575

Control Room Equipment

4

4.1ANNUNCIATORS AND ALARMS 580

Introduction 581History 582Principles of Operation 583

Operating Sequences 583Annunciator Types 586

Integral Annunciator 586Remote Annunciator 587Semigraphic Annunciator 588Recording Annunciators 589Vocal Annunciators 590Relay-Type Annunciators 590Solid-State Annunciators 593

Annunciator Cabinets 595Hazardous Area Designs 595Intrinsically Safe Designs 595

Pneumatic Annunciators 596Bibliography 597

4.2CONTROL CENTERS AND PANELS—TRADITIONAL 598

Introduction 599Traditional Control Rooms 599Control Rooms for DCS Systems 600Traditional Control Panels 601

Flat Panels 601Breakfront Panels 601Consoles 601

Traditional Front Panel Layouts 602Large-Case Instruments 602Miniature Instruments 602High-Density Instruments 603Graphic Panels 603Back-of-Panel Layout 607Panel Materials of Construction 607

Panel Specifications 608Human Engineering 608Panel Tubing and Wiring 610

Tubing 610Fittings 611Panel Wiring 611

Control Center Inspection 615Panel Shipment 616Conclusions 616Reference 616Bibliography 616

4.3CONTROL CENTER UPGRADING 618

Baseline Evaluation 619Original Design Perspective 620Information Zones and Task Analysis 621Building a New Control Room 622Technology Advances 623Computerized Procedure Systems 626Phased Approach 627Planning Ahead 630HMI Standards 630Maintainability 631Bibliography 631

© 2006 by Béla Lipták

576 Control Room Equipment

4.4CONTROLLERS—ELECTRONIC ANALOGAND DIGITAL 633

Introduction 634Analog vs. Digital Controllers 634The Controller’s Function 635Feature Checklist 635

On/Off and Direct-Connected Controllers 636On/Off Relay Outputs 636Direct-Connected Controllers 636

Analog Controllers 637Input Variations 638Control Modes 639Nonlinear Controllers 640Special Features 641Displays 642Balancing Methods 643Mounting 644Servicing 645

Digital Electronic Controllers 645Advantages and Disadvantages 645Hardware Components 646Software Capability 647Faceplates and Programmers 648

Bibliography 649

4.5CRT DISPLAYS 650

Introduction 651Display Options 651The Total System 653

Data Display Options 654Keyboard 656

Display Capabilities 657Refresh Memory 657Character and Format Control 658Vector Generator 658Display Initiation 659Propagation and Termination 661

Conclusions 662Bibliography 662

4.6DCS: BASIC TRENDS AND ADVANCES 663

Introduction 666Connectivity and Integration 666

Organizing the Project 667The Future 669

Control Advances 669Basic PID Algorithms 669Auto-Tuning 671Model-Based Control Algorithms 671DCS Bid Package 673

Costs 674

Conclusions 674References 676

4.7DCS: CONTROL AND SIMULATION

ADVANCES 677

Introduction 677Performance Monitoring 678Controller Tuning 678

On-Demand Tuning 679Adaptive Tuning 679

Fuzzy Logic Control 679Model Predictive Control 681Neural Network Applications 682Process and Control Simulation 684Conclusion 686Reference 686Bibliography 686

4.8DCS: INSTALLATION AND COMMISSIONING 687

Introduction 687Installation 688

Power and Grounding 688System Assembly 688HVAC and Heat Tracing 689Field Wiring and Checkout 689Bus Installation 689Installing HART Networks 690

Commissioning 690Training and Preliminary Checkout 690Fieldbus Testing 691Process Startup 691Commissioning of Control Loops 692Advanced Control 692

Conclusion 692References 692Bibliography 692

4.9DCS: INTEGRATION WITH BUSES AND NETWORKS 693

Introduction 693Bus Integration 693

DCS Fieldbus Support 694Field Networks 694Fieldbus Devices 695Function Blocks 696

Network Integration 697Recent Integration Trends 698

Conclusions 698References 698Bibliography 699

© 2006 by Béla Lipták

Contents of Chapter 4 577

4.10DCS: INTEGRATION WITH OTHERSYSTEMS 700

Introduction 700Existing Systems 700

MODBUS Interface 700OPC Interface 702

Motor Controls 702Fieldbus Interface 703

Safety Systems 703Conclusions 705Reference 705Bibliography 705

4.11DCS: MANAGEMENT OF ABNORMALCONDITIONS 706

Introduction 706Abnormal Condition Management 706

Types of Control 707Need for Operator Intervention 707

Psychological Basis for Intervention 707Detect Phase 708Sort/Select and Monitor Phases 709Plan/Act Phase 709Response Time 709Planning the Intervention 709Types of Operations 709

Managing Abnormal Conditions 710Control Room Design 711Operator Training 712Alarm System Design 712Graphical User Interface 716

Conclusions 718Acknowledgments 718References 718Bibliography 718

4.12DCS: MODERN CONTROL GRAPHICS 720

Introduction 720Function Block Representation 720

Standard for Process Control 721Function Block Modes 721Function Block Types 722

Sequential Function Chart (SFC) 723Ladder Diagrams 724Batch S88 725Safety Logic 725Conclusions 725Bibliography 726

4.13DCS: OPERATOR’S GRAPHICS 727

Introduction 727Operator Console Equipment 727

Video Display 728Keyboards 728Peripheral Devices 729

Remote and Web-Based Stations 729Remote Clients 729Web Pages 730

Operator Graphics 730Types of Displays 731

Overview Graphic Displays 731Graphic Displays 731Faceplate with Detailed Display 732Trend Displays 732

Static Graphic Components 732Dynamic Elements 732

Dynamos 733Aliases 734Display Access 735

Process Performance Monitoring 736Process Graphic Data Interfaces 736Conclusion 738Bibliography 738

4.14DCS: SYSTEM ARCHITECTURE 739

Introduction 740Analog Control 740

Direct Digital Control 741Distributed Control System 741

Functional Components 742DCS Control Network 742Operator Console 744Core Architectural Components 745International Fieldbus Standards 749

Data Highway Designs 749Control Network 749Ethernet Configuration 749

Alarm Management 750Alert Processing 750

DCS Attributes 752Reliability 753Mean Time between Failure 753

Pricing 754Bibliography 755

4.15DIGITAL READOUTS AND GRAPHIC DISPLAYS 757

Introduction 758Human Factors 759Size and Contrast 759Application Notes 760

© 2006 by Béla Lipták

578 Control Room Equipment

Mechanical and Electrical Counters 760Gas Discharge Displays 761Cathode Ray Tube Displays 762Rear Projection Displays 763Light-Emitting Diode Displays 763Liquid Crystal Displays 764

Passive Matrix Liquid CrystalDisplays 765

Active Matrix Liquid CrystalDisplays 765

Vacuum Fluorescent Displays 767New Trends in Graphic Displays 768

Plasma Displays 768Field Emission Displays 768Electroluminescent Displays 769

References 769Bibliography 769

4.16FIELDBUSES AND NETWORKPROTOCOLS 770

Introduction 770Communications Hierarchy 770

Field Level 771Control Level 771Operations Level 771Enterprise Level 772Data Models 772

Network Basics 772OSI Reference Model 772Physical Layer 773Data Link Layer 775Network Layer 777Transport Layer 777Application Layer 777

Fieldbus Protocols 778AS-i 778HART 780PROFIBUS DP/PROFIBUS PA 781FOUNDATION Fieldbus 782MODBUS 784ControlNet 785Industrial Ethernet 785Netwide Data Exchange 786

OPC Servers 786XML 787FDT/DTM 787

Conclusion 788References 788Bibliography 789Acronyms 789

4.17HUMAN–MACHINE INTERFACE EVOLUTION 790

Introduction 790Functions of the Control System HMI 790

Visualization and Control 791Process Alarming 792Trending 792

DCS Consoles 793DCS Console Graphic Standards 793DCS HMI Redundancy 794DCS HMI Chronological Evolution 795

The Open HMI 795Open HMI Display Standards 796Documentation 796Open HMI Evolution Chronology 796

Evolution of HMI Architecture 797Evolution of Plant Networking 799Evolution of Control Rooms 800Evolution of the Process Operator 8012005 and Beyond 802

Distributed and Mobile Control 802Remote Operation of the Plant 803The Future 803

References 804

4.18INDICATORS, ANALOG DISPLAYS 805

Terminology 805Electrical Movements 806Indication of Measurements 806

Fixed-Scale Indicators 807Movable-Scale Indicators 808

Parametric Indication 809Digital Indicators 810Acoustic Indicators 810Bibliography 811

