EDITORIAL VIEWPOINT

INTRODUC'[ION stand the operation ofthe control sys- keys) for operators, supervisors, engi- We often think of a control system tern or cannot operate it properly, he ricers, and maintenance personnel.

primarily in terms of its architecture, or she will tend not to use it. Any advanced control strategy can be de- TECHNOLOGY OF THE IN~RFACE control capability, and other features

such as communications and record feared ifthe operator, through misun- keeping. Every control system, re- derstanding or because of a bad The technology of the i,lterface gardless of the architecture, provides experience, leaves the loop in manual, has changed dramatically over the last some form of operator interface. This [I] decade. Most of the control systems

installed ill refineries, petrochemical collection of displays, indicators, and plants, and other large processes are controls allows the operator to view WHAT I$THEOPERATOR? known as "distributed control sys- the operation of the process, to ma- When we refer to the "operator" tems" - - systems that compromise nipulate the set points and outputs, we are always talking about the per- many microprocessors, each of which and to operate motors, valves, and son viewing the displays or manipu- performs some function such as con- other equipment, lating the control system. Usually this trolling PID type loops or recording

The selection anddesign oftheop- person is not an expert on process data. erator interface, as well as the training control or on digital systems but, in- Most DCSs use video displays of the operator, are as critical to the stead, has, or should have, knowledge (typically CATs), with associated successful and safe operation of t'~e and understanding of the operation keyboards, as the operator interface. process as is the advanced control ca- process. All operator activity takes place pability. The duties of a process operator through the displays and keyboards.

IMPORTANCE OF THE OPERATOR include, of course, the operation of Distributed control systems offer the process. They also often include both advantages and disadvantages

INTERFACE some functions that relate to the con- when compared to the more tradi- We usually place emphasis on such trol system, such as maintaining pen tional analog panelboard instru-

aspects of a control system as the ar- and ink recorders, correcting paper ments. chitecture, advanced control capabil- breaks and jams in printers, and so A well-known disadvantage of the ity, etc. Yet, in spite of the advances on. Usually the operator is not in- CAT operator interface is the narrow in automation it is still the process volved in actual control system main- "window" of the process presented to operator who operates the process, tenance activities such as changing the operator. This effect is often particularly in the start-up of a con- circuit boards. The operator will, known as "keyhole control." When tinuous process and the handling of however, have to be able to detect using a panelboard system, the opera- upset conditions, improper control system operation or tor will typically spend the time scan-

"['he increased use of more ad- diagnostic messagesin order tonotify ning across the board, walking if vanced (and complex) control the proper maintenance personnel, necessary, in order to be aware of the schemes places additional importance Fo: these reasons, most DCSs pro- operation of the entire process. on the design of the operator inter- vide different levels of access (limited Video-based interfaces allow the face. If the operator cannot under- by methods such as pass words or operator to see only a small part of

VOLUME 31 • NUMBER 3.1992 5

1 HE t4UMAN IN I L.I.(i~/',,CL - - Kt LPING 1fiE. t'l-I !SOr,,I I:J " t4f- LOOP

theprocess at onetime, i':or example, appli(x'l, the interface can c:'use ,~g- WhatTra in ln~ t0GIveOpera t0 rs

if the operator has three CR'rs, each nificant reduction in the operator's displaying 20 coaitrol loops., he or she perfi~rmance during upset condi- If'tile process is new (or if the up- can see only 60 control IooF,s without tions, er;ltor is new to the process) most of

,tae training will concern th, l.,iocess changing displo's. This requires that It is true that sonietimes the opera- itself, incl,ding the basic design of the operator repeatedly c~.ll up vari- tor is to blame, and ,he solution is ous display pages to look over each training or perhaps even replacement the process, start-up, shutdown, and

normal and emergency operation. If part oftheprocess, lt can be tempting of the operator. However, there are the control system '.; replacing an for the operator to leave only an over- some mistakes that tven tt~e most view type of display on eac.h CRT; skilled, educ;:ted, and n~otiv~ted up- older c,~ntrol system on an ,. l,;l~ng however, this prevents observati,~,.-, of erator will, on rare occas.ons, make. process, then the operator will not

necessarily be trained on the F, rocess. critical details. But an operator error will be just as Still, the control system replacement

