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1、The Tao of Measurement: A Philosophical View of Flow and SensorsThe Tao of Measurement: A Philosophical View of Flow and SensorsBy Jesse Yoder and Dick MorleyCopyright 2015 International Society of Automation67 T.W. Alexander DriveP.O. Box 12277Research Triangle Park, NC 27709All rights reserved.Pri

2、nted in the United States of America.10 9 8 7 6 5 4 3 2 1ISBN: 978-0-876640-91-3No part of this work may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, with-out the prior written permission of the

3、 publisher.NoticeThe information presented in this publication is for the general education of the reader. Be-cause neither the author nor the publisher has any control over the use of the information by the reader, both the author and the publisher disclaim any and all liability of any kind aris-in

4、g out of such use. The reader is expected to exercise sound professional judgment in using any of the information presented in a particular application. Additionally, neither the author nor the publisher have investigated or considered the affect of any patents on the ability of the reader to use an

5、y of the information in a particular application. The reader is responsi-ble for reviewing any possible patents that may effect any particular use of the information presented.Any references to commercial products in the work are cited as examples only. Neither the author nor the publisher endorses

6、any referenced commercial product. Any trademarks or tradenames referenced belong to the respective owner of the mark or name. Neither the au-thor nor the publisher makes any representation regarding the availability of any referenced commercial product at any time. The manufacturers instructions on

7、 use of any commercial product must be followed at all times, even if in conflict with the information in this publi-cation.Library of Congress Cataloging-in-Publication in processThis book is dedicated with thanks to my mother and her prayers, and to the loving memory of my father.Jesse YoderTo Jes

8、se, and to the silk purse staff, Susan Colwell and Deb Morrison.Tuff going and they managed us well. Dick MorleyviiAcknowledgmentsI developed the ideas for this book over a period of 35 years. Some of my knowledge of mathematics and set theory go back to tutorials on set theory at The Rockefeller Un

9、iversity with Leslie Tharp. I discussed my ideas for Circular Geometry at length on the Geometry Forum with John Conway and others. Some of this discussion is reproduced at .I am grateful to my professors at The Rockefeller University for their patient critiques of my papers written for weekly tutor

10、ials in philosophy of mind and other areas. Chief among these were Donald Davidson and Joel Feinberg. Norton Batkin was a good friend and colleague during this time. At the University of Massachusetts at Amherst, Gareth Matthews shepherded me through the dissertation process with great skill, and wa

11、s also a friend to me. Belinda Burum served as my editor for the book, and is responsible for any catchy phrases that may appear in the book. She has been a wonderful friend to me for 25 years, served as a partner in building Flow Research, and has been a source of inspiration throughout this time.

12、My assistant, Nicole Riordan, has brought both humor and organization to my work life, and has been a joy to work with. For more than 10 years, I have worked with Matt Migliore of Flow Control, who has helped in topic selection and then in publishing many of my articles.Dick Morley helped me develop

13、 my ideas through multiple discussions in order to make this book possible. I would like to thank him for his incisive contributions to the book in the form of “Morleys Points.” I am grateful to Susan Colwell of ISA for guiding us both through the process of completing the book.Half of this book is

14、about temperature, pressure, and flow. Many of the ideas expressed here were developed in the course of 24 years of market research, most of it at Flow Research. Flow Research would not be possible without the support of viii our many clients over many years. I cannot thank them enough for their sup

15、port. I would single out four as especially important and helpful to me: Mark Heindselman of Emerson Process Management, Mike Touzin of Endress+Hauser, Matt Olin of Sierra Instruments, and Randy Brown of Fluid Components Intl. They have been both colleagues and friends.More than anyone else, I am gr

16、ateful to Vicki Tuck for 23 years of love, joy, and humor. More than anyone else, she has been my muse and my reason for being. Philosophy and flow remain my greatest loves, apart from Vicki.Jesse YoderixTable of ContentsChapter One: Beginning Point . 1Scope 2Chapter Two: Temperature .3Chapter Three

17、: Pressure .4Chapter Four: Flow .6New-Technology Flowmeters 6Traditional Technology Flowmeters .6Chapter Five: Time .7The Invention of Mechanical Clocks 9Clock Time and Biological Rhythms 9Decimal Time and Flow Time 10Chapter Six: Length . 11Arriving at a Unit of Measurement . 11Oh Line, Where Is Th

