CHAPTER Sensors and actuators 3 Industrial controllers, or computers in control systems monitor the operating states and working conditions of the perceive equipment. Through sensors, the controllers and computers vital infor- mation about states and conditions, which allows adjustments to be made far more quickly and accurately than mechanical systems can do them by themselves. Sensors convert measurements of temperature, pressure, density, strength, position, or other quantities into either digital or analog electric signals. Industrial controllers or computers in control systems use data received from sensors to control or drive different equipment or systems by the use of actuators. The actuators are electrome- chanical devices which can generate electrical, magnetic, pneumatic, hydraulic, optical or other forces to drive shafts, or movements of the controlled equipment. In many industrial control systems, those sensors and actuators constitute a network with connections of various types of Fieldbus. Industrial control systems can be very complex, and are usually structured into several hierarchical levels. The networks that consist of sensor and actuator