The process opcrat,:," .r'.,:,t first se- costly even ifwe can blame the oper- training offers a chance to provide led each loop for control before ma- ator. The rnost effective wav to re- nipt, l,',ting it. The same hardware, duce this cost is u':ually to re(lute the "brushup training" on ,?rocess opci a- keyboards, video units, etc., are u.~ed chances of error, an,: the design of tions and procedures. to control each loop, som,:times lead- the interface can reduce the chance of Training also will cover the func- ing to the common error of manipu- error, tions of the control system that are iating the wrong loop. The part of lhe operator's responsibility, panelboajd opcJator knows "w]acrc" TRAINING such as printing reports, handlil,g the

archiving of data, and so on. he or she is in the process by the We are of,,en faced with operators While the operator is not normally location at the board. Typically, the who are unfamiliar with the control expected (or allowed) to perform process "flows" from left to right on system that ~hey must use to operate maintenance beyond certain specific the board with each successive por-

' the process. The most obviot,s situa- hlnctions such as maintaining printer tion of the process occupying a par- ticular section ofthe board. With the tion is when a plant is first con- paper, etc., the operator should be ability to obtain any display page on structcd. Many of the operators are give,~ basic information such as ob- any CP, T, the layout of the console newly hired and must undergo rigor- tainting diagnostic inl)~rmation, ~.nd

e'Is and thorough training. Other sit- contacting and communicating with becomes oriented by function, rather uations also call for operator training, system maintenance personnel. than by process area, causing the up-

When a new generation control sys- The growing use ofhome comput- erator to lose the physical relation- ship between the process and the tern replaces an existing control sys- ers and the coverage of computers in controls. [2] tern in a process plant, the operators the popular press has increased the

Distributed control systems are should be expected to know the pro- operator's interest and understanding covered in a previous issue of ISA tess well, but they must be trained on of digital systems and curiosity about Transactions. 13] the new control system, the internal working of the control

Whether an operator is newly system. The operator probably will hired or involved in a replacement of show interest in and appreciation of OPERATOR ERROR REDUCTION an existing control system, a deter- coverage of technical details about

People make mistakes. That sire- mining factor in the operator's per- the architecture of the system. Some pie fact sl;otald guide the develop- formance (and, therefore, the understanding of these technical is- ment of the process control sy.':iem, performance of the control system) is sues will increase the"comfort factor" The design of the operator into:face operator training. The operator must of operator, but probably will not depends upon, and should start with, be trained not only to understand the otherwise increase his or her ability to an analysis of some of the types of process, but also to understand the perform the specific job. Architec- errors commonly m~de by oper:.ors, control system and its operation, rural information should be given to These errors can be organized into Often we make tlae mistake of as- the operator, but not to the extent types, and certain guidelines for the suming that all control systems are that it detracts from other instr,ac- control system design can be devel- the same ~ that anyone who has tions. oped around these types of errors. ,lsed one control system can simply

A well designed operator interface and easily switch to another without H0wI0 Train Operators can improve the operation of a plant any training. However, control sys- during normal operation without sig- terns from different generations and While control engineers and main- nificantly reducing the performance from different manufacturers differ tenancepersonnel are often trained at during upset conditions. Improperly in their terminology and operation, the control system manufacturer's fa-

6 ISA TRANSACTIONS

[..DI'i.3RtAL VILWI~OINI

cilities, mo~t operators are trained at process simulation allow the process is that, with no additional c:ost pcr the plant site. If possible, they should to be operated in all normal and ab- alarm, the uoer can (and often discs) be trained in the actual control room, normal modes d~at the operator will specify too many alarms. Anod~er using the same equipment (or identi- likely encounter, including start-up rather disturbing ,aspect of the trend cal equipment, if necessary) that they and emergency shutdown, to eliminate panelboard-typc annun- will use to operate the plant. If the Training simulators provide at ciators from control rooms is placing operators are to receive process train- least two functions: simulations of reliance on the DCS for all process ing, it is best to mix theprocess train- the process and the process control alarms. This total reliance on the ing v, ith appropriate control system system. Optionally, the simulator I)CS has several disadvantages: trainiLg. For example, the operators may provide an instructor station and (1) CRT-based operations make it may receive information and opera- provision for analysis of the student tional instruction about a particular operator's performance. process area and then study the dis- The simulation is simply a mathe- plays and other ton:rol system lea- matical model of the process. The tures for that area. process control system includes the

