Industrial Communication Guide

COMPONENTS AND STRUCTURE OF AUTOMATION SYSTEMS

2.3. ACTUATORS

The operating principle of an actuator is the reverse of a sensor: an actuator converts electrical signals from a control computer into physical quantities. Electrical impulses are converted into pressure, sound, temperature, movement or other physical quantities by me- ans of an actuator. As with sensors, it is possible to distinguish between different types of actuators. Actuators are categorized as electromechanical, elec- tromagnetic, pneumatic, hydraulic or other forms, according to the conversion process used.

Actuator

Receives signal

Physical quantity

Frequency converter

Electric motor

Example of pneumatic actuator In a cylinder (pneumatic actuator), the required signals are transmit- ted by the control computer to a valve. The valve works by means of an integrated solenoid which opens or closes, depending on the given voltage. When the valve is open, compressed air flows through the cylinder, which then extends. When the valve is closed, the air in the cylinder escapes, and the cylinder retracts once again. One example of this is an automatic brake. The brake only opens if com- pressed air is available, otherwise the brake operation is carried out automatically.

Electric signal

Physical quantity e.g. Pressure

Temperature Movement

Example of electromechanical actuators In an electric motor (electromechanical actuator), the required si- gnals are transmitted by the control computer to a frequency con- verter. This signal might contain the desired rotational speed, for example. The frequency converter receives the signal and supplies the electric motor with the required current.

Physical quantity

Receives signal

Valve

Cylinder

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