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| About
Magnets |
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| The
magnetizer (magnetizing pulse generator) consists of a power
supply operating off line AC current which produces DC current
at a very high voltage, at moderate current levels. The current
is then stored in a bank or banks of capacitors. In order to
insure proper operation, both the value of the capacitance and
charge voltage must be matched to the fixture which is in use.
A switch capable of carrying very high currents is then closed
to allow the magnetizing pulse to flow. In Oersted Technology
products these are solid-state SCR (silicon controlled rectifier)
devices, which are fast-acting and have very little voltage
drop or lost power. The load fixture stores energy in its magnetic
field, and behaves electrically like a nonlinear inductance.
If the inductance is high enough, the current would surge forward,
then slow up, stop, and reverse direction, which is called ringing.
Reversed current in the fixture would be disastrous, because
it would destroy the capacitors and also partially demagnetize
the part. Reversed current into the capacitors is blocked by
separate diodes (which only conduct electrical current in one
direction), one for each bank. If the current were to be abruptly
cut off in the fixture, however, the voltage across the fixture
would rise to a very high value, until it forced a path to dissipate
the stored energy. That would destroy the electrical insulation
of the fixture, burn out the blocking diodes, and possibly cause
a fire or endanger the operator. Instead, a large diode (the
freewheeling, or "flyback" diode) is provided to allow
the energy to continue out one side of the fixture winding and
back into the other, until it is dissipated safely in the electrical
resistance of the fixture.
Many magnetizer designs use line-frequency transformers to
obtain the high charging voltage. Oersted Technology uses
a high-frequency design instead which saves weight and space.
It also results in even charging, so that the capacitor banks
are charged faster for the same maximum line current, with
less stress on the capacitors. |
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