The mixture of process and con- PID controllers, other control func- trol system training is often provided tions, and the operator interface. The jointly by process plant personnel and operator interface is a key to the oper. by personnel from the control system ator training simulators. vendor. Several configurations of simula-

tor/control systems are available. The Simulators choice depend, upon the use of the

A common and important use of simulation and the available re- sou rces,

real-time interactive simulators is the Industrial ir~strumentation train- training of process operators. This .

Jng was covered in more detail in pre- application is similar to pilot train- vious issue of ISA Transactions. 14] ing, which has been conducted on simulators since before World War ALARMS II. Simulators were used for many years to train nuclear power plant cp- A critical aspect of the operator in- erators and in more recent years to terrace is the alarm capability pro- train chemical plant and refinery op- vidcd by the control system. In erators, panelboard systems the alarms took

In process training, the operator the form of standard annunciators-- learns how to operate a particular a set of "windows," each of which process, including how to start up would indicate the alarm status of a and shut down the process, For this single point, in typical practice, the type of training the simulator should annunciators would be mounted at exactly duplicate the process. How- the top of the control panels. All ever, it is often not necessary to ex- alarm points would be clearly visible actly duplicate the control system or to the operator at all times. With the its operator interface. If the main put- conversion to CRT-based control sys- pose is to teach the operator the vari- tcms the alarms have become buried ous features ofthe control system and in the control system, with the alarms how to perform such tasks as chang- being indicated on the CRT displays ing a control status or responding to through the use of color, flashing, an alarm, the exact duplication of the background color, etc. In the early process is less important than the D e s installations the annunciators exact duplication of the control sys- remained a part of the control room. tern interface. It is important that the More recently the trend has been to operator become familiar with the eliminate the annunciators and rely operation of the control system, in- exclusively on the CRT-based alarms. eluding such features as CRT re- One problem with the incorpora- sponse. It is also important that the tion of alarms into the control system

diffict:lt for the operator to quickly see an alarm. Usually the operator will receive an au- dible alarm and then have to select a target or push a button to bring up a display to view the alarm. When several alarms occur at the same time (a typical case) the time re- quired can be excessive. This is contrasted with the annuncia- tor, which is visible at all times.

(2) Distributed control systcms often have too many alarms configured. When a process upsct occurs, the operator is presented with an avalanche of alarms. This large quantity of alarms often overwhelms the operator and masks the most important ones. The reasons for this are simple: there is no limit and no cost to alarms in the Des . Often, during the configuration, the control en- gineer is presented with a choice of alarm values for every loop. It sometimes takes more effort to leave an alarm off a loop than to include an alarm value. An annunciator, on the other hand, requires the user to carefully choose which points are to be alarmed due to the limits on number of points and the cost of adding alarm points. This discipline keeps the use of the annunciator to a more reasonable level.

(3) Another disadvantage of ex- clusive reliance o:1 the DCS- based alarms is the rdative low

VOLUME 31 • NUMBER 3 • 1992 7'

