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 xiAcknowledgments xiiiIntroduction xv1 Calibration Principles and Terminology 11.1 What Is Calibration? 11.2 Calibration-Related Terminology 21.2.1 Calibration Range 21.2.2 Error and Accuracy 31.2.3 Precision and Repeatability 41.2.4 Tolerance 41.2.5 Stability 51.2.6 Test Uncertainty Ratio 51.2.7 Uncertainty 51.2.8 Combined Effects on Uncertainty:Worst Case Versus Probable 51.2.9 Zero and Span Errors 61.2.10 Linearity and Hysteresis Errors 71.3 Calibration Methods 101.3.1 Loop Calibration Versus Device Calibration 101.3.2 Bench Versus Field Calibration 111.4 Fundamentals of Metrological Traceability 121.5 Summary 14Review Questions 14References 162 The Calibration Program 172.1 Introduction 172.2 Planning the Program 172.3 What to Calibrate? Loops and Components 182.4 How Important Is It? Instrument Criticality Classification 192.5 How Good Does It Need to Be? Loop Tolerance 202.6 When Should It Be Calibrated? Calibration Confirmation Interval 212.7 Calibration Equipment 232.7.1 Accuracy 232.7.2 Certification 242.7.3 Environmental Conditions 242.7.4 Safety 242.8 How is the Calibration Performed? Calibration Procedures 242.9 Calibration Record System 262.10 Who Performs Calibrations – Staff Qualifications and Training 292.10.1 The Control System Technician 292.10.2 Characteristics of a CST 302.10.2.1 Honesty and Integrity 302.10.2.2 Attention to Detail 302.10.2.3 Excellent Documentation Practices 302.10.2.4 Understanding Processes 302.11 Loop and Component Performance Verification 312.12 Safety Considerations 312.13 Summary 32Review Questions 32References 333 Control System Documentation 353.1 Piping and Instrumentation Diagrams 353.2 Loop Diagrams 363.3 Instrument Specification Forms/Instrument Database 373.4 Project Specifications 383.5 Manufacturer’s Specifications 393.6 Summary 39Review Questions 39References 404 Calibration Equipment and Systems 414.1 What Does Field Calibration Equipment Do? 414.2 Types of Calibration Standards 414.3 Selecting Equipment 414.4 Is the Calibration Equipment Accurate Enough? 424.4.1 Calculating TUR 424.4.2 Calculating Test Accuracy Ratio 444.5 Adjusting for Local Conditions 444.6 Calibration Management Software Systems 45Review Questions 45References 465 Temperature Instruments 475.1 What Is Temperature? 475.2 Temperature Terms and Units of Measure 475.3 Temperature Instruments 475.3.1 Thermocouples 475.3.2 RTDs 495.3.3 Thermistors 515.3.4 Thermometers – Filled-Bulb and Bimetal 515.3.5 Thermowells 525.3.6 Signal Conversion (Transmitters and Input Cards) 535.4 Temperature Measurement Uncertainty 535.4.1 RTD Error 545.4.2 Transmitter 545.4.3 PLC Input Card 555.4.4 Calculating Loop TPE/Loop Tolerance 555.5 Temperature Calibration 565.5.1 Introduction 565.5.2 Temperature Calibration Equipment 565.5.3 Safety 585.5.4 Temperature Calibration Examples 595.5.4.1 Dial Thermometer Example 595.5.4.2 Temperature Loop Example 615.5.4.3 RTD Calibration Check Example 635.5.4.4 Temperature Transmitter Example 655.5.4.5 Analog Input Card Example 665.5.4.6 Temperature Switch Example 67Review Questions 67References 686 Pressure Instrument Calibration 716.1 What Is Pressure? 716.2 Pressure Terms and Units of Measure 716.3 Types of Pressure Instruments 746.3.1 Pressure Gauges 746.3.2 Pressure Transmitters 756.3.3 Smart Transmitters 756.3.4 Pressure Switches 776.4 Pressure Measurement Uncertainty 776.4.1 Introduction 776.4.2 Transmitter 796.4.3 Calculating Loop TPE 796.5 Pressure Calibration 806.5.1 Introduction 806.5.2 Pressure Calibration Equipment 806.5.2.1 Pressure Sources 806.5.3 Safety 866.5.4 Pressure Calibration Examples 876.5.4.1 Pressure Calibration: Pressure Gauges 876.5.4.2 Example Pressure Calibration: Pressure Loop 896.5.4.3 Example Pressure Calibration: 4–20mA Pressure Transmitter 916.5.4.4 Example Pressure Calibration: Pressure Switch 91Review Questions 93References 947 Level Instrument Calibration 957.1 What Is Level? 