Introduction to Engineering Experimentation

Anthony J. Wheeler received a Ph.D. in Mechanical Engineering from Stanford University in 1971. Dr. Wheeler is a licensed Professional Engineer in the State of California. He is currently Emeritus Professor of Engineering at San Francisco State University where he taught courses in Fluid Mechanics and Thermodynamics, and lectures and laboratories in Experimental Methods. His development activities in laboratories in experimentation were the precursors to the present textbook.

Professor Ahmad R. Ganji received his Ph.D. from the University of California, Berkeley in 1979. He is a professional engineer in the State of California. He has served as a faculty member at San Francisco State University since 1987, teaching courses in the areas of thermal-fluids, experimentation, and air pollution, and publishing over 40 works. Dr. Ganji has been the director of Industrial Assessment Center–a US DOE sponsored project since 1992. In this capacity he has managed hundreds of energy assessments of manufacturing facilities. As a consultant in energy efficiency projects, he has directed and managed numerous measurement and verification (M&V) projects that involve the formulation of detailed measurement protocols based on national and international standards.

Previous Edition TOC

CHAPTER 1 Introduction 1

1.1 Applications of Engineering Experimentation and Measurement 1

1.1.1 Measurement in Engineering Experimentation 1

1.1.2 Measurement in Operational Systems 3

1.2 Objective and Overview 3

1.3 Dimensions and Units 3

1.4 Closure 5

CHAPTER 2 General Characteristics of Measurement Systems 6

2.1 Generalized Measurement System 6

2.2 Validity of Measurement 7

2.2.1 Measurement Error and Related Definitions 8

2.2.2 Calibration of Measurement Systems 15

2.3 Dynamic Measurements 23

2.4 Closure 27

References 27

Problems 28

CHAPTER 3 Measurement Systems with Electrical Signals 34

3.1 Electrical Signal Measurement Systems 34

3.2 Signal Conditioners 35

3.2.1 General Characteristics of Signal Amplification 36

3.2.2 Amplifiers Using Operational Amplifiers 42

3.2.3 Signal Attenuation 48

3.2.4 General Aspects of Signal Filtering 50

3.2.5 Butterworth Filters Using Operational Amplifiers 53

3.2.6 Circuits for Integration, Differentiation, and Comparison 57

3.3 Indicating and Recording Devices 58

3.3.1 Digital Voltmeters and Multimeters 58

3.3.2 Oscilloscopes 59

3.3.3 Strip-Chart Recorders 61

3.3.4 Data Acquisition Systems 62

3.4 Electrical Transmission of Signals Between Components 63

3.4.1 Low-Level Analog Voltage Signal Transmission 63

3.4.2 High-Level Analog Voltage Signal Transmission 65

3.4.3 Current-Loop Analog Signal Transmission 66

3.4.4 Digital Signal Transmission 66

References 67

Problems 68

CHAPTER 4 Computerized Data-Acquisition Systems 70

4.1 Introduction 70

4.2 Computer Systems 71

4.2.1 Computer Systems for Data Acquisition 71

4.2.2 Components of Computer Systems 72

4.2.3 Representing Numbers in Computer Systems 74

4.3 Data-Acquisition Components 77

4.3.1 Multiplexers 77

4.3.2 Basics of Analog-to-Digital Converters 78

4.3.3 Practical Analog-to-Digital Converters 85

4.3.4 Digital-to-Analog Converters 88

4.3.5 Simultaneous Sample-and-Hold Subsystems 89

4.4 Configurations of Data-Acquisition Systems 90

4.5 Software for Data-Acquisition Systems 92

4.5.1 Commercial Software Packages 92

References 92

