inductive loop
As can be seen from the name, induction loops are a larger loop consisting of several wires laid in rooms and halls as well as under roadways and highway ramps. In acoustics, induction loops are part of public address systems and can provide acoustic information to hearing aid users. In traffic engineering, induction loops are used for traffic flow measurements and to control traffic lights or barriers of parking garages.
The operating principle of such a loop is based on induction. In sound engineering, a transformer winding is laid in a room for this purpose and power amplifiers are used to feed in the sound- frequency signals. The secondary coils of the transformer are located in the hearing aids and transmit the induced current to the hearing aid.
In traffic technology, a current is induced in the loops as soon as a vehicle passes over the loop. The resulting induction voltage can be used to determine the number of vehicles that have passed over the induction loop. If two induction loops are laid only a few meters behind each other, the time difference between the two induction voltages can be used to determine the speed of the vehicles traveling over them and, in conjunction with the number of vehicles, the traffic density. The data from the induction loops are transmitted to the state and federal reporting centers.