Calibration

Michael P. Cable is the Lead Controls Engineer at United Therapeutics in Durham, NC, as well as a Level 3 Certified Control System Technician and certified Project Management Professional. His career spans Navy Nuclear Power Program electronics work, pharmaceutical technical services at Eli Lilly and Performance Solutions, and operations technology roles at cell therapy companies.

Alan W. Bryant is a licensed professional engineer in Texas with over 30 years in the upstream oil and gas industry. His career includes hands-on field instrumentation work, control system engineering, and leadership of automation and multidiscipline projects. A longtime volunteer with the International Society of Automation, he supports the development of control system professionals.

About the Authors xi

Acknowledgments xiii

Introduction xv

1 Calibration Principles and Terminology 1

1.1 What Is Calibration? 1

1.2 Calibration-Related Terminology 2

1.2.1 Calibration Range 2

1.2.2 Error and Accuracy 3

1.2.3 Precision and Repeatability 4

1.2.4 Tolerance 4

1.2.5 Stability 5

1.2.6 Test Uncertainty Ratio 5

1.2.7 Uncertainty 5

1.2.8 Combined Effects on Uncertainty:Worst Case Versus Probable 5

1.2.9 Zero and Span Errors 6

1.2.10 Linearity and Hysteresis Errors 7

1.3 Calibration Methods 10

1.3.1 Loop Calibration Versus Device Calibration 10

1.3.2 Bench Versus Field Calibration 11

1.4 Fundamentals of Metrological Traceability 12

1.5 Summary 14

Review Questions 14

References 16

2 The Calibration Program 17

2.1 Introduction 17

2.2 Planning the Program 17

2.3 What to Calibrate? Loops and Components 18

2.4 How Important Is It? Instrument Criticality Classification 19

2.5 How Good Does It Need to Be? Loop Tolerance 20

2.6 When Should It Be Calibrated? Calibration Confirmation Interval 21

2.7 Calibration Equipment 23

2.7.1 Accuracy 23

2.7.2 Certification 24

2.7.3 Environmental Conditions 24

2.7.4 Safety 24

2.8 How is the Calibration Performed? Calibration Procedures 24

2.9 Calibration Record System 26

2.10 Who Performs Calibrations - Staff Qualifications and Training 29

2.10.1 The Control System Technician 29

2.10.2 Characteristics of a CST 30

2.10.2.1 Honesty and Integrity 30

2.10.2.2 Attention to Detail 30

2.10.2.3 Excellent Documentation Practices 30

2.10.2.4 Understanding Processes 30

2.11 Loop and Component Performance Verification 31

2.12 Safety Considerations 31

2.13 Summary 32

Review Questions 32

References 33

3 Control System Documentation 35

3.1 Piping and Instrumentation Diagrams 35

3.2 Loop Diagrams 36

3.3 Instrument Specification Forms/Instrument Database 37

3.4 Project Specifications 38

3.5 Manufacturer's Specifications 39

3.6 Summary 39

Review Questions 39

References 40

4 Calibration Equipment and Systems 41

4.1 What Does Field Calibration Equipment Do? 41

4.2 Types of Calibration Standards 41

4.3 Selecting Equipment 41

4.4 Is the Calibration Equipment Accurate Enough? 42

4.4.1 Calculating TUR 42

4.4.2 Calculating Test Accuracy Ratio 44

4.5 Adjusting for Local Conditions 44

4.6 Calibration Management Software Systems 45

Review Questions 45

References 46

5 Temperature Instruments 47

5.1 What Is Temperature? 47

5.2 Temperature Terms and Units of Measure 47

5.3 Temperature Instruments 47

5.3.1 Thermocouples 47

5.3.2 RTDs 49

5.3.3 Thermistors 51

5.3.4 Thermometers - Filled-Bulb and Bimetal 51

5.3.5 Thermowells 52

5.3.6 Signal Conversion (Transmitters and Input Cards) 53

5.4 Temperature Measurement Uncertainty 53

5.4.1 RTD Error 54

5.4.2 Transmitter 54

5.4.3 PLC Input Card 55

5.4.4 Calculating Loop TPE/Loop Tolerance 55

5.5 Temperature Calibration 56

5.5.1 Introduction 56

5.5.2 Temperature Calibration Equipment 56

5.5.3 Safety 58

5.5.4 Temperature Calibration Examples 59

5.5.4.1 Dial Thermometer Example 59

5.5.4.2 Temperature Loop Example 61

5.5.4.3 RTD Calibration Check Example 63

5.5.4.4 Temperature Transmitter Example 65

5.5.4.5 Analog Input Card Example 66

5.5.4.6 Temperature Switch Example 67

Review Questions 67

References 68

6 Pressure Instrument Calibration 71

6.1 What Is Pressure? 71

6.2 Pressure Terms and Units of Measure 71

6.3 Types of Pressure Instruments 74

