The Logic Behind The Magic. “Line Monitored Signal conditioning"

Signals from the various field F&G detectors and push button are processed by the Safety Shutdown System by means of dedicated functions implemented as standard within the Safety Shutdown System.

The line monitoring facility discriminates between open-circuit, short-circuit and true alarm conditions.

the  line monitoring faults is handled as follows:

 

 

This type of logic usually have 3 signals output and 3 input status that are shown in the control room,
 Input:

1. Loop Monitoring Status "healty"
2. Digital Input "Activated "
3. Reset Command "reset".
4. Inhibit Request "Changed"

Output:

1. Loop Monitoring Status "Faulty"
2. Exec. Action "Trip" 
3. DI status alarm
4. Inhibit status "accepted"

The logic are:

1. Alarms and pre-alarms are overriden by fault signals.
2. Sensor alarm  is sent to the Control Room whatever the inhibit status is
3.  If the digital input activated, Exec. trip will be activated until reset command or inhibit status is active

Sample of the logic is shown below: