 | This article needs additional citations for verification .(January 2020) |
A photoelectric sensor is a device used to determine the distance, absence, or presence of an object by using a light transmitter, often infrared, and a photoelectric receiver. They are largely used in industrial manufacturing. There are three different useful types: opposed (through-beam), retro-reflective, and proximity-sensing (diffused).
A self-contained photoelectric sensor contains the optics, along with the electronics. It requires only a power source. The sensor performs its own modulation, demodulation, amplification, and output switching. Some self-contained sensors provide such options as built-in control timers or counters. Because of technological progress, self-contained photoelectric sensors have become increasingly smaller.
Remote photoelectric sensors used for remote sensing contain only the optical components of a sensor. The circuitry for power input, amplification, and output switching is located elsewhere, typically in a control panel. This allows the sensor, itself, to be very small. Also, the controls for the sensor are more accessible, since they may be bigger.
When space is restricted or the environment too hostile even for remote sensors, fibre optics may be used. Fibre optics are passive mechanical sensing components. They may be used with either remote or self-contained sensors. They have no electrical circuitry and no moving parts, and can safely pipe light into and out of hostile environments. [1]
A through-beam arrangement consists of a receiver located within the line-of-sight of the transmitter. In this mode, an object is detected when the light beam is blocked from getting to the receiver from the transmitter.
A retroreflective arrangement places the transmitter and receiver at the same location and uses a reflector to bounce the inverted light beam back from the transmitter to the receiver. An object is sensed when the beam is interrupted and fails to reach the receiver.
A proximity-sensing (diffused) arrangement is one in which the transmitted radiation must reflect off the object in order to reach the receiver. In this mode, an object is detected when the receiver sees the transmitted source rather than when it fails to see it. As in retro-reflective sensors, diffuse sensor emitters and receivers are located in the same housing. But the target acts as the reflector so that detection of light is reflected off the disturbance object. The emitter sends out a beam of light (most often a pulsed infrared, visible red, or laser) that diffuses in all directions, filling a detection area. The target then enters the area and deflects part of the beam back to the receiver. Detection occurs and output is turned on or off when sufficient light falls on the receiver.
Some photo-eyes have two different operational types, light operate and dark operate. The light operates photo eyes become operational when the receiver "receives" the transmitter signal. Dark operate photo eyes become operational when the receiver "does not receive" the transmitter signal.
The detecting range of a photoelectric sensor is its "field of view", or the maximum distance from which the sensor can retrieve information, minus the minimum distance. A minimum detectable object is the smallest object the sensor can detect. More accurate sensors can often have minimum detectable objects of minuscule size.
| Name | Advantages | Disadvantages |
|---|---|---|
| Through-beam |
|
|
| Reflective |
|
|
| LASER-Reflective |
|
|
| Diffuse |
|
|
Radar is a system that uses radio waves to determine the distance (ranging), direction, and radial velocity of objects relative to the site. It is a radiodetermination method used to detect and track aircraft, ships, spacecraft, guided missiles, motor vehicles, map weather formations, and terrain.
Lidar is a method for determining ranges by targeting an object or a surface with a laser and measuring the time for the reflected light to return to the receiver. Lidar may operate in a fixed direction or it may scan multiple directions, in which case it is known as lidar scanning or 3D laser scanning, a special combination of 3-D scanning and laser scanning. Lidar has terrestrial, airborne, and mobile applications.
A photodiode is a semiconductor diode sensitive to photon radiation, such as visible light, infrared or ultraviolet radiation, X-rays and gamma rays. Photodiode is a PN semiconductor material that produces current or voltage Photovoltaics when it absorbs photons Semiconductor Optoelectronics . The physics of electron excitation for photodiodes are similar to Photoconductivity typically implemented as a Photoresistor or as switches in Thyristor#Photothyristors. Photodiodes can be used for detection and measurement applications, or optimized for the generation of electrical power in solar cells. Photodiodes are used in a wide range of applications throughout the electromagnetic spectrum from IR, visible light, UV photocells to gamma ray spectrometers.
A retroreflector is a device or surface that reflects radiation back to its source with minimum scattering. This works at a wide range of angle of incidence, unlike a planar mirror, which does this only if the mirror is exactly perpendicular to the wave front, having a zero angle of incidence. Being directed, the retroflector's reflection is brighter than that of a diffuse reflector. Corner reflectors and cat's eye reflectors are the most used kinds.
A smoke detector is a device that senses smoke, typically as an indicator of fire. Smoke detectors/Alarms are usually housed in plastic enclosures, typically shaped like a disk about 150 millimetres (6 in) in diameter and 25 millimetres (1 in) thick, but shape and size vary. Smoke can be detected either optically (photoelectric) or by physical process (ionization). Detectors may use one or both sensing methods. Sensitive alarms can be used to detect and deter smoking in banned areas. Smoke detectors in large commercial and industrial buildings are usually connected to a central fire alarm system.
