| 摘要 |
So that the coding of a key card having magnetically readable information points can be made invisible from outside and cannot be duplicated or changed without destroying it, but can be read off without movable parts, a perforated plate made of non-magnetisable material, covered on both sides by plates of non-magnetisable material, is provided in the direction of insertion with a plurality of rows of holes for magnetic sensing and identification which are ordered relative to one another according to a code system. The holes are filled with ferromagnetic material, for example circular metal discs and/or iron powder. For the laterally correct insertion of the key card into the lock, the edges of the two cover plates are connected firmly to one another in the plane of one cover plate. Each row of holes is assigned a reading head having a permanent magnet which is aligned with the holes and the magnetic lines of flux of which are varied in dependence on the position of insertion of the key card in the lock during the change between air and metal. This has the effect of abrupt changes in magnetic induction which are converted into electrical counting signals by a measurement transducer designed as a magnetoresistor and which are fed to an evaluation circuit.
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