Technology & Engineering
Thermometry
Thermometry is the science of measuring temperature. It involves the use of various instruments and techniques to quantify thermal energy. Thermometers, thermocouples, and infrared sensors are commonly used in thermometry to accurately determine temperature in a wide range of applications, from industrial processes to medical diagnostics.
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12 Key excerpts on "Thermometry"
- Myer Kutz(Author)
- 2015(Publication Date)
- Wiley(Publisher)
CHAPTER 14
TEMPERATURE MEASUREMENT
PETER R. N. CHILDSSummary 14.1 Introduction 14.1.1 The measurement process 14.1.2 Calibration 14.2 Selection 14.3 Invasive temperature measurement 14.3.1 Liquid-in-glass thermometers 14.3.2 Manometric Thermometry 14.3.3 Bimetallic thermometers 14.3.4 Thermocouples 14.3.5 Resi stance temperature devices 14.3.6 Semiconductor devices 14.3.7 Diode thermometers 14.3.8 Noise Thermometry 14.3.9 Pyrometric cones 14.4 Semi-invasive methods 14.4.1 Peak temperature-indicating devices 14.4.2 Temperature-sensitive paints 14.4.3 Thermographic phosphors 14.4.4 Thermochromic liquid crystals 14.5 Noninvasive methods 14.5.1 Infrared Thermometry 14.5.2 Thermal imaging 14.6 Conclusions Nomenclature ReferencesSUMMARY
The requirement to measure temperature arises in process control, production, environmental observation, and laboratory research. The range of techniques available for measuring temperature is extensive. Many phenomena are dependent on temperature and this can be exploited in instrumentation. A given application may permit direct contact between a measuring device or system and the medium of interest. Alternatively, remote observation of, for example, infrared radiation or fluorescence may be possible using an optical system. This chapter outlines various forms of invasive, semi-invasive, and noninvasive temperature measurement devices and systems. In addition, this chapter describes the fundamental definitions of temperature and the issues that need to be considered in determining the temperature of a given medium, be it a solid body, surface, liquid, or gas.14.1 INTRODUCTION
Temperature can be defined qualitatively as a measure of hotness of a body. Temperature is the property that determines whether a system is in thermal equilibrium with other systems. If the temperature of two bodies in thermal contact with each other is same, then there will be no net transfer of thermal energy. Quantitatively, temperature can be defined from the second law of thermodynamics in terms of the rate of change of entropy with energy.
- Richard S. Figliola, Donald E. Beasley(Authors)
- 2019(Publication Date)
- Wiley(Publisher)
Suggested Reading 313 S U M M A R Y Temperature is a fundamentally important quantity in science and engineering, both in concept and practice. Thus, temperature is one of the most widely measured engineering variables, providing the basis for a variety of control and safety systems. This chapter provides the basis for the selection and installation of temperature sensors. Temperature is defined for practical purposes through the estab- lishment of a temperature scale, such as the Kelvin scale, that encompasses fixed reference points and interpolation standards. The International Temperature Scale 1990 is the accepted standard for temperature measurement. The two most common methods of temperature measurement use thermocouples and RTDs. Standards for the construction and use of these temperature measuring devices have been established and provide the basis for selection and installation of commercially available sensors and measuring systems. Installation effects on the accuracy of temperature measure- ments are a direct result of the influence of radiation, conduc- tion, and convection heat transfer on the equilibrium temperature of a temperature sensor. The installation of a temperature probe into a measuring environment can be accomplished in such a way as to minimize the uncertainty in the resulting temperature measurement. R E F E R E N C E S 1. Patterson, E. C., Eponyms: Why Celsius? American Scientist 77(4): 413, 1989. 2. Klein, H. A., The Science of Measurement: A Historical Survey, Dover, Mineola, NY, 1988. 3. Committee Report, the International Temperature Scale of 1990, 4 Metrologia 27(1): 3–10, 1990. (An Erratum appears in Metrologia 27(2): 107, 1990.) 4. Temperature Measurement, Supplement to American Society of Mechanical Engineers PTC 19.3, 1974. 5. Diehl, W., Thin-film PRTD, Measurements and Control, 155–159, December 1982.
