TABLE OF CONTENTS Chapter 3 defined the outside view of process cells. Figure 5-5 shows the elements within a process cell. The scope of a process cell is a batch, and the boundaries of process cells can be defined using the following general guidelines:
A process cell is the collection of all equipment required for the production of a batch.
Process cell boundaries are often where batches lose or change their identity, such as when they are mixed together, or are separated into sub lots and processed differently.
Process cell boundaries may be defined by a span of operator control, such as when processing is performed in different geographical locations, or when there are different departments in charge of different processing stages.
Process cell boundaries may also be defined to provide the span of control for emergency situations, such as being able to stop or abort an entire batch.
Process cells may be as small as a single unit or as large as hundreds of units. There is no general rule for process cell size because it is based on organizational and safety boundaries, not just the physical processes.
The logic within a process cell can be very complex. It must interface to the operator, create control recipes, execute the control recipe procedure, make the linkage to units, generate batch records, coordinate shared resources, and manage common control modules.
Fortunately, much of a process cell's control functionality is available from commercial-off-the-shelf (COTS) recipe-execution systems and...