957.2 Level Terms and Units of Measure 957.3 Types of Level Instruments 967.3.1 Hydrostatic Pressure 977.3.2 Capacitance 1007.3.3 Ultrasonic 1007.3.4 Radar 1027.4 Level Measurement Uncertainty 1027.4.1 Top-Down Level Measurement Errors 1037.4.2 Capacitance Level Measurement Errors 1037.4.3 Hydrostatic Level Measurement Errors 1037.5 Level Calibration 1037.5.1 Introduction 1037.5.2 Level Calibration Equipment: Gauge Tapes, Bobs, and Bars 1047.5.3 Safety 1067.5.4 Calibrating a Differential Pressure Level Transmitter 1067.5.4.1 Procedure 1067.5.4.2 Suppressed/Elevated Zero 1077.5.4.3 Specific Gravity 1087.5.4.4 Dry andWet Legs 1087.5.4.5 Diaphragm Seals and Filled Capillary Tubes 1107.5.4.6 Dual Sensors, Remote Sensors, and Multiple Transmitters 1117.5.4.7 Interface Measurement with DP 1117.5.5 Calibrating a Capacitance Level Instrument 1127.5.5.1 GWR 1137.5.5.2 Calibrating an Ultrasonic Level Instrument 1137.5.5.3 Method 1 1137.5.5.4 Method 2 1147.5.6 Calibrating a Level Loop Using Manual Gauging 114Review Questions 114References 1158 Flow Instrument Calibration 1178.1 What Is Flow? 1178.2 Flow Terms and Units of Measure 1178.3 Types of Flow Instruments 1188.3.1 Differential Pressure 1198.3.2 Magnetic Flowmeter 1208.3.3 Ultrasonic Flowmeter 1238.3.4 Vortex-Shedding Flowmeter 1248.3.5 Turbine Flowmeter 1258.3.6 Coriolis Mass Flowmeter 1268.3.7 Thermal Mass Flowmeter 1268.3.8 Electronic Gas Measurement System 1278.4 Flow Measurement Uncertainty 1288.4.1 Flow Measurement Criticality, Tolerance, and Calibration Frequency 1288.4.2 Uncertainty 1298.4.3 Example: Uncertainty of an Orifice Meter 1298.4.4 Example: Uncertainty of a Coriolis Meter 1298.5 Flowmeters Calibration 1318.5.1 Introduction 1318.5.2 Meter Proving 1328.5.3 Flow Calibration Equipment 1328.5.3.1 Gas Flow 1328.5.3.2 Liquid Flow (Meter Provers) 1338.5.3.3 Tank Provers 1338.5.4 Safety 1368.5.5 Examples 1368.5.5.1 Example: Gas Orifice Meter and EGM 1378.5.5.2 Example: Coriolis Meter for Natural Gas 138Review Questions 139References 1399 Final Control Devices Calibration 1419.1 What Are Final Control Devices? 1419.2 Flow Control Loop with Control Valve Final Control Element 1419.3 Examples 1459.3.1 Example: Calibrating an I/P Transducer 1469.3.2 Example: Calibrating a Valve Positioner 1479.3.3 Example: Calibrating a Control Valve 147Review Questions 148References 14810 Process Analytical Instrument Calibration 14910.1 Analytical Applications 14910.2 Analytical Units of Measure 14910.3 Types of Analytical Instruments 14910.4 Examples 15010.4.1 Example: pH 15010.4.2 pH Calibration Procedure 15610.4.3 Diagnostic Test for pH Electrodes 15610.4.4 Measuring Electrical Conductivity and Resistivity 15710.4.5 Calibration of Electrical Conductivity 15810.4.6 Calibration Uncertainty for GC 159Review Questions 160References 16011 Fixed Gas Detectors 16111.1 What Are Gas Detectors? 16111.2 Gas Detection Terms and Units of Measure 16111.3 Types of Gas Detectors 16111.4 Calibration 162Review Questions 163Appendix A Piping and Instrumentation Diagram (P&ID) 165Appendix B Loop Diagrams 167Appendix C Instrument Data 169Appendix D Calibration Procedures 177Appendix E Test Equipment 191Appendix F Unit Conversions 199Appendix G Answers to Review Questions 201Bibliography 217Index 219