Fundamentals of Instrumentation v.1.2 - CERTH

1 Practical Process Control Copyright 2005 by Control Station, Inc. All Rights Reserved ControlControlControlStation StationStation Innovative Solutions from the Process Control Professionals Practical Process Control Fundamentals of Instrumentation and Process Control Practical Process Control Copyright 2005 by Control Station, Inc. All Rights Reserved Practical Process Control Fundamentals of Instrumentation and Process Control Copyright 2005 by Control Station, Inc. All rights reserved. No portion of this book may be reproduced in any form or by any means except with the explicit, prior, written permission of Control Station, Inc.

2 Practical Process Control Copyright 2005 by Control Station, Inc. All Rights Reserved Table of Contents Table of Contents .. 3 1. Introduction to Process Control .. 1 Objectives:.. 1 Introduction .. 2 Why do we need Process Control? .. 2 2 Quality .. 2 Profit .. 2 What is a Process? .. 4 What is Process Control?.. 5 Basics of Process Control .. 8 What is Open Loop Control? .. 8 What are the Modes of Closed Loop Control? .. 12 Manual 12 On-Off Control .. 13 PID Control .. 15 Time Proportion 16 What are the Basic Elements of Process Control?

3 17 The 18 18 Final Control Elements .. 18 The Controller .. 18 Process Characteristics .. 19 Objectives:.. 19 Introduction: Process 19 First Order Processes .. 20 LLeessssoonn What is a First Order Process? .. 20 What is Process Dead Time? .. 21 Measuring Dead 21 What is the Process Time Constant? .. 22 Measuring the Time 22 Controllability of a Process .. 23 What is Process Gain? .. 24 Measuring Process Gain .. 24 Making Gains Unitless .. 25 Values for Process 26 What is Process Action? .. 27 Process Action and Controller Action.

4 27 PPrroocceessss 28 Higher Order Processes .. 28 What are Higher Order Processes? .. 28 Over-damped Response .. 29 First Order Fit of Higher Order Over-Damped 30 First Order Fit of Higher Order Under-Damped Response .. 31 Critically Damped Response .. 32 What is a Linear Process?.. 33 What is a Nonlinear Process? .. 34 Dealing with Nonlinearity .. 35 Disturbance 35 Set Point 36 Process 37 What are Self-Regulating Processes? .. 37 What are Integrating Processes? .. 38 Dead time, Time Constants and Gain in an Integrating Process.

5 39 Practical Process Control Copyright 2005 by Control Station, Inc. All Rights Reserved Dead Time in an Integrating Process .. 39 Time Constants in an Integrating Process .. 39 Gain in an Integrating Process .. 39 Introduction to Instrumentation .. 42 Objectives:.. 42 Instrumentation Basics .. 43 What are Sensors and Transducers? .. 43 43 44 What are the Standard Instrumentation 45 Pneumatic .. 45 Current Loop .. 46 Loop Scaling .. 46 Output Scaling .. 46 Input Scaling .. 46 0 - 10 46 What are Smart Transmitters? .. 47 Digital Communications.

6 47 47 Signal Conditioning .. 47 47 What Instrument Properties Affect a Process? .. 48 Range and Span .. 48 Match Range to Expected 48 Measurement Resolution .. 49 Accuracy and Precision .. 50 % Error Over a 50 Absolute Over a Range .. 50 Accuracy vs. 51 Instrumentation 52 Instrument Gain .. 52 Instrument Time Constants .. 52 Instrument Dead Time .. 52 What is Input Aliasing?.. 53 Correct Sampling Frequency .. 54 Determining the Correct Sampling 55 What is Instrument Noise? .. 56 Effects of Noise .. 56 Eliminating Noise.

7 57 Low Pass Filters .. 57 Selecting a Filter by Cut-off Frequency .. 57 Selecting a Filter by Time 58 Selecting a Filter by Alpha Value .. 59 Process 60 What is Temperature?.. 60 Units of Temperature .. 60 What Temperature Instruments Do We Use? .. 61 Thermocouples .. 61 Junctions .. 61 Junction Misconceptions .. 62 Lead Wires .. 62 Linearization .. 63 Gain .. 63 Thermocouple Types .. 64 Resistive Temperature Devices .. 65 The Importance of the Temperature Coefficient alpha .. 65 Lead Wire Resistance .. 66 2 Wire RTDs .. 66 3 Wire RTDs.

8 67 Practical Process Control Copyright 2005 by Control Station, Inc. All Rights Reserved Self Heating .. 67 68 Infrared .. 69 Emittance .. 69 Field of View .. 70 Spectral Response .. 70 What is Pressure? .. 71 Units of 71 Absolute, Gauge and Differential 71 What is Level?.. 73 Point and Continuous 73 Common Level Sensing Technologies .. 74 Non-Contact Level Measurement .. 74 Ultrasonic Measurement .. 74 Radar / 74 Nuclear Level 75 Contact Level Measurement .. 76 Pressure Measurement .. 76 RF Capacitance / Resistance.

9 77 Guided Wave 78 What is Flow?.. 79 Factors Affecting Flow 79 Viscosity .. 79 Temperature and Pressure Effects on Viscosity .. 80 Units of Viscosity .. 80 Viscosities and Densities of Common Household 81 Conversion 82 Fluid 84 Newtonian Fluids .. 84 Non-Newtonian Fluids .. 84 Reynolds Number .. 85 Laminar 85 Turbulent 86 Transitional Flow .. 86 Flow 87 Common Flow Instruments .. 88 Units of Volumetric Flow .. 90 Positive Displacement Flow 91 Magnetic Flow Meters .. 91 Orifice Plate** .. 91 Orifice Plate** .. 92 Units of Mass 94 Coriolis Flow Meters.

10 94 Turndown .. 95 Installation and 95 Valves .. 97 What is a Control Valve? .. 97 Shut-Off Service .. 97 Divert Service .. 97 Throttling Service .. 97 Parts of a Control Valve .. 98 What is an Actuator? .. 99 What is a Positioner? .. 100 What is Cv? .. 101 What are Valve Characteristics?.. 102 Inherent Characteristics .. 102 Rangeability .. 103 Gain .. 103 Equal Percentage 104 Linear 105 Quick Opening Valves .. 105 Practical Process Control Copyright 2005 by Control Station, Inc. All Rights Reserved Installed .. 106 What is Valve Deadband.