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A report on Proximity Sensor


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A project report on proximity sensor

Published in: Engineering
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A report on Proximity Sensor

  2. 2. CONTENTS: i. Definition ii. Types of proximity sensors iii. Inductive Proximity Sensor iv. Capacitive Proximity Sensors v. Ultrasonic Proximity Sensors vi. Optical Proximity Sensor vii. Conclusion viii. Reference
  3. 3. DEFINITION: A proximity sensor is a sensor able to detect the presence of nearby objects without any physical contact. A proximity sensor often emits an electromagnetic field or a beam of electromagnetic radiation (infrared, for instance), and looks for changes in the field or return signal. The object being sensed is often referred to as the proximity sensor's target. Different proximity sensor targets demand different sensors. For example, a capacitive or photoelectric sensor might be suitable for a plastic target; an inductive proximity sensor always requires a metal target. Types of Proximity Sensors: There are various types of proximity sensors. Among them four types of sensors havewiderangeof applications. They are: 1. InductiveProximity Sensors 2. Capacitive Proximity Sensors 3. Ultrasonic Proximity Sensors 4. Optical Proximity Sensors Among these Ultrasonic Proximity Sensors are of two types: Active & Passive. OpticalProximity Sensors areof basically of two types:
  4. 4. Thru beam and Reflective, in which Reflective Proximity Sensors are divided in three types: a) Direct Reflection b) Reflection with reflector c) Polarized reflection with reflector INDUCTIVE PROXIMITY SENSORS: Inductive proximity sensors are used for non-contact detection of metallic objects. Their operating principle is based on a coil and oscillator that creates an electromagnetic field in the close surroundings of the sensing surface. The presence of a metallic object in the operating area causes a dampening of the oscillation amplitude. The rise or fall of such oscillation is identified by a threshold circuit that changes the output of the sensor. The operating distance of the sensor depends on the actuator's shape and size and is strictly linked to the nature of the material. COMPONENTS AND WORKING PRINCIPLE: The main components of Inductive Proximity Sensors are coil, oscillator,
  5. 5. detector and the output circuit. The operating distance of the sensor depends on object’s shape and size and strictly linked to the nature of the material. WORKING: The coil generates high frequency magnetic field in front of the face. When the metallic target comes in this magnetic field it absorbs some of the energy. When a piece of conductive metal enters the zone defined by the boundaries of the electromagnetic field, some of the energy of oscillation is transferred into the metal of the target. This transferred energy appears as tiny circulating electrical currents called eddy currents. This is why inductive proximity sensors are sometimes called eddy current sensors. This creates a small amount of power loss in the form of heat (just like a little electric heater) so the amplitude (the level or intensity) of the sensor’s oscillation decreases. Eventually, the oscillation diminishes to the point that another internal circuit called a Schmitt Trigger detects that the level has fallen below a pre-determined threshold. This threshold is the level where the presence of a metal target is definitely confirmed. Upon detection of the target by the Schmitt Trigger, the sensor’s outputis switched on.
