Table of Contents

Athana International

All About Degaussers and
Erasure of Magnetic Media

Introduction

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.

This information 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 operating costs.

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.

Degaussing takes 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 recorded signals.

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.

About Degaussers

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.

Magnetic media 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 Created

Fig 1. Magnetic field lines inside and around a magnet and a solenoid.

Operation of Degaussers

For occasional 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. it

Savings

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 processing.

Recording onto Magnetic Tape

Fig 2. Diagram showing recorded flux pattern on a magnetic tape

Procurement

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 following section:

1. Media Types

  • 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??

2. Performance

  • Quantity of material to be degaussed - are you involved in long runs?
  • Is the speed of your operation critical?
  • Is complete erasure vital?
  • Do you require semi-automatic operation or would manual feed of the media to be degaussed be acceptable?

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 Considerations

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

Coercivity or coercive force - The field strength required to bring the flux density to zero in a magnetic material.

Degauss - 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.

High energy tape - Magnetic tape having coercivity higher than 600 Oersted.

Magnetic flux - The magnetic lines of force produced by a magnet for electric current.

Magnetic field strength - The magnitude of a magnetic field vector, usually expressed in Oersted or ampere-turns per meter.

MMF 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 turns.

Maxwell - A unit of magnetic flux.

Oersted - A unit of magnetic field strength.

 

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