Interlocking in PLC

Interlocking in general is called protocol action. It means defined bunch action to be taken when certain conditions occur.

In a view of PLC, Interlocking is an action that is defined in the PLC program to control the process when certain conditions occur f.e. temprature exceeding its limit,flow below requirement or any parameter exceeding beyond its safe operating limits.

Lets take an example; there is a flow transmitter.our requirement is to maintain the flow in certain range.Now there is one valve in the pipe through which flow goes.Function of this valve is to adjust the flow by opening or closing.when flow exceeds valve should shutoff.when flow is in the limit valve should open to allow flow. Hence we can say valve is interlocked with flow value defined in PLC as interlock.

Sometimes it’s not just some parameter but a sequence that needs to be followed. In such case interlocking is PLC program written for assuring that actions are performed in predefined order as well skipping of order can generate significant alarm conditions like stopping the process or sounding a hooter.

In general Interlocking in PLC is the action that its has to take to control process execution when abnormal conditions occur.

credits - Vipul Patel

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