Temperature Measurement

Bela G. Liptak

• Publisher: CRC Press
• Year: 2022
• Print ISBN:
  9780801983856
• eBook ISBN:
  9781000153064
• Topic: Technology & Engineering
• Subtopic: Electrical Engineering & Telecommunications
• Index: Technology & Engineering

Temperature Measurement covers nearly every type of temperature measurement device, in particular, bimetallic thermometers, filled bulb and glass stem thermometers, thermistors, thermocouples, and thermowells. Includes suppliers and prices.

Béla G. Lipták speaks on Post-Oil Energy Technology on the AT&T Tech Channel.

1 Application and Selection

D. BALL (1969) B. G. LIPTÁK (1982, 1993)

DOI: 10.1201/9781003063919-1

Temperature is an expression denoting a physical condition of matter, just as are mass, dimensions, and time. Yet, the idea of temperature is a relative one, arrived at by a number of conflicting theories. The classic theory depicts heat as a form of energy associated with the activity of the molecules of a substance. These minute particles of all matter are assumed to be in continuous motion which is sensed as heat. Temperature is a measure of this heat.

To standardize on the temperature of objects under varying conditions, several scales have been devised. The Fahrenheit scale arbitrarily assigns the number 32 to the freezing point of water and the number 212 to the boiling point of water and divides the interval into 180 equal parts. The Centigrade or Celsius scale calls the freezing point of water 0 and its boiling point 100.

In line with the classic theory, some relation to the point where molecular motion is at a minimum had to be established, and the Kelvin scale, using Centigrade divisions, was drawn. Zero Kelvin was determined to be −273.19°C. The Rankine scale places its zero at −459.61°F using Fahrenheit divisions in the same arbitrary way in which Lord Kelvin used the Celsius scale.

THE INTERNATIONAL PRACTICAL TEMPERATURE SCALE (IPTS)

The International Practical Temperature Scale is the basis most present-day temperature measurements. The scale established by an international commission in 1948 with text revision in 1960.¹ A revision² of the scale was adopted in 1990 and is reproduced in Tables 1a and 3a. scale is defined by reproducible temperature points established by physical constants of readily available 1832°F (1000°C) and by platinum-platinum and 10% rhodium thermocouples when it is more. The National

TABLE 1a Primary Temperature Points Defined by the International Practical Temperature Scale (IPTS-90)

Equilibrium Point	°K	°C
Triple Point of Hydrogen	13.81	−259.34
Liquid/Vapor Phase of Hydrogen at 25/76 Std. Atmosphere	17.042	−256.108
Boiling Point of Hydrogen	20.28	−252.87
Boiling Point of Neon	27.102	−246.048
Triple Point of Oxygen	54.361	−218.789
Boiling Point of Oxygen	90.188	−182.962
Triple Point of Water	273.16	.01
Boiling Point of Water	373.15	100
Freezing Point of Zinc	692.73	419.58
Freezing Point of Silver	1235.08	961.93
Freezing Point of Gold	1337.58	1064.43

ORIENTATION TABLE

The range in temperature within the universe varies from the near zero of black space to the billions of degrees in the nuclear fusion process deep within the stars. But the practical range on earth can be considered as extending from 1°R upward about five decades to around 20,000°R. This is still a tremendous range, and no single sensor could possibly cover it. Therefore, one of the restrictions on the temperature sensor concerns the temperature range over which it can stay reasonably accurate. Table A (at the front of this volume) has been prepared to show the approximate temperature ranges of each of the sensor types. The many types of sensors are listed on the left, while some of their characteristics are shown horizontally across the top. If it is not known what general type of sensor will do a specific job, the table can help point the way to the right selection.

Once the class of sensors has been found, the data in the table will give a rough idea of the applicability of that design.

When the possible choices of selection have been narrowed down to a few instrument types, the reader should turn to the corresponding sections of this volume. In the front of each section there is a summary of basic features, such as accuracy, cost, and range. Inspecting these briefly, one can determine if the instrument generally meets the requirements or not. If it does, one should read the section which describes the design and its available variations in detail. If some of the features are unacceptable, one should proceed to the next choice noted in the orientation table.

