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PROXIMITY AND PRESSURE S E N S O R S

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WHAT ARE.SENSORS ??A sensor (also called detector) is a converter that measures a physical quantity and converts it into a signal which can be read by an observer or by an (today mostly electronic) instrument.A sensor is a device which receives and responds to a signal when touched. A sensor's sensitivity indicates how much the sensor's output changes when the measured quantity changes. Sensors are used in everyday objects such as touch-sensitive elevator buttons (tactile sensor) and lamps which dim or brighten by touching the base. There are also innumerable applications for sensors of which most people are never aware. Applications include cars, machines, aerospace, medicine, manufacturing and robotics.

PROXIMITY SENSORS A proximity sensor is a device which detects objects when they get within a certain distance from the sensor. The proximity sensor will then usually send a signal to an electronic circuit to perform a simple action, such as opening a door, turning on a light or sounding an alarm Many proximity circuits detect anything that comes too close. Others are designed to pick up on a particular type of object and ignore everything else. Proximity switches are devices which detect when an object is nearby. When an object gets within a certain distance, they will turn on a circuit to perform some basic function, such as opening a door or turning on a light or an alarm. Some proximity switches are designed to detect certain kinds of objects, while others will detect pretty much anything.

PROXIMITY SENSORS IN

Android phones, like the iPhone, include a piece of hardware known as the proximity sensor. This device senses when the phone is close to an object by emitting a beam or pulse of light to detect the distance between the phone and other objects. Ideally, it senses when you are holding the phone to your ear and turns off the display. Because you are talking on the phone, you do not need to see your phone as opposed to talking via speakerphone while completing other tasks on your phone. The proximity sensor is generally located next to the speaker, near the top of the phone.

Benefits:The proximity reduces usage of your phone's battery when it turns off the display because large displays use a lot of power. Furthermore, the sensor prevents accidental screen touching from your face or ear. Because touch-screen phones are sensitive to touches from other body parts, you may accidentally press a number on the dialer or even hang up on the person with whom you are speaking when holding your phone, especially i

WORKING:::O. Mainly proximity sensor sends an electromagnetic signal or a light signal to a particular range. If light given off by the infrared proximity switch bounces off an object and back to the switch, it means the object is too close and the corresponding electrical circuit will shut off or turn on

CAPACITIVE PROXIMITY SENSORSO The capacitive proximity switch's oscillator measures any change in the capacitance between the target and the switch's plate. The capacitance reading increases as the target gets closer to the sensor. When a preset point is reached, the oscillator will oscillator's activity is detected by the detection respond. The circuit, which will then cause the switch to change its state.APPLICATIONSO A capacitive proximity switch is most often used for targets that are made of plastic, glass, wood, paper, powder, granular materials or cloth. It's also commonly used to control liquid levels in a bin or hopper. Capacitive switches are well suited for this purpose, because they can bypass the container's outer material to detect its contents.

INDUCTIVE PROXIMITY SENSORS An inductive sensor is an electronic device that utilizes proximity sensor technology to detect metallic objects without physical contact

Inductive sensors contain an induction loop, or electromagnetic detection system. Electric currents in the inductive sensor create a magnetic field, or a force field created by a magnetic object. The magnetic field collapses, creating a current when input electricity is added. The presence of metal, since metal is a comparably strong inductor, increases the flow of current inside the induction loop. This change in current is detected by the circuitry, which can then send an appropriate signal when it senses a metal object Inductive sensors are commonly utilized for automated industrial processes or other applications where physical contact or access can be difficult. Inductive sensors may be used for such applications as traffic lights and metal detectors. An inductive proximity sensor uses radio waves to detect objects. Thanks to a coil and an oscillator, the switch creates a field. When the field is disrupted by an object, the switch activates.

APPLICATIONS-Parktronic, car bumpers that sense distance to nearby cars for parking(uses ultrasonic and electromagnetic sensors.)-Ground proximity warning system for aviation safety-Vibration measurements of rotating shafts in machinery -Top dead centre (TDC)/camshaft sensor in reciprocating engines.-Sheet break sensing in paper machine.-Anti-aircraft warfare-Roller coasters-Conveyor systems-Touch screens on mobile devices that come in close proximity with the face.. and many more

PRESSURE SENSORSPressure sensors are used for control and monitoring in thousands of everyday applications. Pressure sensors can also be used to indirectly measure other variables such as fluid/gas flow, speed, water level, and altitude. Pressure sensors can alternatively be called pressure transducers, pressure transmitters, pressure senders, pressure indicators and piezometers, manometers, among other names.Pressure sensors can vary drastically in technology, design, performance, application suitability and cost. A conservative estimate would be that there may be over 50 technologies and at least 300 companies making pressure sensors worldwide

