Which device operates under the control of a signal from a controller to perform a mechanical action?

An actuator is a device that converts a control signal into mechanical motion. This mechanical action may involve moving a component, opening or closing a valve, or any other physical alteration necessary for a process to occur. Actuators typically work in response to a controller, which sends the signal based on input data or predefined programming. This interaction between the controller and the actuator is essential in automated systems, enabling precise control over various mechanical functions.

In contrast, a transducer is a device that converts one form of energy to another, such as converting mechanical energy into electrical energy or vice versa. Although transducers are crucial in systems that involve signals and data, they do not perform mechanical actions on their own.

Sensors, on the other hand, detect physical phenomena and convert them into signals that can be read by other devices, such as a controller. They serve a vital role in monitoring and providing feedback but do not execute mechanical actions themselves.

The controller is responsible for sending commands to the actuator, making decisions based on input from sensors or other data sources. However, the controller is not the device that directly carries out mechanical actions; that function belongs to the actuator. Therefore, the actuator is the correct choice because it is the component that responds to the controller's signals