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In 2003 the US government did research on magnetic fields by testing Magnetic field strength measurements being made to eight hand-held and 10 walk-through metal detectors.
Special magnetic field probes specifically designed for metal detector measurements were used. A non-metallic positioning apparatus was designed and fabricated. Magnetic field strength measurements were collected on one hand-held metal detector in the laboratory. The remaining data was collected at airport terminals, federal and state government buildings, and a local high school.
Waveforms for walk-through metal detectors varied with most being saw-toothed or pulsed.
The results found that walk-through metal detectors had considerably higher magnetic field strengths [up to 299 Am(-1) p-p (3,741 mG)] than hand-held metal detectors [up to 6 Am(-1) p-p (76 mG)].
So what is notable is the magnetic field strength on a walk through metal detector is 3,741 mG (miliGauss). Also the magnetic field will be much higher at the sides than at the centre of the walk through detector. It should be noted that your watch on your wrist will be much closer to the sides of the metal detector and will therefore have a higher magnetic field applied to it than if it is at the centre of the walk through detector.
The closer a watch is to the magnet the stronger will be the magnetic force.
What does this mean you might say?
The magnetic field of a walk through metal detector is 3,741 milligauss
A small bar magnet is about 100,000 milligauss.
An electric razor is about 100 milligauss at 6 inches.
A microwave oven has 100 milligauss at 6 inches.
An electric mixer has 600 milligauss at 6 inches.
A refridgerator has only 40 milligauss at 6 inches.
All household appliances are significantly less in Gauss than the strength of a walk through detector.
Some walk through detectors can be 1-1.5 feet long, and if your watch is only a few inches from the side of the detector then you may be subjecting your watch to significantly more than 3,700 milligauss.
It is conceivable that the effect on ones mechanical watch may be affected by a metal detector to affect the accuracy by several seconds per day. The more the watch is subjected to the magnetic field the more it may tend to vary from it’s regulated time.
It should also be remembered that the operator of a walk through detector is able to change the detection level and at airports the levels may be turned up quite high.
I have been advised by an operator of a walk through detector that there are stronger forces in the detector at about waist level and that the magnetic force will be much greater at the sides or closer to the walk through frame of the detector. Head or shoulder height in the centre of the detector is where the least amount of magnetic force may be found.
I have personally found that wearing a Rolex and walking through with my arm by my side has triggered the detector. However, when I immediately try again, if I raise my arm and place it upon or near my head (e.g. scratching my nose) as I walk through the detector the Rolex does not register on the metal detector. So if the detector is not sounding an alert then the magnetic field is not being affected and accordingly, the level of magnetic force upon the watch is lower.
Try this next time, you don’t have to take your watch off when going through a metal detector.
The other issue is if you do take your watch off and it goes through the x-ray machine, I don’t know what forces and strengths are being applied.
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