Problems 93

CHAPTER 5 Discrete Sampling and Analysis of Time-Varying Signals 95

5.1 Sampling-Rate Theorem 95

5.2 Spectral Analysis of Time-Varying Signals 100

5.3 Spectral Analysis Using the Fourier Transform 105

5.4 Selecting the Sampling Rate and Filtering 110

5.4.1 Selecting the Sampling Rate 110

5.4.2 Use of Filtering to Limit Sampling Rate 111

References 115

Problems 115

CHAPTER 6 Statistical Analysis of Experimental Data 118

6.1 Introduction 118

6.2 General Concepts and Definitions 120

6.2.1 Definitions 120

6.2.2 Measures of Central Tendency 122

6.2.3 Measures of Dispersion 123

6.3 Probability 124

6.3.1 Probability Distribution Functions 125

6.3.2 Some Probability Distribution Functions

with Engineering Applications 129

6.4 Parameter Estimation 139

6.4.1 Interval Estimation of the Population Mean 140

6.4.2 Interval Estimation of the Population Variance 146

6.5 Criterion for Rejecting Questionable Data Points 149

6.6 Correlation of Experimental Data 151

6.6.1 Correlation Coefficient 151

6.6.2 Least-Squares Linear Fit 155

6.6.3 Outliers in x—y Data Sets 159

6.6.4 Linear Regression Using Data Transformation 163

6.6.5 Multiple and Polynomial Regression 164

6.7 Linear Functions of Random Variables 168

6.8 Applying Computer Software for Statistical Analysis

of Experimental Data 169

References 169

Problems 170

CHAPTER 7 Experimental Uncertainty Analysis 180

7.1 Introduction 180

7.2 Propagation of Uncertainties–General Considerations 180

7.3 Consideration of Systematic and Random Components

of Uncertainty 184

7.4 Sources of Elemental Error 190

7.5 Uncertainty of the Final Results for Multiple-Measurement

Experiments 195

7.6 Uncertainty of the Final Result for Single-Measurement

Experiments 199

7.7 Step-by-Step Procedure for Uncertainty Analysis 202

7.8 Interpreting Manufacturers’ Uncertainty Data 203

7.9 Applying Uncertainty Analysis in Digital

Data-Acquisition Systems 204

7.10 Additional Considerations for Single-Measurement

Experiments 208

7.11 Closure 210

References 211

Problems 211

CHAPTER 8 Measurement of Solid-Mechanical Quantities 222

8.1 Measuring Strain 222

8.1.1 Electrical Resistance Strain Gage 222

8.1.2 Strain Gage Signal Conditioning 227

8.2 Measuring Displacement 232

8.2.1 Potentiometer 232

8.2.2 Linear and Rotary Variable Differential Transformers 233

8.2.3 Capacitive Displacement Sensor 237

8.2.4 Digital Encoders 239

8.3 Measuring Linear Velocity 239

8.3.1 Linear Velocity Transducer 239

8.3.2 Doppler Radar Velocity Measurement 240

8.3.3 Velocity Determination Using Displacement

and Acceleration Sensors 241

8.4 Measuring Angular Velocity 242

8.4.1 Electric Generator Tachometers 242

8.4.2 Magnetic Pickup 243

8.4.3 Stroboscopic Tachometer 244

8.4.4 Photoelectric Tachometer 245

8.5 Measuring Acceleration and Vibration 245

8.5.1 Piezoelectric Accelerometers 245

8.5.2 Strain-Gage Accelerometers 248

8.5.3 Servo Accelerometer 249

8.5.4 Vibrometer 249

8.6 Measuring Force 250

8.6.1 Load Cells 250

8.6.2 Proving Rings 252

8.7 Measuring Rotating Shaft Torque 253

References 255

Problems 256

CHAPTER 9 Measuring Pressure, Temperature, and Humidity 261

9.1 Measuring Pressure 261

9.1.1 Traditional Pressure-Measuring Devices 261

9.1.2 Pressure Transducers 268

9.1.3 Measuring a Vacuum 270

9.2 Measuring Temperature 274

9.2.1 Thermocouples 274

9.2.2 Resistance-Temperature Detectors 281

