Industrial Alarm and status monitor

In many industrial applications sensors need to be monitored. If situations need attention, the alarm status becomes effective. After a while the alarmcondition itself may disappear. In that case the monitor needs to remember the fact that an alarm has been detected.

Normally a standard SR flipflop will do the job of remembering that an alarm situation has been detected. In Realizer the following scheme would do that job.



In more sophisticated systems a Buzzer device is added to attract the attention. When the operator pays attention and presses the Accept button, the Buzzer stops. If the alarm is still there, he wants to be able to see this visually on Alarm light.

As soon as the alarm disappears, the Alarm light will go out als well.
Studying this functionality carefully we see that the alarm monitor has 3 steady states: Idling, Alarming and Active.


To implement this in whatever system we need to have some means of storing 3 situations. Compared to the diagram above, this may seem quite difficult. At least we need another flipflop and some And and Or symbols to do so. The testing of such a control scheme is quite a job.

Realizer however has a very comfortable way to implement such requirements. It is called state diagrams (also known as: state machines). It is shown in the following diagram.



Note that each circle is a state, a steady situation in which the system can be. The symbol with the dubble circle is the default state of the state machine.

Using the Simulator

To check the code the diagram can be simulated. Use probes or a oscilloscope to show the value of an output. Inputs can be triggered with an adjuster.



Download

Alarm.zip

Prepared for devices: ST6200C ST7FLite10 PIC12F508 PIC16F88 other devices can be used by reconnecting I/O pins.