With many control systems, it is helpful to mimic the look and action of “old school” electrical and electronic controls that are being replaced or enhanced with new software systems. Old annunciators flashed lamps behind a translucent alarm point legend when a new alarm occurred. Then, when the acknowledge button was pushed, the lamps would shut off if the alarm was no longer present, or become steady-on if the alarm was currently active. This made it very easy to know that an alarm had occurred, and also to know whether or not it was still occurring.
Most Machine-Level Operator Interfaces allow alarms to be displayed that are either “historical” or “currently active” or both. If you develop only one alarm screen, you need to choose one alarm-list format. If you choose historical, this will usually display all alarms that occurred, whether they are currently active or not. This is an important troubleshooting tool, but it may not be easy to distinguish which alarms are currently causing a problem, especially when equipment is down, and people are scrambling to correct the problem. That is why I always add a “currently active” alarm screen, where the alarms disappear after they have been acknowledged, if they are no longer present. I do not allow alarms to be deleted from either screen since that defeats much of the purpose of having alarms.
I espeically appreciate software that has “canned” objects to make mimicking old controls quick and easy. To me, it seems the programmers behind some HMI sofrtware packages don’t like simple and easy, since they give integrators a kind of virtual “easel” to develop all kinds of custom objects, but not many more standard, pre-developed ones that may work well for most applications. I find that custom objects result in much more time being required for development, and the customer gets a custom monstrosity that is difficult for all to modify and work with. Speaking of “old school,” whatever happened to the rule of, when possible, “Keep it Simple, Stupid?” I guess it’s been customized.
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