Measurement and Instrumentation, Second Edition: Theory and Application

694 Pages·2015·29.46 MB·English

by  Alan S Morris

Measurement and Instrumentation
Theory and Application
Second Edition
Alan S. Morris
Reza Langari
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Preface
The foundations of this book lie in the highly successful text, Principles of Measurement and Instru-
mentation by Alan Morris. The first edition of this was published in 1988, and a second, revised and
extended edition appeared in 1993. This was followed, in 2001, by a text with further revisions to the
contentandanewtitle,MeasurementandInstrumentationPrinciples.
The first edition of this current text then followed in 2011. In developing this, the opportunity was
taken to strengthen the book by bringing in a second author, Professor Reza Langari of Texas A&M
University, who has made significant contributions especially in the areas of data acquisition and
signal processing and the implementation of these using industry-standard LabView software. As well
as this new contribution by Professor Langari, this edition covered many new developments in the
field of measurement. In particular, it covered the significant recent advances that have been in smart
sensors, intelligent instruments, microsensors, data acquisition, digital signal processing, digital re-
corders, digital fieldbuses, and new methods of signal transmission. The rapid growth of digital com-
ponents within measurement systems also created a need to establish procedures in the book for
measuring and improving the reliability of the software that is used within such components. Formal
standards governing instrument calibration procedures and measurement system performance were
extended beyond the traditional area of quality assurance systems (ISO9000) into new areas such as
environmental protection systems (ISO14000). Thus, when published in 2011, the book was reason-
ablyuptodatewithalltherecentdevelopmentsinmeasurementsystemsuptothattime.
One notable developmentinthislatesteditionisthat there isa largeincreaseinthe amountofma-
terialonmeasurementuncertainty.Thisincludesanextendeddiscussiononinducedmeasurementnoise
andthevarioussourcesofthis,suchasinductivecoupling,capacitive(electrostatic)coupling,noisedue
to multiple earths, noise in the form of voltage transients, thermoelectric potentials, shot noise, and
electrochemicalpotentials.Thereisalsoasignificantincreaseinthenumberofworkedexamples.Asa
consequence,thisexpansionhasnecessitatedsplittingtheprevioussinglechapteronthistopicintotwo
chapters.
The past four years have also seen continual developments of new sensors, and especially micro-
scale (MEMS)andnanoscale(NEMS) ones. These developments are covered inthechapter on sensor
technologies and also in later chapters devoted to sensors for measuring particular physical variables.
Atthesametime,thecontinuedusageofdevicesbuiltonoldertechnologieshasbeenreviewed,result-
ing in the exclusion of those that are now very uncommon. The number of end-of-chapter student
problems has also been expanded significantly, as the process of solving such problems is felt to be a
valuableaidinthelearningprocessforstudents.
The overall aim of the book continues to be to present the topics of sensors and instrumentation,
and their use within measurement systems, as an integrated and coherent subject. Measurement sys-
tems, and the instruments and sensors used within them, are ofimmense importance in a widevariety
of domestic and industrial activities. The growth in the sophistication of instruments used in industry
xvii
Preface
has been particularly significant as advanced automation schemes have been developed. Similar de-
velopmentshavealsobeenevidentinmilitaryandmedicalapplications.
Unfortunately, the crucial part that measurement plays in all of these systems tends to get over-
looked,andmeasurement is therefore rarely given theimportance that it deserves. For example, much
effort goes into designing sophisticated automatic control systems, but little regard is given to the ac-
curacy andqualityoftheraw measurementdata thosesuchsystems useastheirinputs. This disregard
of measurement system quality and performance means that such control systems will never achieve
their full potential, as it is very difficult to increase their performance beyond the quality of the raw
measurementdataonwhichtheydepend.
Ideally, the principles of good measurement and instrumentation practice should be taught
throughoutthedurationofengineeringcourses,startingatanelementarylevelandmovingontomore
advanced topics as the course progresses. With this in mind, the material contained in this book is
designedbothtosupportintroductorycoursesinmeasurementandinstrumentation,andalsotoprovide
in-depth coverageofadvancedtopicsforhigher-level courses.Inaddition, besidesitsroleasa student
course text, it is also anticipated that the book will be useful to practising engineers, both to update
their knowledge ofthe latest developments inmeasurement theoryandpractice,andalsotoserve as a
guide to the typical characteristics and capabilities of the range of sensors and instruments that are
currentlyinuse.
