Induction loop

An induction loop (also inductive loop, loop sensor or loop ring ) is in principle a simple loop of wire that is used for various purposes, in particular for signaling and transmission of information by means of the principle of electromagnetic induction.

Application in road traffic

In traffic engineering, an induction loop is used for vehicle detection on the track. There are large, embedded in the pavement or moved under its cable loops for application, preferably before the stop lines on-demand traffic lights to turn from red light surveillance cameras or to open and Wiederabsenken barriers in car parks or at toll booths, etc.

Operation

The induction loop acts as a coil. It is connected in parallel with a capacitor so as to form a resonant circuit whose resonance frequency (to be added ), and the inductance of the coil ( of the induction loop ) depending on the capacitance of the capacitor. A metal object is located (e.g., a vehicle ) in the region of the induction loop, the inductance of the coil is changed. Characterized the resonance frequency of the resonance circuit changes. This is analyzed by the electronics.

Otherwise the following principles are described:

• The loop / coil is flowed through by a constant direct current. If a metal body in the static magnetic field to change it, which results in a measurable change of the coil current ( inductor current ).
• Vehicles direct from the geomagnetic field by bundling it in their metal mass. Due to the change of the magnetic flux (induction principle) can be carried along in the movement of the magnetic field through the coil a voltage pulse measured.

Utility functions

Traffic-actuated traffic controllers freely switch the direction in question, if, by means of induction loop, a vehicle is reported. In addition, can be extended as far depending on the type of control the release until a gap is detected in the vehicle power.

Through a laid at the stop line induction loop can be determined if a vehicle has entered the intersection. Red light violations can be detected so automatically (see velocity monitoring). In addition, induction loops are used for traffic counting.

Through the analysis of the measured envelope, it is possible to distinguish the vehicles covered by type (eg passenger cars, motorcycle, truck). With a double loop ( two induction loops have been installed at a short distance behind the other ) can (eg small to large vehicles or trailer combinations ) and the velocity can be determined in addition to a finer type discrimination.

By designing the reception sensitivity to certain frequencies (around 10 kHz), for example, ambulances with appropriate signaling devices provide the traffic signals for their preferred direction of travel to green to move faster.

Induction loops for controlling a traffic light are generally optimized for motor vehicles. Whether cyclists are detected by the induction loop depends on the set sensitivity. And the metal portion of the wheel has a role. As a cyclist, you should go as possible over the edge of the loop, since there is magnetic interference effect is greatest. Cyclists riding through the middle of an induction loop, may be not detected.

Application in rail transport

In rail transport, induction loops are used for data transmission in train protection and train control systems as SELCAB or in Linienzugbeeinflussung. The lined-up loops are referred to here because of the straight, continuous leadership within a cable as a line manager.

Application for hearing impaired people

An induction loop system enables hearing aid users, interference-free audio signals such as music in cinemas and theaters, verbal contributions at events and lectures, for example, to receive in churches etc. wirelessly through the hearing aids. This requires a hearing aid via a so-called telecoil ( T- coil short ) feature that receives the alternating electromagnetic field of the induction loop.