All About Degaussers and
Erasure of Magnetic Media
The purpose of
this document is to provide a basic understanding
of the functionality and benefits of magnetic media
degaussers. It will also explain how you should
approach specifying the type of degausser, its
operation and the procurement considerations.
will be of value to media end users, professional media
manufacturers and software duplicators from the video, audio, computer
and broadcasting industries. Such benefits
include significant improvements in the quality
of their Products together with sizeable savings in
Degaussing is used
for security purposes, to conform to privacy laws and
to reuse the media. Some media, for example 1/4" Mini
Cartridges, are in most cases pre-formatted or servo-written. Degaussing
may require new formatting, which can become difficult.
So care has to be taken to determine which media to degauss.
its meaning from the Gauss; the unit measure for
the magnetic flux density. It is used today to
describe the process of erasing magnetic media,
removing from the media remnants of previously
About Magnetic Media
The term magnetic
media covers a vast range of material from audio
and videotapes and cassettes to computer
diskettes and reels, supplied in a wide choice of
sizes and complexities. All of them however,
perform in the same basic way.
The media consists
of material that is coated with minute magnetic
particles that react to magnetic influences
applied to them. Such influences fall into two
types: The first is the intended influence during recording
of a signal that creates the desired orientation of the
magnetic particles in response to the recording signal.
This magnetic pattern is used to produce the desired
"play-back" after recording. Ideally the replay should replicate
the original recording, whether this is from an
audio, video or computer data source. The second
influence is the unwanted signal, which can take
the form of distortion, bias, corruption or
interference and can produce undesirable effects
such as poor quality in audio or video media or
software glitches in data material. Clearly any
process, which enhances the first and eliminates
the second is desirable, degaussing magnetic
media can help to achieve this.
The process of
degaussing is achieved by passing the magnetic
media through a powerful alternating magnet field to
rearrange the magnetization of the magnetic particles, completely
removing any resemblance of the previously
recorded signal. Degaussers are constructed
in such a way as to enable the
generated magnetic field cover the entire magnetic
media when it is transported through it, either
by physically holding the media by hand and
moving it through the field or automatically
conveyed by a belt transporter.
is characterized by its coercivity, which is a measure
for the media's resistance to erasure. The higher the
coercivity the higher the degaussing field has to be.
So-called High Energy Media has very high coercivities.
Generally speaking the field produced by a degausser
should exceed the media coercivity by a factor of 3-4.
Further degaussing effectiveness can be achieved by using
more than one coil in multi-axial orientation.
Additional improvements can be obtained by
rotating the coils during the degaussing process.
How a Magnetic Field is
Fig 1. Magnetic field
lines inside and around a magnet and a
Operation of Degaussers
and laboratory use hand held degaussers are adequate.
In a production environment conveyor based
degaussers are commonly used, which allows
the magnetic media to be placed on a small belt, which
in turn, passes the media through or over the
degaussing coils at a constant speed, assuring the
most uniform degaussing. Custom designed
degaussers can assist with the specialist needs
of bulk operators with belt feed conveyors and
collection hoppers available to deal with tapes,
disks and reels, all helping in making the
operation effective and efficient.
In general multiple
passes of the media through the degausser does not improve
the effectiveness of the degaussing, however if
the media is rotated by 90° then some
improvement can be achieved. To benefit from this experience,
some of our degaussers employ
a rotating coil technique where the media passes
on a variable speed conveyor belt through a field
generated by two powerful coils which are
rotating, one above the media the other beneath.
The controlled application of
degaussers to the processes involved in the production
and operation of magnetic media can achieve considerable savings.
In many cases suspect magnetic media is being discarded
that with a careful process of degaussing
applied to it would considerably extended
its life. Some operators claim to benefit by up to
twice the useful life of some types of media. But
further direct and indirect savings can be
achieved. Diskette duplicators claim to gain upwards of 25%
better production yields directly attributable to
degaussing their bulk blank diskettes, prior to
Recording onto Magnetic
Fig 2. Diagram showing
recorded flux pattern on a magnetic tape
It can be seen
that there are a considerable number of
decisions that have to be made before placing an
order for degaussing equipment that you require.
There are erasers designed to run continuously
for high volume duplication operations. They
perform reliably and last for years in the heavy
demands of the high production environment.
However such degaussing models are expensive and
may not provide the most cost efficient solution
to the particular needs of your operation. It is
important that due consideration is given to the
practical considerations that are detailed in the
- Variety of
material - do you have a range of
different formats and media coercivities?
- Do you
expect changes in these requirements?
- Do you need to degauss high energy
or high-density media??
- Quantity of
material to be degaussed - are you
involved in long runs?
- Is the speed
of your operation critical?
complete erasure vital?
- Do you
require semi-automatic operation or would
manual feed of the media to be degaussed
5. Operational Environment
- Where will
the degausser be located?
- Is there
enough room to house and operate it?
- Can its
weight be supported safely?
- Can the heat
it generates be dissipated effectively?
Health and Safety
As with all
electrical equipment connected to the main
electricity supply it is vital to follow the
customary safety precautions, including, ensuring
that the equipment is properly grounded and
regularly inspected by a competent, qualified
electrician. Degaussers generate heat when they
are in operation, particular care should be taken
to ensure that adequate ventilation is available
and that any heat generated can be safely
dissipated. Research into the effects of magnetic
fields to humans has failed to show any link with
any form of injury in the short or long term.
What Will A Degausser Cost
There are magnetic
degaussers available that cost as little as $150
and these can be adequate for occasional degaussing
requirements where speed and depth of erasure are
not important factors. Such a degausser would not
be appropriate for the professional users where
continuous operation to deal with large batches
would be required, nor would these utility models
be adequate for professional use in the video or
audio applications in the broadcasting industry.
Professional degaussers are ranged in cost from
$2,000 to $10,000 for standard models, however
additional refinements to provide bespoke
features cost more For example an eraser designed
to process 400 - 500 cassettes per hour,
including thermal shut-down time, is likely to
cost between $2,000 - $3,000. Units that are
required to handle large computer reels and run
continuously would be pitched at circa $10,000.
Whatever the cost of the investment the potential
savings gained by the re-use of previously
discarded material, plus the increased
efficiencies resulting from better quality all
add up to a conclusion that such an investment in
a degausser is most worthwhile.
GLOSSARY OF TERMS
or coercive force - The field strength
required to bring the flux density to zero in a
- To return the magnetization in a media coating
or in a head to a zero state by applying a
decaying and alternating magnetic field.
Gauss - A
unit of magnetic flux density.
energy tape - Magnetic tape having
coercivity higher than 600 Oersted.
flux - The magnetic lines of force
produced by a magnet for electric current.
field strength - The magnitude of a
magnetic field vector, usually expressed in
Oersted or ampere-turns per meter.
magnetomotive force - The magnetic
analogue of electromotive force, which, when due
to a current in a coil, is proportional to the
product of current in amperes and the number of
Maxwell - A
unit of magnetic flux.
Oersted - A
unit of magnetic field strength.