Magtek InSpec 9000 Manuel d'utilisateur télécharger pdf (Page 60)

InSpec 9000 Encoded Card Tester

Think of the iron rod as a "bit". We can define the left to right direction of magnetization as a

ONE bit and right to left direction as a ZERO bit. In order to make this iron rod useful as a

storage device, we need to sense the magnetic field direction in order to determine whether the

bit is a ONE or ZERO. This single bit, iron rod storage device is far from practical in today's

world where hundreds of megabytes (a million bits) of disk storage is common place and

relatively inexpensive. However, we do want to take this iron rod concept further.

Modern Magnetic Tape

A means to compact or compress a bunch of iron rods is necessary for magnetic recording to be

practical. This is done by grinding up the iron rod into a powder. This iron (or ferric) powder

forms the basic magnetic component of all magnetic media. The magnetic powder goes through

a complex process of oxidation resulting in an iron oxide called gamma ferric oxide (γFe

Gamma ferric oxide is the most commonly used magnetic particles for "low coercivity" magnetic

tape. ("Coercivity" is described later.) When mixed with a liquid "binder", the iron oxide can

then be coated onto a number of "substrates". Typically, for plastic card manufacture, the

substrate is a polyester film which is later slit to narrow widths for transference to cards or for

direct application on cards.

Encoding Process

The electric current used to produce a magnetic field in the iron rod is also used with an

encoding "head" to generate a magnetic field to magnetize the magnetic tape in order to store

ONES and ZEROES. Figure A-3 shows the internal workings of a typical encoding head.

Figure A-3. Encoding Head Model

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Magtek InSpec 9000 Manuel d'utilisateur Page 60