Device and a method for detecting a magnetizable marker element
First Claim
1. A device for detecting a magnetizable marker element, adapted to be attached to an object to be protected against unauthorized removal, comprising:
- (a) a transmitter for generating a periodically alternating magnetic excitation field for reversing the magnetic state of the marker element;
(b) a receiver arranged in said alternating magnetic excitation field for generating an electrical output signal corresponding to a signal received upon a said magnetic state reversal;
(c) a signal processing means including a band pass filter for filtering said output signal of said receiver, the resultant filtered output signal having a superimposition of signal components, the frequencies of which are integral multiples of the fundamental frequency of the excitation field;
(d) means for comparing the time interval between two successive maximum signal values of different polarities of the filtered output signal to a predetermined tolerance range associated with half the period duration of the excitation field, and for generating a first output signal when the time interval is within said predetermined tolerance range; and
(e) an indicator generating a first indication signal upon receiving a first output signal from said comparing means.
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Accused Products
Abstract
To detect a marker element, a transmitter generates an alternating magnetic field. A receiver arranged in this field generates an electrical signal having a waveform corresponding to the magnetic flux density of the alternating magnetic excitation field superimposed by peaks produced upon reversal of the magnetic state of the marker element. The position of these peaks, relative to the alternating magnetic excitation field, is determined, and if different from half the period duration of the alternating magnetic excitation field by less than a predetermined value, a first state of the marker element may be detected. Otherwise, it may be determined that, either, no marker element is present in the alternating magnetic excitation field, or that the marker element is in a second state different from the first state.
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Citations
11 Claims
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1. A device for detecting a magnetizable marker element, adapted to be attached to an object to be protected against unauthorized removal, comprising:
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(a) a transmitter for generating a periodically alternating magnetic excitation field for reversing the magnetic state of the marker element; (b) a receiver arranged in said alternating magnetic excitation field for generating an electrical output signal corresponding to a signal received upon a said magnetic state reversal; (c) a signal processing means including a band pass filter for filtering said output signal of said receiver, the resultant filtered output signal having a superimposition of signal components, the frequencies of which are integral multiples of the fundamental frequency of the excitation field; (d) means for comparing the time interval between two successive maximum signal values of different polarities of the filtered output signal to a predetermined tolerance range associated with half the period duration of the excitation field, and for generating a first output signal when the time interval is within said predetermined tolerance range; and (e) an indicator generating a first indication signal upon receiving a first output signal from said comparing means. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. A method for detecting a magnetizable marker element attached to an object to be secured against unauthorized removal, comprising the steps of:
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(a) exposing said marker element to a periodically alternating magnetic excitation field such that the magnetic state of said marker element is periodically reversed; (b) receiving a signal resulting from said magnetic state reversals of said marker element and converting it to a corresponding electrical signal, the electrical signal comprising the superimposition of a carrier signal corresponding to the periodic alternation of said alternating magnetic excitation field and a signal portion corresponding to said magnetic state reversals of said marker element; (c) subjecting said electrical signal to a band pass filter, the obtained filtered signal comprising a superimposition of harmonics of the carrier signal of the electrical signal; (d) defining a tolerance range associated with the value of half the period duration of the alternating magnetic excitation field; (e) comparing the time interval between two maximum signal values of different polarities of said filtered signal to the defined tolerance range; and (f) generating an output signal if the time interval is within the defined tolerance range.
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Specification