The Physics of Metrology (eBook)

Acknowledgements 5
Preface 6
Table of contents 8
Illustrations 14
1 The measurement of length 21
Trundle wheel 21
Chains and tapemeasures 23
Distance measurement 23
Triangulation 24
Theodolites 26
Optical distance meters 28
Reflective distance meters 29
Beam-modulation telemetry 30
Global Positioning System 33
Ruler and gage blocks 34
Caliper 36
Micrometers 38
Dial indicators 39
2 Angles and arcs 42
Cross staff angle measurement 44
Astrolabe and quadrant 45
Sextant 48
Levels 49
Inclinometers and laser levelers 50
Protractor and the carpenter’’s bevel 50
Sine-bar 51
Digital theodolites and encoders 52
3 Clocks and the measurement of time 58
Water clocks 60
Gravity-driven timepieces 65
Candle clocks 68
Sandglasses 69
Mechanical clockworks 70
The foliot escapement 71
Pendulum escapement 72
Balance wheel escapement 75
Spring-driven clockworks 76
Electric clock 77
Tuning fork ratchet control 77
Crystal-controlled watches 78
Clocks and the atom 80
A truly nature-based frequency standard 81
Building an atomic clock 82
4 Velocity and acceleration 84
Tachometer 84
Pickups 88
Sound and ultrasound 91
Echo sounding 94
Piezoelectric probes 95
Radar 96
Doppler shift radar 97
A glimpse at relativity 98
Velocity and acceleration 100
Liquid flow metering 102
Orifice flowmeters 104
Variable-area flowmeter 105
Positive displacement meters 106
Gasometers 109
5 Force, mass, weight, and torque 111
Strain gages and the Wheatstone bridge 112
Measuring deflection 115
Crystal strain gauges 117
From levers to scales and balances 118
Scales and weights 119
Torque 125
Motor torque and de Prony’s brake 127
Eddy current dynamometer 129
6 Vibrations 132
Aeolian harp – the dawn of music 133
The omnipresent vortex 133
Waves and the sine line 135
String theories 139
Aeolian vibrations 139
Practice meets theory 142
Ill winds 143
Wind power of the nasty kind 143
Controlling aeolian vibrations 145
Vibration dampers 145
Monitoring vibration damping 147
Terra not so firma 148
Earthquake detection 150
Vibration sensors 153
Displaying signals 154
Frequency measurement instrumentation 154
Forced oscillations 156
Crank mechanics 158
Some fascinating crank-driven machinery 162
Analog frequency meters 164
Digital metering 164
In comes the computer! 165
Noncontact measurements 166
Doppler vibrometer 168
7 Thermodynamics 170
Six’s thermometer 170
Gas thermometer 171
Thermoelectric temperature sensors 172
Resistance thermometry 176
Radiation pyrometry 179
Thermistors 182
Calorimetry 183
Berthelot’s bomb calorimeter 185
Berthelot’s bomb calorimeter 185
Specific heat capacity 187
Nernst calorimeter 188
Thermophore 192
Specific heat energy of gases 193
Apparatus of Cle´ment and Desormes 193
Entropy and the heat-death 195
8 Pressure 197
Mercury barometer 198
Dial barometer 202
Low and rough grade vacuum 203
Once upon a time • • • 204
Bourdon tube manometer 205
Membrane-actuated manometers 206
Energy via airmail 207
The “incompressible” fluids 210
Hydraulic ram 212
Down and under • • • 212
Diamond anvil cell 214
The other face of the coin 215
Capacitancemanometer 217
McLoid vacuum meter 219
Pirani heat transfer manometer 220
New age machine design 222
Ladder diagram 223
The not so missing link 224
Typical applications of pneumatic cylinders 227
Valves, the gray eminence 228
Pneumatics and hydraulics 230
Pressure sensors 231
The atmosphere and the cosmos 232
9 Density of solids, liquids, and gases 234
Density and atomic mass 235
Measurements of gas density 235
Effusiometer 236
Hydrogen and helium 237
Acoustic gas density meter 238
Density of solids 241
Density of liquids 242
Pycnometer 242
Nicholson’s hydrometer 245
Mohr (Westphal) balance 245
Hydrometer 247
Hare’s apparatus 250
Oscillating tube densitometer 251
Density of extrasolar objects 253
10 Light and radiation 256
Vanishing grease blot 256
Clap hands – here comes the semiconductor! 258
The finite velocity of propagation of light 262
I see the light! 264
The enchanted land of lenses 266
Binoculars 269
The roots of white light 270
Reflecting telescopes 273
Newtonian reflectors 273
Schmidt–Cassegrain telescopes 275
From extreme to extreme 276
Electron microscope 278
Spectrometry 280
Prism spectroscope 282
Diffraction grating spectroscope 283
11 Acoustics 285
The symphony orchestra in the living room 285
Sound propagation 287
The wave nature of sound 291
Audio systems 293
The two faces of the dynamic speaker 296
Piezoelectric transducers 298
Technology of piezoelectrics 300
An application of piezoelectric transducers 302
Ribbon microphone 302
Condensermicrophones 304
Electrostatic speakers 305
Sound tracking 307
Echo sounding 308
Ultra- and hypersound 309
Sonography 311
Sonoluminescence 312
Addendum 313
12 Electrical and electronic instruments 314
Volt and ampere 315
D’Arsonval galvanometer 316
Transistorized multimeter 321
Iron-vane instrument 323
Bimetal ammeter 326
Power meters 327
Resistance meters 328
Cross coil instruments 329
Tenacious oddball 330
Let’s get digitized! 331
The LED at the end of the tunnel 339
Digital measurement of analog magnitudes 341
Analog-to-digital conversion 341
Successive-approximation converter 344
Slope integrating ADC 345
13 Automation – instruments that think 347
Thermostats 348
Electronic temperature controllers 349
Operation of ON OFF mode controllers 353
Luminosity control 356
CO2 control in exhaust gases 357
Sulfur dioxide measurement 359
Humidity control 360
Moisture control 361
Conductivity of fluids and liquids 363
Some control theory 364
Proportional control 365
Pneumatic control systems 366
Flashback to the roots of automation 370
Bibliography 372
For further reading 373
Index of names 374
Subject index 376

