An inductive loop or inductive loop is an electromagnetic communication or detection system that uses a moving magnet or alternating current to induce an electric current on a nearby cable. Induction loops are used for transmitting and receiving communications signals, or for detecting metal objects in metal detectors or vehicle presence indicators. A common modern use for induction loops is to provide hearing aids to users of hearing aids.
Video Induction loop
Apps
Audio
Audio induction circles provide assistance to users of hearing aids. This system has one or more loops in the area where hearing device users will be present. Many different configurations can be used depending on the application. The receiver of such induction loop is classically a very small iron inductor (telecoil). These systems generally use analog power amplifiers that are matched to the low impedance of the transmission loop. Transmission is usually direct rather than superimposed or modulated on the carrier, although a multi-channel system has been implemented using modulation. Many hearing aids contain telecoils that allow the user to receive and hear the magnetic field and remove the normal audio signal provided from the hearing aid microphone site. This loop is often referred to as a hearing loop or an audio induction loop.
Since no "tuning" is available, since the telecoils directly take up all the audio-frequency magnetic fields, a careful system design is required where more than one induction loop is used in a building; for example, adjacent theaters or lecture halls. Telecoils can also take sound from non-audio sources such as power cables, lights, or CRT monitors.
Vehicle detection
The detection of a loop vehicle, called the inductive-loop traffic detector , can detect vehicles passing or arriving at a particular point, such as approaching a traffic light or in highway traffic. An isolated electrical loop is installed on the sidewalk. The electronic unit transmits energy into the wire loop at frequencies between 10 kHz to 200 kHz, depending on the model. The inductive loop system serves as a set of electrical circuits in which the loop and lead-in cables are inductive elements. When a vehicle passes a loop or stops inside the loop, the vehicle induces an eddy current in the wire loop, which lowers their inductance. The decrease in inductance drives an electronic unit output relay or an isolated optical solid-state output, which sends a pulse to a traffic signal controller signifying a vehicle's path or presence. The parking structure for cars can use an inductive loop to track incoming and outgoing (occupancy) traffic or can be used by access gates or ticket systems to detect vehicles while others use guide systems and parking information. The railway can use an induction loop to detect the train line past a given point, as an electronic pedal.
The relatively coarse nature of the loop structure means that only the mass of metal above a certain size is capable of triggering the relay. This is good because the loop does not produce very many "false positive" triggers (for example, by pedestrians crossing loops with pockets full of loose metal changes) but sometimes it also means that bicycles, scooters and motorcycles are stopped at the intersection may never be detected by them (and therefore the risk is ignored by the switch/signal). Most loops can be adjusted manually to consistently detect the presence of scooters and motorcycles at least.
Vehicle classification
Loop inductance has also been used to classify vehicle types. Sampling loops at high frequencies produce a unique signature for each vehicle that allows for the classification of body types.
Metal detector
Different types of "induction loops" are applied to metal detectors, where a large coil, which is part of a resonance circuit, is effectively "detuned" by a coil close to a conductive object. The detected object may be metallic (metal and cable detection) or conductive/capacitive (detection stud/cavity). Another configuration of this equipment uses two or more receiver coils, and the detected object modifies the inductive coupling or converts the phase angle of the induced voltage in the receiving coil relative to the oscillator coil.
An anti-submarine indicator loop is a tool used to detect submarines and surface ships using specially designed submerged cables connected to the galvanometer.
Maps Induction loop
See also
- Induced coil
External links
- Loop and infrared systems - for deaf and hard-to-hear people (fact sheets) A handy guide from the Royal National Institute for the Deaf in the UK.
- Traffic sensors from How It Works.
References
Source of the article : Wikipedia
0 Comments