A security alarm is a system designed to detect intrusions, such as unauthorized entry, into a building or other areas, such as a home or school. Security alarms protect against burglary (theft) or property damage, as well as against intruders. Examples include personal systems, neighborhood security alerts, car alarms, and prison alarms.
Continuous-wave radar is a type of radar system where a known stable frequency continuous wave radio energy is transmitted and then received from any reflecting objects. Individual objects can be detected using the Doppler effect, which causes the received signal to have a different frequency from the transmitted signal, allowing it to be detected by filtering out the transmitted frequency.
A passive infrared sensor is an electronic sensor that measures infrared (IR) light radiating from objects in its field of view. They are most often used in PIR-based motion detectors. PIR sensors are commonly used in security alarms and automatic lighting applications.
A motion detector is an electrical device that utilizes a sensor to detect nearby motion. Such a device is often integrated as a component of a system that automatically performs a task or alerts a user of motion in an area. They form a vital component of security, automated lighting control, home control, energy efficiency, and other useful systems.
Level sensors detect the level of liquids and other fluids and fluidized solids, including slurries, granular materials, and powders that exhibit an upper free surface. Substances that flow become essentially horizontal in their containers because of gravity whereas most bulk solids pile at an angle of repose to a peak. The substance to be measured can be inside a container or can be in its natural form. The level measurement can be either continuous or point values. Continuous level sensors measure level within a specified range and determine the exact amount of substance in a certain place, while point-level sensors only indicate whether the substance is above or below the sensing point. Generally the latter detect levels that are excessively high or low.
The Medicina Radio Observatory is an astronomical observatory located 30 km from Bologna, Italy. It is operated by the Institute for Radio Astronomy of the National Institute for Astrophysics (INAF) of the government of Italy.
A light curtain is a safety device that detects when a beam of infrared light has been broken by a person passing through an area.
Electro-optical sensors are electronic detectors that convert light, or a change in light, into an electronic signal. These sensors are able to detect electromagnetic radiation from the infrared up to the ultraviolet wavelengths. They are used in many industrial and consumer applications, for example:
A proximity sensor is a sensor able to detect the presence of nearby objects without any physical contact.
Ultrasonic transducers and ultrasonic sensors are devices that generate or sense ultrasound energy. They can be divided into three broad categories: transmitters, receivers and transceivers. Transmitters convert electrical signals into ultrasound, receivers convert ultrasound into electrical signals, and transceivers can both transmit and receive ultrasound.
The AN/FPS-17 was a ground-based fixed-beam radar system that was installed at three locations worldwide, including Pirinçlik Air Base in south-eastern Turkey, Laredo, Texas and Shemya Island, Alaska.
Radar engineering is the design of technical aspects pertaining to the components of a radar and their ability to detect the return energy from moving scatterers — determining an object's position or obstruction in the environment. This includes field of view in terms of solid angle and maximum unambiguous range and velocity, as well as angular, range and velocity resolution. Radar sensors are classified by application, architecture, radar mode, platform, and propagation window.
An optical beam smoke detector is a device that uses a projected beam of light to detect smoke across large areas, typically as an indicator of fire. They are used to detect fires in buildings where standard point smoke detectors would either be uneconomical or restricted for use by the height of the building. Optical beam smoke detectors are often installed in warehouses as a cost-effective means of protecting large open spaces.
Beam park is a radar mode used for space surveillance, particularly tracking space debris. In beam-park mode, a radar beam is kept in a fixed direction with respect to the Earth, while objects passing through the beam are tracked. In 24 hours, as a result of the Earth’s rotation, the radar effectively scans a narrow strip through 360° of the celestial sphere. The scattered waves are detected by a receiver and the measurements obtained during the observations can be used to determine object radar cross-section, time of peak occurrence, polarization ratio, doppler shift and object rotation. The obtained information for each object is then processed and matched against data from previously catalogued objects. The beam-park mode can be used to detect both previously known and uncatalogued objects at any altitude, provided that the reflected power captured by the receiver can be distinguished from the noise. This limits the use of radar-based beam park observations to objects in Low-Earth Orbit (LEO). Optical instruments, in turn, have very good performance for objects in Geostationary Earth Orbit (GEO) and in Geostationary Transfer Orbit (GTO). The radar technique typically outperforms optical facilities in LEO and can conduct observations for longer periods, both during day and night, independently of the weather and object illumination by sunlight.
Photopyroelectric As known that Photopyroelectric can be regarded as –Photo +Pyroelectric，which means any optical systems using a pyroelectric detector or imaging system, In addition, pyroelectricity could be depicted as the capability of the components formulating the transient voltage when heated or cooled. Once the temperature on which they depend changes, the position of the atom will change slightly in the crystal structure. This process of change can also be referred to as the polarization of the material. As a result, the voltage across the crystal will be triggered by this change in polarization. To further explain, when the temperature in the engine is kept constant for a period of time, the voltage in the photovoltage will gradually disappear due to the leakage current. In this sense, leakage is mainly caused by several ways, for example, electrons going through the crystal, ions going through the air, or current leaking through a voltmeter connected to the crystal.
