CLASSIFICATION OF THE VARIABLES IN A CHEMICAL PROCESS

The variables (flowrates, temperatures, pressures, concentrations, etc.) associated with a chemical process are classified into:

a. Input variables, which denote the effect of the surroundings on a chemical process, and

b. output variables, which denote the effect of the process on the surroundings.

The input variables can be further classified into the following categories:


i.Manipulated (or adjustable) variables, if their values :can be adjusted freely by the human operator or a control mechanism and

ii. disturbances, if their values are not the result of adjustment by an operator or a control system.

The output variables are also classified into the following categories:

i. Measured output variables, if their values are known by directly measuring them, and

ii. -unmeasured output variables, if they are not or cannot be measured directly.