18、y Point? 12Wide Line Geometry .13Defining Continuity 14Measuring Locations when Measuring Distance 14American vs. Metric Standards 15Chapter Seven: Area . 15Chapter Eight: Sensors and Measurement .16Morleys Point: Why Write the Book? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

19、10Chapter Two: The Hot and Cold of Industrial Temperature Measurement 23The Historical Question: How to Measure Temperature .24A Matter of Scale 25Sensing the Change: Methods of Industrial Temperature Measurement 29The Nitty Gritty: Technology of Industrial Temperature Sensors . 31Thermocouple Techn

20、ology .32x RTD Technology 36Thermistor Technology .36Infrared Technology 37Fiber Optic Temperature Sensor Technology .39Its Hard to Play Favorites: The Relative Advantages of Different Temperature Sensors .40Morleys Point: Temperature 43Chapter Three: Measurement Under Pressure 47What Is Pressure? 4

21、7Pressure Transmitters Feel the Pressure .48Four Types of Pressure Transmitters 49From Roman Nozzles to Stolzs Universal Orifice Equation: How Pressure Measurement Evolved 49Piezoresistive Sensors Lead the Pressure Sensing Technologies . 51 Piezoresistive Sensors . 51Strain Gages 52Capacitive Sensor

22、s. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52Other Types 53What Is a Differential Pressure Flowmeter? 53Energy Conservation The Theory of Differential Pressure Measurement 54Primary Elements Not Glamorous, but Essential 56Orifice Measuring Points 56Pitot Tubes .58Ve

23、nturi Tubes .59Flow Nozzles 59Wedge Elements .60Other Primary Elements . 61Advantages and Disadvantages of Various Primary Elements 61xiThe Future of Pressure Measurement .62Units of Pressure .64PSIA and PSIG 64Morleys Point: Pressure 65Chapter Four: Flow Measurement How Do You Measure Continuously

24、Moving Flow . 69Flow Measurement Is Vital to Water Chapter 3 - Pressure; Chapter 4 - Flow; Chapter 5 - Time; Chapter 6 - Length; Chapter 7 Area; and Chapter 8 - Theory of Measurement. Dick Morley shares his perspective at the end of every chapter, including this one. The book concludes with Chapter

25、9, written by Dick.Chapter OneBeginning PointBecause the world is round, it turns me on. from “Because” by the Beatles2 The Tao of MeasurementThis chapter is written more like an executive summary than an introduction. As you read through this chapter, you will gain an insight into the main points m

26、ade in the book. You can then go to the chapter or chapters that interest you most. For example, if your area of interest is fluid flow, you may want to start with Chapter Four. If you are fascinated by time, go to Chapter Five. Each chapter is designed as a stand-alone treatment of the topic of tha

27、t chapter. The only exception is Chapter Eight, which attempts to bring the areas of sensing and measuring together into a broader theory. Of course, we want you to read the entire book, but thats up to you.ScopeThis book covers both sensing and measuring. These are broad topics, but we have selecte

28、d six subjects within those topics that are of special interest. First, we focus on sensing and then measuring these three parameters: Temperature Pressure FlowThe discussion of sensing temperature, pressure and flow centers mainly on the different types of sensors that are used to sense these param

29、eters. We then talk about how they are measured. There are a number of different technologies involved in sensing and measuring temperature, pressure and flow, and they are discussed in Chapters 2, 3 and 4.In measuring, we have chosen three parameters that are especially interesting and important: T

30、ime Length AreaChapters 5, 6 and 7 center on the units used to measure these parameters. The structure of each of these chapters is similar. The first part of each chapter explores the historical origins of many of the units that we still commonly use to measure time, length and area. The origins of

31、 the terms and practices in use today go back over two Beginning Point 3thousand years, to the Greeks and Romans in some cases. The second part of each of these three chapters describes the generally accepted methods for measuring the parameter in question. The last part of each chapter proposes a n

32、ew perspective that hopefully avoids some of the pitfalls in the way measurement is done today. These new ideas include flowtime, Wide Line Geometry and Circular Geometry. The last section of each chapter includes a list of the units of measurement that are associated with the subject of the chapter

