Introduction TOC_Chap1 MaintOfI-n-S 2nd Goettsche

8/10/2019 Introduction TOC_Chap1 MaintOfI-n-S 2nd Goettsche

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Maintenance ofInstruments & Systems

2nd Edition

Lawrence D. Goettsche, Editor

Practical Guides

for Measurement and Control


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v

Table of Contents

About the Editor and Contributors xi

Chapter 1 Introduction 1Overview 1

History of Instrumentation and Control Maintenance 1

Need for Instrumentation and Control Maintenance and Engineering 6

Chapter 2 Fundamental Principles 9Overview 9

Electronic Field Instrumentation 9

Why Maintain? 10

Maintenance vs. Troubleshooting 19

Calibration and Reasons to Calibrate 20

Troubleshooting 21

Basic Troubleshooting Techniques 22

Designed with Maintenance in Mind 25

Chapter 3 Diagrams, Symbols, and Specifications 31Overview 31

Process (Piping) & Instrumentation Diagram 31

Instrument Loop Diagrams 32

Logic Diagrams 39

Highway Drawings 49

Specifications 51

Instrument Symbols 54

Instrument Symbols 58

Chapter 4 Maintenance Personnel 73Overview 73

Multi-Disciplined 74

Continuous Training 74Training of Maintenance Workers 74

Multicraft/Multiskilled, Multi-Disciplined 78

Knowledge Factors 80

Skills 85

Job Titles and Descriptions 88

Credentialing 91

Certification 94


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Table of Contents

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Chapter 5 Maintenance Management and Engineering 97Overview 97

The Need for Maintenance Management 98

Maintenance Philosophy 98

Maintenance Management Organization 99

Basic Requirements for a Maintenance Department 100

Planning and Scheduling 102Work Order System 102

MTTF, MTTR, and Availability 104

Training Maintenance Workers 107

Preparing Functional Specifications 109

Computerized Maintenance Management Systems 110

Office/Shop Layout 115

Centralized/Decentralized Shops 118

Chapter 6 Pressure and Flow Instruments 121Overview 121

Pressure Transmitters 121

Differential Pressure Technology 132

Level Transmitters 138

Flow Transmitters 143

Magnetic Flowmeters 146

Mass Flowmeters 151

Turbine Flowmeters 156

Open Channel Flowmeters 158

Vortex Shedding Flowmeter 161

Vortex Shedding Meters 161

Positive Displacement Flowmeters 162

Positive Displacement Meters 164

Target Flowmeters 164Thermal Mass Flowmeters 166

Ultrasonic Flowmeters 167

Variable Area Flowmeters 168

Insertion (Sampling) Flowmeters 170

Chapter 7 Maintenance Engineering 171Overview 171

Engineering Assistance 173

Maintenance Involvement in New Projects 174

Successful Maintenance 177

The High Maintenance System 178

Documentation Control 179Alternative Methods of Maintenance 180

Service/Contract Maintenance 180

In-House Maintenance versus Contract Maintenance 181

New Systems Installations and Checkout 184

Preventive Maintenance 185

Power, Grounding, and Isolation Requirements 186

Instrument Air Requirements 196

Communication Requirements 197

Heating, Ventilating, Cooling, and Air Conditioning Systems 198


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Chapter 8 Temperature Devices 201Overview 201

Thermocouples 206

Resistance Temperature Devices 213

Thermistors 217

Integrated Circuit Temperature Transducer 218

Infrared Temperature Transducers 218Optical Fiber Thermometry 220

Thermometers 220

Chapter 9 Panel and Transmitting Instruments 233Overview 233

Panel and Behind-Panel Instruments 233

Panel Meters 241

Discrete Switches 241

Potentiometers 242

Recorders 242

Transducers 242

Smart Transmitters 244

Chapter 10 Analytical Instruments 259Overview 259

Field Analytical Instrument Systems 259

Field Analytical Instruments 260

Organization 262

Personnel 262

Maintenance Approaches 263

Service Factor 263

Maintenance Work Load 264

Spare Parts 265Vendor Support 265

Application Unique Issues 265

Installation Issues 266

Chapter 11 Primary Elements and Final Control Devices 267Overview 267

Temperature 267

Primary Elements 273

Primary Element Location 276

Control Valves 277

Troubleshooting Guide 283

Chapter 12 Pneumatic Instruments 287Overview 287

Instrument Air Requirements 287

Pneumatic Field Instruments 288


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Table of Contents

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Chapter 13 Calibration 299Overview 299

