What is the difference between open-loop and closed-loop control?

Open-loop control applies a predetermined action without feedback - output is not affected by process response (e.g., timed irrigation). Closed-loop control continuously measures the process variable, compares to setpoint, and adjusts output to minimize error (e.g., thermostat). Closed-loop provides automatic correction for disturbances and process variations, making it essential for precise process control. Most industrial control systems use closed-loop (feedback) control.