4.19LIGHTS 812

Introduction 812Light Source Characteristics 813

Light Selection 814Colors and Flashing 814Lenses and Operating Environments 814Light Components 814

Lamp Types 815Incandescent Lamps 815Neon Lamps 815Solid-State Lamps (LEDs) 816Virtual Lights 816

Checklist 816Conclusions 816Bibliography 817

© 2006 by Béla Lipták

Contents of Chapter 4 579

4.20RECORDERS, OSCILLOGRAPHS, LOGGERS,TAPE RECORDERS 818

Introduction 819Sensor Mechanisms 819

Galvanometric Recorders 820Light-Beam Recorders (Oscillographs) 820Potentiometric Recorders 820Open Loop Recorders 821Linear Array Recorders 821

Recording Methods 822Ink-Writing Systems 822Inkless Systems 822Paperless Systems 822

Charts and Coordinates 822Circular Chart Recorders 823Strip-Chart Recorders 824Multiple Recorders 824X–Y Recorders 825Event Recorders 826

Tape Recording 826Data Loggers 827Bibliography 828

4.21SWITCHES, PUSHBUTTONS, KEYBOARDS 829

Introduction 830Switch Designs and Operation 830

Switching Action 831Contact Arrangements 831Switching Elements and Circuits 831Grades of Switching Devices 833

Types of Switching Devices 833Pushbuttons 833Toggle Switches 836Rotary Switches 837Thumbwheel Switches 838

Application and Selection 839Human Factors 839Display Movement 841Error Prevention 842Mechanical Features 844Environmental Considerations 844

Bibliography 844

4.22TOUCH-SCREEN DISPLAYS 845

Introduction 845Touch Technology 845

Advantages 845Touch-Screen Designs 845Evaluating Touch Technologies 848

Overall System Design 851Mechanical Considerations 851Physical Attributes 851Programming Considerations 852

Bibliography 853

4.23UNINTERRUPTIBLE POWER AND VOLTAGESUPPLIES (UPS AND UVS) 854

Introduction 854Uninterruptible Voltage Sources (UVS) 855Uninterruptible Power Supply (UPS) Features 856Networks and Buses 856Power Failure Classifications 857

Source Failure 857Equipment Failure (Inverter) 858Common Bus Branch (Load) Failure 860

System Components 861Rotating Equipment 861Batteries 862Static Inverters 863Bus Transfer Switches 865Protective Components 865

Standby Power Supply Systems 865Multicycle Transfer System 865Sub-Cycle Transfer System 866No-Break Transfer System 866

System Redundancy 866Specifications 866Bibliography 867

4.24WORKSTATION DESIGNS 868

Classification of Workstations 868Hardware Architecture 868Function 869

Hardware Components 870Software Features 871Selection of Correct Platform 871Comparing Various Operating Platforms 872

Cost 872Reliability 872Manageability and Administration 873Scalability 873Security 873Error Handling 873Integration of Software and Hardware 873Openness 874

Conclusions 874Glossary 874Bibliography 875

© 2006 by Béla Lipták

580

4.1 Annunciators and Alarms

J. A. GUMP (1972, 1985) B. G. LIPTÁK (1995, 2005)

E. M. MARSZAL (2005)

Types: A. Audiovisual Annunciators: integral, remote, and semigraphic systems with audibleand visual display and electromechanical (relay) or solid-state (semiconductor)designs

B. Recording Annunciators: integral, solid-state systems with recorded printout C. BargraphsD. Vocal Annunciators: integral, solid-state systems with audible command message

Cost per Alarm Point: Integral cabinet costs $75 to $175; remote system, $125 to $250; semigraphic system,$125 to $250; recording annunciator or annunciator with communications will addabout 30% to the cost per point. These figures are budgetary in nature (± 20%), anda number of variables can affect the price. These factors include system size, windowsize, number of alarm points per board, field contact voltages, type of lamp, com-munications options, and required certifications (e.g., Class I, Div. 2, etc.).

Partial List of Suppliers: 4B Components Ltd. (A) (www.go4b.com)Acromag Inc. (A) (www.acromag.com)Adaptive Micro Systems Inc. (A) (www.adaptivedisplays.com)Advotech Inc. (D) (www.advotechcompany.com)Ametek Power Instruments (A, B, mosaic graphic) (www.ametekpower.com)Barnett Engineering Ltd. (A) (www.barnett-engg.com)Beta Calibrators div. Hathaway Process Instrumentation Corp. (A, B) (www.the-esb.com)CAL Controls Inc. (www.cal-controls.com)CEA Instruments Inc. (www.ceainstr.com)Cole-Parmer Instrument Co. (www.coleparmer.com)CTC Parker Automation (www.ctcusa.com)Daytronic Corp. (A) (www.daytronic.com)Devar Inc. (A) (www.devarinc.com)Draeger Safety Inc. (www.draeger.com/gds)Druck Inc. (www.pressure.com)Fisher Controls International Inc. (A) (www.fisher.com)Flow Tech Inc. (www.flowtechinc.com)Fluid Components International (www.fluidcomponents.com)Foxboro Co. (A) (www.foxboro.com)GE Kaye div. General Electric Co. (A)General Monitors (www.generalmonitors.com)Graybar Electric Co. (www.graybar.com)

ImageVision Inc. (www.imagevisioninc.com)Mauell Corp. (A) (www.mauell-us.com)Matrikon Inc. (www.matrikon.com)Metrix-PCM/Beta (A) (www.metrix1.com)Moore Industries Inc. (www.miinet.com)North American Manufacturing Co. (A) (www.namfg.com)Oceana Sensor (www.oceanasensor.com)Phonetix Inc. (www.sensaphone.com)Powers Process Control, A Unit of Mark Controls Corp. (A)(www.powerscontrols.com)

Precision Digital Corp. (www.predig.com)

LAL

TAH

PAHL

Low levelalarm

High temperaturealarm

High and lowpressure alarm

Flow sheet symbol

© 2006 by Béla Lipták

Honeywell Industry Solutions (www.iac.honeywell.com)

4.1 Annunciators and Alarms 581

ProSys Inc. (www.prosysinc.com)Puleo Electronics Inc. (A) (www.annuciator.com)Raco Manufacturing and Engineering (www.racoman.com)Robicon div. High Voltage Engineering Corp. (A) (www.robicon.com)Ronan Engineering Co. (A, B, mosaic graphic) (www.ronan.com)Schneider Electric/Square D (www.squared.com)Scott Aviation div. Tyco Inc. (A) (www.tycoelectronics.com)Seekirk Inc. (D) (www.seekirk.com) Sierra Monitor (www.sierramonitor.com)Swanson Engineering & Manufacturing (A) (www.amtonline.org)Texmate Inc. (A) (www.texmate.com)Thermo Brandt Instruments (www.brandtinstruments.com)Tips Inc. (www.tipsweb.com)Transmation Inc. (D) (www.transmation.com)Trip-A-Larm (A) (www.modicon.control.com)Visi-con div. Visicomm Industries (A) (www.alarmpanels.com)Vorne Industries Inc. (A) (www.vorne.com)Western Reserve Control (www.wrcakron.com)White Electronic Designs Corp. (C) (www.motionnet.com)Wilkerson Instrument Co. (A) (www.wici.com)Zetron Inc. (A) (www.zetron.com)

In addition to this section, safety alarm systems are discussedin several other parts of this handbook, particularly in connec-tion with DCS and CRT systems in Chapter 4 and PLCs inChapter 5. The subject of process alarm management is sepa-rately covered in Section 1.6. This section concentrates ondedicated, conventional annunciators and other alarm devices.

INTRODUCTION

The purpose of an alarm system (annunciator) is to bringattention to an abnormal or unsafe operating condition in theplant. Traditional annunciators used discrete alarm modulesfor this purpose. These dedicated hardware units are dimin-ishing in numbers yet are still used in installations wheresimplicity is desired or where separation from the basic pro-cess control system is required for safety reasons.

In some installations where traditional units have beenreplaced by PLC- or DCS-based annunciators, the recogni-tion of and response to alarm conditions have deterioratedbecause on computer screens they are not very visible andcan go unnoticed. In addition, because of the low incrementalcost of adding new alarm points, excessive numbers of alarmsbeen configured. Because of the floods of alarms, an impor-tant new component of safety system design is alarm ratio-nalization and alarm management (Section 1.6).

It is possible to connect conventional annunciators as front-end devices to DCS systems through various communicationlinks. There is a wide variety of such links available, rangingfrom serial links employing MODBUS protocol to Ethernetlinks utilizing Object Linking and Embedding (OLE) for Pro-cess Control (OPC). This hybrid solution adds the visibility,reliability, and built-in redundancy of dedicated annunciatorsto the flexibility and record-keeping convenience of DCS-based systems.