Field Calibration 300

Calibrating in Hazardous Locations 313

In-Shop Calibration 324

Other Aspects of Calibration 328

Chapter 14 Tuning 337Overview 337

Loop Classification by Control Function 337

Control Algorithms 339

Loop Tuning 347

Flow Loops 351

Chapter 15 Distributed Control Systems 353Overview 353

Distributed Control System Maintenance 353

Maintenance Goals and Objectives 353

Programmable Logic Controllers 368

Chapter 16 Software and Network Maintenance 373Overview 373

Computer Operating Environment 374

21st Century Maintenance Technology 383

Chapter 17 Safety 389Overview 389

Electrical Hazards 390

Hazardous Areas 392

Contamination 398Pressures and Vacuums 399

High Voltage 400

Moving and Rotating Machinery 401

High and Low Temperatures 401

Gases and Chemicals 402

Heights and Confined Spaces 403

Program Changes, Software Control 404

Process Considerations 406

Communication 406

Cryogenic Considerations 406

Nuclear Plants 409

Ergonomics 412Acknowledgment 413

Standards and Recommended Practices 413

Chapter 18 Fiber Optics 417Overview 417

Construction 418

Classification 418

Sensing Modes 418

Advantages 419


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Table of Contents

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Disadvantages 419

Applications 420

Analog Input/Output Modules 423

Sensors 423

Appendix A Glossary of Terms 427

Appendix B Bibliography 441

Index 447


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1

Introduction

Overview

TheMaintenancevolume is key to the Practical Guides Series and certainly akey to the profitability of companies through ensuring that the control system ismaintained so the plant can produce its products. This volume includes some his-tory and speculates about future advances of instrumentation and control (I&C)

system maintenance; it also covers some of the fundamental principles, vocabu-lary, symbolism, standards, and safety. It suggests the necessary basic knowledgerequired of I&C technicians and the interaction of maintenance in the retrofittingand start-up of control systems.

History of Instrumentation and Control Maintenance

From pneumatic instrumentation to computer-controlled systems what achange! Is a seasoned instrument mechanic expected to troubleshoot a state-of-the-art computer-controlled system? Should a new instrument technician be ex-pected to maintain pneumatic instrumentation? This volume documents expe-riences in the older types of systems as well as in the newer, state-of-the-artsystems.

1930s

Distributed control is not new. In 1938, when Chemical Processingpublishedits first issue, mechanisms for control were indeed distributed throughout theplant. Process control consisted of operator adjustments to hand valves that werebased on direct readings of local gages. Control room instrumentation has takensome dramatic turns along the way from large-scale pneumatic recorders tominiature analog electronic controllers to microprocessor-based digital systems.

Chemical and petroleum plants were among the first to use control systemsfor their processes. Pneumatic instrumentation became the leader in automaticcontrol because of its safety. Pipe fitters were asked to perform maintenance onthese early pneumatic instruments. In many cases, outmoded control room hard-ware is still operating effectively today a tribute to the worldwide manufactur-ers of process control instrumentation.

In the late 1930s and early 1940s, operators relied on local instrument gagesto monitor production processes. Control panels that did exist were located in thefield near process sensing points. Typically, only a handful of indicators, record-ers, and controllers were mounted on a local panel. Often, the process fluids werepiped directly into control panels.

Where fill fluids were needed, mercury was commonly used. Control panelsserved as a convenient means for improving control coordination by allowing op-erators to adjust valves in response to visual instrument readings.


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Introduction

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1940s

In the 1940s the use of pneumatic proportional controllers was increasing, sothe early pipe fitters had to understand more of the theory of process and control.New words such as integral, derivative, sensors, and final control elements wereadded to their vocabularies.

By the late 1940s, a trend toward the concentration of controls in centralized

locations had begun.

