Handbook of Modern Sensors (eBook)

Preface 7
Contents 9
1 Data Acquisition 18
1.1 Sensors, Signals, and Systems 18
1.2 Sensor Classification 24
1.3 Units of Measurements 26
References 28
2 Sensor Characteristics 30
2.1 Transfer Function 30
2.2 Span (Full-Scale Input) 32
2.3 Full-Scale Output 33
2.4 Accuracy 34
2.5 Calibration 35
2.6 Calibration Error 36
2.7 Hysteresis 37
2.8 Nonlinearity 37
2.9 Saturation 39
2.10 Repeatability 40
2.11 Dead Band 40
2.12 Resolution 40
2.13 Special Properties 41
2.14 Output Impedance 41
2.15 Excitation 42
2.16 Dynamic Characteristics 42
2.17 Environmental Factors 46
2.18 Reliability 48
2.19 Application Characteristics 50
2.20 Uncertainty 50
References 52
3 Physical Principles of Sensing 54
3.1 Electric Charges, Fields, and Potentials 55
3.2 Capacitance 61
3.3 Magnetism 67
3.4 Induction 73
3.5 Resistance 76
3.6 Piezoelectric Effect 83
3.7 Pyroelectric Effect 93
3.8 Hall Effect 99
3.9 Seebeck and Peltier Effects 103
3.10 SoundWaves 109
3.11 Temperature and Thermal Properties of Materials 111
3.12 Heat Transfer 116
3.13 Light 128
3.14 Dynamic Models of Sensor Elements 130
References 136
4 Optical Components of Sensors 140
4.1 Radiometry 142
4.2 Photometry 146
4.3 Windows 149
4.4 Mirrors 151
4.5 Lenses 153
4.6 Fresnel Lenses 154
4.7 Fiber Optics andWaveguides 157
4.8 Concentrators 161
4.9 Coatings for Thermal Absorption 162
4.10 Electro-optic and Acousto-optic Modulators 163
4.11 Interferometric Fiber-optic Modulation 165
References 166
5 Interface Electronic Circuits 168
5.1 Input Characteristics of Interface Circuits 168
5.2 Amplifiers 173
5.3 Excitation Circuits 181
5.4 Analog-to-Digital Converters 192
5.5 Direct Digitization and Processing 203
5.6 Ratiometric Circuits 207
5.7 Bridge Circuits 209
5.8 Data Transmission 218
5.9 Noise in Sensors and Circuits 221
5.10 Batteries for Low Power Sensors 239
References 242
6 Occupancy and Motion Detectors 244
6.1 Ultrasonic Sensors 245
6.2 Microwave Motion Detectors 245
6.3 Capacitive Occupancy Detectors 250
6.4 Triboelectric Detectors 254
6.5 Optoelectronic Motion Detectors 255
References 268
7 Position, Displacement, and Level 270
7.1 Potentiometric Sensors 271
7.2 Gravitational Sensors 273
7.3 Capacitive Sensors 275
7.4 Inductive and Magnetic Sensors 279
7.5 Optical Sensors 292
7.6 Ultrasonic Sensors 303
7.7 Radar Sensors 306
7.8 Thickness and Level Sensors 310
References 315
8 Velocity and Acceleration 318
8.1 Accelerometer Characteristics 320
8.2 Capacitive Accelerometers 322
8.3 Piezoresistive Accelerometers 324
8.4 Piezoelectric Accelerometers 326
8.5 Thermal Accelerometers 326
8.6 Gyroscopes 330
8.7 Piezoelectric Cables 336
References 338
9 Force, Strain, and Tactile Sensors 340
9.1 Strain Gauges 342
9.2 Tactile Sensors 344
9.3 Piezoelectric Force Sensors 351
References 353
10 Pressure Sensors 356
10.1 Concepts of Pressure 356
10.2 Units of Pressure 357
10.3 Mercury Pressure Sensor 358
10.4 Bellows, Membranes, and Thin Plates 359
10.5 Piezoresistive Sensors 361
10.6 Capacitive Sensors 366
10.7 VRP Sensors 367
10.8 Optoelectronic Sensors 369
10.9 Vacuum Sensors 371
References 374
11 Flow Sensors 376
11.1 Basics of Flow Dynamics 376
11.2 Pressure Gradient Technique 378
11.3 Thermal Transport Sensors 380
11.4 Ultrasonic Sensors 384
11.5 Electromagnetic Sensors 387
11.6 Micro.ow Sensors 389
11.7 Breeze Sensor 391
11.8 Coriolis Mass Flow Sensors 393
11.9 Drag Force Flow Sensors 394
References 395
12 Acoustic Sensors 398
12.1 Resistive Microphones 399
12.2 Condenser Microphones 399
12.3 Fiber-Optic Microphone 400
12.4 Piezoelectric Microphones 402
12.5 Electret Microphones 403
12.6 Solid-State Acoustic Detectors 405
References 408
13 Humidity and Moisture Sensors 410
13.1 Concept of Humidity 410
13.2 Capacitive Sensors 413
13.3 Electrical Conductivity Sensors 416
13.4 Thermal Conductivity Sensor 418
13.5 Optical Hygrometer 419
13.6 Oscillating Hygrometer 420
References 421
14 Light Detectors 424
14.1 Introduction 424
14.2 Photodiodes 428
14.3 Phototransistor 435
14.4 Photoresistors 437
14.5 Cooled Detectors 440
14.6 Thermal Detectors 442
14.7 Gas Flame Detectors 456
References 458
15 Radiation Detectors 460
15.1 Scintillating Detectors 461
15.2 Ionization Detectors 464
References 472
16 Temperature Sensors 474
16.1 Thermoresistive Sensors 478
16.2 Thermoelectric Contact Sensors 498
16.3 Semiconductor P-N Junction Sensors 505
16.4 Optical Temperature Sensors 508
16.5 Acoustic Temperature Sensor 512
16.6 Piezoelectric Temperature Sensors 513
References 514
17 Chemical Sensors 516
17.1 Chemical Sensor Characteristics 517
17.2 Specific Difficulties 517
17.3 Classification of Chemical-Sensing Mechanisms 518
17.4 Direct Sensors 520
17.5 Complex Sensors 529
17.6 Chemical Sensors Versus Instruments 537
References 547
18 Sensor Materials and Technologies 550
18.1 Materials 550
18.2 Surface Processing 560
18.3 Nano-Technology 564
References 572
Appendix 574
Index 596
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10 Pressure Sensors (p. 339-340)

