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.
WORKING PRINCIPLE OF PROXIMITY SENSOR
working principle of the proximity sensor is similar as the IR obstacles detector sensor.it 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
WORKING PRINCIPLE OF INDUCTIVE 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 objects.in 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.
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 )
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 wave.it 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
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
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.
disruption of the light between sensor and reflector is detected.it 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.
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 rays.so it is important to use the reflective targets.