Unit Control

The batch control system transmits its batch requests to the control system through a series of tags that are mapped to the memory of the control system. One group of these requests handles the unit Hold, Restart, and Abort.

When the batch control system needs to change the status of a recipe, it writes to a tag in the control system that corresponds to the particular unit control bit. Similar to the phase control bits, these commands are typically packed into a word to maximize control system memory.

In the control system program, the unit control word can be monitored continuously or upon a change of status. Each of the commands is read as a one-shot action, and only one request is transmitted at a time. The particular control bits are used within each phase block associated with the particular unit, and the phase operation responds accordingly.

Transfer phases that use a unit placed on Hold act according to customer specifications. Usually, when the unit is the source of the transfer, the phase is Hold, and when the unit is the destination of the transfer, the phase continues to completion.

We recommend that the control system also contain unit status bits. These status bits are not monitored by AVEVA Batch Management System, but they are very useful within the operation of the control system program.

The batch control system provides an enhanced Unit Control option which consists of two Hold propagation modes that you can use to propagate a phase Hold during batch processing.