"To learn something new,
first, you must know something old."
- My physics teacher

10.1 Concepts of Pressure

The pressure concept was primarily based on the pioneering work of Evangelista Torricelli, who, for a short time, was a student of Galileo [1]. During his experiments with mercury-filled dishes, in 1643, he realized that the atmosphere exerts pressure on Earth. Another great experimenter, Blaise Pascal, in 1647, conducted an experiment, with the help of his brother-in-law Perier, on the top of the mountain Puy de Dome and at its base. He observed that pressure exerted on the column of mercury depends on elevation. He named the mercury-in-vacuum instrument they used in the experiment a barometer. In 1660, Robert Boyle stated his famous relationship: The product of the measures of pressure and volume is constant for a given mass of air at fixed temperature. In 1738, Daniel Bernoulli developed an impact theory of gas pressure to the point where Boyle’s law could be deducted analytically. Bernoulli also anticipated the Charles–Gay–Lussac law by stating that pressure is increased by heating gas at a constant volume. For a detailed description of gas and .uid dynamics, the reader is referred to one of the many books on the fundamentals of physics. In this chapter, we briefly summarize the basics which are essential for the design and use of pressure sensors.

In general terms, matter can be classi.ed into solids and .uids. The word fluid describes something which can flow. That includes liquids and gases. The distinction between liquids and gases are not quite definite. By varying pressure, it is possible to change liquid into gas and vice versa. It is impossible to apply pressure to fluid in any direction except normal to its surface. At any angle, except 90., fluid will just slide over, or .ow. Therefore, any force applied to .uid is tangential and the pressure exerted on boundaries is normal to the surface. For a .uid at rest, pressure can be de.ned as the force F exerted perpendicularly on a unit area A of a boundary surface [2]:

p = dF/ dA (10.1)

Pressure is basically a mechanical concept that can be fully described in terms of the primary dimensions of mass, length, and time. It is a familiar fact that pressure is strongly in.uenced by the position within the boundaries; however, at a given position, it is quite independent of direction.We note the expected variations in pressure with elevation:

dp = - wdh (10.2)

where w is the specific weight of the medium and h represents the vertical height. Pressure is unaffected by the shape of the con.ning boundaries. Thus, a great variety of pressure sensors can be designed without concern for shape and dimensions.

If pressure is applied to one of the sides of the surface con.ning a .uid or gas, the pressure is transferred to the entire surface without diminishing in value.