Actuator
An actuator is a device that converts a control signal into physical motion or force to manipulate a process. Common examples include valve positioners, motors, hydraulic and pneumatic cylinders, and solenoids that move final control elements in response to controller commands.
Actuators sit at the output end of a control loop, translating electrical, pneumatic, or hydraulic signals into the mechanical action needed to open a valve, move a damper, or position a robot arm. They are characterised by their force, stroke, speed, and resolution. Actuators matter because they are the muscles of automation: without reliable, accurate actuation, even the best sensing and control algorithms cannot influence the physical process being regulated.