Following the usual pattern with measurement textbooks, the early chapters deal with the princi-
plesandtheoryofmeasurementandthensubsequentchapterscovertherangesofinstrumentsandsen-
sors that are available for measuring various physical quantities. This order of coverage has been
chosen so that the general characteristics of measuring instruments, and their behavior in different
operatingenvironments,arewellestablishedbeforethereaderisintroducedtotheproceduresinvolved
in choosing a measurement device for a particular application. This ensures that the reader will be
properly equipped to appreciate and critically appraise the various merits and characteristics of
differentinstrumentswhenfacedwiththetaskofchoosingasuitableinstrumentinanygivensituation.
It should be noted that, while measurement theory inevitably involves some mathematics, the
mathematical content of the book has deliberately been kept to the minimum necessary for the reader
to be able to design and build measurement systems that perform to a level commensurate with the
needs of the automatic control scheme or other system that they support. Where mathematical pro-
cedures are necessary, worked examples are provided throughout the book to illustrate the principles
involved.Self-assessmentquestionsarealsoprovidedincriticalchapterstoenablereaders totest their
levelofunderstanding.
Theearlychaptersareorganizedsuch that alloftheelements ina typicalmeasurementsystem are
presented in a logical order, starting with the capture of a measurement signal by a sensor and then
proceedingthroughthestagesofsignalprocessing,sensoroutputtransducing,signaltransmission,and
signal display or recording. Ancillary issues, such as calibration and measurement system reliability,
are also covered. Discussion starts with a review of the different classes of instruments and sensors
available, and the sort of applications in which these different types are typically used. This opening
discussionincludesanalysisofthestaticanddynamiccharacteristicsofinstrumentsandexplorationof
how these affect instrument usage. A comprehensive discussion of measurement system errors then
follows, with appropriate procedures for quantifying, analyzing, and reducing errors being presented
across two chapters. The importance of calibration procedures in all aspects of measurement systems,
andparticularlytosatisfytherequirementsofstandardssuchasISO9000andISO14000,isrecognized
bydevotingafullchaptertotheissuesinvolved.Thisisfollowedbyachapterexplainingdataacquisi-
tion techniques and discussing the various analog- and digital signal-processing procedures that are
xviii
Preface
used to attenuate noise and improve the quality of signals. Following this, the next chapter is devoted
to presenting the range of variable conversion elements (transducers) and techniques that are used to
convert non-electrical sensor outputs into electrical signals, with particular emphasis on electrical
bridge circuits. The problems of signal transmission are considered in the next chapter, and various
means of improving the quality of transmitted signals are presented. The following chapter then dis-
cusses the various indicating and test instruments that are used to display and record electrical mea-
surement signals. This chapter also covers data presentation methods and related issues such as least-
squares curve fitting, confidence tests, and correlation tests. The next consideration is the subject of
intelligent devices and the related issues of digital computation techniques, inputeoutput interfaces,
databuses,datanetworks,andfieldbustechnologies.Thefollowingchapterthendiscussestheissueof
measurement system reliability, andthe effect of unreliability on plant safetysystems. This discussion
also includes the subject of software reliability, since computational elements are now embedded in
manymeasurementsystems.Thenextchapterprovidesacomprehensiveintroductiontothefeaturesof
theLabviewsoftwarepackage.Variousexamplesareprovidedinthischapterthatexplainstheapplica-
tion of LabView to implement the data acquisition and digital signal processing techniques covered
earlier in Chapter 6. Finally, thisinitial set of chapters covering measurementtheory concludeswith a
chapter on the various sensor technologies that are in use. This coverage includes discussion on
recently developed technologies and, particularly, the advances in micro-machines structures (MEMS
andNEMS)devices.
Subsequent chapters then provide comprehensive coverage of the main types of sensors and in-
strumentsthatexistformeasuringallthephysicalquantitiesthatapracticingengineerislikelytomeet
in normal situations. However, while the coverage is as comprehensive as possible, the distinction is
emphasized between(1) instruments that are current andin common use, (2) instruments that are cur-
rent but not widely used except in special applications, for reasons of cost or limited capabilities, and
(3) instruments that are largely obsolete as regards new industrial implementations, but are still
encountered on older plant that was installed someyears ago. As well as emphasizingthis distinction,
some guidance is given about how to go about choosing an instrument for a particular measurement
applicationandhowtoimplementappropriatecalibrationtechniques.Itshouldbenotedthatthereader
familiar with first edition will notice the exclusion of some devices previously included, as a result of
theirusebeinglargelynowdiscontinued.
