Magnetic Fields - Horotec MSA19.907 Manual De Instrucciones

MAGNETIC FIELDS

A magnetic field is manifested by a force affecting certain materials in its environment, and
acting on moving electrical charges. The magnitude of this force decreases as a function of
the distance between the magnetic field emitter and its action point. Magnetisation is a vector
quantity which characterises on a macroscopic scale the magnetic behaviour of a material
sample. It is measured in amperes per metre (A/m) or in teslas (T).
Ferromagnetism designates the ability of certain material samples to become magnetised under
the effect of an external magnetic field, and to retain part of this magnetisation.
On a microscopic scale, a ferromagnetic material can be described as a set of independent
magnetic domains (Weiss domains).
When the magnetic moments of the domains are not aligned, the total magnetostatic energy of
the material is minimised: the material is not magnetised.
For demagnetisation purposes, a damped magnetic excitation field is applied so that certain
domains are reversed more than others, depending on the magnetic excitation force passing
through them. This leads to a state of magnetic disorder equivalent to the state of a non-magnetised
material.
There are relatively intense magnetic fields all around us in daily life. It goes without saying that
mechanical watches are influenced by them, and thereby undergo potentially significant opera-
ting variations, i.e. which affect the rate precision. It should be noted that the Earth's magnetic
field varies between 25 and 65 µT, depending on geographic position.
The most significant items in everyday life which can affect the rate of a mechanical watch by
means of a magnetism effect are computers, mobile phones, TVs, refrigerators, etc. Magnetic
flux measurements (taken at 10 cm from the source) have revealed values of 60 µT for an
electric toothbrush, 75 µT for a mobile phone and 110 µT for a computer. Consider too that
watchmaking tools often have a magnetic charge capable of disrupting the rate of a watch!
The distance at which a watch is placed from the magnetising object is an important factor.
Although watch manufacturers regularly equip their cases with protective materials or opt for
non-magnetic components, nevertheless rate problems due to magnetism remain very common.
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