1950s

In the 1950s, operating unit control rooms were built to centralize operationsand to accommodate operators assigned to monitor control boards on a full-timebasis. With the growing number and complexity of the indicators, recorders, andcontrollers and the need to operate the plant remotely from these panels, the in-strument mechanic was specialized to maintain the pneumatic control systems.

By the mid 1950s, electronic analog instrumentation had been formally intro-duced but did not win industry acceptance until the late 1950s and early 1960s.With the exception of chemical and petroleum plants, most new plants used elec-tronic analog instrumentation because of the greater cost of tubing work between

pneumatic transmitters and controllers and the expensive pneumatic auxiliaries,such as air compressors, filters, and dryers.

Increasing plant complexity necessitated increasing amounts of accurate, up-to-date operating information.

Now the instrument mechanic needed to know electronics and electricity inaddition to pneumatics. Larger plants formed Electrical and Instrument (E&I), In-strument and Electronic (I&E), or Electrical and Control (E&C) groups; someformed an Instrument and Control (I&C) Group and had both instrument mechan-ics and instrument technicians. The knowledge required by I&C mechanics andtechnicians meant training was necessary, so vendors provided training on theequipment they sold.

1960s

Digital computers began to appear in control rooms in the 1960s. The com-puters initial role was essentially that of a data logging device from which paperprintouts could be obtained. However, the concept of direct digital control (DDC)gained notoriety in the 1960s.

1970s

By the mid 1970s, the drawbacks to DDC had become apparent. The centralcomputer approach depended on the availability of a single large computer.Highly trained computer personnel were needed to maintain the computer hard-ware and to deal with the high-level software languages.

Single-loop analog control continued to flourish during the early 1970s.Thousands of electronic signal wires crisscrossed central control rooms, addingcomplexity to the pursuit of improved coordination. Recognizing multiple func-tions inherent in panel instruments, split architecture systems were introduced.Analog display stations were segregated from rack-mounted printed circuit cardsin the quest for functional modularity.

I&C groups flourished, everyone was retrofitting and updating plants, andnew plants provided more and more instrumentation requirements. Instrumenta-tion vendors were training the instrument mechanics and electricians to maintaintheir equipment.


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History of Instrumentation and Control Maintenance

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Standards for instrumentation were being developed, and manufacturersstarted listening to ISA when developing their new instruments.

A marriage between single-loop electronic analog control and pneumatic con-trol developed because of the need for powerful control valve actuators.

The simplicity and accuracy of electronic controllers, recorders, and indicatorsmade them the choice for instrument panels.

Current-to-pneumatic converters and pneumatic-to-current converters linkedelectronic instruments to pneumatic instruments and sensors and actuators. Chem-ical plants used pneumatic instruments in the hazardous areas along with signalwires to transmit the signals to central control rooms in safe areas.

Most plants built after the mid 1970s used electronic rather than pneumatic in-strumentation. Pneumatic valves, however, are still used almost exclusively forthrottling control and even on-off control. About the same time in this periodHoneywell and Yokogawa introduced the first distributed digital control sys-tems (DDCS), now called the distributed control system (DCS). Multiple mini-computers, geographically and functionally distributed, performed monitoring

and control tasks that had been previously handled by the central DDC computer.Each microprocessor-based controller was shared by up to eight control loops. Se-rial bit communication over coaxial cable linked individual system devices.

As these distributed control systems became the standard for newer chemicaland petroleum plants and the older single-loop pneumatic and electronic control-lers were replaced, the I&C groups were trained on the new DCS. This was thefirst introduction of computers to the I&C technicians, and DCS manufacturersdesigned their systems to be configured and maintained by I&C groups nothighly trained computer personnel. As a technological breakthrough, the micro-processor accelerated advances in control system design. At the operator interfacelevel, distributed control contributed to an unforeseen development. For the firsttime, CRT display consoles gained acceptance as the primary operator interface,

and conventional single-loop analog stations were reduced to an emergencybackup role at many early distributed control system installation sites. Long,floor-to-ceiling panelboards were replaced with low-profile CRT workstationconsoles. Keyboards, CRTs and printers served as modern tools for seated controlroom operators.

By the end of the 1970s, control system innovations had advanced beyond in-dustrys capacity to keep pace. Most plant sites contained an assortment of controltechnologies that spanned three decades. Instrumentation and control specialists(mechanics, technicians, and engineers) were commonplace in industry. SpecialI&C groups were established, as shown in the organizational chart of Figure 1-1.

