Magtek InSpec 9000 Manuel d'utilisateur télécharger pdf (Page 67)

Appendix A. Magnetic Encoding

There is one more important parameter that the Tester measures. It deals with the position of the

Start Sentinel from the physical right hand edge of the card. The ISO standard requires that the

“center line” of the first bit in the start sentinel on either Track 1 or 2

to be 0.293 inches ± 0.020”

from the right hand edge of the card. The ISO standard allows the tolerance for the Start

Sentinel position on Track 3

to be ± 0.040”. The reason the start sentinel position is important is

because it provides the reader with enough leading clocking bits for synchronization and an

expectation for where valid data starts from the physical edge of the card.

The F2F encoding technique also permits reading in reverse. That is, instead of passing the card

across a read head with the start sentinel first, it is possible to pass the card across the read head

with the LRC and end sentinel first. Whether any particular reader can function in reverse

depends on whether it was designed to do so.

Next, the parameter “jitter” and why it is an important parameter to measure and control. The

Tester measures jitter and reports values for each of the jitter terms described below.

Jitter

Jitter is a term used as a short version for: Variations in Flux Transition positions. Jitter is more

precisely stated in the ISO standard as Flux Transition Spacing Variation, Subinterval Spacing

Variation, Adjacent Bit Cell Variation, and Adjacent Subinterval Spacing Variation, Bin+1 for

Adjacent Bit Cell Variation and Sin+1 for Adjacent Subinterval Spacing Variation. We will use

the ISO shortened terms (Bin, Sin, Bin + 1, and Sin +1) in this section. All four parameters have

one thing in common. They are all distance measurements between flux transitions. While all

four parameters are distance measurements, it is common to state the measured value in terms of

a percent.

Average Flux Transition Spacing Variation - Ba

This term means a measurement of the overall or average bit density for the encode track.

Individual Flux Transition Spacing Variation - Bin.

Flux Transition Spacing Variation is the distance measurement between clocking flux transitions

or Zero Bit flux transitions over the bit density for the track.

For example, if the distance between the flux transitions for a Zero bit on Track 1 measured to be

0.004350, the Flux Transition Spacing Variation would be stated as -8.7% meaning that the flux

transition that made a zero bit were 8.7% too close together.

1 2 ... 62 63 64 65 66 67 68 69 70 71 72 ... 89 90

Pas de commentaire

Magtek InSpec 9000 Manuel d'utilisateur Page 67