Walk Through Metal Detectors / Knife Arches

Not too long ago the only places we would see walkthrough metal detectors in the UK was at airports, prisons and some embassies and government premises. But these days they have become far more common, typically used in schools, colleges, public buildings, night clubs, sports stadiums, courts and office blocks. These security detectors are also now commonly used to help prevent theft from warehouses, distribution depots, transportation hubs, factories and manufacturing facilities. UK Government plans to combat knife crime have resulted in the use of both security arches and handheld metal detector wands in schools.

How Does a Walkthrough Metal Detector Work?

Most walk through metal detector arches use what is called pulse induction (PI) technology to detect metal objects. The pulse induction system sends a short burst of current (pulse) through a coil of wire (transmitter) located in the side of the archway. This creates an electromagnetic field around the coil which covers the area through which a person must walk under the arch. Typically, a PI based system will send around 100 pulses per second but this can vary, depending on the make and model. If a person walking through the arch is carrying a metal object this will cause the pulsing magnetic field to be disturbed and reflected. This is picked up by another coil of wire (receiver) and used to trigger an alert to tell the operator that the person is carrying something metallic. The very best security arches feature what`s called dual-side detection, wherein transmission and reception coils are in place on both sides of the arch. This feature supports uniform detection throughout the arch and provides better noise cancellation which makes it much easier to install and setup.

Pinpoint Target Zones

The most basic form of walkthrough metal detector provides what`s called single zone detection. This means that if someone is carrying a metal object the system simply detects its presence, but does not locate where the item is on the persons body. Multi zone walk through metal detectors will locate the whereabouts of any detected metal objects. The more detection zones supported by the device then the more accurate the location. For example, the excellent Garrett PD6500i features an amazing 33 pinpoint zones enabling the accurate identification of multiple metal object locations on a persons body. This is clearly advantageous when dealing with queues of people as it speeds up the search process.

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