6.3.1 Pressure Gauges 74

6.3.2 Pressure Transmitters 75

6.3.3 Smart Transmitters 75

6.3.4 Pressure Switches 77

6.4 Pressure Measurement Uncertainty 77

6.4.1 Introduction 77

6.4.2 Transmitter 79

6.4.3 Calculating Loop TPE 79

6.5 Pressure Calibration 80

6.5.1 Introduction 80

6.5.2 Pressure Calibration Equipment 80

6.5.2.1 Pressure Sources 80

6.5.3 Safety 86

6.5.4 Pressure Calibration Examples 87

6.5.4.1 Pressure Calibration: Pressure Gauges 87

6.5.4.2 Example Pressure Calibration: Pressure Loop 89

6.5.4.3 Example Pressure Calibration: 4-20mA Pressure Transmitter 91

6.5.4.4 Example Pressure Calibration: Pressure Switch 91

Review Questions 93

References 94

7 Level Instrument Calibration 95

7.1 What Is Level? 95

7.2 Level Terms and Units of Measure 95

7.3 Types of Level Instruments 96

7.3.1 Hydrostatic Pressure 97

7.3.2 Capacitance 100

7.3.3 Ultrasonic 100

7.3.4 Radar 102

7.4 Level Measurement Uncertainty 102

7.4.1 Top-Down Level Measurement Errors 103

7.4.2 Capacitance Level Measurement Errors 103

7.4.3 Hydrostatic Level Measurement Errors 103

7.5 Level Calibration 103

7.5.1 Introduction 103

7.5.2 Level Calibration Equipment: Gauge Tapes, Bobs, and Bars 104

7.5.3 Safety 106

7.5.4 Calibrating a Differential Pressure Level Transmitter 106

7.5.4.1 Procedure 106

7.5.4.2 Suppressed/Elevated Zero 107

7.5.4.3 Specific Gravity 108

7.5.4.4 Dry andWet Legs 108

7.5.4.5 Diaphragm Seals and Filled Capillary Tubes 110

7.5.4.6 Dual Sensors, Remote Sensors, and Multiple Transmitters 111

7.5.4.7 Interface Measurement with DP 111

7.5.5 Calibrating a Capacitance Level Instrument 112

7.5.5.1 GWR 113

7.5.5.2 Calibrating an Ultrasonic Level Instrument 113

7.5.5.3 Method 1 113

7.5.5.4 Method 2 114

7.5.6 Calibrating a Level Loop Using Manual Gauging 114

Review Questions 114

References 115

8 Flow Instrument Calibration 117

8.1 What Is Flow? 117

8.2 Flow Terms and Units of Measure 117

8.3 Types of Flow Instruments 118

8.3.1 Differential Pressure 119

8.3.2 Magnetic Flowmeter 120

8.3.3 Ultrasonic Flowmeter 123

8.3.4 Vortex-Shedding Flowmeter 124

8.3.5 Turbine Flowmeter 125

8.3.6 Coriolis Mass Flowmeter 126

8.3.7 Thermal Mass Flowmeter 126

8.3.8 Electronic Gas Measurement System 127

8.4 Flow Measurement Uncertainty 128

8.4.1 Flow Measurement Criticality, Tolerance, and Calibration Frequency 128

8.4.2 Uncertainty 129

8.4.3 Example: Uncertainty of an Orifice Meter 129

8.4.4 Example: Uncertainty of a Coriolis Meter 129

8.5 Flowmeters Calibration 131

8.5.1 Introduction 131

8.5.2 Meter Proving 132

8.5.3 Flow Calibration Equipment 132

8.5.3.1 Gas Flow 132

8.5.3.2 Liquid Flow (Meter Provers) 133

8.5.3.3 Tank Provers 133

8.5.4 Safety 136

8.5.5 Examples 136

8.5.5.1 Example: Gas Orifice Meter and EGM 137

8.5.5.2 Example: Coriolis Meter for Natural Gas 138

Review Questions 139

References 139

9 Final Control Devices Calibration 141

9.1 What Are Final Control Devices? 141

9.2 Flow Control Loop with Control Valve Final Control Element 141

9.3 Examples 145

9.3.1 Example: Calibrating an I/P Transducer 146

9.3.2 Example: Calibrating a Valve Positioner 147

9.3.3 Example: Calibrating a Control Valve 147

Review Questions 148

References 148

10 Process Analytical Instrument Calibration 149

10.1 Analytical Applications 149

10.2 Analytical Units of Measure 149

10.3 Types of Analytical Instruments 149

10.4 Examples 150

10.4.1 Example: pH 150

10.4.2 pH Calibration Procedure 156

10.4.3 Diagnostic Test for pH Electrodes 156

10.4.4 Measuring Electrical Conductivity and Resistivity 157

10.4.5 Calibration of Electrical Conductivity 158

10.4.6 Calibration Uncertainty for GC 159

Review Questions 160

References 160

11 Fixed Gas Detectors 161

11.1 What Are Gas Detectors? 161

11.2 Gas Detection Terms and Units of Measure 161

11.3 Types of Gas Detectors 161

11.4 Calibration 162

Review Questions 163

Appendix A Piping and Instrumentation Diagram (P&ID) 165

Appendix B Loop Diagrams 167

Appendix C Instrument Data 169

Appendix D Calibration Procedures 177

Appendix E Test Equipment 191

Appendix F Unit Conversions 199

Appendix G Answers to Review Questions 201

Bibliography 217

Index 219