More sophisticated annunciator designs can incorporatebargraph-type displays, color computer graphics, and event-recording or data-logging systems. Much of the new devel-opment in annunciator system designs involves enhancedmethods of communication and reporting. As a consequence,annunciator status can be logged and used for tasks such asalarm management and abnormal event analysis.

Graphic displays can be dynamic, where flow in pipes isshown by actual movement, and CRT displays can concen-trate large amounts of information into a single display.Figure 4.1a illustrates such a display, where the CRT displays

FIG. 4.1a The overall safety status of the plant can be displayed on a singleCRT.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16A

B

C

D

E

F

G

H

I

J

K

L

Area 3-H of plant layoutis flashing in coded color

Color code:1-Combustibles2-Smoke3-Fire4-High pressure

5-CO6-SO27-Vinyl chloride

© 2006 by Béla Lipták

582 Control Room Equipment

the plot plan of the plant as the background. Such a plot plancan be separated into small square segments, so that if anunsafe condition is detected in a particular segment, the cor-responding square can start flashing in the color that corre-sponds to the type of safety problem detected. This type ofannunciator display is easily and quickly comprehended andcan provide a summary report on a large number of safetyconditions in an efficient manner.

HISTORY

The term “drop” was initially applied to individual annunci-ator points, from which we may infer that annunciator sys-tems developed from paging systems of the type used inhospitals and from call systems used in business establish-ments to summon individuals when their services are needed.These systems consisted of solenoid-operated nameplatesthat dropped when deenergized. The drops were grouped ata central location and were energized by pressing an electricalpushbutton in the location requiring service. The system alsoincluded an audible signal to sound the alert.

Similar systems were used for fire and burglar alarms. Thedrops were operated either by manual switches or by troublecontacts that monitored thermal and security conditions invarious building locations. The use of these systems in thechemical processing industry was a logical development whenalarm switches became available.

This development, however, was preceded by explosion-proof, single-station annunciators that were designed to oper-ate in the petroleum and organic chemical process plantsconstructed immediately before, during, and after World WarII. They were usually installed on control panels locatedeither outdoors near the process unit or in local controlhouses. A drop-type system could not be used in these loca-tions because they were electrically hazardous.

By the late 1940s, centralized control rooms wereintroduced. Drop-type annunciators were suited for these

general-purpose central control rooms. However, morecompact, reliable, and flexible annunciators were subse-quently introduced.

In the early 1950s, the plug-in relay annunciator was devel-oped. Instead of utilizing solenoid-operated drops, it used elec-trical annunciator circuits with small telephone-type relays tooperate alarm lights and to sound a horn when abnormal con-ditions occurred. The alarm lights installed in the front of theannunciator cabinets were either the bull’s-eye type or back-lighted nameplate designs.

The annunciators were compact, reliable, and because ofthe hermetically sealed relay logic modules, they could alsobe mounted in certain hazardous areas in addition to thegeneral-purpose control rooms. In order to be mounted inClass 1 explosion-proof areas, they required purging(Figure 4.1b). Miniaturization of instruments and the use ofgraphic control panels initiated the development of remoteannunciator systems, consisting of a remotely mounted relaycabinet connected to alarm lights installed at appropriatepoints in the graphic or semigraphic diagram.

Solid-state annunciator systems with semiconductorlogic modules were developed in the late 1950s. Thesepermitted additional miniaturization and lowered both theoperating power requirements and the amount of heatgenerated. The semigraphic annunciator was introducedin the late 1960s and fully utilized the high-density capa-bilities of solid-state logic. It has permitted the designs ofvery compact and flexible semigraphic displays in controlcenters.

With the spread of digital communication networks andmicroprocessor-based smart instruments, the number ofalarm points increased, their management as a function ofimportance (Section 1.6) became a separate field, and theirdisplays were further miniaturized. These days, with thegreater availability and reliability of integrated circuit logiccomponents, alarms can be displayed on handheld tools inthe field, on computer screens at workstations, or on CRTsin DCS systems.

FIG. 4.1b Local annunciators were available in explosion-proof designs or were mounted in air-purged enclosures when mounted in Class 1 areas.(Courtesy of Bebco Industries.)

SupplierOptional pressure loss alarm switch

or electrical power control unit

Venturi orifice

Enclosurepressure indicator

Reference out

Required enclosureprotection vent

Enclosurewarning

nameplate

Installer

Purginggas supply

Rapid exchange pressurecontrol filter regulator

Rapid exchangepressure gauge

Rapid exchangecontrol valve

Supply in ProtectedenclosureEnclosure pressure

control valve

© 2006 by Béla Lipták

4.1 Annunciators and Alarms 583

PRINCIPLES OF OPERATION

The annunciator system consists of multiple alarm points. Eachalarm circuit includes a trouble contact (alarm switch), a logicmodule, and a visual indicator (Figure 4.1c). The individualalarm points are operated from a common power supply andshare a number of annunciator system components, includingan audible signal generator (horn), a flasher, and acknowledgeand test pushbuttons. In normal operation the annunciator sys-tem and individual alarm points are quiescent.

The trouble contact is an alarm switch that monitors aparticular process variable and is actuated when the variableexceeds preset limits. In electrical annunciator systems it isnormally a switch contact that closes (makes) or opens(breaks) the electrical circuit to the logic module and therebyinitiates the alarm condition. In the alert state, the annunciatorturns on the visual indicator of the particular alarm point, theaudible signal, and the flasher for the system. The visualindicator is usually a backlighted nameplate engraved withan inscription to identify the variable and the abnormal con-dition, but it can also be a bull’s-eye light with a nameplate.The audible signal can be a horn, a buzzer, or a bell.

The flasher is common to all individual alarm points andinterrupts the circuit to the visual indicator as that point goesinto the alert condition. This causes the light to continue toflash intermittently until either the abnormal conditionreturns to normal or is acknowledged by the operator.

The horn acknowledgment pushbutton is provided witha momentary contact: when it is operated, it changes the logicmodule circuit to silence the audible signal, stop the flasher,and turn the visual indicator on “steady.” When the abnormalcondition is corrected, the trouble contact returns to normal,and the visual indicator is automatically turned off.

The lamp test pushbutton with its momentary contact testsfor burned-out lamps in the visual indicators. When activated,

the pushbutton closes a common circuit (bus) to each visualindicator in the annunciator system, turning on those lampsthat are not already on as result of an abnormal operatingcondition.

Operating Sequences

A wide variety of sequences are available to define the oper-ation of an individual alarm point in the normal, alert,acknowledged, and return-to-normal stages in the annuncia-tor sequence. The five most commonly used annunciator

code designation of the Instrumentation, Systems, and Auto-mation Society (ISA). These sequences were specified by theISA-recommended practice RP-18.1, which has since beenrevised and updated into standard ISA 18.1.

Because the old sequence designations are still used insome plants, some of their more common versions are listed

nations of the present standard ISA 18.1 will also be discussedbelow.

The Old ISA Sequence Designations ISA Sequence 1B, alsoreferred to as flashing sequence A, is the one most frequentlyused. The alert condition of an alarm point results in a flashingvisual indication and an audible signal. The visual indicationturns off automatically when the monitored process variablereturns to normal.

ISA Sequence 1D (often referred to as a dim sequence)is identical to Sequence 1B except that ordinarily the visualindicator is dim rather than off. A dimmer unit, common tothe system, is required. Because all visual indicators arealways turned on—for dim (normal), flashing (alert), orsteady (acknowledged)—the feature for detecting lamp fail-ure is unnecessary.

ISA Sequence 2A (commonly referred to as a ring-backsequence) differs from Sequence 1B in that followingacknowledgment the return-to-normal condition produces adim flashing and an audible signal. An additional momen-tary contact reset pushbutton is required for this sequence.Pushing the reset button after the monitored variable hasreturned to normal turns off the dim flashing light and silen-ces the audible signal. This sequence is applied when theoperator must know if normal operating conditions have beenrestored.

ISA Sequence 2C is like Sequence 1B except that thesystem must be reset manually after operation has returnedto normal in order to turn off the visual indicator. Thissequence is also referred to as a manual reset sequence and,like Sequence 2A, requires an additional momentary contactreset pushbutton. Sequence 2C is used when it is desirableto keep the visual indicator on (after the horn has beensilenced by the acknowledgment pushbutton) even thoughthe trouble contact has returned to normal.

ISA Sequence 4A, also known as the first-out sequence,is designed to identify the first of a number of interrelated

FIG. 4.1cThe main components of a traditional annunciator system.

