Basic element of the Systems of Automation, the sensor can be used in control of processes continues or discrete to convert the physical 0 variable of entrance into 0 variable of exit signal so that it is shown, stored or manipulated, serving of entrance for devices or systems. The majority of the sensors is electric transducers, therefore they convert the largeness of entrance for an electric largeness, that can be measured and be indicated by a called eletroeletrnico signal of measurer. (Telecurso 2000). For Rosary 2005, a sensor can be defined as a transducer that modifies its internal physical characteristic due to a external physical phenomenon. The sensor is a device capable to monitor the variation of a physical largeness and transmits this information to an indication system that is intelligible for the element of control of the system. (Telecurso 2000). A sensory change its behavior under the action of a physical largeness, being able to indirectly supply directly or a signal that indicates this largeness and converting one physical amount in an electric signal.
(Dally, Riley and McConnel, 1993). Sensors are frequently transducers, that are devices that convert an energy form into another one. We can define sensors then as: the element that perceives the state of 0 variable that monitorial during the processes, informing to the control systems. The signal of a sensor can be used to detect and to correct shunting lines in systems of control, and the instruments of measurement, that frequently are associates to the Systems of Control of closed mesh. The Main types of sensors used in the industry are: Of Proximity? mechanic, optic, inductive and capacitive. Of Position and Speed? potentiometer, LVTD, absolute and relative tacogeradores, potentiometers. Of force and Pressure? Inductive, capacitive, piezoeltrico, piezoresistivo.
Of temperature? Thermocouples, termoresistncia (RTD), thermisters. Of vibration and Acceleration. Main Characteristics of the sensors. Linearity: degree of proportionality between the generated signal and the physical largeness. Band of performance: intervals of values of the largeness where the sensors can be used. Classification how much to the types of controlled 0 variable. Continuous sensors? they carry through measurements you continue of the 0 variable. Discrete sensors? they present only two states, ' ' on or desligado' '. Classification how much to its functioning. Auto fed or passive: the proper element produces the exit signal, without external feeding, example of this sensor is the thermocouple, that converts the temperature into electric signal. With active external feeding or: This requires the feeding of energy for attainment of the exit signal, can give as example the sonar, that emits a signal stops with the reflection esteem in the distance of the object.