Often process control strategies require the use of multiple loops to perform a control task. Cascade control uses a primary and a secondary (or inner loop) variable, each with its own PID controller, to manipulate one valve for the purpose of maintaining the primary variable at its set point.

Ratio control can be used for mixing two flows or for other purposes when it is important to maintain one flow at the same ratio as another flow.

Override control will sacrifice the control of one controlled variable in order to hold another variable at a limit.

These forms of multiple loop control are explained in the pages accessible from the menu.