Power supply

Com

mon

syst

emco

mpo

nent

sIn

divi

dual

alar

m p

oint

s

Lamptest

Flasher

Visualindicators

Logicmodules

Troublecontacts

(process alarmswitches)

Audiblesignal

generator(horn)

Hornacknowledge

© 2006 by Béla Lipták

in Table 4.1d and also described below. The sequence desig-

sequences are shown in Table 4.1d, identified by the original

584 Control Room Equipment

variables that have exceeded normal operating limits. Anoff-normal condition in any one of a group of process vari-ables will cause some or all of the remaining conditions inthe group to become abnormal. The first alarm causes flash-ing, and all subsequent points in the group turn on the steadylight only. This sequence monitors interrelated variables.The visual indication is turned off automatically when con-ditions return to normal after acknowledgment.

The New ISA Sequence Designations In the updated annu-nciator standard ISA 18.1, the sequence designations aredifferent, as shown in Table 4.1e. The most widely usedsequence, the basic flashing sequence, is now designated as

sequence A. The sequence designations in ISA 18.1 use thefollowing letter codes:

A = Automatic ResetM = Manual ResetR = RingbackF = First-out

Therefore, using the ISA 18.1 sequence designations A-13means that the annunciator has automatic reset and is pro-vided with Option 13, which suggests the presence of a dimlamp monitor. For definitions of less frequently used

TABLE 4.1dThe Old ISA Designations of Annunciator Sequences

ISA Code forthe Sequence

AnnunciatorCondition

Process Variable Condition(Trouble Contact) Visual Indicator Audible Signal Use Frequency

IB Normal Normal Off Off 55%

Alert Abnormal Flashing On

Acknowledged Abnormal On Off

Normal again Normal Off Off

Test Normal On Off

ID Normal Normal Dim Off 1%

Alert Abnormal Flashing On

Acknowledged Abnormal On Off

Normal again Normal Dim Off

2A Normal Normal Off Off 4%

Alert Abnormal Flashing On

Acknowledged Abnormal On Off

Return to normal Normal Dim flashing On

Reset Normal Off Off

Test Normal On Off

2C Normal Normal Off Off 5%

Alert Abnormal Flashing On

Acknowledged Abnormal On Off

Return to normal Normal On Off

Reset Normal Off Off

Test Normal On Off

4A Normal Normal Off Off 28%

Alert Abnormal

Initial Flashing On

Subsequent On Off

Acknowledged Abnormal

Initial On Off

Subsequent On Off

Normal again Normal Off Off

Test Normal On Off

All others 7%

© 2006 by Béla Lipták

sequences, refer to ISA 18.1.

4.1 Annunciators and Alarms 585

Optional Operating Features Annunciator sequences maybe initiated by alarm switch trouble contacts that are eitheropen or closed during normal operations. These are referredto as normally open (NO) and normally closed (NC)sequences, respectively, and the ability to use the same logicmodule for either type of trouble contact is called an NO-NCoption. It is important because some alarm switches are avail-able with either an NO or an NC contact but not with both,and therefore without the NO-NC option in the logic moduletwo types of logic modules would be required. The logicmodule is converted for use with either form of contact by aswitch or wire jumper connection.

The relationship between the NO and NC sequencesrequired in the logic module to match the various troublecontacts and analog measurement signal actions is shown inFigure 4.1f. A high alarm in a normally closed annunciator

system requires a normally closed trouble contact operatedby a direct-acting analog input.

If an increase in the measured variable results in anincreased output signal, the detector is direct acting; if theoutput signal is reduced, it is a reverse-acting sensor. If thetrouble contacts in all alarm switches in the plant are standard-ized such that normal operating conditions will cause all troublecontacts to be NC (or NO), the required annunciator sequence

Annunciator systems are fail safe or self-policing if theyinitiate an alarm when the logic module fails because of relaycoil burnout. The feature is standard for most NO and NCannunciator sequences; annunciators using NC trouble con-tacts are also fail safe against failures in the trouble contactcircuit.

The lock-in option locks in the alert condition initiatedby a momentary alarm until the horn acknowledgment buttonis pushed, preventing loss of a transient alarm condition untilthe operator can identify it. The logic module is usuallychanged from lock-in to non-lock-in operation by either addi-tion of a wire jumper or operation of a switch. The lock-infeature is useful for monitoring unstable or fluctuating processvariables.

Test and Repeater Features The test feature in a standardannunciator serves only to test for burned-out lamps in thevisual indicators. The operational test feature provides a testof the complete annunciator system, including logic modules,lamps, flasher, audible signal, and acknowledgment circuits.The operational test circuit usually requires an additionalmomentary contact pushbutton, which can replace the regularlamp test pushbutton.

The logic module of relay-type annunciators may havespare (electrically isolated) auxiliary contacts that can operateshutdown and interlock systems when alarm conditionsoccur. The auxiliary contacts are wired to terminal blocks inthe annunciator cabinet for connection to external circuitry.

TABLE 4.1eThe New ISA Designations of Annunciator Sequences as Defined by ISA Standard ISA 18.1

SequenceSignal Device Normal Alert

Condition-sensing Returns to Normal

Before Acknowledge AcknowledgeCondition-sensing Returns to Normal

Return to Normal Reset Remarks

A Visual Off Flash Flash On Off — Flasher memory

Audible Off On On Off Off —

A-5 Visual Off On On On Off — Memory

Audible Off On On Off Off —

A-4 Visual Off Flash Off On Off — Flasher

Audible Off On Off Off Off —

A-4-5 Visual Off On Off On Off —

Audible Off On Off Off Off —

A-13 Visual Dim Flash Flash On Dim — Memory—flasher

Audible Off On On Off Off — Continuous lamp test

FIG. 4.1f Logic trees for the NO and NC annunciator sequences.

Off-normal limit

Annunciator sequence

Sensor action

Off-normal limit

High alarm

Low alarm

High

NC

NC NC

Direct Direct ReverseReverse

NO

NO NO

Annunciator sequence

Sensor action

Trouble contact-“on shelf”

Trouble contact-“on shelf”

Low

NC

NC NC

Direct Direct ReverseReverse

NO

NO NO

© 2006 by Béla Lipták

is also NC (or NO), and Figure 3.1f need not be consulted.

586 Control Room Equipment

Repeater lights may be located away from the commonlogic module and serve to alert operators in other areas.Annunciator cabinet terminals for connecting these repeaterlights in parallel with the annunciator visual indicator areavailable.

It may also be desirable to actuate a horn in more thanone location. The electrical load of multiple audible signalsrequires an interposing relay, called a horn-isolating relay,operated by the logic modules. This relay has contacts ofadequate capacity to operate multiple audible signals. Horn-isolating relays may be installed either in the annunciatorcabinet or in a separate assembly.

Annunciator systems can be used for several operationalsequences without changing system wiring, and many logicmodules can supply more than one operational sequence.This multiple sequence capability is sometimes useful whenthe sequence has not yet been determined.

ANNUNCIATOR TYPES

The audiovisual annunciator can be packaged as an integral,remote, or semigraphic annunciator.

Integral Annunciator

The integral annunciator, a cabinet containing a group ofindividual annunciator points wired to terminal blocks forconnection to external trouble contacts, power supply, hornand acknowledge and test pushbuttons, is the most econom-ical of the various packaging methods available in terms ofcost per point. It is also the simplest and cheapest to install.

Two methods of packaging integral annunciators are illus-trated in Figure 4.1g. In the nonmodular type, plug-in logicmodules are installed inside the cabinet and connected toalarm windows on the cabinet door through an interconnectingwiring harness; in the modular type, individual plug-in alarmpoint assemblies of logic module and visual indicator aregrouped together.

The nonmodular and modular cabinet styles are bothdesigned for flush panel mounting with the logic modulesand visual indicators accessible from the front. Electricalterminals for the external circuitry are located in the rear ofthe cabinet and are accessible from the back.

Integral annunciators are used on nongraphic and onsemigraphic control panels in which physical association ofthe visual indicators with a specific location in the graphic

FIG. 4.1gIntegral annunciator cabinets are available in modular (right) and nonmodular (left) construction.

Rear view of terminal enclosure(1) Nonmodular

Visualindicators

Front view with door open

Relay type logic modules

Back lightedname plates

Front view-door closed

Solid statealarm module

Lamp module Window bezel

Pushbuttonstations

Mounting clampAlarm point

terminals

Power and systemfunction terminals

Rear view with cover removed

(2) Modular typeFilter

module

Front view

© 2006 by Béla Lipták

4.1 Annunciators and Alarms 587

process flow diagram is not required. Integral annunciatorcabinets occupy more front but less rear panel space than theequivalent remote designs. The electrical terminals are in ageneral-purpose enclosure at the rear of the cabinet, and troublecontacts can be wired directly to them, thus eliminating theneed for and resultant costs of intermediate terminal blocksfor trouble contact wiring.

