131
CHAPTER 5
TEMPERATURE AND FLOW TRANSDUCERS
Robert J. Moffat
Department of Mechanical Engineering
Stanford University
Stanford, California
1
INTRODUCTION
132
2 THERMOCOUPLES
132
2.1
Types and Ranges
132
2.2
Peripheral Equipment
133
2.3
Thermoelectric Theory
135
2.4
Graphical Analysis of Circuits
137
2.5
Zone-Box Circuits
138
2.6
Laws of Thermoelectricity
139
2.7
Switches, Connectors, Zone
Boxes, and Reference Baths
142
2.8
Obtaining High Accuracy with
Thermocouples
144
2.9
Service-Induced Inhomogeneity
Errors
144
2.10 Thermoelectric Materials
Connected in Parallel
147
2.11 Spurious emf due to
Corrosion and Strain
148
2.12 Self-Validating Thermocouples
149
2.13 Thermocouple Probe Designs
for Gas Temperature
Measurements
150
2.14 Thermocouple Installations for
Surface Temperature
Measurement
151
3 RESISTANCE TEMPERATURE
DETECTORS
152
3.1
Types and Ranges
152
3.2
Physical Characteristics of
Typical Probes
152
3.3
Electrical Characteristics of
Typical Probes
153
3.4
Thermal Characteristics of
Typical Probes
153
3.5
Measuring Circuits
155
3.6
The Standard Relationships for
Temperature versus Resistance
157
3.7
Interpreting Temperature from
Resistance: Common Practice
158
4 THERMISTORS
161
4.1
Types and Ranges
161
4.2
Physical Characteristics of
Typical Probes
161
4.3
Electrical Characteristics of
Typical Probes
163
4.4
Thermal Characteristics of
Typical Probes
163
4.5
Measuring Circuits and
Peripheral Equipment
165
4.6
Determining Temperature from
Resistance
166
5 OPTICAL METHODS
167
6 ELECTRON NOISE
THERMOMETERS
171
7 ACOUSTIC VELOCITY PROBES
172
8 TEMPERATURE-SENSITIVE
COATINGS
173
9 FLOW RATE
174
9.1
Nomenclature
174
9.2
Basic Principles Used in Flow
Measurement
175
9.3
Orifice, Nozzle, and Venturi
Meters
176
9.4
Variable-Area Meters
177
9.5
Laminar Flowmeters
179
9.6
Instability Meters
180
9.7
Ultrasonic Flowmeters
181
REFERENCES
185
Reprinted from Instrumentation and Control, Wiley, New York, 1990, by permission of the publisher.
Mechanical Engineers’ Handbook: Instrumentation, Systems, Controls, and MEMS, Vol