AC demagnetiser

AC Demagnetisers are suitable for small, low field demagnetisation, i.e. cathode ray tubes and certain steel applications.

They are the simplest form of demagnetiser. A coil or demagnetisation fixture is connected to a mains supply that may or may not be controlled by electronics to control the magnetic field’s magnitude. For the smallest and simplest of cases a hand held AC demagnetiser may be used.

To achieve the demagnetising effect, the applied oscillating field needs to reduce over time. This can be achieved by relative movement of the fixture and work piece or electrically reducing the current in the fixture.

For relative movement, the fixture is moved away from the work piece, or the work piece is moved away from the static fixture. Either way the resultant demagnetisation is very dependent upon the speed of relative movement. If this relative movement is made by an operator, then the efficiency of the demagnetisation process can be seriously impaired. It is therefore usual for the fixture to be supplied with a conveyor belt system to give good smooth control of this relative movement.

For the electrically controlled system, a control box is fitted to the fixture. This electronically reduces the peak current that flows into the coil on each successive oscillation of the mains, thereby reducing the magnetic field experience by the work piece. The time for the current to reduce to zero is adjustable of the order of a few seconds dependent upon the components to be demagnetised.

A variation on a mains demagnetiser is to incorporate a resonant technique to offer higher fields with low continuous input current. Dependent on the application, this can achieve effective demagnetisation without the need for component removal from the demagnetising location.

This technique can be adopted for small and large applications.



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Hirst Magnetic Instruments Ltd. received funding from the BIG2 Project funded from the ERDF as part of the European Structural and Investment Funds Growth Programme 2014-2020