1980s

DCS operator interfaces were refined in the 1980s (see Figure 1-2). IntelligentCRT stations utilized multiple-display formats to condense and organize exten-sive operating information. Hierarchical arrangements of plant-, area-, group-, andloop-level displays simplified on-screen database presentation. Real-time colorgraphics added further comprehensive overviews of unit operations.

Most microprocessor-based control systems had a vast array of alarms and di-agnostics to help operators and maintenance personnel determine if there wereany problems. Distributed control systems had many on-line and off-line diagnos-tics, including process and input alarms, reportable events, error messages, andhardware and software failure reporting.


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Introduction

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1990s

Trends for the 1990s were computer-integrated manufacturing (CIM) and

management information systems (MIS). These interfaced the real-time devices(field devices at the machinery/process level) through distributed controllers tomultiple-station coordination, then on to scheduling, production, and managementinformation to the plant level for overall planning, execution, and control. Furtherdevelopment of artificial intelligence and expert systems gave advanced controlnew meaning.

With the introduction of computers and databases, maintenance managementsystems (MMS) helped maintenance and management personnel determine repairfrequency and spare parts availability and made decisions on when to replace ob-solete equipment.

Distributed control systems (DCS), programmable logic controllers (PLC),computer control systems (CCS), supervisory control and data acquisition(SCADA) and smart field devices were the norm. A digital signal was superim-

posed on the 4-20 mA signal for ranging and calibrating field devices. The Interna-tional Organization for Standardization (ISO) Open Systems Interconnection (OSI)model and interconnection of devices made by different manufactures has openedsystems architecture, replacing proprietary communications among devices.

2000s

Historically, factory floor maintenance methods and practices have been de-veloped across a wide range of vertical industries, where the focus was to keep theassembly lines and processes running rather than preserving assets. Today, manu-facturers are focused on the long-term benefits of factory floor support practices

Figure 1-1. Typical 1970s I & C Group Organization Chart.

PROCESS

ENGINEERING

FACILITY

ENGINEERINGMECHANICAL ELECTRICALSTORES

MILLWRIGHTWAREHOUSE

PIPEFITTERSHIP/REC

LABORERSBUYERS

SHIFT 2I&C

SHIFT 3ELECTRONICS

OPERATORS

SHIFT 1ELECTRICAL PROCESSMECHANICAL

CHEMICALELECTRICAL

QUALITYI&C

OPERATIONS

MANAGER

XYZ COMPANY


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Need for Instrumentation and Control Maintenanceand Engineering

Maintenance of instrumentation and process control systems from simplegages to complex distributed control systems is essential for the continuation ofour industry. Statements such as this have been repeated thousands of times bycompany presidents, manufacturing directors, and production superintendents.

Maintenance personnel should be involved with new installations and upgrad-ing older installations. They should ensure that the system is ergonomically easyto repair and well documented. Training should be done before a new system ar-rives so the maintenance department can help in installing and checking it out.

Equipment manufacturers provide engineering and start-up assistance. So themajority of the new opportunities to work in the I&C field is through originalequipment manufacturers or service contract employees.

Because of the equipments complexity, assistance is needed from the originalequipment manufacturer. Configuration of control systems and instrumentsshould be done by those very familiar with the system requirements and system/instrument capabilities.

Instrumentation tells us the process parameters in which we are operating. Asimple gage tells the temperature or pressure; the more complex instrumentation

Figure 1-3. Typical Gas Fired Electrical Generating Plant Organization Chart.

PskdjkjdidP

MAINTENANCE

MANAGER

PLANT

ENGINEER

PRODUCTION

MANAGER

ENVIRONMENTAL

AND HEALTH

(CHEMIST)

WELDER

ELECTRICIAN

I&C

MACHINIST(M-F 8 hrs)

SHIFT

SUPERVISORS

WATER/LAB TECH.

AUX. OPERATOR(Outside)

CONTROL

OPERATOR12 hr shift

Rotating 24/7

PLANT

MANAGER


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Need for Instrumentation and Control Maintenance and Engineering

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tells much more about the process. Proper operation of all equipment is requiredto make a quality product and to do it safely.