Resources for instructors: A solution manual is available by registering at http://textbooks.
elsevier.com/9780128008843.
xix
Acknowledgement
The Author gratefully acknowledges permission by John Wiley and Sons, Ltd, to reproduce
some material that was previously published in Measurement and Calibration Requirements
for Quality Assurance to ISO9000 by A S Morris (published 1997). The material involved is
Tables 1.1, 1.2 and 3.1, figures 3.1, 5.2 and 5.3, parts of sections 2.1, 2.2, 2.3, 3.1, 3.2, 4.2,
4.3, 4.4, 4.5, 4.6, 4.7, 5.3 and 5.4, and Appendix 1.
xxi
CHAPTER 1
Fundamentals of Measurement Systems
Chapter Outline
1.1 Introduction 1
1.2 Measurement Units 2
1.3 Measurement System Design 4
1.3.1 Elements ofa Measurement System 4
1.3.2 Choosing Appropriate Measuring Instruments 7
1.4 Measurement System Applications 9
1.5 Summary 10
1.6 Problems 11
1.1 Introduction
Measurement techniques have been of immense importance ever since the start of
human civilization, when measurements were first needed to regulate the transfer of
goods in barter trade in order to ensure that exchanges were fair. The industrial
revolution during the nineteenth century brought about a rapid development of new
instruments and measurement techniques to satisfy the needs of industrialized production
techniques. Since that time, there has been a large and rapid growth in new industrial
technology. This has been particularly evident during the last part of the twentieth
century, because of the many developments in electronics in general and computers in
particular. In turn, this has required a parallel growth in new instruments and
measurement techniques.
The massive growth in the application of computers to industrial process control and
monitoring tasks has greatly expanded the requirement for instruments to measure,
record, and control process variables. As modern production techniques dictate working
to ever tighter accuracy limits, and as economic forces to reduce production costs
become more severe, so the requirement for instruments to be both accurate and cheap
becomes ever harder to satisfy. This latter problem is at the focal point of the research
and development efforts of all instrument manufacturers. In the past few years, the most
cost-effective means of improving instrument accuracy has been found in many cases to
be the inclusion of digital computing power within instruments themselves. These
intelligent instruments therefore feature prominently in current instrument
manufacturers’ catalogs.
MeasurementandInstrumentation.http://dx.doi.org/10.1016/B978-0-12-800884-3.00001-0
Copyright©2016ElsevierInc.Allrightsreserved. 1
2 Chapter 1
This opening chapter will cover some fundamental aspects of measurement. First, we will
look at how standard measurement units have evolved from the early units used in barter
trade to the more exact units belonging to the Imperial and metric measurement systems.
We will then do on to study the major considerations in designing a measurement system.
Finally, we will look at some of the main applications of measurement systems.
1.2 Measurement Units
The very first measurement units were those used in barter trade to quantify the amounts
being exchanged and to establish clear rules about the relativevalues of different
commodities. Such early systems of measurement were based on whatever was available
as a measuring unit. For purposes of measuring length, the human torso was a convenient
tool, and gave us units of the hand, the foot and the cubit. Although generally adequate for
barter trade systems, such measurement units are of course imprecise, varying as they do
from one person to the next. Therefore, there has been a progressive movement toward
measurement units that are defined much more accurately.
The first improved measurement unit was a unit of length (the meter) defined as 10(cid:1)7
times the polar quadrant of the earth. A platinum bar made to this length was established
as a standard of length in the early part of the nineteenth century. This was superseded by
a superior quality standard bar in 1889, manufactured from a platinumeiridium alloy.
Since that time, technological research has enabled further improvements to be made in
the standard used for defining length. First, in 1960, a standard meter was redefined in
terms of 1.65076373(cid:3)106 wavelengths of the radiation from krypton-86 invacuum. More
recently, in 1983, the meter was redefined yet again as the length of path traveled by light
in an interval of 1/299,792,458s. In a similar fashion, standard units for the measurement
of other physical quantities have been defined and progressively improved over the years.
The latest standards for defining the units used for measuring a range of physical variables
are given in Table 1.1.
The early establishment of standards for the measurement of physical quantities proceeded
in several countries at broadly parallel times, and in consequence, several sets of units
emerged for measuring the same physical variable. For instance, length can be measured
in yards, meters, or several other units. Apart from the major units of length, subdivisions
of standard units exist such as feet, inches, centimeters, and millimeters, with a fixed
relationship between each fundamental unit and its subdivisions.
