DEGREES OF FREEDOM ANALYSIS IN-PROCESS CONTROL

In developing the control system for a process it is desirable to know precisely the number of process variables which the system designer is entitled to attempt to regulate, commonly known as the ''degrees of freedom'' of the process. An extremely simple procedure is described; the maximum degrees of freedom for any process is shown to be the total number of process streams, including streams of heating and cooling media. If inventory in processing units is excluded unless, it affects some more significant variable, such as pressure or composition, then the effective degrees of freedom are generally determined by subtracting one from the total for every additional phase contained in a unit.