- 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.
2. Spacing Losses
Spacing loss is a condition that occurs when the magnetic pole pieces at the gap
of the magnetic head losses inanimate contact with the magnetic media. The loss
of contact with the magnetic media has a direct bearing on the ability of the
magnetic head to write, overwrite and on read output. (See below) Spacing losses
are most usually caused by dirt build up on the head or uneven wear due to
hard/soft material (scalloping). Dirt build up usually occurs at the leading and
trailing edges of the contour, causing the magnetic media to loss contact with
the gap.
Note: Read signal decreases exponentially with the distance between the magnetic
head gap and the magnetic media.
| Spacing Loss | OutPut | OutPut Loss | |
| .0000 | 40 Mv | 00% | |
| .0005 | 20 Mv | 50% | |
| .0010 | 12 Mv | 70% | |
| .0002 | 6.4 Mv | 84% | |
3. Rapid Wear
The PFD (pole face depth) is the primary factor controlling the life of a
magnetic head. A typical new Brush magnetic head would have a PFD of .015/.017.
As the magnetic head wears the PFD decreases, resulting in increasing output and
decreasing saturation current. The faster the magnetic head wears the more
dramatic the dynamic changes seem. Soft core Mu-Mtetal heads can experience very
rapid wear, such that a new head can reach end of life in as few as 50,000
transactions. The dynamic changes occurring in this type of head would be very
noticeable. supermium® ceramic coated heads can realize as many as 11 million +
transactions before realizing end of life, dynamic or performance changes seem
very subtle as they occur over and extended period of time.
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