Communications: electrical – Continuously variable indicating – With meter reading
Patent
1997-10-28
2000-07-25
Holloway, III, Edwin C.
Communications: electrical
Continuously variable indicating
With meter reading
34082534, 3405687, 194206, 235451, G07D 700
Patent
active
060941472
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a method for detecting an electroconductive element in a document according to the preamble of claim 1.
A method of the aforementioned kind is known e.g. from DE 43 39 417 A1. In the known method, the high-frequency signal produced by an oscillator is applied to a transmitting electrode. The transmitted signal is transmitted via the electroconducive security thread to the receiving electrode and evaluated in an evaluating circuit. The security thread is recognized as genuine by the evaluating circuit if amplitude and phase position of the transmitted signal match the input signal on the transmitter.
A problem in detecting security threads in a document is that for example a moist document can cause a signal due to the electrolytic conduction although the document has no security thread. Reliable differentiation of the signal transmitted from the transmitting to the receiving electrode due to the metallic conduction of the security thread from a signal caused by the electrolytic conduction in the document is impeded, however, by the high capacitive coupling resistances present between the transmitting and receiving electrodes. At a working frequency in the 100 kHz range these resistances can be in the order of magnitude of megaohms for example, and are thus very much greater than the resistance of the metallic security thread, which can be e.g. in the kiloohm range. Due to the high capacitive coupling resistances, the contribution of the security thread can no longer be exactly detected during measurement. This is important in order to ensure reliable detection of the security thread in the document.
The invention is thus based on the problem of proposing a simple and more reliabie method for detecting an electroconductive element in a document.
this problem is solved according to the invention by the features stated in characterizing part of he "independent" claims.
The basic idea of the invention is that for detecting an electroconductive element in a document a signal with a modulated carrier frequency is coupled to at least one transmitting electrode and transmitted by means of the electrconductive element to at least one receiving electrode, the received modulated signal being evaluated for detecting the electroconductive element. The electroconductive element acts as a capacitive coupling element between the transmitting and receiving electrodes.
The capacitively transmitted modulated carrier frequency signal is preferably mixed onto the modulation frequency on the receiver side. The signal with the modulation frequency can then be evaluated as to amplitude for detecting the electroconductive element. The signal can be filtered and amplified prior to evaluation. By reason of component availability and costs, a value of e.g. 455 kHz as is usual in radio technology is preferably selected as the modulation frequency. For modulating the carrier frequency signal one can use amplitude modulation, whereby the carrier frequency can be in the MHz range and the modulation frequency in the kHz range.
By using a very high carrier frequency in comparison to the modulation frequency one can reduce the capacitive coupling resistances between the transmitting and receiving electrodes considerably, e.g. by a factor of 10.sup.3, which permits more exact detection of the electroconcuctive elements. Due to the low capacitive coupling resistances, which are e.g. in the kiloohm range, the inventive method is insensitive to moisture in the documents.
Since the modulated carrier frequency is mixed with the same carrier frequency, only a UHF oscillator is required for the transmitting and receiving electrodes. One can use e.g. a simple LC oscillator. This permits the method to be carried out with low technical effort.
In a development, a plurality of transmitting and receiving electrodes can also be provided for detecting the electroconductive element in the document. The transmitting and receiving electrodes of an electrode pair are disposed linearly to each other. Each electrode pair corresponds to
REFERENCES:
patent: 4255652 (1981-03-01), Weber
patent: 5417316 (1995-05-01), Harbaugh
patent: 5419424 (1995-05-01), Harbaugh
patent: 5614824 (1997-03-01), Dames et al.
Giesecke & Devrient GmbH
Holloway III Edwin C.
LandOfFree
Method for detecting an electroconductive element in a document does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for detecting an electroconductive element in a document, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for detecting an electroconductive element in a document will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1339528