Safety interlocks ensure the safety of operating personnel, protect plant equipment, and protect the environment. These interlocks are initiated by equipment malfunctions and usually cause shutdowns. Often, a separate system implements safety interlocks. This system includes the necessary redundancy and fault tolerance and is independent from the other control functions. An example of a safety interlock is the stopping of a centrifugal compressor when its oil gear pump has failed, thus preventing mechanical damage.
Safety interlocking serves a different purpose than process interlocking and permissive interlocking. Process
interlocking can be safety-related, but it is primarily associated with the process. An example of a process interlock is to stop charging a material if the agitator is not running. A permissive interlock establishes an orderly progression of sequences. An example of a permissive interlock is to not allow the feeding of an extruder before the barrel temperature has reached a minimum value.
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