- DesignGuide 3
- Likely Causes of Inconsistent Dynamic Performance
Magnetic Heads Used in High Traffic Fare Collection Applications
By Larry W. Ditty, Executive V. P. Technology, brush Industries, Inc.
The Gap in a Magnetic Head (non-magnetic material
inserted between the two polepieces) is a very critical element in maintaining
optimum Magnetic Head Performance. It has a direct impact on Write current and
Read Output. The gap size (thickness/length) is the most critical component of
the Magnetic Head Design.
Maintaining a consistent uniform gap size with well defined edges is necessary
for a Magnetic Head to have uniform dynamic performance over its operating life.
1. Gap Definition and length varying as the Magnetic Head wears.
Soft Core Mu-Metal Magnetic Head
Many times the gap on a standard soft-core head becomes ragged and irregular
(smeared / shunted) as the Magnetic Head wears. The soft Mu-Metal core material
is smeared or abraded into the gap material by the constant abrasive action of
the magnetic media moving under pressure across the top of the Magnetic Head.
As the smearing and shunting of the Gap takes place the dynamic performance
changes with the changing Gap Size.
The Gap Size on a hard core ferrite head will
experience the opposite effect of a Mu-Metal magnetic head. Instead of the Gap
smearing and becoming smaller, the edges of the ferrite material start to erode
away and the Gap size becomes larger and losses its size and definition. This
phenomenon is a result of the brittle nature of ferrite. The constant impacting
of tickets into the magnetic head cause minute particles of the ferrite at the
Gap to fracture and break away. This eroding of the Gap is the same as
increasing the Gap size and has a corresponding effect on the dynamic
performance.
Magnetic Heads manufactured with Supermium® Pole
Pieces will not be effected by gap smearing or gap erosion. The Hardness (48/52
RC) and Toughness (not brittle) of Supermium® core material maintains a uniform
size, well defined gap throughout the life of the head insuring consistent
dynamic performance.
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