For the own solution a yoke with air gap and with electromagnetic field generation has been selected.
During the development valuable experiences were used, which were obtained with measurement systems for hard magnetic materials, particularly with regard to
- the shaping the geometry of the yoke
- the selection of flux-conducting materials used
- the geometry and the arrangement of the field coils.
In the air gap (length l = 30mm) the flux densities B ≥ 1.2 T are achieved within a rectangular cross-section with a width b = 100mm.
By the design of the poles the field is very homogeneous about the indicated breadth.
For erasing the data the disks/ cassettes are placed in a box and then driven through the magnetic field. The indoor of this box corresponds to the size of 3.5 “hard disc drives. Other formats are embedded in appropriately sized adapter and then inserted into the box.
The forward and return movement of the data medium is used for control
- of the field current
- of the measurement of the max. reached flux density value B along three lanes.
The operation of the degausser (including input of data of discs and cassettes) and display the progress of the erasure and the measured size of the flux density B is done via a touch screen.
For safe operation of the degausser the individual functional units are provided with separate microcontroller units.
By optimisation of the magnetic circuit of the field coil and current sources it is sufficient to supply the degausser by the 230V grid (at 16A).
The developed device with its adjustable power supply control, yoke with field coils, automatic transport of the data medium as well as software modules with microcontroller controls is suitable for additional applications.
When designing the degausser (strong homogeneous dc field, adjustable power supply control, yoke with field coils, transport solution for data medium or sample-holders, software modules with microcontroller controls) specific requirements were also considered which must be fulfilled for further potential uses of the solution.
The system can be converted to a powerful device by changes (sample-holders) and with special supplements (measuring sensors, measuring and evaluation electronics), in which among others tasks such as
- determination of the specific saturation magnetisation σS according to IEC 60404-14
- determination of a ferromagnetic phase in cemented carbides)
- magnetising pieces/ samples of hard magnetic materials (limited by achievable field strengths)
can be processed with a high precision.
For that the field strength can be increased significantly by reducing the air gap length (30mm).