What is override (selector) control and when is it used?

Override/selector control uses logic (high/low select) to choose between multiple controller outputs to protect against constraint violations. Examples: low select between temperature controller and high temperature limiter protects against overheating; high select between level controller and low level override protects against pump cavitation. Implementation: multiple controllers calculate outputs, selector passes winning output to valve. Requires external reset (anti-reset windup) on controllers not selected to prevent integration. Used extensively for constraint handling and protection.