A cascade control system typically consists of a primary or master controller that generates a control function that serves as the setpoint for a secondary or slave controller. That controller in turn utilizes the actuator to apply its control function directly to the secondary process. The secondary process then generates a secondary process variable that serves as the control function for the primary process.
An illustration of a cascade control is shown below:
From the figure above, it is clear that the outer loop controller (primary controller) becomes the setpoint for the inner controller (secondary controller). The inner loop actually functions like a conventional feedback control system with a setpoint, a process variable, and a controller acting on a process by means of an actuator. The outer loop does a similar task except that it uses the entire inner loop as its actuator.
You may also read:
- Benefits of Cascade Control
- Control Modes in Automation Systems
- Ratio Control
- Key Causes of Uncertainty in Control Systems
- The Performance Limits for PID Controllers
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