An advantage of the modular-type cabinet is that it canbe expanded by enlargement of the panel cutout and by theaddition of modular alarm point assemblies. Nonmodular cab-inets cannot be expanded, and new cabinets must be installedto house additional alarm points. Consequently, one shouldinclude more spare points when specifying the cabinet sizefor a nonmodular system. The modular cabinet is also morecompact, takes up less panel space, and has a greater visualdisplay area per point than the nonmodular design.

Figure 4.1h illustrates various configurations of visualindicators that can be supplied with integral annunciator cab-inets. Many of these groupings are also available in single-unit assemblies for remote annunciator systems.

Remote Annunciator

The remote annunciator differs from the integral annunciatorin that the visual indicators are remote from the cabinet orchassis containing the logic modules. Remote annunciatorswere developed to allow the visual indicators to be placed intheir actual process location in the graphic flow diagram.

They are used with full and semigraphic control panels andin nongraphic applications in which an integral annunciatorcabinet may require too much front panel space. Figure 4.1i

FIG. 4.1h Integral annunciator window configurations. 1. Modular single-point annunciator. 2. Modular double-point annunciator. 3. Modular triple-point annunciator. 4. Modular quadruple-point annunciator. 5. Nonmodular single-point. 6. Nonmodular triple-point. 7. Nonmodular single-point with small nameplate.

(1)

(2) (4)

(3)

(5)

(6)

(7)

FIG. 4.1i General purpose, remote annunciator cabinets.

(1) Chassis with general purpose enclosure

(2) Chassis

© 2006 by Béla Lipták

588 Control Room Equipment

illustrates a remote annunciator chassis with optional cabinetenclosure. The chassis contains spare positions for plug-in logicmodules and a system flasher. Auxiliary system modules, suchas horn-isolating relays, may also be plugged into the logicmodule chassis positions.

The chassis and cabinet enclosure are designed for wallor surface mounting behind the control panel. Each chassisposition has terminal points for connecting the visual indi-cator and trouble contact. In addition, the chassis has a systemterminal block for connecting electrical power, horn, flasher,and acknowledge and test pushbuttons.

The disadvantages of remote annunciators include higherequipment and installation costs and an increased require-ment for back panel space. In addition, the wiring connec-tions from field trouble contacts must be made to intermediate

terminal blocks rather than directly to the cabinet terminals,as with the integral annunciator.

These terminal blocks, the terminal enclosure, and therequired wiring result in higher installation costs and extraspace requirements. Finally, the remote annunciator is diffi-cult to change, and modification costs of remote systems aresubstantially higher than those of the integral type, partiallybecause spare visual indicators cannot be installed initially.

Semigraphic Annunciator

The semigraphic annunciator developed in the late 1960scombines some of the advantages of the integral annunciatorwith the flexibility to locate visual indicators at appropriatepoints in a graphic flow diagram. Figure 4.1j illustrates asemigraphic annunciator.

FIG. 4.1j Construction of a typical semigraphic annunciator, showing the plug-in modules,the lamp nesting panel, and the arrangement of the terminalblocks on the rear of the unit.

Replaceabletranslucent

drawing sheet

Lampnestingpanel

Terminals locatedunder rear cover

Annunciator logic-rack,plug-in modules and power supplies

Knockouts

Aluminumhousing

Removable transparentplastic protective panel

Lamps

Detailed view of the grid(lamp nesting panel)

S15 S14 S13 S12 S11 S10 S9 S8 S7 S6 S5 S4 S3 S2 S1 FC FC FC

S15 S14 S13 S12 S11 S10 S9 S8 S7 S6 S5 S4 S3 S2 S1 FC FC FC

S15 S14 S13 S12 S11 S10 S9 S8 S7 S6 S5 S4 S3 S2 S1 FC FC FC

A15 A14 A13 A12 A11 A10 A9 A8 A7 A6 A5 A4 A3 A2 A1

B15 B14 B13 B12 B11 B10 B9 B8 B7 B6 B5 B4 B3 B2 B1

G15 G14 G13 G12 G11 G10G9 G8 G7 G6 G5 G4 G3 G2 G1 FC FC FC

G15 G14 G13 G12 G11 G10 G9 G8 G7 G6 G5 G4 G3 G2 G1 FC FC FC

G15 G14 G13 G12 G11 G10 G9 G8 G7 G6 G5 G4 G3 G2 G1 FC FC FC

1-15

1-14

1-13

1-12

1-11

1-10 1-9

1-8

1-7

1-6

1-5

1-4

1-3

1-2

1-1

2-15

2-14

2-13

2-12

2-11

2-10 2-9

2-8

2-7

2-6

2-5

2-4

2-3

2-2

2-1

3-15

3-14

3-13

3-12

3-11

3-10 3-9

3-8

3-7

3-6

3-5

3-4

3-3

3-2

3-1

4-15

4-14

4-13

4-12

4-11

4-10 4-9

4-8

4-7

4-6

4-5

4-4

4-3

4-2

4-1

12 10 8

11 8 7 11 9 7 11 9 7 11 9 7 11 9 7

12 10 8 12 10 8 12 10 8 12 10 8

POS.

POS.

POS.

POS.

FC FC FC F2 F1 FR R K T C (+) (−)HV CN L1L2LC

FC FC FC F2 F1 FR R K T C (+) (−)HV CN L1L2LC

FC FC FC F2 F1 FR R K T C (+) (−)HV CN L1L2LC

Main bus terminals

(Accessory)

Main bus terminals(Power)

Window position numbers(4 high by 15 wide)

Pin numbers of socket

Pin numbers of socket

To signal terminalsof row 4 wired for

transformers

Rear view showing terminal block arrangement

© 2006 by Béla Lipták

4.1 Annunciators and Alarms 589

It consists of a cabinet containing annunciator logic mod-ules wired to visual indicators placed in a 3/4-inch (18.75-mm)lamp insertion matrix grid forming the cabinet front. Thesemigraphic display is placed between the lamp grid and atransparent protective cover plate, and the visual indicatorsare positioned to backlight alarm name plates located in thegraphic display.

The protective cover and lamp grid are either hinged orremovable to provide access to the logic module and lampassemblies. The lamp assemblies are connected to intermedi-ate terminals located behind the lamp grid, and the terminalsin turn are connected to the logic modules. Terminal pointsfor trouble contact wiring are in the back of the cabinet.

The semigraphic annunciator is flexible, and changes inthe annunciator system, graphic display, and related panelmodifications can be made easily and cheaply. It is practicalto prepare the graphic displays in the drafting room ormodel shop, thus protecting proprietary process informationof a confidential nature.

The graphic display has little or no effect on completingeither the annunciator or the control panel because it can beinstalled on site or at any time. The semigraphic annunciatorhas a high density of 40 alarm points per linear foot (0.3 m)and a solid-state rather than relay-type logic design. Powersupplies are self-contained in the semigraphic annunciatorcabinet.

Front panel layouts illustrating integral, remote, andsemigraphic annunciators are shown in Figure 4.1k. Integralsystems similar to the one shown at the left in the figure arenormally specified on nongraphic control panels. Thegraphic panel in the center contains a remote annunciator

with backlighted nameplates (shaded rectangles) and pilotlights (shaded circles) for visual indication. The remote sys-tem may also be used with miniature lamps in a semigraphicdisplay similar to the one shown at the right.

Recording Annunciators

Solid-state, high-speed, recording annunciators are availableto amend or substitute a printed record of abnormal eventsfor only visual and/or audible alarms. These systems printout a record of the events and identify the variable, the timeat which the alarm occurs, and the time at which the systemreturns to normal. They can also discriminate among a num-ber of almost simultaneous events and print them out in thetime sequence in which they occurred. A number of optionalfeatures, including secondary printers at remote locations,supplementary visual indication, and computer interfacing,are also available. The typical unit consists of logic, control,and printer sections.

The input status is continuously scanned. If a change inthe trouble contacts has occurred since the preceding scancycle, the central control places the exact time, the alarmpoint identification, and the new status of the trouble contact(normal or abnormal) into the memory and initiates the oper-ation of the output control unit (Figure 4.1l).

The output control unit accepts the stored informationand transfers it to the printer, which logs the event. Followingthis, the memory is automatically cleared of the data and isready to accept new information. In addition to or in placeof the printer (if a permanent record is not required), a CRTdisplay can serve as the event readout. Trouble contacts are

FIG. 4.1k Control panels with integral, remote, and semigraphic annunciators.

A T

A

T

Integral Remote Semigraphic

A

T

© 2006 by Béla Lipták

590 Control Room Equipment

connected to terminal points in the logic cabinet, and a cableconnects the cabinet and the printer.

