We recently underwent some training for a new distributed control system (DCS). Like many systems, this one prided itself on its many advances in information presentation. One "advance" got a big laugh from all of us at Beville.
The DCSís animation capability was touted as being able to graphically show movement of fluid in the display of pumps and piping. It is bewildering that anyone would think that (a) this is an improvement and (b) it is even necessary. Most of us drive a car daily without a display on the dash board showing the pistons in the engine moving. If I apply pressure to the gas and the engine "revs up", I can pretty much surmise that the pistons are doing their job, without having any direct indication of piston movement. As a driver, until the engine ceases to fulfill its function, I donít give much thought to the mechanics of what is allowing me to carry out my primary function of transportation. Let me know my speed, and maybe RPM and engine temperature. Likewise, display designers should be focusing on displays that help an operator do their job (maximizing the safe production of on-spec product), highlighting those variables on which the operator should be focusing most of their attention.
Focusing too much on the hardware can actually degrade operator performance. The same DCS that is able to show fluid in pumps also shows increasing height of the flames in a furnace with increasing valve output. However, since increased valve output may not actually result in increased flame height (plugged burners, no fuel gas), the display could mislead the operator. An operator shouldnít really care about what the DCS is showing as the height of the flames, but whether the desired outlet temperature has been optimally obtained. The operator error at Three Mile Island included a misinterpretation of valve demand as actual valve position.
Better display design is not showing more detail, but showing necessary detail. Better display design is not reflecting physical reality, but operator information requirements.
Copyright © 1999 Beville Engineering, Inc.
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David Strobhar's book, "Human Factors in Process Plant Operation," is now available in both hardcover and Kindle e-book.
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