In this part you become familiar with Interlock, IS groups and I-groups and their components.
Overview
Action performed in the IS are called IS-group (Interlock Safety) and actions performed in the
DCS are called I-group (Interlock).
Due to a considerable higher cost of IS than DCS hardware, consideration has been given to
define which actions (groups) are to be performed in the IS system and which actions are to be
performed in the DCS. In order to establish guidelines for the distinction of those actions, the
following rules are applied:
Trips in IS groups are generally based on 2-out-of-3 voting.
IS-groups must protect:
– personnel against safety hazards
– critical plant equipment
– unit trips which will result in a significant production loss when initiated
I-groups must protect:
– auto start and stop of motors
– avoidance of PSV relief
– switching of operating mode