- Ketil Motzfeldt(Author)
- 2012(Publication Date)
- Wiley(Publisher)
3 Temperature MeasurementsPreamble
This chapter deals with an important subject. To quote from the preface in the textbook of McGee (1988):During a scientific career as an engineering professor I have observed that the most common mistake a scientist makes is to accept a temperature reading without question. The scientific literature is full of papers about otherwise fine research that is based on temperature measurements of uncertain quality.In the years since McGee wrote this, his own book, and a number of other textbooks that have appeared, have hopefully led to an improved situation. Some of the books are mentioned specifically at the end of this chapter, otherwise they are included in the general list of references. The present text represents an attempt to cover part of the same material within a more limited frame and restricted to high temperature measurements.For practical reasons, Chapter 3 covers only methods using a solid sensor in contact with the hot object (in particular thermocouples) while radiation pyrometry is treated in Chapter 4.3.1 Fundamentals of Temperature Measurement
3.1.1 The Concept of Temperature
From early childhood we experience the difference between hot and cold, or in other words, differences in temperature. The concept is familiar, and yet it is not easy to define.What is Temperature?
A partial answer is given by Zemansky (1964): Temperature is a property of matter . Other partial definitions have been tried. For instance, if two bodies A and B are in thermal contact with no heat flux between them, the two are at the same temperature. This is sometimes referred to as the zeroth law of thermodynamics, but it is not very informative.We will attempt another approach, considering the concept of energy .Generally, energy is equivalent to work or anything that may be converted into work. We note that each form of energy may be written as the product of an intensive factor and an extensive
- Richard S. Figliola, Donald E. Beasley(Authors)
- 2015(Publication Date)
- Wiley(Publisher)
Chapter 8 Temperature Measurements 8.1 INTRODUCTION Temperature is one of the most commonly used and measured engineering variables. Much of our lives is affected by the diurnal and seasonal variations in ambient temperature, but the fundamental scientific definition of temperature and a scale for the measurement of temperature are not commonly understood. This chapter explores the establishment of a practical temperature scale and common methods of temperature measurement. In addition, errors associated with the design and installation of a temperature sensor are discussed. Upon completion of this chapter, the reader will be able to describe the primary standards for temperature, state the role of fixed point calibration and the necessity for an interpolation method in establishing a temperature standard, describe and analyze thermal expansion Thermometry, state the physical principle underlying electrical resistance Thermometry, employ standard relationships to determine temperature from resistance devices, analyze thermoelectric circuits designed to measure temperature, describe experiments to determine thermoelectric potential for material pairs, state the principles employed in radiation temperature measurements, and estimate the impact of loading errors in temperature measurement. Historical Background Guillaume Amontons (1663–1705), a French scientist, was one of the first to explore the thermodynamic nature of temperature. His efforts examined the behavior of a constant volume of air that was subject to temperature changes. The modern liquid-in-glass bulb thermometer traces its origin to Galileo (1565–1642), who attempted to use the volumetric expansion of liquids in tubes as a relative measure of temperature. Unfortunately, this open tube device was actually sensitive to both barometric pressure and temperature changes. A major advance in temperature measurement occurred in 1630 as a result of a seemingly unrelated event: the 309
- Richard S. Figliola, Donald E. Beasley(Authors)
- 2023(Publication Date)
- Wiley(Publisher)
C H A P T E R 8 Temperature Measurements 8.1 INTRODUCTION Temperature is one of the most commonly used and measured engineering variables. Although much of our lives is affected by the diurnal and seasonal variations in ambient temperature, the fundamental scientific definition of tempera- ture and a scale for the measurement of temperature are not commonly understood. This chapter explores the establish- ment of a practical temperature scale and common methods of temperature measurement. In addition, errors associated with the design and installation of temperature sensors are discussed. Upon completion of this chapter, the reader will be able to: • Describe the primary standards for temperature • State the role of fixed point calibration and the necessity for an interpolation method in establishing a temperature standard • State the physical principle underlying electrical resistance Thermometry • Employ standard relationships to determine temperature from resistance devices • Analyze thermoelectric circuits designed to measure temperature • State the principles employed in radiation temperature measurements • Estimate the impact of loading errors in temperature measurement Historical Background Guillaume Amontons (1663–1705), a French scientist, was one of the first to explore the thermodynamic nature of temperature. His efforts examined the behavior of a constant volume of air that was subject to temperature changes. The modern liquid-in-glass bulb thermometer traces its origin to Galileo (1565–1642), who attempted to use the vol- umetric expansion of liquids in tubes as a relative measure of temperature. Unfortunately, this open tube device was sensitive to both barometric pressure and temperature changes. A major advance in temperature measurement occurred in 1630 as a result of a seemingly unrelated event: the development of the technology to manufacture capillary glass tubes.
