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Old 01-06-2012, 03:04 AM
ksrctpravin ksrctpravin is offline
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Default Metal detector housing

Hi guys i have one ought ,the industrial metal detector housing is made up of steel and the magnetic field inside the housing will be emitting rays,

my confusion is the emitted rays will always be detecting the housing ,bec the housing is also a steel which is a metal ,so any one help me to clear my confusion

how the industrial metal detector is made and how the rays not affect the housing

help me guys
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Old 01-06-2012, 06:44 AM
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thatoneguy thatoneguy is offline
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The housing is most likely molded from austenite, which is non-magnetic form of steel, it is the crystal lattice that forms when low carbon steel is heated to very high temperatures and cooled quickly, lower temperature produces ferrite, which is also paramagnetic.

When more carbon is present, or when steel is heated to red hot and quenched, the result is either martensite, or cementite cyrstal formation, these structures are all ferromagnetic (to varying degrees, depending on carbon content) while austenite is paramagnetic. Paramagnetic materials only hold a magnetic field when an external field is applied, and returns to non-magnetic when the external magnetic field is removed.

In other words, austenite "passes" magnetic fields without becoming permanently magnetized itself, unlike ferromagnetic materials, which become magnetized when exposed to a magnetic field.

Lastly, metal detectors don't emit rays, they create an oscillating magnetic field, and typically have a co-mounted coil antenna to receive any magnetic abnormalities below the surface, such as an item becoming magnetized, or having a small electric current induced in it from the detectors' transmitting coil, which creates a small magnetic field.
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Old 01-06-2012, 12:11 PM
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There is also a possibility of any metallic housing for a search coil acting as a "shorted turn", that is, reducing the effectiveness of the coil due to eddy-current effects. This is likely to become worse as the operating frequency increases, but may be an issue even at audio frequencies.

Apart from using low frequencies and accepting some impairment, part of the housing may actually be made out of non-conductive material. This may only need to be a small section, just enough so that less than a complete shorted "turn" is formed. This may not be obvious, for instance steel plates or tubes may be interrupted by an insulating joint made of plastic etc. which may not be seen on casual inspection.
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Old 01-06-2012, 01:00 PM
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THE_RB THE_RB is offline
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Any stationary metal in the detect zone can be "nulled out" easily enough so it is not detected.

However it will reduce the overall sensitivity of the metal detector, which may or may not be a problem.
Roman Black - PICs and electronics. Author of BTc PIC-sound encoder, Shift1-LCD project, the TalkBotBrain talking PIC controller, LiniStepper open-source microstepping motor driver, the Black Regulator 2-transistor SMPS, and probably some other stuff;
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