A recording annunciator can perform more sophisticatedmonitoring than an audiovisual annunciator and is correspond-ingly more expensive on a per-point basis. System cost perpoint decreases as the system size increases. Higher equipmentcost, however, is offset in part by savings in control panel spaceand in installation costs. Recording annunciators are frequentlyused by the electrical power generating industry but may beapplied to advantage in any industrial process that must mon-itor large numbers of operating variables and analyze abnormalevents efficiently.

Vocal Annunciators

Vocal annunciators are unique in the type of abnormal audiblemessage they produce. The audible output is a verbal messageidentifying and describing the abnormal condition when itoccurs and repeating the message until the operator acknowl-edges the difficulty. The system continuously scans the trou-ble contacts, and when an abnormality is found, it turns ona flashing visual indicator and selects the optional properverbal message for broadcast.

The visual indicator is turned off by the system when thepoint returns to normal. The control unit also arranges themessages to be broadcast in the order in which the difficultiesoccur. In the event of multiple alarms, the second messageis played only after the first has been acknowledged. Theflashing visual indicator for each point, however, turns on

when the point becomes abnormal. The verbal message maybe broadcast simultaneously in the control room and relatedoperating areas, thus permitting personnel at the operatingunit to correct the problem immediately.

Relay-Type Annunciators

The basic element of this annunciator is an electrical relaywired to provide the logic functions required to operate aparticular sequence. Figure 4.1m illustrates some of the basicrelay designs.

At least two relays per logic module are necessary formost sequences. The relays are installed and wired in a plug-in assembly, which is the logic module for a single alarmpoint. The plug-in module assembly is usually hermeticallysealed in an inert atmosphere to prolong the life of the relaycontact. The sealing also makes the logic module acceptablein certain hazardous electrical areas.

Figure 4.1n is a semischematic electrical circuit for aremote system with sequence operation according to old ISASequence 1B (new Sequence A): Two logic modules areshown; one is in normally closed operation and the other isin normally open operation. The remote visual indicators foreach alarm point, the horn, the flasher, and the acknowledgeand test pushbuttons common to the system are also shown.Each logic module has two relays, A and B, shown in theirdeenergized state according to normal electrical convention.The operation of these circuits during the various stages ofsequence operation is as follows:

Normal The trouble contact of the NC alarm point is wiredin series with the A relay coil at point terminals H and NC.In the normal condition, the trouble contact is closed, relays

FIG. 4.1l Functional block diagram of a digital, recording annunciator withits printer, which can be replaced by a CRT.

Field mounted

NO or N

C

trouble

contacts

Input

status

logic

Scan

control

Central

control

Memory

Digital

clock &

calendar

Output

control

Printer

FIG. 4.1mStandard electro-mechanical relay structures include: A) the clapper-type, B) the phone-type, C) the balanced-force, and D) the Reedrelay.

Armature

Armature

SpacerForm

BForm

A

Coil

Coil

Coil

Spring

Permanent magnet

GlasscapsulePivot

A B

DC

CoilNS

© 2006 by Béla Lipták

4.1 Annunciators and Alarms 591

A and B are energized, and all A and B relay contacts are inthe state opposite that shown.

Relay A is energized from power source H through theclosed trouble contract, relay coil A, resistor R, terminal K,

and jumper to the neutral side of the line N. Relay B is alsoenergized from H through the normally closed acknowledgepushbutton to terminal C, closed contact A2, and relay coilB, to N. Relay B is locked in by its own contact B2, which

FIG. 4.1nSemischematic diagram of a relay-type annunciator designed for ISA new sequence A (old sequence 1B), which sequences are describedin Tables 4.1d and 4.1e.

KNFTRCH

KNFTRCH

KNFTRCH

Internalwiring

ofplug-in

Internalchassiswiring

Fieldwiring

Flasher Logic module Logic module

F2

F1

M

A1A

A5

A7

A6

B6

B5

B2

B3 B4B

A2 A3 A4B1

A1A

A5 B5

A7 B6

A6 B2 A2 A3 A4

B3 B4

B1

B

9 6 4 7 8 10 11 9 2 1 5 7 4 3 6 8 10 11 9 2 1 5 7 4 3 6

R R

Resis-tor

SL H L B ANC NO SL H L B ANC NO Typical set of point terminals

No troublecontact

Main busterminals

Lock-injumper

NC Troublecontact

No auxiliarycontact

terminals

Remote lamp

Lock-injumper

LL

“H” wire commonto allsignallamps

Power supply

Audible silence(acknowledge)

T R CLamptest

Audiblesignal

NH

Condition

NormalAlertAudible silenced(acknowledged)Normal againLamp test

TroublecontactNormalAbnormalAbnormal

NormalNormal

OffFlashingSteady−on

OffSteady−on

Signallamps

Audiblesignal

OffOnOff

OffOff

“A” relay “B” relay

EnergizedEnergized

EnergizedEnergized

EnergizedDeenergizedDeenergized

EnergizedEnergizedDeenergized

Operational sequence

© 2006 by Béla Lipták

592 Control Room Equipment

closes when relay B is energized. The visual indicator isturned off by open contact A5. The audible signal and theflasher motor are turned off by open contacts A3 and B4 inthe same circuit.

Alert The trouble contact opens, deenergizing relay A and

The visual indicator is turned on, flashing through circuit H,lamp filament, terminal L, closed contacts A5 and B6, bus F,and flasher contact F1, to N. The flasher motor is driventhrough circuit C, closed contacts A3 and B3, R bus, and theflasher motor to N, and the audible signal is turned on by thesame circuit.

Acknowledged Relay B is deenergized by operating (open-ing) the momentary contact horn acknowledgment pushbuttonand is locked out by open contact A2. All B relay contacts

indicator is turned on steady through closed contact B5 to Nand is disconnected from flasher contact F1 by open contactB6. The flasher motor and audible signal are turned off by thehorn acknowledgment pushbutton and remain off as a resultof open contact B3.

Normal Again When the variable condition returns to nor-mal, the trouble contact closes to energize relay A, the visualindicator is turned off by open contact A5, relay B is ener-gized by closed contact A2, and all circuits are again in thestate described under normal.

Lamp Test The lamp test circuit operates the visual indi-cators of only those alarm points that are in the normalcondition. The circuit is completed through power source H,lamp filament, terminal L, closed contact A6, bus T, andnormally open momentary contact lamp test pushbutton, toN. Closing the lamp test pushbutton to N completes thecircuit and lights the visual indicators. Alarm points that arein the off-normal condition (either alert or acknowledged) donot operate because their A relays are deenergized and theA6 contact is open. The visual indicators of these abnormalalarm points are already turned on (either flashing or steady)through the operation of the alarm sequence.

Lock-In The lock-in feature operates to prevent an annun-ciator alert condition (caused by a momentary alarm) fromreturning to normal until the horn acknowledgment button ispushed. Point terminals H and SL are jumpered to providethe lock-in feature (see Figure 4.1n). When the trouble con-tact opens, the A relay is deenergized, and power source His applied to the N side of the relay through closed contactsA1 and B1.

The power is dissipated through resistor R, terminal K,and jumper to N. If the trouble contact returns to normal,relay A will remain deenergized because potential H is onboth sides of the coil. If the acknowledgment button ispushed before the trouble contact closes again, relay B will

be deenergized, opening contact B1 and the lock-in circuit,thus permitting the system to return automatically to normalwhen the trouble contact closes.

If the acknowledgment button is pushed after the troublecontact has reclosed, contact B1 opens momentarily, allowingthe A relay to reenergize. Contact A1 opens, and the circuitsare reestablished in their normal operating state.

Operational Test Full operational test is incorporated in theannunciator sequence shown by replacement of the jumperconnection between main bus terminals K and N with anormally closed momentary contact pushbutton, which whenpushed opens all annunciator circuits, thus initiating the alertcondition of all alarm points in the normal condition.

Auxiliary Contacts Normally closed contact A7 connectedto point terminals A and B is available for auxiliary controlfunctions.

Relay Fail-Safe Feature Two parallel circuits, one consist-ing of closed contact A3 and open contact B3 and the otherof open contact A4 and closed contact B4, operate an alertsignal when there is a failure of either the A or the B relaycoil. A failure of the former initiates a normal alert in the sameway as the trouble contact. A failure of the B relay turns onthe audible signal through closed contacts A4 and B4.

Normally Open Trouble Contacts The annunciator sequenceand features described for NC trouble contacts operate inessentially the same way when NO contacts are used. In theNO system, however, the trouble contact is wired in parallelwith the A relay coil to point terminals H and NO, and a wirejumper is installed between point terminals H and NC. Nor-mally, the trouble contact is open and the A relay is energizedfrom terminals H and jumper to terminal NC. In the alertcondition, the trouble contact closes to deenergize the A relayby applying power source H to the N side of the relay.