The technological advances of the past few years and the trends for moretechnical and specialized equipment require better trained and educated mainte-nance personnel. The types of equipment in control systems cover many disci-plines: mechanical, electrical, electronic, computer science, chemical, andenvironmental, among others.

The instrumentation and control field is more than electronics it is a systems

experience. It is necessary to know the physics of heat, light, noise, and mechani-cal advantage, as well as to have mechanical dexterity and aptitude, logical

thought, computer literacy, process knowledge, and the ability to work with others in dif-ferent disciplines.

Because of the many different knowledge factors, the individual crafts (elec-trician, mechanic, pipe fitter, etc.) have to work together, and finger pointing willsometimes occur. Electrical engineers, mechanical engineers, chemical engineers,and process engineers must understand each other and determine where their re-sponsibilities start and stop.

The field has grown with the application of computers, artificial intelligence,self-tuning, computer-integrated manufacturing (CIM), and so on. Largercompanies train pipe fitters to be instrument mechanics in pneumatic plants and

electricians to be instrument technicians in electronic plants. Knowledge of theprocess is needed to design new systems; therefore, all engineering disciplines getinvolved with the instrumentation and control system. Those who were fortunateto get involved in early instrumentation and control systems have become the I&Cmaintenance personnel and the control systems engineers of today.

The complexity of control loops and systems requires specialists. The systemsconcept requires more varied knowledge and the overall concept of control ratherthan component troubleshooting and replacement.

When the control system doesn't work, the plant doesn't produce. The controlsystem design can determine the profitability of a company. If it is maintainableand the mechanics, technicians, and engineers are trained, the production outputof the plant will be high.

Corrective, preventive, and operational maintenance must be performed by

qualified and experienced I&C maintenance personnel.Because of the complexity of existing control systems that utilize many fields

of expertise, several maintenance backgrounds are also required. This group isnow required to maintain, troubleshoot, and calibrate pneumatic, electrical, elec-tronic, and computerized instruments and systems. The systems approach, whichlooks at the whole picture to gain an understanding of the process, is the specialattribute of I&C maintenance personnel.

When assistance is needed, I&C personnel must have someone to go to forhelp. In the past, maintenance supervisors had a broad knowledge of most of theequipment and could make decisions on how to repair, when to repair, and so on.A few years ago, many supervisors were instrument mechanics, but contemporarymaintenance supervisors are managers who know very little about the operationand maintenance of the wide variety of instruments and control systems used to-day, since most have never been instrument mechanics or technicians. In fact,many of them know very little about pneumatics, electronics, or computers. To-day, knowledge of the process, knowledge of the overall system, and knowledgeof the expertise of their employees is far more important than knowledge of howto repair an individual instrument.

Who should the maintenance supervisors and managers go to for expert ad-vice on the control system? Instrumentation and control system engineers ormaintenance engineers with an I&C background. Instrumentation and control sys-tem engineers assist the mechanics and technicians and keep the supervisors and


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Introduction

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managers informed. They need to be a part of the design and start-up of the con-trol systems.

Much money is being spent for training, fault tolerant systems, redundancy,and new techniques. One simple but essential area that may be neglected is the ex-perience of the past and what that may teach about the present.

We learn from our past experiences. Being involved in the problems we en-

countered and the solutions that were found yesterday helps us make better deci-sions today. The learning technology that produces greater retention levels usesthe most senses, such as hearing, seeing, and feeling. The applications of oldersystems should be used as the basis for designing newer and generally faster con-trol systems. New problems are encountered in newer systems, but past applica-tion experience will help solve the new problems.

Dont neglect the knowledgeand experience gained in thepast.

Good maintenance saves money. With the equipment working properly, theprocess quality and production will be high. When equipment fails, productionnormally stops, and many production personnel cannot do their jobs. With goodmaintenance management, spare parts are available quickly to reduce the meantime to repair (MTTR). When the equipment is repaired properly, the mean timebetween failures (MTBF) is extended. The proper frequencies of preventive main-tenance should provide less down time, and the down time that occurs can be

scheduled. We can become pro-active instead of reactive.

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Introduction TOC_Chap1 MaintOfI-n-S 2nd Goettsche