33、. Chapter Two: TemperatureChapter Two begins by tracing the origins of the thermometer. Galileo is credited with inventing the first thermometer in the 1590s. It was an air thermometer made of a glass bulb with a long tube attached. While Galileo called it a thermoscope, it worked enough like a ther

34、mometer to earn him the title of the inventor of the thermometer.There are three main temperature scales that are commonly used today: Fahrenheit Celsius KelvinThis chapter compares the origins of these scales and shows how they compare to each other. Another important scale is the Rankine scale, wh

35、ich is mainly used for specialized engineering applications.Most of the rest of Chapter Two is devoted to a discussion of the following five types of temperature sensors: Thermocouples Resistance Temperature Detectors (RTDs) Thermistors Infrared Thermometers Fiber Optic SensorsThe first three types

36、on this list are contact temperature sensors, while infrared and fiber optic are non-contact types. Infrared thermometers sense the temperature and also display it, so they are also measuring devices.4 The Tao of MeasurementThere are a number of different types of thermocouples that are distinguishe

37、d ac-cording to the type of metals making them up. Each one is designated with an alpha-betical letter, and they are designed for different temperature ranges. The two main types of RTDs are wirewound and thin film. Thermistors are less robust than RTDs and have a more narrow temperature sensing ran

38、ge, but are more sensitive than RTDs within that range. They are widely used for food applications. Infrared thermometers are used to measure temperature at a distance. Many of them are used in a “point and shoot” method of measuring, where the temperature is read off the material that the infrared

39、beam is aimed at. Fiber optic sensors use optical fibers in making temperature measurements.This chapter concludes with a discussion of the relative advantages and disadvan-tages of the different types of temperature sensors. For example, thermocouples can be used at higher temperatures than RTDs an

40、d respond more quickly, but RTDs are more stable than thermocouples and are more accurate than thermocouples within their more limited temperature range.Chapter Three: PressureThis chapter begins by looking at different definitions of pressure. Most of the chapter is then devoted to pressure transmi

41、tters, especially differential pressure transmitters, which play an important role in flowrate measurement. Transmitters accept input from a sensor, amplify it, and convert its value into a signal that can be transmitted to a recording or controlling device. Differential pressure (DP) transmitters a

42、re one of four types of pressure transmit-ters. These four types are as follows: Multivariable Differential pressure Gage AbsoluteThe early part of the chapter traces the history of differential pressure measure-ment. Bernoulli developed his famous equation for flowrate calculation in 1738. Differen

43、tial pressure transmitters rely on a constriction in the flowstream to create a Beginning Point 5difference between upstream and downstream pressure. Differential pressure transmit-ters then use this difference in pressure as a variable in Bernoullis equation to calcu-late the rate of fluid flow thr

44、ough a pipe.The constriction is created by what is called a primary element. The most widely used type of primary element is the orifice plate. The first commercial orifice plate was introduced in 1909. Since that time a great deal of work has been done by the American Gas Association (AGA) and the

45、American Society of Mechanical Engineers (ASME) in studying DP flowmeters and how they perform under various conditions. Both the AGA and ASME have issued standards for the use of DP flowmeters as a result of their research.Chapter Three also describes the following three pressure sensor technologie

46、s: Piezoresistive Strain gage CapacitiveThese three technologies are used by differential pressure sensors to detect up-stream and downstream pressure in differential pressure transmitters.Differential pressure sensors are an essential component of DP flow measurement, but primary elements are equal

47、ly important, since they create the difference in pres-sure in the flowstream that makes DP flow measurement possible. The main kinds of primary elements are: Orifice plates Venturi tubes Pitot tubes Flow nozzles Wedge elementsOrifice plates consist of a round, usually metal plate with an opening (o

48、rifice) in it to enable fluid to pass through. They are used to measure the flowrate of liquid, steam and gas flowstreams. Venturi tubes are especially useful for fluids with suspended solids because of their wide openings. Flow nozzles are especially suited to measuring high-speed flows, and can ha

49、ndle fluids containing particles. Pitot tubes are widely used for 6 The Tao of Measurementmeasuring air flow. Averaging Pitot tubes contain more than one measuring port and provide higher accuracy than single port Pitot tubes. They are also used to measure fluid flow in large pipes. Wedge elements are manufactured by only a few companies. They are designed to handle fluids with a high solids content.Chapter Four: FlowChapter Four is devoted to discussing the different types of flowmeters used to measure flowrate, w