FIG. 1b Uncertainties in calibrating different temperature sensors at various temperatures. (From NBS Technical Note No. 262)

Temperature sensors should be selected to meet the requirements of specific applications. Table 1c can assist the reader in this task.³ If the application engineer determines the required temperature level, the nature of the information required (point or average temperature), and the nature of the process environment, this table can be used to determine the suitability of various sensors to that application. The most difficult temperature measurement applications are those where high temperatures are to be detected within a hostile environment, such as that which exists within a fluid-bed coal gasifier.

TABLE 1c Temperature Sensor Selection Table

Measured Temperature	Under 500°C				Above 500°C
Reading ^1	Point		Average		Point		Average
Hostile Environment ^2	No	Yes	No	Yes	No	Yes	No	Yes
Interference ^3	No Yes	No Yes	No Yes	No Yes	No Yes	No Yes	No Yes	No Yes
Sensors ^4 Color Indicators	G(L) G(L)	G(L) G(L)			G(L) G(L)	G(L) G(L)
Bimetallic Units	G F	G(P) F(P)
Filled Elements	G F	G(P) F(P)	G(L) F	F(P) F(P)
Resistance Bulbs	E F	E(P) F(P)	E F	E(P) F(P)	E F	G(P) F(P)	G(L) F	G(P,L) F(P,L)
Thermistors	E(L) F	G(P) F(P)	E(L) F	G(P) F(P)
Thermocouples	G F	G(P) F(P)	F(L) F(L)	F(L) F(L)	E F	E(P) F(P)	F(L) F(L)	F(L,P) F(L,P)
Quartz Crystals	E(L) F
Radiation Pyrometers					E(L) G(L)	E(L) G(L)	E(A,L) G(A,L)	E(A,L) G(A,L)
Infrared Pyrometers	E(L) E(L)	E(L) G(L)			E(L) E(L)	E(L) E(L)
Spectroscopic (Fraunhofer) Sensors								A A
Thermopile			G(A) F(A)				G(A) F(A)
Acoustic Time Domain Reflectometry (TDR)			D D	D D			D D	D D
CODE LETTERS: D-in development L-limited F-fair G-good E-excellent P-protective well reduces speed of response A-detects the average temperature of an area
EXAMPLE: G(D)—This combination of code letters refers to a device which is a good selection for the particular service, but is not yet commercially available.
1 This device either detects a point or the average temperature of some section of the process or of the refractory.
2 The term “hostile environment” here is used to mean processes such as fluid beds, where the sensor is likely to experience the mechanical impact of high velocity solid particles.
3 “Interference” refers to need to overcome temperature interferences due to hot refractories or to temperature differences between the carrier gas and the solid particles in it.
4 For considerations of measurement error, span, cost stability, response time, linearity, materials of construction, etc., refer to the text.

THE MANY WAYS OF MEASURING TEMPERATURE

It is believed that Galileo invented the liquid-in-glass thermometer around 1592. The principle behind the thermocouple—the existence of the thermoelectric current—was discovered in 1821 by Thomas Seebeck. The same year Sir Humphry Davy noted the temperature dependence of metals, but the first resistance temperature detector (RTD) was not constructed until 1932, by C. H. Meyers. The development of temperature sensors was a slow process until the middle of the twentieth century. Today there are nearly 20 differ...

Table of contents

• Cover
• Half Title
• Title
• Dedication
• Contents
• Contributors
• 1 Application and Selection
• 2 Bimetallic Thermometers
• 3 Calibrators and Simulators
• 4 Color Indicators, Crayons, Pellets
• 5 Fiber-Optic Thermometers
• 6 Filled-Bulb and Glass-Stem Thermometers
• 7 Integrated Circuitry (IC) Transistors and Diodes
• 8 Miscellaneous Temperature Sensors
• 9 Pneumatic and Suction Pyrometers
• 10 Pyrometric Cones
• 11 Radiation and Infrared Pyrometers
• 12 Quartz Crystal Thermometry
• 13 Resistance Temperature Detectors (RTDS)
• 14 Temperature Switches and Thermostats
• 15 Thermistors
• 16 Thermocouples
• 17 Thermowells
• 18 Ultrasonic Thermometers
• Index