eBook - ePubMetrology and Instrumentation
Practical Applications for Engineering and Manufacturing
- Samir Mekid(Author)
- 2021(Publication Date)
- Wiley-ASME Press Series(Publisher)
In contrast to basic standards such as length and mass, temperature is measured by indirect comparison. To determine temperature, a standardized calibrated device is required. Various primary effects causing temperature changes can be used to measure temperature, such as variations in physical or chemical conditions, electrical properties, radiation ability, or physical dimensions. The temperature signal has a response affected by:- Level of thermal conductivity and heat capacity of the element and the fluid surrounding the element;
- Coefficient of heat transfer of the film;
- Surface area per unit mass;
- Mass velocity of the hosting fluid.
- Thermal expansion where the materials exhibit a change in size with change in temperatures;
- The changes of the electrical resistance of a conductor;
- Thermoelectric technique mostly known as thermocouples;
- Radiative temperature measurement.
- Thermocouples with all types;
- Pressure thermometers;
- Liquid‐in‐glass thermometers;
- Bimetallic strip thermometers;
- Resistance temperature detectors (RTDs);
- Thermistors.
For noncontact‐type sensors, we measure the radiant power of the infrared or optical radiation received by the object. Instruments such as radiation or optical pyrometers determine the temperature; the noncontact‐type sensors include:- Fiber‐optic thermometers;
- Radiation pyrometers;
- Optical pyrometers.
11.7 Temperature Measured through Thermal Expansion Materials
Liquid‐in‐glass thermometer.Figure 11.211.7.1 Liquid‐in‐Glass Thermometer
Temperature can be measured basically by the thermal expansion of a liquid. Example is the liquid‐in‐glass (LiG) thermometer. A LiG thermometer possesses a glass capillary tube inside a stem with a liquid‐filled bulb at one end.
eBook - ePubMeasurement and Instrumentation
Theory and Application
- Alan S. Morris, Reza Langari(Authors)
- 2011(Publication Date)
- Butterworth-Heinemann(Publisher)
14.6. Thermography (Thermal Imaging)
Thermography, or thermal imaging, involves scanning an infrared radiation detector across an object. The information gathered is then processed and an output in the form of the temperature distribution across the object is produced. Temperature measurement over the range from −20°C up to +1500°C is possible. Elements of the system are shown in Figure 14.14 .Figure 14.14 Thermography (thermal imaging) system. The radiation detector uses the same principles of operation as a radiation pyrometer in inferring the temperature of the point that the instrument is focused on from a measurement of the incoming infrared radiation. However, instead of providing a measurement of the temperature of a single point at the focal point of the instrument, the detector is scanned across a body or scene, and thus provides information about temperature distributions. Because of the scanning mode of operation of the instrument, radiation detectors with a very fast response are required, and only photoconductive or photovoltaic sensors are suitable. These are sensitive to the portion of the infrared spectrum between wavelengths of 2 and 14 μm.Simpler versions of thermal imaging instruments consist of hand-held viewers that are pointed at the object of interest. The output from an array of infrared detectors is directed onto a matrix of red light-emitting diodes assembled behind a glass screen, and the output display thus consists of different intensities of red on a black background, with the different intensities corresponding to different temperatures. Measurement resolution is high, with temperature differences as small as 0.1°C being detectable. Such instruments are used in a wide variety of applications, such as monitoring product flows through pipe work, detecting insulation faults, and detecting hot spots in furnace linings, electrical transformers, machines, bearings, etc. The number of applications is extended still further if the instrument is carried in a helicopter, where uses include scanning electrical transmission lines for faults, searching for lost or injured people, and detecting the source and spread pattern of forest fires.
