SA) ADCs ………………………………………………….. 612
9.7.2 Tracking or Servo ADCs ………………………………………………………………………… 614
9.7.3 Dual-Slope Integrating ADCs ………………………………………………………………… 616
9.7.4 Flash (Parallel) ADCs …………………………………………………………………………….. 617
9.7.5 Dynamic Range, Floating Point ADCs…………………………………………………… 620
9.7.6 Delta-Sigma ADCs …………………………………………………………………………………. 621
9.7.7 Data Acquisition Cards for PCs …………………………………………………………….. 625
9.8 The IEEE-488 Instrumentation Bus (GPIB) ……………………………………………………….. 626
9.8.1 The GPIB Bus Structure …………………………………………………………………………. 627
9.8.2 GPIB Operation………………………………………………………………………………………. 628
9.9 Serial Data Communications Links…………………………………………………………………… 630
9.9.1 The RS-232C and D Interfaces ……………………………………………………………….. 630
9.9.2 The RS-422, RS-423 and RS-485 Interfaces……………………………………………… 633
9.9.3 The Universal Serial Bus (USB) ……………………………………………………………… 634
9.9.3.1 Overview of USB Functioning ………………………………………………….. 635
9.9.3.2 Summary…………………………………………………………………………………… 637
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9.10 The CAMAC (IEEE-583) Modular Instrumentation Standard,
and the VXI Modular Instrumentation Architecture ………………………………………… 637
9.11 Effect of Transmission Lines on the Transfer of Digital Data …………………………… 640
9.11.1 The Transmission Line Model………………………………………………………………. 640
9.11.2 Reflections on an Improperly Terminated, Lossless
Transmission Line…………………………………………………………………………………. 642
9.12 Data Transmission on Fiber Optic Cables…………………………………………………………. 646
9.12.1 Fiber Optic Cable Basics ………………………………………………………………………. 647
9.12.2 Semiconductor Sources and Detectors Used in FOC
Data Transmission………………………………………………………………………………… 653
9.12.3 FOC Systems ………………………………………………………………………………………… 656
9.13 Virtual Instruments …………………………………………………………………………………………… 657
9.13.1 Introduction………………………………………………………………………………………….. 657
9.13.2 PXI Systems………………………………………………………………………………………….. 658
9.13.3 Summary………………………………………………………………………………………………. 659
9.14 Chapter Summary …………………………………………………………………………………………….. 659
Problems……………………………………………………………………………………………………………………. 660
Chapter 10 Introduction to Digital Signal Conditioning
10.1 Introduction ………………………………………………………………………………………………………. 667
10.2 Digital Filters and the z-transform……………………………………………………………………. 667
10.3 Some Simple DSP Algorithms…………………………………………………………………………… 672
10.4 Discrete and Fast Fourier Transforms and their Applications………………………….. 680
10.4.1 Use of Data Windows to Improve Spectral Resolution ……………………….. 682
10.4.2 Use of the DFT to Characterize Random Signals and
Noise…………………………………………………………………………………………………….. 685
10.4.3 The Fast Fourier Transform………………………………………………………………….. 687
10.4.4 DSP Coprocessor Boards………………………………………………………………………. 688
10.5 Digital Routines for Interpolating Discrete Data………………………………………………. 689
10.5.1 Estimating Missing Data at the Sampling Instants………………………………. 692
10.6 Chapter Summary …………………………………………………………………………………………….. 693
Problems……………………………………………………………………………………………………………………. 694
Chapter 11 Examples of the Design of Measurement Systems
11.1 Introduction ………………………………………………………………………………………………………. 697
11.2 A Self-nulling, Microdegree Polarimeter to Measure Glucose
in Bioreactors…………………………………………………………………………………………………….. 697
11.3 Design of a System to Detect, Measure and Locate Partial
Discharges in High Voltage Coaxial Power Cables…………………………………………… 707
11.4 Design of a Closed Loop, Constant Phase, Pulsed Laser
Ranging System and Velocimeter ……………………………………………………………………… 713
11.5 Design of Capacitive Sensors for the Detection of
Hidden Objects………………………………………………………………………………………………….. 719
11.5.1 Introduction ………………………………………………………………………………………….. 719
11.5.2 Self-balancing Circuits Used to Measure C=Co …………………………………. 721
11.5.3 Summary………………………………………………………………………………………………. 724
11.6 Chapter Summary …………………………………………………………………………………………….. 725
References and Bibliography…………………………………………………………………………………… 727
Index …………………………………………………………………………………………………………………………. 737