2604/2704 Cascade Control Supplement

Cascade control is a technique used to enable processes with long lags to be controlled with the fastest possible response to process disturbances including setpoint changes, whilst still minimising the potential for overshoot. 

This is achieved by controlling a secondary, more responsive process that influences the main process.

The main process is controlled using a master PID loop, the output of which is used to determine the setpoint of the secondary process which is controlled by a second PID loop. 

This second loop is referred to as the slave loop.