eBook - ePub- G. M. S. de Silva(Author)
- 2012(Publication Date)
- Routledge(Publisher)
7
Measurement oftemperature
7.1 Introduction
Temperature is one of the most important measurement parameters from an industrial point of view. Large numbers of temperature measuring instruments such as mercury-in-glass thermometers, dial thermometers, thermocouple sensors, resistance temperature devices (RTDs) and temperature transmitters are used in most industrial systems. It is also an important parameter in health services, for monitoring of the environment and safety systems.7.2 SI units
The SI base unit for temperature is the kelvin, defined as the fraction 1/273.16 of the thermodynamic temperature of the triple point of water. The degree Celsius is also recognized in the SI system and is defined by the relation:(7.1) where t is a temperature in degrees Celsius and T is the equivalent kelvin temperature.7.3 Thermodynamic scale
Temperature is the degree of hotness of an object and is governed by the laws of thermodynamics. The temperature scale based on the first and second laws of thermodynamics is known as the thermodynamic temperature scale. The lowest limit of the thermodynamic scale is absolute zero or 0 kelvin (K). Since the scale is linear by definition only one other non-zero reference point is needed to establish its slope. This reference point was originally defined as the freezing point of water (0°C or 273.15 K). In 1960 the reference point was changed to a more precisely reproducible point, namely the triple point of water (0.01 °C).However, measurement of temperature on the thermodynamic scale is hardly suitable for practical Thermometry. In practice there are three main reasons: (a)It is difficult to measure thermodynamic temperatures. Apart from the technical elaboration required it could take days if not weeks to measure a single thermodynamic temperature.
eBook - PDFMeasurement of Temperature and Chemical Composition
Jones' Instrument Technology
- B E Noltingk(Author)
- 2013(Publication Date)
- Butterworth-Heinemann(Publisher)
1 Temperature measurement C. HAGART-ALEXANDER 1.1 Temperature and heat 1.1.1 Application considerations Temperature is one of the most frequently used process measurements. Almost all chemical processes and reactions are temperature-dependent. Not infre-quently in chemical plant, temperature is the only indication of the progress of the process. Where the temperature is critical to the reaction, a considerable loss of product may result from incorrect tempera-tures. In some cases, loss of control of temperature can result in catastrophic plant failure with the attendant damage and possibly loss of life. Another area where accurate temperature measure-ment is essential is in the metallurgical industries. In the case of many metal alloys, typically steel and aluminium alloys, the temperature of the heat treat-ment the metal receives during manufacture is a crucial factor in establishing the mechanical properties of the finished product. There are many other areas of industry where temperature measurement is essential. Such applica-tions include steam raising and electricity generation, plastics manufacture and moulding, milk and dairy products and many other areas of the food industries. Then, of course, where most of us are most aware of temperature is in the heating and air-conditioning systems which make so much difference to people's personal comfort. Instruments for the measurement of temperature, as with so many other instruments, are available in a wide range of configurations. Everyone must be familiar with the ubiquitous liquid-in-glass thermometer. There is then a range of dial thermometers with the dial attached directly to the temperature measuring element, i.e. local reading thermometers. Remote reading instruments are also available where the measuring system operates the dial directly through a length of metal capillary tubing. The distance between the sensing 'bulb' and the dial, or readout, of these instruments is limited to about thirty metres.
eBook - PDFInstrumentation: Theory and Practice, Part 2
Sensors and Transducers
- Issam Abu-Mahfouz, Abu-Mahfouz Issam(Authors)
- 2022(Publication Date)
- Springer(Publisher)
103 C H A P T E R 6 Temperature Measurements 6.1 INTRODUCTION Temperature is one of the most frequently measured physical variables. Temperature is a mea- sure of the level of molecular energy or vibration. It is agreed that at absolute zero temperature (NUL273 ı C), the molecules have no motion. Like many other variables, accurate temperature mea- surement is of great significance to the health care, agricultural, and manufacturing industries. Several methods have been developed to measure temperature using several mechanical and physical principles. Figure 6.1 shows the basics of temperature scale and units that are com- monly used. Kelvin (K) is the absolute Celsius scale and Rankine (R) is the absolute Fahrenheit scale. There are three main categories of temperature sensors that are discussed in this chapter: mechanical, electrical, and optical. A variety of factors are to be considered when selecting a thermometer. These include temperature range, object or target material, accuracy, health and safety requirements, and cost. 6.2 MECHANICAL THERMOMETERS These are devices that respond to a change in temperature by a change in a mechanical property such as volume or pressure. 6.2.1 BIMETALLIC THERMOMETER The bimetallic temperature sensor is composed of two metal strips (e.g., steel and brass) with different coefficients of thermal expansion that are overlapped, rolled against each other and joined together in a strong diffusion bond along their full lengths. When heated or cooled, this bimetallic strip will deform due to the different rates of expansion or contraction between the two metal strips. This deformation can be calibrated and then used to measure temperature. These types of contact sensors do not require, nor do they generate electric power. Bimetallic thermometers can be used to measure temperatures from below NUL100 ı C to above 500 ı C.
