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A disturbing trend (not the only one) in distributed control system (DCS) conversions is the proliferation of CRTs. Where at one time three CRTs per operator was common, today it is not unusual to see six or more CRTs per operator. Are all these CRTs necessary?

On straight logic, if three CRTs are adequate with an early generation DCS, why would one need more CRTs with the better display capabilities of the current DCS? Shouldn't you need fewer CRTs?

The counter argument (if you can call it an argument) is, "Why not have the additional CRTs if they're available?" Besides the obvious and practical (why pay for something you don't need), there are potential negative effects on operator and system performance if excess CRTs are present. A two-fold effect is possible: (1) display designers might feel compelled to "spread out" the display system to accommodate all the CRTs (note: information systems should be 'compact') and/or (2) the operators will feel that all the CRTs should be used in solving a problem (a common characteristic of problem solving is assuming all available information is relevant, and people actually do better in processing information from a single source). Another related problem is based in signal detection theory: extra, unnecessary CRTs add noise to the information environment, thereby decreasing the ability of the operators to find the information they need.

Can you have too many CRTs? Yes. Are most new DCSs using too many CRTs? Probably. Should refineries pay more attention to CRT selection? Definitely.

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