Metal detectors are used for many purposes and top on this list is security equipment to safeguard precious lives and properties at public places like airports, shopping malls, cinema halls, hospitals, temples etc.
Hand held metal detectors and door frame metal detectors are used to check whether any person is carrying any weapon or other objectionable metal object. Ground search metal detectors are used to trace any metal buried underground which includes gold silver etc. Conveyor metal detectors and needle detectors are used to check any accidental inclusion of needle parts or other metal parts in finished products. Special types of metal detectors are used to find any metal object hidden in walls or any nails in wooden pieces special types of metal detectors like prodders are used to trace any metal objects in bags of wheat rice etc.
How a Metal Detector Works
To understand how a metal detector works let us consider the case of most common device called hand held metal detector (HHMD ) contains a battery, transmitter circuit and a receiver coil. When the battery activates the transmitter circuit it creates a magnetic field all around it. When you bring the HHMD closer to any metal object the magnetic field penetrates through it. The magnetic field makes an electric current flow inside the metal object. The flowing electric current creates another magnetic field all around the object.The magnetic field cuts through the receiver coil making a beeping sound alerting that metal has been detected.
Types of Metal Detectors
A metal detector is an electronic device that's used mainly to detect any metallic object that any person may be carrying/hiding. Metal detectors are also used to trace any metal underground etc. There are mainly three different types of technologies that are used for manufacture of metal detectors:-
(1) Very low frequency (VLF) This is the most common type this type uses two coils, one for transmitter and one for receiver.
(2) Multi-frequency metal detection technology. As VLF technology had some limitations with single frequency to overcome this multi-frequency technology was introduced.
(3) Pulse induction (PI) technology. This type of technology is different instead of using two separate coils,pi metal detectors use only one coil that both transmits and receives electrical currents. These currents are released in pulses with anywhere between 100 to several hundred pulses in a second. Pulses have a very short duration lasting only milliseconds. When the field current is transmitted the time it takes for the field to reverse and collapse is measured. Longer reflected pulse delays indicate the detector has detected a metal different types of metal detectors are available for different applications. The most common of these is hand held metal detector (HHMD) Which is used for general frisking or for pilferage check. The second most popular type is door frame metal detector(DFMD) Or walk through metal detectors. These are in use mostly on airports,shopping malls cinema halls etc these are available in single zone or in multi-zone. The difference between a single zone and multi-zone DFMD is that when you walk through a single zone DFMD leads provided in the display at the top of the DFMD glow according to the metal you are carrying. Generally for example 4 leads glow it appears a person is carrying normal metal such as mobile,belt,watch etc if more than 4-5 leads glow there is need to check what he is hiding.In multi-zone DFMD the leads are provided in the side panel of DFMD.For example if a person is hiding some weapon etc in his pant pocket leads closer to his pant pocket would glow when he enters and this enables the security guard to instantly know in which part of the body metal is being carried DFMD are also available with additional features like battery back-up traffic counter,computer connectivity-IP address for remote monitoring. Latest addition is DFMD with thermal imaging feature apart from above metal detectors for locating metal buried underground or metal detectors to trace metal hidden behind walls are also available. Portable metal detectors in PVC pipe are also available for outdoor use. Conveyor metal detectors and metal detectors to detect pipes and cable are also available latest in the list is pole detector.