eBook - PDFMonitoring Solar Heating Systems
A Practical Handbook
- R. Ferraro, R. Godoy, D. Turrent(Authors)
- 2013(Publication Date)
- Pergamon(Publisher)
4.1 MEASUREMENT: GENERAL 4.2 INSTRUMENT TYPES AND DATA RECORDING 4.2.1 General 4.2.2 Thermocouples 4.2.3 Thermopiles 4.2.4 Resistance Thermometer Devices 4.2.5 Thermistors 4.3 INSTALLATION 4.3.1 General 4.3.2 Thermocouples 4.3.3 Resistance Temperature Devices 4.3.4 Thermistors 4.4 APPLICATIONS 4.4.1 External Ambient Temperature 4.4.2 Internal Space Temperature 4.4.3 Air Temperature Measurements in Ducts and Air Collectors 4.4.4 Liquid Temperature Measurements in Pipes and Collectors 4.4.5 Temperature Measurement of Solids and Surfaces 4.5 CALIBRATION AND ACCURACY 4.5.1 Accuracy Standards 4.5.2 Calibration .Temperature Measurements Chapter 4 82 82 82 83 86 86 90 91 91 92 95 96 96 96 98 98 100 101 103 103 103 Installing thermocouples can be tricky. 81 4 Temperature Measurements 4.1 MEASUREMENT: GENERAL Together with reliable solar radiation measurements, accurate temperature measurements are high on the list of priorities in any solar system/building monitoring exercise. The measurement of temperature is related either directly or indirectly to virtually every item of data which is to be processed and analysed. It is necessary for heat flow measurements, when integrated with fluid flow, and (less obviously) relevant to insolation measurement, where ambient temperature corrections are necessary. The degree of accuracy required is related to application. Where single readings of absolute temperature are required over a fairly wide range, a less accurate device may be acceptable than when differential temperatures of the order of 10°C or less are being measured. Failure to correctly design, select, install and maintain the necessary temperature measuring equipment usually renders the monitoring results unreliable and, at worst, useless. All general remarks made in Section 3.1 of the previous chapter also relate to temperature measuring instruments.
eBook - PDF- Walt Boyes(Author)
- 2002(Publication Date)
- Butterworth-Heinemann(Publisher)
Again, accuracy can be improved somewhat by using thermally conducting grease. Figure 14.40 shows a typical hand-held probe. 14.7.3 Miscellaneous measurement techniques Temperature measurement may be the primary measurement required for the control of a plant. There are, however, many cases where tempera- ture measurement is a tool to get an indication of the conditions in a plant. For instance, in distilla- tion columns it is more convenient and quicker to judge the compositions of the offtake by tempera- ture measurement than to install on-line analyzers, and as a further bonus the cost of temperature measurement is very significantly less than the cost of analyzers. The reverse situation also exists where it is not possible to gain access for a thermometer to the region where the temperature requires to be known. In this instance some indirect measure- ment technique must be resorted to. One case of indirect measurement that has already been dealt with at some length is the case of radiation therm- ometers. 14.7.3.1 Pyrometric cones At certain definite conditions of purity and pres- sure. substances change their state at fixed tem- peratures. This fact forms a useful basis for fixing temperatures, and is the basis of the scales of temperature. For example, the melting points of metals give a useful method of determining the electroniotive force of a thermocouple at certain fixed points on the International Practical Temperature Scale as has been described. In a similar way, the melting points of mixtures of certain minerals are used extensively in the ceramic industry to determine the temperature of kilns. These minerals, being similar in nature to the ceramic ware, behave in a manner which indi- cates what the behavior of the pottery under simi- lar conditions is likely to be. The mixtures, which consist of silicate minerals such as kaolin or china clay (aluminum silicate).
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