Process Control

What is Protective system Override ? & What is Protective Override switch (POS)?

What is Protective system Override?

If two or more circumstances are met at the same moment, command override is used by the Protective system Override. If one of the conditions satisfied for the controller output then output made to be true by override control.

Protective system override is used to Any overriding of a protective system(s) shall be performed only when there is no way to perform the job without it.

The override is normally done for the duration of the actual work rather than the duration of the validity of the permit. Therefore, if necessary, the override can be created while the change license is renewed and recorded appropriately.

The override privilege in PLC / F&G Panel / ESD Panel / DCS is to be kept to share override passwords in the building as per the property leadership procedure.

Operations employees in the plant may therefore only have such passwords for POS (Process Override Switch), whereas MOS (Maintenance Override Switch) is performed by Instrumentation.

What is Protective Override switch (POS)?

Process Override Switch is given to override unhealthy field settings to enable start-up, which will be published automatically upon field entry standardization or preset time, whichever is sooner.

  • In the event that the system situation has not normalized within the preset time, it will lead in a failure to begin and, as the situation may be, abort the start-up or shutdown of the machinery.
  • The override entry will not stop the restart of the logic while the timer is operating, but the alarm status of the field components overridden by POS will not be disguised.
  • The field buttons that POS needs to override to enable start-up are alarmed at the DCS console graphic as follows:
  • If the method is in ordinary working condition, programmatically inhibit the activation of POS.


Instrumentation Engineer

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