Design Phase Blocks

The phase block is the basic building block used for coordinating the control system communication with the batch system. Also called a phase, the phase block is a small portion of control system logic that conducts an independent action within a process or transfer class associated with a batch. Some examples of phase blocks are ramp heat, ramp cool, soak, and bulk add. Phase blocks are associated with each unit or connection in a particular modeling class. For example, you could have an agitator phase block corresponding to a reactor as well as an agitator phase block corresponding to a receiving tank.

We recommend that you design phase blocks as self-contained as possible. This allows you to move the phase block from one control system to another with minimal alterations. Thus, you can have a large library of phase blocks that you can alter and use on an individual basis as you install new equipment or new systems.

The following list describes some of the ultimate goals of phase block logic. While it is likely that processes exist that prevent you from satisfying all of these goals simultaneously, achieving the goals should always be your primary objective.

• Phase logic should be modular for easy duplication and transferability.

• Phase logic must use the standard interface between the control system and the supervisory computer.

• Phase blocks can be written independently of one another.

• Phase blocks should be independent of control systems.

• The control system memory map should not be confining.

• The addition of process equipment should be done easily with little code revision.

• Phase logic structure should be standardized for ease of troubleshooting.

• Phase logic should be available for multiple uses within the operational program.

• Phase logic should consist of a minimum amount of code without compromising functionality or safety.

• Phase logic complexity should be geared to the level of the technical support staff.