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The lowest level of procedural element in the procedural control model.

The smallest element of procedural control that can accomplish a process-oriented task is a phase. A phase may be subdivided into smaller parts. The steps and transitions as described in IEC 848: 1988 document one method of defining subdivisions of a phase. 

A phase can issue one or more commands or cause one or more actions, such as

The execution of a phase may result in

The intent of the phase is to cause or define a process oriented action, while the logic or set of steps that make up a phase are equipment specific. Examples of phases include the following:

Specification notes

You can use  SFC diagrams for phases.