Electromechanical relays are available for use with avariety of AC and DC voltages, but 120 AC, 50 to 60 Hz,and 125 DC are the most popular. Power consumption of thelogic modules is normally less than 10 voltamperes (AC) and10 watts (DC). Special low-drain and no-drain logic modulesare available; these consume no power during normal oper-ation. Visual indicators consume different amounts of power,depending on the type. Small bull’s-eye lights and back-lighted nameplates use approximately 3 watts, whereas largeunits require 6 to 12 watts, depending on whether one or twolamps are used.

Electromechanical annunciator systems are reliable andmay be used at normal atmospheric pressures and ambienttemperatures in the 0 to 110°F (–17.8 to 43.3°C) range. Theyare not position sensitive. They will generate a substantialamount of heat during plant shutdown when a large numberof points are askew, and therefore power should be discon-nected during these periods. The principal disadvantages of

© 2006 by Béla Lipták

returning all A relay contacts to the state shown in Figure 4.1n.

are returned to the state shown in Figure 4.1n. The visual

4.1 Annunciators and Alarms 593

the relay-type annunciator are size, power consumption, andheat generation.

Solid-State Annunciators

A solid-state logic module consists of transistors, diodes, resis-tors, and capacitors soldered to the copper conductor networkof a printed circuit board supplying the required annunciatorlogic functions. The modules terminate in a plug-in printedcircuit connector for insertion into an annunciator chassis; theymay also contain mechanical switching or patching devices toprovide lock-in and NO-NC options.

remote system with ISA Sequence 1B. The logic moduleshown is in normally closed operation. Remote lamps for twopoints and a flasher-audible module, speaker, and acknowl-edge and test pushbuttons common to a system are alsoincluded. Switch S1 is the NO-NC option switch and is shownin the NC operating position. Switch S2 is the lock-in optionswitch and is shown in the lock-in position. The followingdescription uses negative logic, i.e., a high equals a negativevoltage, whereas a low is approximately 0 volts.

Normal The trouble contact of the NC alarm point is con-nected to an input filter circuit consisting of resistors R13and R50 and capacitor C1. This provides transient signalsuppression as well as voltage dropping. The slide switch S1connects the trouble contact and filter network to resistor-R14. In this state transistor T1 is conducting, causing the fullnegative voltage to be dropped across resistor R17, resultingin a low voltage at the bottom end of resistor R20. TransistorsT2 and T3 are the active elements of the input memory andare roughly equivalent to the A relay of an electromechanicalmodule (see Figure 4.1n).

The base of T2 has four inputs, including resistor R20,either directly from the trouble contact in NO operation orfrom the collector of T1 in NC operation; resistor R19 witha locking signal from the alarm memory transistor T5; resis-tor R28 and capacitor C2, which form a regenerative feed-back from T3; and resistor R15 from the test circuit. Thebase of T3 has one input, resistor R29 from the collector ofT2. In normal operation, all four inputs to the base of T2 arelow, T2 is not conducting, and T3 is conducting. Conversely,when a high signal is present at any one of the four inputsto the base of T2, T2 conducts and T3 turns off.

Transistors T4 and T5 are the active elements of the alarmmemory and are approximately equivalent to the B relay ofan electromechanical module. T4 and T5 together with biasresistors R30 and R33 and cross-coupling resistors R31 andR32 form a bi-stable (flip-flop). In normal operation T4 is offand T5 conducts. The upper end of capacitor C4 is connectedto the collector T2. When T2 is off, its collector is at a highand capacitor C4 will change from top to bottom, minus toplus. Transistor T7 is a high-capacity lamp amplifier and T6is its preamplifier. In normal operation the base of T6 is highand T6 is on, T7 is off, and the visual indicator is off.

Before completion of the description of the normal con-dition, the operation of the flasher-audible module in

The first is a 3-Hz unit generating a signal that is amplifiedand supplied to the logic modules through the Fl bus. Thesecond is a 700-Hz oscillator generating a signal that is ampli-fied and supplied to the audible signal through the R bus.

The audible signal is a permanent magnet-type trans-ducer (speaker) that converts the electrical energy intosound. Initiated by an audio oscillator, the active elementsof which are transistors T1 and T2, these transistors togetherwith passive components (capacitors C1 and C2 and diodesD3 and D4) form an unstable multivibrator when an inputis present on the FR bus. In the normal conditions there isno FR signal, the voltage necessary to turn on transistor T1is missing, and the oscillator will not operate. This is thenormal, or quiescent, condition.

Alert The trouble contact opens and the base of T1becomes low, turning off T1. This action produces a high onthe base of T2 through R20, which turns on T2 and turns offT3. The negative end of C4 is clamped to common throughT2, causing a positive pulse at the base of T5 through diodeD12, turning T5 off and T4 on. With T2 conducting, the baseof T6 becomes low through resistor R6, and with T5 off theclamp on the flasher signal is removed through diode D4 atthe junction of R1 and R2. The flasher source provides analternating high and low voltage at the Fl bus, which turnsT6 on and off, which in turn turns T7 and the light off and on.

The flasher signal is generated by transistors T8 and T9,which are the active elements of an unstable multivibratorused as an on/off signal to the output driver stage. ResistorR24 and capacitor C6 decouple the oscillator from the powerlines so that its frequency is not affected by that of the otheroscillators. The output driver stage consists of transistors T10and T11, a switching inverter, and an emitter follower stage,which produces an alternating high and low voltage of F1bus through R23. Transistor T11 is a high-current transistorcapable of driving a multiple lamp load.

The audible signal is initiated by a high on the FR bus,which turns on an audio oscillator, the elements of which aretransistors T1 and T2. The audio oscillator output is amplifiedin an audio amplifier stage composed of transistors T3, T4,T5, and T6 connected in two pairs—one T3 and T5; the otherT4 and T6.

The input components to the stage from the audio oscil-lator are opposite each other, i.e., whenever one is high (neg-ative voltage) the other is low (near zero), causing only onepair of transistors to conduct at a time. When T5 is off, T6is on and the capacitor is discharged. This alternating actioncauses an alternating current to flow in the speaker coil,giving an audible signal.

Acknowledged A negative voltage is applied to the base ofT5 through resistor R40 by closing the acknowledge push-button. This turns T5 on and T4 off, and the FR bus becomes

© 2006 by Béla Lipták

Figure 4.1o will be described. The module has two oscillators.

Figure 4.1o is a semischematic electrical circuit for a

594C

ontrol Room

Equipm

ent

FIG. 4.1oSemischematic diagram of a solid-state annunciator designed for ISA new sequence A (old sequence 1B), which sequences are described in Tables 4.1d and 4.1e.

Logic module Flasher−audible moduleMain busterminals

T K FR C F1 (+)

Resistors

Capacitors (1) filternetworkrequiredper chassis

Main bus terminals R S G F2 CN (−)

ΤΚ

FRC

F1

Typical set ofpoint terminals

L1 S G

S1 Shown for NC field contactsS2 Shown for ‘lock-in’ onmomentary alarms

D4

D2

6 11 12 1 2 3

S2

D12R41

C4C2

5 7 10 9 8 1 2 3 9 11 5 8 12

T7

T6

D1D3

C1

S1

T1 T2 T3 T4 T5

D14

T5

T6

T4

D2

D1

C2D4

C1

D5

T3

R S G

D3

T1 T2

T11

T10

D6

T9

T8

C5R17

R19R20

R24

R22

R9R5R3

R13

R4

R18

R23R15

R12R14

R11

R10

R2 R1

R21

R8R7

R6R40

R30R34

R33R32

R35R31

R19R25R28R24

R20

R10

R43

R23

R29

R21

R17

R14R16

R48

R13R50

R9R6R2

R1R15

No troublecontact

NC troublecontact

Remote lamps

CapacitorSpeaker

Volumecontrol

Functionaltest

Audiblesilence

(acknowledge)

Toadditional

signallamps

ConditionNormalAlertAudible silenced(Acknowledged)Normal againFunctional test

Trouble Nameplate AudibleContact Signal lamps SignalNormalAbnormalAbnormal

NormalNormal

OffFlashingSteady-on Off

Off

T1 T1 T2 T3 T4 T5 T6 T7NO NC Off On Off On Off On On OffOff Off On Off On Off On/Off Off/OnOff Off On Off Off On Off OnOff On Off On Off On On OffOff On On Off On Off On/Off Off/On

Symbols:

Resistor DiodeCapacitors

Padno.

