Interlocks

Interlocks are conditional statements that can prevent the start of a particular phase block. Phase blocks can have any number of Interlocks, as well as share Interlock conditions with multiple phase blocks. The Interlocks are found in the Interlock section of the program that corresponds to the unit or connection with which they are associated. Usually, the Interlocks correspond to an output device. If a particular Interlock condition exists, the respective Interlock bit is set, the phase status Interlock bit is set, and the phase block is unable to be started. Interlock conditions must be changed for the interlock to clear and the block to become ready. Also, Interlock conditions are unavailable if the phase block is in operation. Some examples of phase block interlocks are:

• A reactor discharge valve that is open prevents the operation of any phase block that adds bulk ingredients to the reactor.

• The level in a reactor must be a certain height before the agitator phase block can start.