The Pure Annunciator Model

Despite the problems detailed above, many monitoring systems follow the pure annunciator model. Almost exclusively, such systems consist of large annunciator panels, lists of messages, etc. The inherent simplicity of the idea behind a pure annunciator system can be very appealing to the designer. Human conscious thinking is strongly dominated by strictly ordered rankings and on/off choices (A is superior to B is superior to C, X is good, Y is evil, etc.). The human perceptual system, however — as well as the world in general — do not work this way.

A pure annunciator design packs a great deal of information into a small space, and seems to present easy choices to the operator. Some part of the system being monitored can either be working fine or be broken (sometimes, the notion of marginal performance is added — just like the yellow light in the traffic signal).

When a monitor relies on annunciators only to covey information, it begins to suffer from the problems described previously. The operator is not aware of any deterioration in the system until it reaches a critical level. If the monitoring parameters are incorrectly set, the alarm might come in error, too late or not at all. Even when it becomes clear that the parameters are wrong, the pure annunciator system is unlikely to be useful until these parameters are adjusted. Also, a single fault can trigger multiple annunciators at once, causing confusion.