In the Power Plant video, an alarm annunciator is shown. The annunciator monitors between a few hundred to a few thousand alarm points, (e.g., the temperature of an electric transformer, which should not be too high) in an electric power plant.

The annunciator lists, in real-time, the occurence of anomalies (indicated by lines with an "N" for New alarm) and their eventual dissapearance (indicated by lines with an "R" for Return to normal).

Mockup of the alarm annunciator (circa 1985, but still in use in some places) from the Power Plant video. Red line items denote major (critical) events, yellow denotes minor events, and green means (returned to) normal condition. Inverse video means that an alarm message that has not yet been acknowledged.

The operator can acknowledge a single message with the acq button or acknowledge all messages with the acqp button. Once acknowledged, the message changes its display to light text on a black background. The operator can remove acknowledged "N" and "R" pairs (i.e., alarm points that have returned to a normal state) by pushing the rap button. Thus, pressing acqp then rap, will remove from the list the alarm messages for all anomalies that are no longer active.

Operator behaviour: In the case of a fairly important event in a power plant, that is, one that generates more than 10 alarm messages in a few seconds, the operator will first look at the control panel (see photograph, below) showing the entire plant, rather than look at the alarm list, and then try to stabilize the plant. Only after that will the operator look at the annunciator and immediately push the acqp and rap buttons, thereby erasing the history of the event. The operator then turns attention to the remaining alarms.

Power plant control room (circa 1995). The annunciator is on the monitor at far right. The control panel fills the entire background of the picture.

You should first view the video clip and try to understand the behaviour of the operators, as described in the paragraphs above, rather than the behaviour shown in the video. Your task is then to suggest how an improved annunciator should behave to help the operators in their job.

Note that:

• the operators are experts. They were trained for several years before getting their assignment; they use this annunciator in 12 hour shifts
• the HMI shown is a mock-up of annunciators used at Hydro-Québec; some are still in use, but are becoming rare
• the "D" and "P" push-buttons are absent from the real interface and should be ignored
• the "son" push-button stops the auditory warning (until the next alarm)
• the push-button usage seen in the video is not typical of actual usage by an operator (as described earlier); rather, it is simply to illustrate how the controls operate
• the time indicated in the top section is not coherent with the time stamps of the alarm messages because the alarms are coming from a file (this is a mock-up)
• message colors: red = major (critical); yellow = minor; green = returned to normal condition.
• inverse video means an alarm message that has not yet been acknowledged
• the "sens" box is a Visual Basic artifact used to enable control of the annunciator from the keyboard. It is not present in the real annunciators.