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In gate automation and access control, there are two applications for vehicle detection – egress control to open and close gates, shutters and barriers as a vehicle approaches; and safety to prevent the gates, shutters or barriers closing onto vehicles.
So, egress control governs the opening of gates, shutter doors or barriers, or the operation of access control equipment such as keypads, card readers or traffic lights.
And safety applications prevent gates, shutters or barriers from coming into contact with vehicles.
There are a variety of different vehicle detection systems and some are for egress, some for safety and some can be used for both.
The simplest set ups feature infra-red safety beams. These emit a beam of infra-red light and use a detector/receiver to recognise when the beam is broken by a vehicle.
Used only for egress control, a combined transmitter and detector/receiver unit sends a beam to a passive reflector unit and receives the reflected beam unless a vehicle interrupts the beam. This set up only requires power to the transmitter/receiver unit as the reflector is passive.
By using powered transmitter and powered receiver units, the safety beam system can be made practical for both egress and safety. In this case, the transmitter units can be supplied wired or battery powered and with a transmitter range of between 7 and 15m. The receiver unit always requires power to be connected by wire.
Inductive loops operate using the principles of electromagnetism. A loop of special cable is laid in a loop in the driveway substrate. When current flows through the cable, it generates an electromagnetic field. When a large metallic object, such as a car, interacts with the electromagnetic field produced by the loop as it drives over it, the electronic control (loop detector) controlling the loop generates a signal for gate controls etc.
Inductive loops can be used for safety and egress control, but they have to be installed correctly. Channels wide enough to accommodate the cable must be cut into the drive or road. These have to be 50mm deep, have mitred corners to avoid damaging the cable and be positioned more than 1m away from large metallic objects.
Once dug and the cables inserted into the channels, bitumen is used to backfill the channels to ensure water cannot reach the cables and to prevent any cable abrasion caused by vibration.
Magnetoresitive systems use a variation on the inductive loop theme. Here, only a single channel (rather than a large loop-shaped channel) needs to be cut into the driveway. This allows a single slimline detector and its cable to be installed in front of the barrier, gates or shutters. The detector is small and two can easily be laid close together. With a maximum radius of 5ft, these can also be used for egress and safety control.
The controllers have sensitivity settings to allow fine tuning to avoid interference and subsequent false signals.
With a 12 inch long cylindrical detector, there is a magnetoresistive detector that can be mounted alongside the side of the road to provide an operating radius of up to 12 feet. However, as vehicles need to be moving at 5mph or more to be detected, this system is designed only for egress operation.
The control unit allows the selection of one of ten sensitivity levels and it can be mains, battery or solar powered
Other technologies for detecting vehicles use ultrasonic detectors or motion detection to identify metallic vehicles.
For further information on vehicle detection for safety and egress in gate, shutter and barrier automation and installation, call Linkcare on 01895 232 626.