"12 Electrical and electronic instruments (S. 301-302)

In the late 1990s, General Motors ventured into a trial run of 1100 electric cars in compliance with California’s legislation, which demanded dominance of electric vehicles by the year 2000. Dubbed EV1, 800 such cars were initially leased for 3 years to third parties, but as soon as the lease expired, got heartlessly crushed along with all the rest of zero-emission cars. Why did this foray into the kingdom of unpolluted air, intact ozone layer, and freedom from the global warming threat, end in such an undigni?ed demise?

Should GM have followed Alva Edison’s market strategy of selling the ?rst twoyears production of lightbulbs at a loss in order to generate a market for his invention wile fending off potential competitors? After all, why should consumers have coughed up some USD 30,000.00 for an electric car while gasoline cars were available at 1=3 of that price? Let alone the costs for replacement batteries within the ?rst 3 years of use. But even that could hardly have been the reason for the regulators to let go of such a popular law so willingly. So, what happened?

By comparison, the familiar gasoline-guzzling car with an average of, say, 20 miles to the gallon of gas, uses up 5 gallons per 100 miles driven. With 0.68 for the density of commercial gasoline, and 3.785 liter to the gallon, those 5 gallons convert into 5 x 3:785 x 0:68 ¼ 12:87 kg of gasoline. From the heat of combustion of gasoline, 11700 Cal=kg, and the conversion factor of 860 Cal ¼ 1 kilowatt x hour ðkWhÞ, the electric equivalent of the 5 gallons (12.87 kg) of gas per 100 miles becomes 12:87 x 11700=860 ¼ 75 kWh per 100 miles: However, the output of the internal combustion engine in our cars is limited to the Carnot process value, namely, some 34% of the energy input, while 3% of the remainder get lost in the gearbox and power train; that leaves us with about 32% of 175 kWh “energy on the wheels”, namely, 0:32 x 175 ¼ 56 kWh.

To compare this performance ?gure with that of an electrically powered car, we ?gure backwards from those 56 kWh to ?nd out how much energy must be generated to supply them. Utilities generate electricity at a somewhat better rate than the engines in our cars, namely, at about 40% and up, but some 7.2% of their power output is lost in transmission through power lines and substations. On the other hand, electric cars consume extra energy in a number of ways: First of all, present days batteries deliver in the average only 0.80 kWh for every 1 kWh they get charged with, and the car’s electric motors can be expected to run at about 90% ef?ciency.

Here again, another 3% go into frictional losses in the cars’ transmission train. Summing it all up, we get 20 þ 7:2 þ 10 þ 3 ¼ 40:2% of losses, which brings the demand of an electric car to 56=ð1 x 0:402Þ ¼ 93:65 kWh per 100 miles. Generated at 40% ef?ciency, this becomes 93:65=0:40 x 234 kWh utilities have to come up with. Compared with the 175 kWh per 100 miles of the standard car, this is 234=175 ¼ 1:34 times higher. Rather than providing clean air, the use of electric cars in the cities would boost CO2 pollution by a whopping 34%; however, electricity for charging up those cars would be produced far from the cities where they strive. Call it the counties’ contribution to better city air, but it still wouldn’t help cleaning the atmosphere or mobilizing voters in the project’s support."