proximity sensors report
- 1. PROXIMITY SENSORS sensing instrumentation practise PROXIMITY SENSORS K.BHOLANATH - EDM18B030 RAVIRAJKUMAR.P - EDM18B043 S.Y.P NARASIMHA - EDM18B045 I. INTRODUCTION Basically Sensor is a device or system which purpose is to detects events or changes in the environment and to send that information to the electronic devices connected to it mostly the computer processor. II. TYPES OF SENSORS There are different types of sensors available. Some of them are: • Vision and imaging sensors • Temperature sensors • Radiation sensors • Proximity sensors • Pressure sensors • Position sensors A. Proximity sensor A proximity sensor is a sensor able to detect the presence of nearby objects without physical contact. It often emits an electromagnetic field and looks for the change in the field or for the incoming signal. The proximity sensors have high reliability and long func- tional life because there is no physical contact between the sensor and the objects. These are applied in many areas like Mobile devices, con- veyor systems,parking systems, Anti aircraft missile systems. 1) Common types of Proximity sensors:: • Inductive Proximity sensor • Capacitive proximity sensor • Optical proximity sensors • Ultra sonic Proximity sensor III. INDUCTIVE PROXIMITY SENSOR An Inductive proximity sensor is an electronic proximity sensor , which detects metallic objects without touching them Inductive sensors operate on the basis of Faraday’s Law. One way to state Faraday’s Law is that a change in magnetic flux in a coil of wire will induce a voltage in a nearby coil. This is applied in inductive proximity sensors Gambar 1. INDUCTIVE PROXIMITY SENSOR Gambar 2. INDUCTIVE PROXIMITY SENSOR A. WORKING PRINCIPLE The Main Components Of The Inductive Proximity Sensor Are. Coil, Oscillator, Detector And The Output Circuit The operation of a typical inductive proximity sensor is shown The sensor itself contains an oscillator circuit and a coil from which an electromagnetic field radiates out and induces eddy currents in any nearby metallic objects. So when we keep any metallic object near the sensor The eddy currents have the effect of attenuating the oscillations from the amplifier. EDM18B030,EDM18B043,EDM18B045 1 / 5
- 2. PROXIMITY SENSORS sensing instrumentation practise This reduction in oscillations is registered as the presence of a metallic object. B. WHY ONLY METALLIC OBJECTS? Because only metallic objects have inductive properties, inductive sensors can’t be used to detect plastic or cardboard or other non-metallic objects. However, different metals have different inductive properties and the type of metal being sensed will influence the sensing distance C. ADVANTAGES • They are very accurate compared to other technologies. • They have a high switching rate. • They are capable of working in harsh environmental conditions. • It has longer life D. DISADVANTAGES • The sensing range of an inductive sensor dependents on the type of metal being detected, its shape, its size and also coil size used in the design. Due to above reason, inductive sensor has distance limitations for sensing • It can detect metallic targets only. E. APPLICATIONS The use of inductive proximity sensors is increasing glob- ally, on the back of industrial applications such as: the search coil magnetometer that is used in electromagnetic waves measurement; metal detectors; traffic lights; car washes; and a host of other automated industrial processes. IV. CAPACITIVE PROXIMITY SENSOR Gambar 3. CAPACITIVE PROXIMITY SENSOR Capacitive proximity sensors are similar in function to inductive sensors but have certain unique design specifications and operating parameters. Capacitive proximity sensors sense ”target” objects due to the target’s ability to be electrically charged. Since even non-conductors can hold charges, this means that just about any object can be detected with this type of sensor. A. COMPONENTS The Main Components Of The Capacitive Proximity Sensor Are Plate, Oscillator, Threshold Detector And The Output Circuit. Gambar 4. CAPACITIVE PROXIMITY SENSOR B. WORKING PRINCIPLE Inside the sensor , 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 tries to charge a capacitor. we also know 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. C. ADVANTAGES • It can be used to detect non-metallic targets. • It can detect through containers of certain types also. • It is simple in construction and adjustable. • It can detect dense targets and liquids. • It is lower in cost. • It has higher sensitivity and can be operational with small magnitude of force. • It can be used for the measurement of force, pressure and humidity etc. EDM18B030,EDM18B043,EDM18B045 2 / 5
- 3. PROXIMITY SENSORS sensing instrumentation practise • It has very good resolution (as low as 0.003 mm) and frequency response. D. DISADVANTAGES • It is very much sensitive to changes in environmental conditions such as temperature, humidity etc. This will affect the performance. • The measurement of capacitance is hard compare to measurement of resistance. • Capacitive proximity sensor are not so accurate compare to inductive sensor type. E. RANGE Capacitive proximity sensors usually have a larger sensing range than their inductive counterparts, and it typically falls between 5 and 40 millimeters. The detection distance depends on plate diameter F. APPLICATIONS Capacitive sensors are used in the measurement of brake disc deformation. Due to the high temperature development, very few sensors are suitable for operating close to the measurement object. Capacitive transducers detect changes in the nanometer range and measure the wear on the brake disc V. PHOTOELECTRIC PROXIMITY SENSOR Gambar 5. PHOTOELECTRIC PROXIMITY SENSOR A sensor which detects the presence of object by the action of light. The main components of this sensor are emitter, detector and associated electronics. Emitter (Light Emitting Diode, laser diode) sends a beam of light. The detector (photo diode or phototransistor) detects emitted light.An associated electronics required to amplify the detected signal. The emitter sometimes called the sender transmits a beam of either visible or infrared light to the detecting receiver. All photoelectric sensors