1 HE t-IUMAN INTI.RIAC[- K[EPING lt4E PERSON IN lt4E LOOP

reliibiii~y of the DCS com. operator interfaces for other indus- "An Object-Oriented Operator's In- pared to the annunciator, tries as well, terrace for Real-Time Procms Con-

tr,A Expert Systems." One approach is to keep the THEFbrrURE panelboard-style annunciators along with the DCS-based alarm system. The rapid improvement in technol- LoamlngAl:~=ll~O~rator The mo~t important alarms are indi- ogy will certainly affect the operator in- Three papers describe the needs of cared using a wall-mounted annunci- terrace just as it affects the other die operator. Shaw ('Consider theOp- atGr; !e:s urgen', r.larms =re ~hown on functions of process c:.mtrol systems, erator Interface in Control Sys:em Up- the CRTs only. Not only does this CRTs will have higher resolution and a gr,des") asks us to take a closer look at separate the most urgent alarms for faster update rate. This will improve the the operator interface when replacing immediate attention, but it provides operator interface, but the most impor- older control system; with DCSs. mot,' reliability, rant improvement will come only ifthe Gingrich, Kuespert, ai,a McAvoy, in

control system designers use the in- "Modeling Human Operators Using STANDARD ACTIVITY creased technology to provide an easier Neural Networks,",describe a method of

to use and more reliable interface, learning more al,,mit the operator. The Instrument Society of America Worthington tells h¢,w graphical inter-

has several existing and draft standards IN THIS ISSUE rices are redefining die computer inter. and recommended practices that affect In this issue of the ISA Transactions face in manufacturing ("The operator interface design. ISA has we will concentrate on the operator, the PersonaliTation of Manufacturing: Re- adopted several standards tllat relate to training, and the control system's inter- defining the Human Interface"). the operator interface. One standard of face to the operator. As'tides are taken particular interest to DCS users is from papers presented at ISA/90 and Se!eeUnganlnteaaee ANSItlSA-S5.5, Graphic Symbols for ISA/91. Finally, in "The Process ofSdecting a Process Displays, which defines the Man-Madfine Interface Software Pack- process symbols that are used in pro- 1"mining age for Use in a Process Control Sys- cess diagrams on video displays. An- The first fourpapercover training. In tern," Jensen, Holland, Tomasello, other, ANSIIISA.SI8.1, describes the ,, Distributed Control Systems ~ Per- Heidrich, and Etterich provide several sequences and specifications of sonnel Skills Training" John "I'human viewpoints on selecting software pack- panelboard-rype annunciator systems. Payne discusses the skills needed by ages. ISA-RP60.3 recommends the human DCS personnel, In "A Manufacturer's I:IEFFd:iEJ~It~S engineering design of control centers, Approack, to DCS Training Past, Pres- while ISA.RP60.6 recommends design ent and Future," Delembo, Voorhees, for nameplates, labels, and tags for con- and Frisina describe the training offered trol centers. Several new standards are by one control system manufacturer, being developed for the operator inter- Gokhale and Rice ("Real-Time Simula- face in the power industry, toe for FCCU Operator Training") de-

The draft standard dSP77.61, scribe the use of a simulator for training Human-Machine Interface: Control refinery operators. In "Customers Im- Panel Layout and Design, covers basic prove the Quality of Training" Daniels human engineering principles relative to tells how customers can improve the the design of control panels with era- training they receive. phasis on their labeling and marking. dS7L63 addresses the environment, in- Technology cluding illumination, atmospheri~ con- The technology used to produce the ditions, noise, etc. dS77.64, human interface is discussed in three Human-Machine Interface: CRT Dis- papers. First Jessen describes "X Win- plays, covers the design ofCRT disphy dows and the Plant Floor," then Clancy, hardware and the arrangement of the Garrette, and Gersten, in "Real-Time displayed information; dS77.62 ad- Advisory Control Application in the dresses alarms. Petrochemical Industry," describe an

While these draft standards are being application for artificial intelligence to c.~" devdoped for the power industry, they aid process operators. Adams proposes a should be of assistance to the design of new model for the interface design in

1. Shaw, J. A., "Human Factors As- pects of Advanced Control," ISA Transactians, Vol. 27, No. 4, 1991.

2. Shaw, J. A., "Reducing Operator Error in Distributed Control Systems," INTECtt, Vol. 29, March, 1989, pp 27.

3. Dist,tDuted Control Systems: Se- lection, Implementation, and Maximization, ISA Transactions, Vol. 30, No. 2, 1991.

4. Industrial Training, ISA Trans- actions, Vol. 29, No. 3,1990.

John Shaw

It ISA TRANSACTIONS