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Alarms

Alarms are a common feature of all control systems. They are a way of letting the control system shout "HEY, STOP WHAT YOU ARE DOING AND LOOK AT THIS" to the operator.

They are set off when a reading such as s temperature or a level, goes beyond the range it is supposed to. If a heater outlet goes too high, this could cause the metal to fail. The engineers who designed the heater will have said what the highest temperature could be. The engineers who set up the control system will have put that temperature into the control system as an alarm. If something went wrong and the temperature rises beyond the safe level, you want to make sure that the operator is aware. You want the control system to shout at them "HEY, STOP WHAT YOU ARE DOING AND LOOK AT THIS TEMPERATURE!".

The system will make a noise. It may flash a light. A message saying what the problem is will be written on a screen.

Whenever an alarm goes off, it should mean that the operator needs to do something. If there is no action that the operator needs to take, then it shouldn't be an alarm.

Priorities

Most control systems allow alarms to be ranked with different priorities. These priorities will be displayed by different colours and sounds.

In theory, this allows the operator to know if the alarm that has just been triggered is a high priority one and can tailor their response time. In practice u have not seen much of a difference. If an alarm sounds, operators tend to respond quickly and work out why the alarm has been triggered. When you have a system making an annoying noise at you, you tend to stop what you are doing to fix it.

Even low priority alarms are shouting at the operator, interrupting what they were doing. When adding alarms, we need to be sure that there is a definite reason for having the alarm, and that that reason is enough to interrupt the operator.

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