Cascadesäätö

Cascadesäätö, often translated as cascade control or ratio control, is a control system strategy used in process industries. It involves linking two or more controllers in a hierarchical arrangement. The primary controller, known as the master controller, sets the setpoint for a secondary controller, the slave controller. The slave controller then directly manipulates the process variable, but its setpoint is determined by the output of the master controller.

This arrangement is particularly useful when a direct control of a primary variable is difficult or leads to undesirable oscillations. For instance, in a heat exchanger, controlling the outlet temperature directly might require frequent and large adjustments to the steam flow, causing instability. Instead, a cascade control system could use a master controller to set the desired outlet temperature, and its output would then dictate the setpoint for a slave controller that directly manipulates the steam flow. This allows the slave controller to react quickly to disturbances in the steam supply, while the master controller makes slower, more deliberate adjustments to achieve the final temperature target.

Another common application is in flow control, where a ratio controller might be used to maintain a specific ratio between two or more flow streams. The master controller could be set to a desired ratio, and its output would adjust the setpoint of a slave controller that regulates the flow of one of the streams. This ensures that the flow of the second stream changes proportionally, maintaining the desired ratio. Cascadesäätö enhances the stability and responsiveness of control loops, leading to improved process performance and product quality.