69
CHAPTER 3
BRIDGE TRANSDUCERS
Patrick L. Walter
Department of Engineering
Texas Christian University
Fort Worth, Texas
1 TERMINOLOGY
69
2 FLEXURAL DEVICES IN
MEASUREMENT SYSTEMS
70
2.1 Cantilever Beams
70
2.2 Bourdon Tubes
70
2.3 Clamped Diaphragms
71
2.4 Error Contributions from the
Flexure Properties
72
3 THE RESISTANCE STRAIN
GAGE
73
3.1 Strain Gage Types and
Fabrication
73
3.2 Gage Factor
75
3.3 Mechanical Aspects of Gage
Operation
75
3.4 Electrical Aspects of Gage
Operation
77
3.5 Technical Societies and Strain
Gage Manufacturers
80
4 THE WHEATSTONE BRIDGE
81
4.1 Bridge Equations
82
4.2 Lead Wire Effects
85
4.3 Temperature Compensation
87
5 RESISTANCE BRIDGE BALANCE
METHODS
91
6 RESISTANCE BRIDGE
TRANSDUCER MEASUREMENT
SYSTEM CALIBRATION
93
6.1 Static Calibration
93
6.2 Dynamic Calibration
95
6.3 Electrical Substitution
Techniques
96
7 RESISTANCE BRIDGE
TRANSDUCER MEASUREMENT
SYSTEM CONSIDERATIONS
102
7.1 Bridge Excitation
102
7.2 Signal Amplification
103
7.3 Slip Rings
104
7.4 Noise Considerations
105
8 AC IMPEDANCE BRIDGE
TRANSDUCERS
111
8.1
Inductive Bridges
112
8.2 Capacitive Bridges
114
REFERENCES
115
BIBLIOGRAPHY
115
1 TERMINOLOGY
A telemetry system responding to a measurand consists of four basic parts—the transducer,
the transmitting system, the receiving system, and the data output or display system:
Telemetry. The transmission of information about a measurand.
Measurand. The object of a measurement. The process to be defined.
Transducer. A component in the telemetry system which provides information about a
process and, as a by-product, transfers energy from the process. Typical bridge trans-
ducers convert physical quantities such as force, pressure, displacement, velocity,
acceleration, temperature, and humidity into electrical quantities for input to the trans-
mitting system.
Reprinted from Instrumentation and Control, Wiley, New York, 1990, by permission of the publisher.
Mechanical Engineers’ Handbook: Instrumentation, Systems, Controls, and MEMS, Volume 2, Third Edition.
Edited by Myer Kut