SV91M Operating & Maintenance Instructions
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SECTION 3: INTRODUCTION
A magnetic recording process is almost always preceded by an erasing process, either by bulk
degaussing or by magnetic head erasure. Erasure is a fundamental step in achieving high quality
recordings.
Bulk erasure is the preferred method due to the considerable reduction in time involved plus the
otherwise use of expensive record/reproduce/erase equipment.
The SV91M bulk degausser functions like a large electro magnet, its erasing field originating as
leakage flux from a large gap in the field structure, the SV91M structure is basically a U section.
The field intensity decreases rapidly as the distance from the degausser surface increases. For
example at a distance of approximately 2.75 inches from the degausser's surface a field strength
of only 50 oersteds exists. Furthermore, the erasing field present at the front edge nearest the
operator is also very low. It is therefore recommended that care should be taken to ensure the
entire width of tape to be erased is exposed to the effective field.
