Document grdj9Qa84pDMyD5L6edb0qjV

HUMAN ENGINEERING nn<!no*d o. e> e <>' 5 ^"iLThT0"' '"T*'"'10"m.wnwnt. In Ih. am'order o, g.na.Po"lonr0a' l^hay rapraxm f0i panTMd00codnlroTMl knWob. ,,In, Ihoot idoln.l..lbourldloenr ap.enthaleirpl,, dldl neering service to analyze the job re* quiremtuu. study all the proposals, recommend a single design that eould be defended scientifically. The human engineers set up experimental materials to simulate the proposed panel orrange* menu. The various component!--*oJ<meters, frequency meter, synchronizing lights, rheostats, snap switches, bus bars--were made out of photostatlc copies of full-size drawings. Each was eemeutod to a small magnet that could hold the component in any position on an iron panel of the same size as the instrument panel This allowed setting up any arrangement within seconds. The most difficult part of such an Investigation Is to set up an experimen tal design that la scientifically sound. A series of trouble-location problems were designed. These were administered to a series of 16 operators under carefully controlled conditions. The time they re quired to locate the source of difficulty was taken as the criterion to choose the best Instrument arrangement. Half of the problem* (four In all) used the graphic feature, the other half did not. Each of the 16 subjects waft pteftented four different versions of the following problems*, source of trouble indicated by (l) meter tlone (2) meter end wtrnlng light (3) meter hnd bus bar (4) meter, warning light and bus bar. Performance times were measured by stop 'watch. Analysis of these limes showed no significant difference. The client was then advised not to entail the extra expense of the illuminated bus-bar feature. Instrument Simplification. Reducing ponent of the system. Unfortunately, there often are very complex system* whose performance characteristics so one really knows. This stems from the high degree of specialization of com* the number el instruments that an op pany departments and personnel. Such erator must read cart sometimes simpli e situation leads to people getting lost fy his job. An Instrument is justified in their worlds without understanding only when U contributes to decision the effect of their performance, upon making. Too often instruments are kept that of others. on a control board after their original Electrical utilities find that central function has become obsolete. ized control In power plants reduces Sometimes Instruments can be com iebor costs. But centralized control bined without increasing reading dif * often means more instruments to watch ficulty. One airline found that funda and raises questions ai to best control- ments) Information was given by the room layout. Increasing use of auto difference In readings of two Instru matic controls gives the operator less ments, rather than the individual read opportunity to practice skills he molt ings themselves. By combining the two use in an emergency. Hera we have s instruments Into one with two pointers, curious situation In which the operator the operator need only respond when has relatively little to do most of the there is a space between the two point- lime (leading to boredom), but during era. Presumably, further simplification an emergency be must immediately do would bo to substitute a light that many things he never has done In ex* would (unction when the two variables actly the same way before. One Inves failed to synchronize. tigator has pointed out that where aoto- System Improvement. Much of hu malio equipment la used, there is > man-engineering activity concentrate* strong tendency <o neglect even tainor on Improving existing control and dis maintenance duties so that equip**1 play devices. A new trend (s to look failures still occur. first at the need for the device befote Several sources influent* decision* attempting to Improve it. Man-machine on power-plant control, end controver systems have the ultimate aim of pro sial issue! constantly arise. For *** ducing goods or a service. This should ample, designs of major equipment" be kept In mind when attempting to boiler, turbine, generator, feedwater improve or modify some internal com* system--ore each assigned to the * se INOINEHINO AND MANAGEMENT SECTION SO*** Survey. Observation of control-room activities in a power plant during a single watch period uncovered these condition* that could cause operating mistakes: 1. The system frequency meter, a major indicator, was on a side panel rather than the main board. 2. The frequency meter had a range of 58 to 62 cycles with graduations of 0.1 cycles. Spacing of graduations de creased with increasing distance from midpoint of 60 cycles, making it diffi cult to estimate pointer position from Center of room. 3. A voltmeter with 0- to 20-kv range was marked for norma) operation at 13.8 kv. The meter face had white fig ures on black background, with 13.8 kv marked in red. Meter could not be read accurately because red did not Contrast sufficiently with the black, and blunt dial pointer obscured scale markings. 4. Recording voltmeters and am-' meters could not be read accurately because of thick stytus line; recording paper could be moved appreciably be cause of loose fit In drive sprockets. 5. Controls on the main board were not arranged In. a pattern similar to their indicator*. This increased ohances of operator using wrong control. nous experts in those fields. But the erer-all Information on the operation ( all these components is fed into a single room. One man often must op erate all these units with understanding pacities increased the number of Insuroncc claims increased: Plant capacity, Number of 1000 lb steam per hr claims yearly 6. Indicators on panel were legible) at no more than two feet from panel Some meter* were too high to bo read without parallax errors. 7. Meters on back of board were only 12 to 30 inches above floor. Making sad skill. Some power-plant experts wonder thether loo much is being asked of the operator. They realize that they must distinguish between facts and fancies or fads. They wish to supplement their engineering knowledge with factual in* formation on human behavior. More de pendable Information is needed on such things as: color of Instruments, color of panels, use of graphics, heights cl Instruments, relationship between switches, relays, protective devices and measurement of important related var 25 to 30 100 to 400 900 and up One fot every S8 boilers One lor every 17 boilers One for every 8 boilers Cltims vary from very expensive to minor. Many of the saute* ean be at. tribuled to the human element. He points out that the modern power plant Is a man-machine system In which the interconnecting link is the instrument operator squat to read Increases chance of error. 8. Four movable telephones had lights on a panel to indicate which was ringing. But since phones were being moved about their position bore no re lation to the Lights. Several limes operator picked up wrong phone. 9. Totalizing wattmeters on back of the main board required hourly check readings. Possible danger slgnala ap pearing on the front indicators would he mlaaed by an operator who was read iables. ' Many of these items are controver sial iaaues that must be faced every time * new installation Is considered. In wme instances, the buyer has strong and the automatic controller. The en gineer must be supplemented by those who understand the characteristics of man so that the over-all system require- menu can be established. ing the meters in back. 10.- Load indicator in the turbine room was in such a position that the control-room Operator had to lean out of a window.and crane his neck to check opinions that all twitches and controls should be clustered, ond separated from the related Instruments. Other buyers fee) jast as strongly that switches and controls should be arranged directly *ith associated Instruments. Issues ol this nature cause difficulty where buy er-dejfgnor reioifona must be . kept Plant instrument users demand me ters of greater readability. But this rep resent* only a surface attack on the problem, ft is more important to find out what kind of information la needed in the first place and how valuable an effect the use of certain indicators will have on system performance. System its readingSummary, Problems of instruments- lion and control that human engineers have dealt with to date are similar to those currently found in central stations. Human engineering appears to offer a ready meant of improving the effective ness of control panels and their indi amicable. analysis has shown repeatedly that be vidual component* It Is important, to In a paper before the Pennsylvania ing able to do certain things better can analyte the man-machine system as a Electric Assn, John C Fleming, The actually causa poorer over-all system whole to determine both the need and Bristol Co, showed that at boiler ca performance. the value ol specific improvements. NOVEMIM 1953 ENGINEERING AND MANAGEMENT SECTION V