Dynamic magnetic information storage or retrieval – General processing of a digital signal – Data verification
Patent
1991-10-25
1994-02-08
Shepperd, John
Dynamic magnetic information storage or retrieval
General processing of a digital signal
Data verification
360 2, 235449, G11B 509, G11B 2504, G06K 708
Patent
active
052853284
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to reading information from magnetic cards and more specifically to a method for evaluating binary data stored in a magnetic track on a magnetic storage card.
2. Prior Art
Magnetic cards have found a wide range of application in the private and commercial sector, for instance as personal identification, as check-cards, as key-cards, etc. The information is stored on one or more tracks in a particular standardized code, such as the code described in International Standard (ISO) Ref. No. 7811/2-1985 (E), referred to as a two-frequency code. In a two-frequency code, flux changes, which are magnetic flux lines with alternating polarities, are imprinted on the track in fixed intervals. To indicate a binary value of 1, an additional flux change is inserted midway between two such fixed flux changes. Is this additional flux change absent, then the interval indicates the binary value 0. In order to read this magnetic information, the magnetic track is passed by an electromagnetic transformer with a more or less constant velocity, for instance by using a motor to move the magnetic card relative to a fixed transformer, or by passing a movable transformer over the stationary card, or by a person passing the magnetic card, by hand, lengthwise through a slot in which the transformer is mounted.
Due to this scanning movement, a voltage is induced in the transformer following the electrodynamic principle, the polarity of which depends on the polarity of the magnetic flux located on the magnetic track. Since the scanning velocity can vary greatly, the length of the time intervals between the flux changes, or rather the induced voltage impulses, must be determined by a calibration before the actual information can be read. For this purpose, according to the mentioned International Standard (ISO), flux changes are imprinted on the magnetic track in intervals indicating the binary value 0, on a sector which precedes the actual information.
In order to guarantee the safe reading of the stored information, the technical and physical properties of a magnetic card must generally lie within certain tolerance limits. This is the case with new and seldom used magnetic cards, but with increasing wear and age these properties of the magnetic card can change negatively. For instance, the card's surface form may be changed by mechanical and thermal influences, and may become bent or rippled. Signs of use, such as scratches, abrasion, dirt or hairline cracks may appear. Furthermore, the magnetic flux imprinted on the magnetic track may be weakened by superimposed interfering magnetic flux and through the influence of temperature. In addition to such changes in the magnetic card's properties, wear of the electromagnetic transformer, such as surface abrasion incorrect magnetization, as well as the presence of dirt, may inhibit the production of voltage impulses. These changes in the magnetic card's as well as the transformer's properties may cause the voltage impulses emitted by the transformer to be layered with interference signals which may either simulate binary information, or deform the curve of voltage impulses to such an extent that it lies outside of a given evaluation-range within which the signal could still be evaluated safely. As a result of this, the stored information may be read incorrectly or incompletely. The magnetic card at that point can no longer serve its intended function and has become worthless for its user.
In the commonly known process for reading a magnetic card, binary information is obtained through an analog evaluation of the voltage impulses. This evaluation is generally preceded by an amplification of the voltage impulses, which are then low-pass filtered and rectified. In order to recognize the maximum values of the rectified voltage impulses, which, as will be explained later, are used to determine the time intervals between impulses and thus gain the stored information, the time curve of the voltage impulses is differentiated
REFERENCES:
patent: 3684967 (1972-08-01), Kelly
patent: 4267595 (1981-05-01), Hernandez
patent: 4626670 (1986-12-01), Miller
patent: 4742403 (1988-05-01), Tropletti
IBM Technical Disclosure Bulletin, "Error Detecting Read Amplifier", Bass, vol. 7, No. 6, Nov. 1964, pp. 430-431.
IBM Tecnical Disclosure Bulletin, "Synchronous Clock", Houdek et al., vol. 14, No. 7, Dec. 1971, pp. 2006-2007.
IBM Technical Disclosure Bulletin, "F/2F Data Separation and Encoding", Beirne, vol. 20, No. 10, Mar. 1978, pp. 4124-4127.
"International Standard (ISO) 7811/2", Part 2. Dec., 1985.
"System Technology/Integrated Circuits", Computer Design, Jul. 1987, pp. 27-31.
Behr Hubert
Fick Wolfgang
Jager Waldemar
Kim Won Tae C.
Shepperd John
Siemens Nixdorf Informationssysteme AG
LandOfFree
Process for evaluating binary data of a magnetic storage card us does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Process for evaluating binary data of a magnetic storage card us, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for evaluating binary data of a magnetic storage card us will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-702367