9.2.3 Thermistor and Integrated-Circuit Temperature Sensors 285

9.2.4 Mechanical Temperature-Sensing Devices 286

9.2.5 Pyrometers and Infrared Thermometers 289

9.2.6 Common Temperature-Measurement Errors 293

9.3 Measuring Humidity 298

9.3.1 Hygrometric Devices 299

9.3.2 Dew-Point Devices 299

9.3.3 Psychrometric Devices 299

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9.4 Fiber-Optic Devices 301

9.4.1 Optical Fiber 301

9.4.2 General Characteristics of Fiber-Optic Sensors 303

9.4.3 Fiber-Optic Displacement Sensors 304

9.4.4 Fiber-Optic Temperature Sensors 305

9.4.5 Fiber Optic Pressure Sensors 307

9.4.6 Other Fiber-Optic Sensors 307

References 308

Problems 309

CHAPTER 10 Measuring Fluid Flow Rate, Fluid Velocity, Fluid Level,

and Combustion Pollutants 313

10.1 Systems for Measuring Fluid Flow Rate 313

10.1.1 Pressure Differential Devices 313

10.1.2 Variable-Area Flowmeters 329

10.1.3 Turbine Flowmeters 332

10.1.4 Mass Flowmeters 333

10.1.5 Positive-Displacement Flowmeters 336

10.1.6 Other Methods of Flow Measurement 336

10.1.7 Calibrating Flowmeters 340

10.2 Systems for Measuring Fluid Velocity 341

10.2.1 Pitot-Static Probe 341

10.2.2 Hot-Wire and Hot-Film Anemometers 343

10.2.3 Fluid Velocity Measurement Using the

Laser-Doppler Effect 345

10.3 Measuring Fluid Level 347

10.3.1 Buoyancy Devices 348

10.3.2 Differential-Pressure Devices 349

10.3.3 Capacitance Devices 350

10.3.4 Conductance Devices 351

10.3.5 Ultrasonic Devices 351

10.3.6 Weight Methods 352

10.4 Measuring Air Pollution Species 352

10.4.1 Nondispersive Infrared Detectors 353

10.4.2 Chemiluminescent Analyzers 354

10.4.3 Flame Ionization Detectors 355

10.4.4 Other Gas-Analysis Devices 356

10.4.5 General Considerations about Sampling and

Measuring Pollutant Gases 357

References 358

Problems 359

CHAPTER 11 Dynamic Behavior of Measurement Systems 363

11.1 Order of a Dynamic Measurement System 363

11.2 Zero-Order Measurement Systems 364

11.3 First-Order Measurement Systems 364

11.3.1 Basic Equations 365

11.3.2 Step Input 365

11.3.3 Ramp Input 366

11.3.4 Sinusoidal Input 368

11.3.5 Thermocouple as a First-Order System 368

11.4 Second-Order Measurement Systems 373

11.4.1 Basic Equations 373

11.4.2 Step Input 374

11.4.3 Sinusoidal Input 376

11.4.4 Force Transducer (Load Cell) as a Second-Order System 377

11.4.5 Pressure-Measurement Devices as Second-Order Systems 380

11.4.6 Second-Order Systems for Acceleration and Vibration 388

11.5 Closure 393

References 394

Problems 394

CHAPTER 12 Guidelines for Planning and Documenting Experiments 397

12.1 Overview of an Experimental Program 397

12.1.1 Problem Definition 397

12.1.2 Experiment Design 398

12.1.3 Experiment Construction and Development 398

12.1.4 Data Gathering 399

12.1.5 Data Analysis 399

12.1.6 Interpreting Data and Reporting 399

12.2 Common Activities in Experimental Projects 399

12.2.1 Dimensional Analysis and Determining

the Test Rig Scale 399

12.2.2 Uncertainty Analysis 403

12.2.3 Shakedown Tests 403

12.2.4 Test Matrix and Test Sequence 404

12.2.5 Scheduling and Cost Estimation 408

12.2.6 Design Review 412

12.2.7 Documenting Experimental Activities 413

12.3 Closure 421

References 421

Answers to Selected Problems 422

APPENDIX A Computational Methods for Chapter 5 425

APPENDIX B Selected Properties of Substances 429

Glossary 434

Index

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