- •6.1 Resistive Displacement Sensors
- •Types of Precision Potentiometers
- •Resistive Element
- •Electrical Characteristics
- •Mechanical Characteristics
- •Mechanical Mounting Methods
- •Implementation
- •6.2 Inductive Displacement Sensors
- •The Single-Coil Linear Variable-Reluctance Sensor
- •The Variable-Differential Reluctance Sensor
- •Variable-Reluctance Tachogenerators
- •Microsyn
- •Synchros
- •Variable-Coupling Transducers
- •Induction Potentiometer
- •Appendix to Section 6.2
- •Variable Distance Displacement Sensors
- •Variable Area Displacement Sensors
- •Variable Dielectric Displacement Sensors
- •Aluminum Type Capacitive Humidity Sensors
- •Tantalum Type Capacitive Humidity Sensors
- •Silicon Type Capacitive Humidity Sensors
- •Polymer Type Capacitive Humidity Sensors
- •Capacitive Moisture Sensors
- •Pulse Width Modulation
- •Square Wave Linearization
- •Feedback Linearization
- •Oscillator Circuits
- •Appendix to Section 6.3
- •6.4 Piezoelectric Transducers and Sensors
- •Single Crystals
- •Piezoelectric Ceramics
- •Perovskites
- •Processing of Piezoelectric Ceramics
- •Piezoelectric Polymers
- •Piezoelectric Ceramic/Polymer Composites
- •Suppliers of Piezoelectric Materials
- •6.5 Laser Interferometer Displacement Sensors
- •Longitudinal Zeeman Effect
- •Two-Frequency Heterodyne Interferometer
- •Single-Mode Homodyne Interferometer
- •6.6 Bore Gaging Displacement Sensors
- •Gages That Control Dimensions
- •Gages That Control Geometry
- •6.7 Time-of-Flight Ultrasonic Displacement Sensors
- •Ultrasound Transducers
- •6.8 Optical Encoder Displacement Sensors
- •Absolute Encoders
- •Incremental Encoders Quadrature Signals
- •Geometric Masking
- •Diffraction-Based Encoders
- •6.9 Magnetic Displacement Sensors
- •6.10 Synchro/Resolver Displacement Sensors
- •Equipment Needed for Testing Resolvers
- •Multispeed Units
- •Applications
- •Resolver-to-Digital Conversion
- •Bandwidth Optimization
- •Encoder Emulation
- •Determining Position Lag Error Due to Acceleration
- •Large Step Settling Time
- •Time Constants
- •6.11 Optical Fiber Displacement Sensors
- •Principle of Operation
- •Fabrication Techniques
- •Bragg Grating Sensors
- •Limitations of Bragg Grating Strain Sensors
- •Principle of Operation
- •Fabrication Procedure
- •Temperature Sensitivity of Long-Period Gratings
- •Knife-Edge Photodetector
- •Bicell Detector
- •Continuous Position Sensor
- •References
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Oscillator Circuits
In many applications, the resultant changes in the capacitance of capacitive transducers can be measured with a suitable ac bridge such as Wein bridge or Schering bridge. However, in a majority of cases, improvised versions of bridges are used as oscillator circuits for capacitive signal processing. The transducer is configured as a part of the oscillatory circuit that causes changes in the frequency of the oscillations. This change in frequency is scaled to be a measure of the magnitude of the physical variable.
As part of the oscillator circuits, the capacitive transducer has excellent frequency response and can measure both static and dynamic phenomena. Its disadvantages include sensitivity to temperature variations and the possibility of erratic or distorted signals due to long lead lengths. Also, the receiving instrumentation may be large and complex, and it often includes a second fixed-frequency oscillator for heterodyning purposes. The difference frequency thus produced can be read by an appropriate output device such as an electronic counter.
References
1.J. P. Bentley, Principles of Measurement Systems, 2nd ed., United Kingdom: Longman Scientific and Technical, 1988.
2.E. O. Doebelin, Measurement Systems: Application and Design, 4th ed., New York: McGraw-Hill, 1990.
3.J. P. Holman, Experimental Methods for Engineers, 5th ed., New York: McGraw-Hill, 1989.
4.F. T. Noth and G. C. M. Meijer, A Low-Cost, Smart Capacitive Position Sensor, IEEE Trans. Instrum. Meas., 41, 1041-1044, 1992.
Appendix to Section 6.3
List of Manufacturers
ANALITE Inc. |
Locon Sensor Systems, Inc. |
24-T Newtown Plaza |
1750 S. Eber Road |
Plainview, NY 11803 |
P.O. Box 789 |
Tel: (800) 229-3357 |
Holland, OH 43526 |
FSI/FORK Standards Inc. |
Tel: (419) 865-7651 |
668 Western Avenue |
Fax: (419) 865-7756 |
Lombard, IL 60148-2097 |
Rechner Electronic Industries Inc. |
Tel: (708) 932-9380 |
8651 Buffalo Avenue, Box 7 |
Gordon Engineering Corp. |
Niagara Falls, NY 14304 |
67 Del Mar Drive |
Tel: (800) 544-4106 |
Brookfiled, CT 06804 |
RDP Electrosense, Inc. |
Tel: (203) 775-4501 |
2216-Dept. B |
Hecon Corp. |
Pottstown, PA |
15-T Meridian Rd. |
Tel: (800) 334-5838 |
Eatontown, NJ 07724 |
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Tel: (800) 524-1669 |
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Kistler Instrumentation Corp. |
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Amherst, NY 14228-2171 |
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Tel: (716) 691-5100 |
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Fax: (716) 691-5226 |
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© 1999 by CRC Press LLC