Proximity sensors



  proximity sensor is a small device which can detect the presence of any nearby object without any physical contact. proximity sensor are more reliable because there is no physical contact between the sensor and  detected object.

images?q=tbn:ANd9GcTnr0MBevtxa2KCKXyOvF1Eke2COyZRb85RPNFW2hjv4zB4LcqQGA Proximity sensors


   working principle of the proximity sensor is similar as the IR obstacles detector consist of  a LED diode and a potoelectric diode. it emits electromagnetic field or any infrared light . if their is any change  in electromagnetic signal which results in presence of  any object. through the line schematic it can easily understand that when the infrared light emits from the IR LED and if their is any type of sensed element then it reflected from  that  element and falls on the photoelectric diode which break the circuit.

Types of  proximity sensors
1.inductive proximity sensor
2.capacitive  proximity sensor
3.ultrasonic proximity sensor
4.photoelectric proximity sensor


   works on the principle of the resonance and eddy currents.    this type of sensor is also known as electronic oscillator. these are basically used to detect the metallic object. it is generally consist of  inductive coil made up of very fine copper wire. A capacitor is also used to store the charge and A power supply to produce the electrical excitation.these inductive type of sensor use currents  induced by magnetic field to detect the metallic the coil high frequency magnetic field generated. if there is any metallic object then this inductive magnetic field produce a current into the metallic object which result to  develop a new magnetic field  and this magnetic field opposes the earlier magnetic field. the net  effective change in the magnetic field is to changes in inductance of the inductive sensor. 
                                                the object which has to be detected must be conductive material and has low resistivity also does not  necessarily feromagnetic. 
inductive-proximity-sensor-cutaway-with-annotation Proximity sensors
 Application  of inductive type of  proximity sensors
1. wind power plant (wind turbine )

 capacitive proximity sensors
                                                   capacitive type of proximity sensors are  similar as the inductive type of proximity sensor.the different is that  capacitive  proximity sensor produces electrostatic field instead of electromagnetic field which is produced by inductive type of proximity sensors.capacitive type of sensors can be used to detect for both type of metal and non metal objects.they use the variation in the capacitance to  detect any nearby object.

Working principle of the capacitive type of proximity sensor
                                                                                                     the working principle is based on the variation in the capacitance. it consist of  plates , threshold detector and oscillator and output circuit.
when  we put the sensor in working condition then a electrostatic  field  is generated by the capacitor plate  and  if their is any object between the sensing field then the capacitance will change as a result oscillator start oscillating . if the target object is very near  to the sensor then the capacitance will increase and vice versa (AS the target moves away from the sensor the oscillator  amplitude decreases )

proximity-sensors-11-638 Proximity sensors

ultrasonic proximity sensor
                                                the main application of these types of sensor is  to measure the distance of any target(object) from the sensor.mainly used to detect the sound waves.

working principle of ultrasonic proximity sensor
                                                                                 it uses a piezoelectric transducer to detect the sound has an acoustic transducer which is vibrating at ultrasonic frequency. the pulse are emitted in form of cone shaped beam and  falls on  the target object. these pulse are reflected from the target object and again receive by the sensor. this sensor calculate the time between this. then velocity can easily be calculate the distance by using basic formula distance = velocity of the sound wave in flow medium*time taken by the sound wave to reflect from the target object to the sensor destination 

5 Proximity sensors

photoelectric proximity sensor 
                                                     this sensor is also used to measure the distance , absence, or presence of any object.  it use the light sensitive element to detect the object. it consist of emitter and a reflector.emitter emits the light which can detect by the detector. Photoelectric sensors consist of a light source (usually an LED, light emitting diode, in either infrared or visible light spectrum) and a detector (photodiode).it can easily be  used in  dusty environment because of high intensity of the light beam emitted by emitter.

there are three type of photoelectric proximity sensor
1.retro-reflective photoelectric proximity sensor
2.through beam  photoelectric proximity sensor
3.Diffuse reflective photoelectric proximity sensor 

1. retro-reflective photoelectric proximity sensor
 this type of proximity sensor is mainly consist of  three types of components
3.retro reflector
emitter  and detector  are placed in  single housing (package) and retro reflector placed at a small distance from the emitter detector housing (package).A reflector is also needed.

April-Photoelectric4 Proximity sensors

disruption of the light between sensor and reflector is can detect the large separation between the sensor and the object because the emitted light totally reflected  by the reflector. it can detect distance about 10 meters.
                                                      One reason for using a retro-reflective sensor over a through-beam sensor is for the convenience of one wiring location; the opposing side only requires reflector mounting. This results in big cost savings in both parts and time. However, very shiny or reflective objects like mirrors, cans, and plastic-wrapped juice boxes create a challenge for retro-reflective photoelectric sensors. These targets sometimes reflect enough light to trick the receiver into thinking the beam was not interrupted, causing erroneous outputs

2.through  beam  photoelectric proximity sensor
                                                                                 in this type of sensor emitter or transmitter and detector (receiver)  is separated  with their housing (packaging). The purchase, installation, and alignment of the emitter and receiver in two opposing locations, which may be quite a distance apart, are costly and laborious.they have industrial and commercial applications.they detect obstructions in the path of garage doors.
Photoelectric_Sensor_TG_Overview_fig1 Proximity sensors

3. Diffuse reflective photoelectric proximity sensor 
                                                                                        in this type of sensor  target is acts as a reflector.the basic installation is same as the retro reflective proximity sensor.main components are  only emitter, detector . the sensor sensitivity is depends on the target material because it works as the reflector in this sensor. if we use the a non-reflective target like matte black paper then the sensor does not work because this target does not reflect any light wave however it absorbs all the light it is important to use the reflective targets.
 April-Photoelectric6 Proximity sensors





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