TYPES OF PRESSURE SENSORS----Piezoresistive strain gaugeUses the piezoresistive effect of bonded or formed strain gauges to detect strain due to applied pressure. Common technology types are Silicon (Mon crystalline), Polysilicon Thin Film, Bonded Metal Foil, Thick Film, and Sputtered Thin Film. Generally, the strain gauges are connected to form a Wheatstone bridge circuit to maximize the output of the sensor and to reduce sensitivity to errors. This is the most commonly employed sensing technology for general purpose pressure measurement. Generally, these technologies are suited to measure absolute, gauge, vacuum, and differential pressures.----CapacitiveUses a diaphragm and pressure cavity to create a variable capacitor to detect strain due to applied pressure. Common technologies use metal, ceramic, and silicon diaphragms. Generally, these technologies are most applied to low pressures (Absolute, Differential and Gauge)

----ElectromagneticMeasures the displacement of a diaphragm by means of changes in inductance (reluctance), LVDT, Hall Effect, or by eddy current principle.----PiezoelectricUses the piezoelectric effect in certain materials such as quartz to measure the strain upon the sensing mechanism due to pressure. This technology is commonly employed for the measurement of highly dynamic pressures.----OpticalTechniques include the use of the physical change of an optical fiber to detect strain due to applied pressure. A common example of this type utilizes Fiber Bragg Gratings. This technology is employed in challenging applications where the measurement may be highly remote, under high temperature, or may benefit from technologies inherently immune to electromagnetic interference. Another analogous technique utilizes an elastic film constructed in layers that can change reflected wavelengths according to the applied pressure (strain).[1]----PotentiometricUses the motion of a wiper along a resistive mechanism to detect the strain caused by applied pressure.Other types

APPLICATIONS1. Touch Screen Devices: The computer devices and smart phones that have touch screen displays come with pressure sensors. Whenever slight pressure is applied on the touch screen through a finger or the stylus, the sensor determines where it has been applied and accordingly generates an electric signal that informs the processor. Usually, these sensors are located at the corners of the screen. So when the pressure is applied, usually two or more such sensors act to give precise location information of the location.2. Automotive Industry: In automotive industry, pressure sensors form an integral part of the engine and its safety. In the engine, these sensors monitor the oil and coolant pressure and regulate the power that the engine should deliver to achieve suitable speeds whenever accelerator is pressed or the brakes are applied to the car.For the purpose of safety, pressure sensors constitute an important part of anti-lock braking system (ABS). This system adapts to the road terrain and makes sure that in case of braking at high speeds, the tires dont lock and the vehicle doesnt skid. Pressure sensors in the ABS detail the processor with the conditions of the road as well as the speed with which the vehicle is moving.Air bag systems also use pressure sensors so that the bags get activated to ensure the safety of the passengers whenever high amount of pressure is experienced by the vehicle.

3. Bio Medical Instrumentation: In instruments like digital blood pressure monitors and ventilators, pressure sensors are needed to optimize them according to patients health and his requirements. 4. Industrial Uses: Pressure sensors are used to monitor gases and their partial pressures in industrial units so that the large chemical reactions take place in precisely controlled environmental conditions. In oil industry, sensors detail with the depth that the oil rig has reached while exploring.5. Aviation: In the airplanes, these sensors are needed to maintain a balance between the atmospheric pressure and the control systems of the airplanes. This not only protects the circuitry and various internal components of the airplane but also gives exact data to the system about the external environment. Also, particular levels of air pressure need to be maintained in the cockpit and the passengers lobby to provide nominal ground like breathing conditions.6. Marine Industry: For ships and submarines, pressure sensors are needed to estimate the depth at which they are operating and for detailing the marine conditions so that the electronic systems can remain safe. Oxygen requirements of under water projects are also regulated by the pressure sensors.

Tachometer

The permanent magnet generates a steady and uniform magnetic field. Relativemotion between the field and the rotor induces voltages, which is proportional to the speed of the rotor.The inductance gives the tachometer a certain time constant so that thetachometer cannot measure fast transient accurately.

DISPLACEMENT AND VELOCITY SENSORS

Optical encodersThese are optical devices to measure angular displacement and angular velocity. A disk of an optical encoder is connected to the rotating shaft. The disk has patterns (holes). On one side of the disk there is a light source and on the other photo-detectors. When the disk rotates the light is going through the holes and the photo-detectors generate series of pulses.There are two types of optical encoders: incremental and absolute.

Optical encodersThe incremental encoder provides a pulse each time the shaft has rotated a defined distance.The disc of an absolute encoder has several concentric tracks, with each track having an independent light source and photo detector.With this arrangement a unique binary or Gray coded number can be produced for every shaft position.

LVDTThe two secondary coils are connected in the opposite phase. When the core is in the middle there is no output voltage. Moving the core from the central position unbalances the secondaries, developing an output.Applications:To measure linear displacement, e.g. for measuring tube lengths in a steel plant,applied in linear servomechanisms, etc.

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