CollectorBase

Emitter

PNP NPN

Transistors

R T C

LCL L

(+)(−)

+

−

TK

C

CN

F2

Off OffFlashing On

(+)

(−)

Operational sequence

On

C3 C4

* *

*

** *

© 2006 by Béla Lipták

4.1 Annunciators and Alarms 595

low, thus silencing the audible signal. When the point isacknowledged, T5 conducts; this restores the clamp at R1and R2, which removes the flash source voltage. T6 is off allthe time, T7 is on all the time, and the light is on steady.

Normal Again When the variable condition returns to nor-mal, the trouble contact closes and the base of T1 becomeshigh, turning T1 on. This produces a low on the base of T2,which turns T2 off and T3 on. All circuits are again in thestate described under the normal condition.

Lamp Test No separate lamp test is normally provided.One initiates a full operational test by pushing the test button,which applies an alternate input signal through resistor R15to the base of transistor T2. This turns T2 on, initiating a fulloperational test of the system as already described.

Lock-In The lock-in feature is provided by a switch S2. Ifthe switch is in the lock-in position (see Figure 4.1o), whenT5 turns off (on the alarm condition), a high at the collectorof T5 is coupled to the base of T2 through R19, which keepsT2 turned on even if the trouble contact returns to normal.Transistor T5 will remain off and keep T2 turned on until theacknowledgment button is pushed.

If the switch is in the non-lock-in position, the circuitbetween the collector of T5 and the base of T2 is open; there-fore, T2 will turn off if the trouble contact returns to normalbefore acknowledgment and return all circuits to normal.

Operational Test See description under lamp test.

Auxiliary Contacts Auxiliary contacts are not supplied aspart of the logic module. Adapter assemblies consisting ofrelays operated by the semiconductor logic, however, areavailable.

Relay Fail-Safe Feature Not available in solid-state circuits.

Normally Open Trouble Contacts The annunciator sequenceand features already explained for NC trouble contacts operatein essentially the same way for NO contacts. The NO-NCoption switch bypasses inverter stage transistor T1. When thecontact closes on an abnormal condition, it turns on T2 thoughR20 and the sequence operation proceeds exactly as describedfor the NC operation.

Solid-state annunciators are for use with DC voltages rang-ing from 12 to 125 DC. Power consumption of the logic mod-ules ordinarily is less than 5 watts. Visual indicators consumedifferent amounts of power, depending on the type. Bull’s-eyelights use approximately 1 watt, whereas back-lighted name-plates use from 1 to 6 watts, depending on the number andwattage of lamps.

Solid-state annunciators are very reliable and are not posi-tion sensitive. They offer the advantages of compactness, lowpower consumption, and little heat generation, factors thatmake them particularly useful in large integral annunciators.

The per-point cost of solid-state systems is slightly higherthan that of their relay-type equivalent, due to the cost ofpower supplies and interfacing accessories that may berequired with solid-state systems. The cost of the logic mod-ules, visual indicators, and cabinets themselves is not exces-sive. Integrated circuit components using recently developedmicrocircuits will most likely reduce size, power consump-tion, and heat dissipation of annunciator systems.

ANNUNCIATOR CABINETS

Annunciator systems are installed in areas ranging from gen-eral purpose to hazardous. Annunciator cabinets are installedindoors and outdoors in a variety of dusty, moisture-laden,and other adverse environments. Industrial annunciator cab-inets are usually designed for general-purpose, dry indooruse. Special cabinets and enclosures are used in hazardous,moist, and outdoor locations.

Hazardous Area Designs

The requirements of Class 1, Division 2 hazardous locationsas defined in Article 500 of the National Electric Code (NEC)are satisfied by the visual indicators and logic modules (eitherrelay or solid state) of most annunciator systems. A manuallyoperated or door-interlocked power disconnect switch is usedwith annunciator cabinets in those locations to turn off powerwhen logic modules are relamped or changed.

Annunciator equipment for Class 1, Division 1 areas isinstalled in cast steel or aluminum housings approved for thehazardous environment. The housings are expensive to pur-chase and install. These annunciators are available in bothintegral and remote configurations. The remote type is gen-erally wired to explosion-proof bull’s-eye lights. Annunciatorpower must be disconnected either manually or automaticallybefore the enclosures are opened to prevent an accidental arcor spark when logic modules are relamped or changed.

One can weatherproof annunciator cabinets installed ineither general-purpose or hazardous areas (class 1, division2) either by housing them in a suitable enclosure or by cov-ering the exposed cabinet front with a weatherproof door.Housings that comply with class 1, division 1 requirementsare also weatherproof. Figure 4.1p illustrates several weath-erproof and hazardous-area enclosures. For the design ofpurging systems, refer to Figure 4.1b.

Intrinsically Safe Designs

Annunciators are classified as intrinsically safe if they aredesigned to keep the energy level at the trouble contact belowthat necessary to generate a hot arc or spark. Care must alsobe taken in installing the system to place wiring so as toprevent a high-energy arc or spark at the trouble contactcaused by accidental short circuit or mechanical damage.Thus, general-purpose trouble contacts may be used with

© 2006 by Béla Lipták

596 Control Room Equipment

intrinsically safe annunciator systems even though they areinstalled in a hazardous area.

The annunciator logic modules and visual indicators,however, must conform to the electrical classification of thearea in which they are installed. (For more on intrinsicallysafe designs, see Section 7.2 in Volume 1 of this handbook.)

PNEUMATIC ANNUNCIATORS

Pneumatic annunciators consist of air-operated equivalentsof the trouble contact, logic module, and visual indicatorstages of an electrical annunciator system. A single-pointsystem furnishing high tank level monitoring is shown inFigure 4.1q.

Power supply to the system is instrument air at 80 to100 PSIG (0.6 to 0.69 MPa), which is reduced to the requiredoperating pressure by pressure regulator (1). The operatingpressure is indicated on pressure gauge (2). A 3 to 15 PSIG(0.2 to 1.0 bar), an analog input signal from a direct-actinglevel transmitter (LT-9) enters high-pressure limit relay (4),which is normally closed and set to open when the high levellimit is exceeded. When this happens (alert condition), aninput at supply pressure from (4) turns on a pneumatic visualindicator (3), and a normally open high-pressure limit relay(6) allows supply air flow to air horn (7), turning it on.Simultaneously, the air output from (4) enters normallyclosed high-pressure limit relay (5) and momentary contactpushbutton (8), which is a normally open acknowledgmentpushbutton for the system. In the alert condition, the pneu-matic indicator and horn are both on.

One acknowledges the alert condition by pushing button(2), closing it, and thereby opening high-pressure limit relay(5). Supply air pressure from (5) closes high-pressure limitrelay (6), which cuts off the operating air to the horn, therebyturning it off. Simultaneously, operating air pressure from (5)is fed back to the inlet of (5).

The feedback pressure locks up (5) so that it will notclose when the acknowledgment pushbutton (8) is released.In the acknowledged condition, the pneumatic indicator is onand the horn is off. The system returns to normal when the3- to 15-PSIG (0.2- to 1.0-bar) analog input falls below thesetpoint. This closes high-pressure limit relay (4) which turnsoff the pneumatic indicator (3). It also closes high-pressurelimit relay (5) by venting the lock-in circuit through relay (4).

Pneumatic annunciators are used when one or two alarmpoints are needed but electrical power is not readily availableand in hazardous electrical areas where an electrical annun-ciator might not be practical. Pneumatic annunciators require

FIG. 4.1p Annunciator enclosures for weatherproof and hazardous areas.

Front view

Slotted-knurledthumbscrew

Backlighted nameplate

Enclosure window

Pushbuttons

Audible signal

Annunciator cabinetin weatherproof enclosure

Annunciator cabinetwith weatherproof door

Integral annunciatorfor class1 division 1

hazardous area

FIG. 4.1q The tubing configuration and components of a pneumatic annunci-ator circuit.

3–15 PSIG(0.2–1.0 bar)

From LT-9

NC

(4)I O

S

(1) OI (2)

80–100 PSIG(0.6–0.69 MPa)Air supply

NC

(5) (6)I O

SI O

S(8)

NO

(7)

(3)

NO: supply (S) connected to output (O)NC: (S) blocked to (O)

ConditionNormal

AlertAcknowledgeNormal again

Relay (4)Closed Closed

ClosedClosed

OpenOpen Open

Open

OpenOpen

Closed

Relay (5) Relay (6)

Closed

Horn (7)Off Off

OffOffOff

On OnOn

Indicator (3)

© 2006 by Béla Lipták

4.1 Annunciators and Alarms 597

a substantial amount of installation space and are expensiveto manufacture.

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© 2006 by Béla Lipták

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