SENSORS <ul><li>Proximity sensors. </li></ul><ul><li>Proximity sensors are used to detect the presence of metallic objects. And giving an electrical out put. </li></ul>
<ul><li>Capacitive proximity sensors </li></ul><ul><li>Variations of electrical capacitance can be used as a means of proximity sensing in which the movement of the object alters the capacitor field. </li></ul><ul><li>Capcitive methods are very sensitive, distance down to one micro inch can be measured. </li></ul>
<ul><li>Inductive proximity sensors </li></ul><ul><li>A proximity sensor in which the sensing coil oscillates at about 100 Kc/ s. As a metal object approches the coil eddy current begines to flow in the object. A point eventually reaches to cease the oscillation.The out put from the oscillater operates a relay. </li></ul>
<ul><li>Optical proximity sensors </li></ul><ul><li>The light sensitive devices translate varriations in light in to electrical signal. A photocell, photo transisters, are used in electronic circuits and the out put is connected to an amplifier and trigger circuit which operates a relay. </li></ul>
<ul><li>Ultrasonic proximity sensing </li></ul><ul><li>Ultrasonic proximity sensing is similar to optical sensing that it requires a transmitter and receiver with either a direct or a deflected path between them.The transmitter is energized continously, the output from the receiver decreasas when the path is obscured. </li></ul>
<ul><li>Radio active tracers </li></ul><ul><li>If a particle of radio active material is fixed to an object, then the approch of the object can be detected with a radiation detector </li></ul>
<ul><li>Piezoresistive Pressure Sensor </li></ul><ul><li>The sensing material is a diaphragm formed piezoresistive pressure sensor, which bends with applied pressure. That bending leading to a change in the resistivity of the material. This change can be an increase or a decrease according to the orientation of the resistors </li></ul>
<ul><li>Hall-Effect Sensor </li></ul><ul><li>Hall-effect sensors are used for highly accurate gear-tooth sensing, direction detection, linear sensing, speed sensing, position sensing and contactless switching. </li></ul>
<ul><li>Vibration Sensors </li></ul><ul><li>Vibration sensors can have from one axis to three axes of measurement, the multiple axes typically being orthogonal to each other. These devices work on many operating principles. The most common types of vibration sensors are piezoelectric, capacitance, strain gage, resonance beam, piezoresistive and magnetic induction </li></ul>
<ul><li>Resonant frequency ( harp sensor) </li></ul><ul><li>Two resonators are stimulated by an ac signal from the processor and surrounding magnetic field. One resonator reacts to tensile strain and the other compression. When the silicon substrate is displaced in either direction, the frequency of the resonators changes in a measurable way according to the degree of displacement. </li></ul>
<ul><li>Strain gage sensors </li></ul><ul><li>Strain gages typically mount the sensor directly on a metallic diaphragm and measure deflection . </li></ul>
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