  6. 6. ADVANTAGES OF INDUCTIVE PROXIMITY SENSORS: Inductive Proximity Sensors are very accurate compared to other technologies. They have high switching rate, and they can be used in harsh environmentalconditions. DISADVANTAGES OF INDUCTIVE PROXIMITY SENSORS: The only disadvantage of Inductive Proximity Sensors is that it can only detect metallic objects. Thus its industry level applications are limited. COMMON APPLICATIONS: Inductive Proximity Sensors are used in metal detectors, car washes etc. Because these sensors does not require physical contact these are useful
  7. 7. where access presents challenge and dirt is prevalent. Sensing range is rarely greater than 6 cm but it has no directionality. CAPACITIVE PROXIMITY SENSORS: Capacitive Proximity Sensors are used for detection of metallic objects as well as non-metallic objects (liquid, plastic, wooden material etc). These sensors use variation of capacitance between the sensors and the object. Variation in distance down to 1 micro inch can be measured accurately. All targets having dielectric constant more than air can be detected. COMPOMENTS AND WORKING PRINCIPLE: The main components of the Capacitive Proximity sensor Are Plate, Oscillator, ThresholdDetector and theOutput Circuit. WORKING: Inside the sensor is a circuit that uses the supplied DC power to generate AC, to measure the current in the internal AC circuit, and to switch the output circuit when the amount of AC current changes. Unlike the inductive sensor, however, the AC does not drive a coil, but instead
  8. 8. tries to charge a capacitor. Remember that capacitors can hold a charge because, when one plate is charged positively, negative charges are attracted into the other plate, thus allowing even more positive charges to be introduced into the first plate. Unless both plates are present and close to each other, it is very difficult to cause either plate to take on very much charge. Only one of the required two capacitor plates is actually built into the capacitive sensor! The AC can move current into and out of this plate only if there is another plate nearby that can hold the opposite charge. The target being sensed acts as the other plate. If this object is near enough to the face of the capacitive sensor to be affected by the charge in the sensor's internal capacitor plate, it will respond by becoming oppositely charged near the sensor, and the sensor will then be able to move significant current into and out of its internal plate.
  9. 9. ADVANTAGES OF CAPACITIVE PROXIMITY SENSORS: The main advantage of Capacitive Proximity Sensors is that it can detect metallic as well as non metallic objects such as wood, liquid, plastics etc. Also detection speed is very high and it has good stability. It uses low power and it is less costly. DISADVANTAGES OF CAPACITIVE PROXIMITY SENSORS: The main disadvantages of these sensors are, they are affected by temperate and humidity. Also these sensors are less accurate than InductiveProximity Sensors. Thesesensors aredifficultto design. COMMON APPLICATIONS: Capacitive touch sensors are used in laptop track pads, digital displays, mobile phones, mobile displays and many more. More and more design engineers are selecting Capacitive Sensors for their versatility, reliability, robustness and costeffectiveness over mechanical switches. ULTRASONIC PROXIMITY SENSOSORS: Ultrasonic sensors are based on measuring the properties of sound waves with frequency above the human audible range. Systems typically use a transducer which generates sound waves in the ultrasonic range,
  10. 10. above 18 kHz, generally in the range of 40 kHz, by turning electrical energy into sound, then upon receiving the echo turn the sound waves into electrical energy which can be measured. The Ultrasonic Sensor can measure distances in centimeters and inches. It provides good readings in sensing large-sized objects with hard surfaces. COMPONENTS AND WORKING PRINCIPLE: Active ultrasound sensors emit sound waves from quartz-crystal transducers. The waves strike objects within the field of detection and as long as there are no movement the waves are not disrupted. However, when movement occurs the sound wave is disrupted and is reflected back to the system’s receiver.
  11. 11. ADVANTAGES OF ULTRASONIC PROXIMITY SENSORS: Ultrasonic proximity sensors are not affected by atmospheric dust, snow, rain etc. These sensors can work in adverse conditions where application of other sensors is not easy. Sensing distance of these sensors is morecompared to inductive or capacitive proximity sensors. DISADVANTAGES OF ULTRASONIC PROXIMITY SENSORS: These sensors find difficulties in sensing reflections from small, curved, thin and soft objects. GENERAL APPLICATIONS OF ULTRASONIC PROXIMITY SENSORS: Ultrasonic Thru beam sensors are used for bottle counting in drink filling machines. The bottles pass the sensor too quickly and the gaps between the bottles are often too small. For this reason, ultrasonic thru-beam sensors are particularly suitable for bottle counting. Even in areas with strong steam generation, reliable detection of bottles is guaranteed with ultrasonic thru-beam sensors. These sensors also find application in vehicle detection in automatic barrier systems, where proximity sensor is used to detect any vehicle under the barrier, if a vehicle is detected
  12. 12. under the barrier, it automatically opens the barrier. OPTICAL PROXIMITY SENSORS: An optical proximity sensor offers non-contact sensing of almost any object up to a range of 10 meters. It includes a light source, (usually an LED in either infrared or visible light spectrum) and a detector (photodiode). The light source generates light of a frequency that the light sensor is best able to detect, and that is not likely to be generated by other nearby sources. Infra-red light is used in most optical sensors. To make the light sensing system more foolproof, most optical proximity sensor light sources pulse the infra-red light on and off at a fixed frequency. COMPONENTS AND WORKING PRINCIPLE: Optical sensors are basically of two types: Thru Beam Optical Sensors and Reflective type Optical Sensors. Reflective type Optical sensors can be again classified in three types: Direct reflection, Reflection with reflector and Polarizedrefectionwithreflector.