operate under similar principles. Dark-on and light- on classifications refer to light reception and sensor output activity. With no reception of light, the output produces then the sensor is dark-on. If output from light received then it is light-on. A. TYPES OF PHOTOELECTRIC PROXIMITY SENSOR There are three main sensing methods of the photoelectric proximity sensor and they are, • Through beam method • Retro-reflective method • Diffuse or Reflective method B. WORKING PRINCIPLE 1) Through beam method: In this type of method, an emitter sends out a beam of light directly in the line-of-sight of the emitter to a receiver. When an object breaks this beam of light, it detects as a presence. This type of setup requires two components they are an emitter and a separate detector, which makes it a bit more complex to install and wire. However, the advantage is that it’s the most accurate of the sensing methods with the longest sensing range. Gambar 6. Through beam New laser diode emitter models can transmit a well- collimated beam 60 m for increased accuracy and detection. At these distances, some through-beam laser sensors are capable of detecting an object the size of a fly, at close range, that becomes 0.01 mm. One ability unique to throughbeam photoelectric sensors is effective sensing in the presence of thick airborne contaminants. 2) Retro-reflective method: In this method, detection occurs when the light path breaks or disturbs. Both the light emitting and light receiving elements are in same housing. The light from the emitting element hits the reflector and returns to the light receiving element. When a target is present, the light gets interrupt. 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. EDM18B030,EDM18B043,EDM18B045 3 / 5
- 4. PROXIMITY SENSORS sensing instrumentation practise 3) Diffuse or Reflective method: As in retro-reflective sen- sors, emitters and receivers located in the same housing. In this Diffuse method, Both the light emitting and light receiving elements contain in a single housing. The sensor receives the light reflected from the target. Diffuse photoelectric sensors are similar in some respects to reflective sensors. This is because like reflective sensors they emit a light beam in the direction of the object to be detected. However, instead of a reflector used to bounce the light back to a detector, the object to be sensed functions as the reflector, bouncing some of the light back to be detected and register an object’s presence. Mostly, the diffuse sensors use in public washroom sinks, where they control automatic faucets. Hands placed under the spray head act as reflector, triggering (in this case) the opening of a water valve. diffuse sensors are somewhat color dependent, certain versions are suitable for distinguishing dark and light targets in applications that require sorting or quality control by contrast. C. ADVANTAGES • The sensor senses all kinds of materials. • It has longer life, long sensing range and very reliability. • Very fast response time and less costly. • Diffuse photoelectric sensor detects small objects includ- ing color mark and label detection. • mostly retro-reflective type sensor can detect transparent objects. • Through beam type can detect long range and it is tolerant of dirty environment. D. DISADVANTAGES • Over coarse of time lens get contaminated. • Generally, the sensing range is affected due to color and reflectivity of the target. • Through beam type requires transmitter (Tx) and receiver (Rx) at two separate locations • Retro reflective type requires reflector in addition to Tx/Rx. This makes system installation complex E. APPLICATIONS • Checking objects on production lines or conveyors • Counting of small objects • Detection of colours • Monitoring bigger areas for objects with light grids • Measuring distance • Logistics and materials handling VI. ULTRASONIC PROXIMITY SENSOR • An ultrasonic sensor is an instrument that measures the distance to an object using ultrasonic sound waves. • An ultrasonic sensor uses a transducer to send and receive ultrasonic pulses that relay back information about an object’s proximity. • High-frequency sound waves reflect from boundaries to produce distinct echo patterns. Gambar 7. ULTRASONIC PROXIMITY SENSOR A. WORKING PRINCIPLE Ultrasonic proximity sensors emit and receive sound waves. The carrier signal is a high frequency, inaudible sound wave. They detect the presence of the target object in one of two configurations. 1) TYPES OF ULTRASONIC PROXIMITY SENSOR: • Diffuse or Reflective • Opposed or Thru-Beam Gambar 8. ULTRASONIC PROXIMITY SENSOR 2) Diffuse or Reflective: Diffuse or Reflective sensors have the transmitter and receiver packaged in the same housing. When a target enters the sensing range of the device, the ultrasonic waves are reflected back to the sensor. EDM18B030,EDM18B043,EDM18B045 4 / 5
- 5. PROXIMITY SENSORS sensing instrumentation practise 3) Opposed or Thru-Beam: Opposed or Thru-Beam sensors have the transmitter and receiver packaged separately. The receiver is mounted facing the transmitter and when an object enters the sensing range of an opposed sensor, it blocks the transmitted signal. Rather than activating the trigger when the frequency is received, the trigger is activated when the signal is broken. B. ADVANTAGES • Not affected by color or transparency of objects • Can be used in dark environments • Advantages and Limitations of Ultrasonic Sensors • Low-cost option • Not highly affected by dust, dirt, or high-moisture envi- ronments C. DISADVANTAGES • limited testing distance • inaccurate readings • inflexible scanning methods D. APPLICATIONS used in many manufacturing and automation applications. Mainly for object detection and distance measurement, they’re commonly used in food and beverage processing and various packaging VII. 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 in- siderailway coaches. The building and automotive sector are further industries using high volumes of proximity sensors. VIII. REFERENCES http://www.fargocontrols.com/sensors.html http://www.ia.omron.com/support/guide/41/overview.html http://www.engineershandbook.com/Components/proximitysensors. html EDM18B030,EDM18B043,EDM18B045 5 / 5