Phase Block Rules of Operation

There are some general rules you need to follow when planning and constructing the operation of a phase block or complete process program. These rules are discussed in greater detail throughout this documentation.

• All items, except outputs, specific to a particular phase block should reside within that phase block.

• An interlock is a pre-run condition of a phase block that prevents the phase block from being operated.

• An alarm is generated by either a run-time conditional error or a device failure.

• Critical alarms put the corresponding phase blocks on hold if they are currently processing.

• On an initial control system power on sequence, the status of all phase blocks should be ready or interlocked, and all of the outputs must be in a de-energized state.

• If a batch system to control system communications error occurs, any phase in the Run state should continue until Done, and the control system should wait for communications to be restored for the next command.

• The manual operation of output devices must be addressed with regard to the status of the phase logic blocks that use the outputs.

• The control system logic must recognize and react to unit control bits. These control bits include Unit Hold, Unit Restart, and Unit Abort.