Yards, feet, and inches belong to the Imperial System of units, which is characterized by
having varying and cumbersome multiplication factors relating fundamental units to
subdivisions such as 1760 (miles to yards), 3 (yards to feet), and 12 (feet to inches). The
metric system is an alternative set of units, which includes, for instance, the unit of the
Fundamentals of Measurement Systems 3
Table 1.1: Definitionsof standard units
PhysicalQuantity StandardUnit Definition
Length Meter Thelengthofpathtraveledbylightinanintervalof
1/299,792,458s
Mass Kilogram Themassofaplatinumeiridiumcylinderkeptinthe
InternationalBureauofWeightsandMeasures,
Sevres,Paris
Time Second 9.192631770(cid:3)109cyclesofradiationfrom
vaporizedcaesium133(anaccuracyof1in1012or
1sin36,000years)
Temperature Degrees Thetemperaturedifferencebetweenabsolutezero
Kelvinandthetriplepointofwaterisdefinedas
273.16K.
Current Ampere Oneampereisthecurrentflowingthroughtwo
infinitelylongparallelconductorsofnegligiblecross
sectionplaced1mapartinvacuumandproducinga
forceof2(cid:3)10(cid:1)7Npermeterlengthofconductor
Luminousintensity Candela Onecandelaistheluminousintensityinagiven
directionfromasourceemittingmonochromatic
radiationatafrequencyof540THz(Hz(cid:3)1012)and
witharadiantdensityinthatdirectionof
1.4641mW/steradian(1steradianisthesolidangle
which,havingitsvertexatthecenterofasphere,cuts
offanareaofthespheresurfaceequaltothatofa
squarewithsidesoflengthequaltothesphere
radius)
Matter Mole Thenumberofatomsina0.012kgmassofcarbon
12
meter and its centimeter and millimeter subdivisions for measuring length. All multiples
and subdivisions of basic metric units are related to the base by factors of 10 and such
units are therefore much easier to use than Imperial units. However, in the case of derived
units such as velocity, the number of alternativeways in which these can be expressed in
the metric system can lead to confusion.
As a result of this, an internationally agreed set of standard units (SI units or Syste`mes
Internationales d’Unite´s) has been defined, and strong efforts are being made to encourage
the adoption of this system throughout the world. In support of this effort, the SI system of
units will be used exclusively in this book. However, it should be noted that the Imperial
system is still widely used in the engineering industry, particularly in the United States of
America.
The full range of fundamental SI measuring units and the further set of units derived from
them are given in Tables 1.2 and 1.3. Conversion tables relating common Imperial and
metric units to their equivalent SI units can also be found in Appendix 1.
4 Chapter 1
Table 1.2: Fundamental SIunits
Quantity StandardUnit Symbol
(a)FundamentalUnits
Length Meter m
Mass Kilogram kg
Time Second s
Electriccurrent Ampere A
Temperature Kelvin K
Luminousintensity Candela cd
Matter Mole mol
(b)SupplementaryFundamentalUnits
Planeangle Radian rad
Solidangle Steradian sr
1.3 Measurement System Design
In this section, we will look at the main considerations in designing a measurement
system. First, we will learn that a measurement system usually consists of several separate
components, although only one component might be involved for some very simple
measurement tasks. We will then go on to look at how measuring instruments and systems
are chosen to satisfy the requirements of particular measurement situations.
1.3.1 Elements of a Measurement System
A measuring system exists to provide information about the physical value of some
variable being measured. In simple cases, the system can consist of only a single unit that
gives an output reading or signal according to the magnitude of the unknownvariable
applied to it. However, in more complex measurement situations, a measuring system
consists of several separate elements as shown in Figure 1.1. These components might be
contained within one or more boxes, and the boxes holding individual measurement
elements might be either close together or physically separate. The term measuring
instrument is commonly used to describe a measurement system, whether it contains only
one or many elements, and this term will be widely used throughout this text.
The first element in any measuring system is the primary sensor: this gives an output
that is a function of the measurand (the input applied to it). For most but not all
sensors, this function is at least approximately linear. Some examples of primary sensors
are a liquid-in-glass thermometer, a thermocouple, and a strain gauge. In the case of the
mercury-in-glass thermometer, the output reading is given in terms of the level of the
mercury, and so this particular primary sensor is also a complete measurement system in