  13. 13. THRU BEAM OPTICAL SENSOR: In Thru Beam Optical Sensors the emitter and the receiver are housed separately. Optical signal, which is pulsated by the pulse generator is sent by emitter and is received by the receiver. Whenever there is an object between emitter and the receiver light beam cannot pass through, thus disrupting the optical signal, which is detected by the sensor and it gives proper output. These sensors allow the longest range of detection.
  14. 14. REFLECTIVE METHOD: Unlike Thru Beam Sensors, in Reflective type sensors emitter and receiver are housed together. In this case reflection occurs either from the target or a reflector, which reflects the beam emitted by emitter, and this reflected signal is received by receiver. These sensors aredivided in three types: DIRECT REFLECTION: In Direct Reflection method the light beam emitted is reflected of the object, which is sensed by the sensor. The sensing range depends upon the surfacetypeand colour of the object.
  15. 15. REFLECTION WITH REFLECTOR: Here the emitter and receiver is housed together at one point, but a separate reflector is needed in another point of the system, which reflects the light beam emitted, this reflected light beam is received by receiver. An object is detected when it interrupts the light beam between the sensor and reflector. These photocells allow longer sensing distances, as the rays emitted are almost totally reflected towards the receiver.
  16. 16. POLARIZED REFLECTION WITH REFLECTOR: Often shiny objects reflect the light beam emitted by emitter in reflection with reflector methods. Thus shiny objects are not properly sensed. This problem is handled by using polarized reflective sensors. Polarized reflective sensors contain polarizing filters in front of the emitter and receiver that orient light into a single plane. These filters are perpendicular or 90° out of phase with each other. The light beam is polarized as it passes through the filter. When polarized light is reflected off an object, the reflected light remains polarized. When polarized light is reflected off a depolarizing reflector, the reflected light is depolarized. The receiver can only detect reflected light that has been depolarized. Therefore, the receiver cannot see (receive) light from reflective objects
  17. 17. that did not depolarize the light. The sensor can “see” a reflection from a reflector, and it cannot“see” a reflection frommostshiny objects. All standard reflectors depolarize light and are suitable for polarized reflective sensing. ADVANTAGES OF OPTICAL PROXIMITY SENSORS: These sensors are effective in Dusty or noisy environments, uses focused beam, higher sensing distance compared to Inductive and capacitive type sensors and they are immune to visible light interference.
  18. 18. DISADVANTAGES OF OPTICAL PROXIMITY SENSORS: The main disadvantageof Opticalsensors is they are costly. APPLICATIONS OF OPTICAL PROXIMITY SENSORS: Optical proximity sensors finds applications in lift door mechanisms, components positioning sensing in electronic industry, security and safety applications, counting of bottles/containers in factories etc. CONCLUSION: The global market for these proximity sensors is expected to grow at a steady rate. Major industries using proximity sensors are machine tools, woodworking machines, packaging machines and other types of machinery. Further applications of proximity sensors are automatic door units such as garage doors or doors inside buildings, elevator doors or doors insiderailway coaches. The building and automotive sector are further industries using high volumes of proximity sensors.
  19. 19. REFERENCES: ments/ca/c116-ca502_-en-p.pdf 1/01 htm 041223/Retroreflective-and-Polarized-Retroreflective.html