Note: Descriptions are shown in the official language in which they were submitted.
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The invention relates to a system for registrating an
article passing through a predetermined area, and comprising
a transmitter and a receiver with a common aerial alternately
transmitting and receiving electromagnetic signals~ as well as
a marker attached ~o each article and receiving said signals
and transmitting other signals at passage through said area3
whereby the transmitting and receiving period changes as the
signals transmitted have a constant signal frequency through
the entire transmitting period, and as a signal processor
counts a predetermined number of signals received uninter~
ruptedly from the marker comprising a tuned circuit and com-
pares the frequency thereof to the frequency of the signals
transmitted by the transmitter during a transmitting period,
whereby the transmitting and receiving aerial is formed by a
multipole loop, preferably looped like an eight and positioned
in one plane.
Such a system is for instance known from Danish Patent
ll~5,169 issued to Security Products International A/S. This
known system is, however, encumbered with the draw-back that
the marker in some orientations may pass without being
detected by the main area.
The system according to the invention is characterised
in that the transmitting period is followed by a first re-
receiving period in which the number of for instance wave peaks
is counted, and at least one additional receiving period in
which the number of peaks is counted too. When the number of
peaks during the first period is sufficiently high, and the
following period does not include too many peaks, it is in-
dicated that a marker is present in the area.
According to a particularly advantageous embodiment of
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the s~7stem alarm is only produced when the difference in num
ber of wave peaks during the first receiving period and the
number of wave peaks during the second period is sufficiently
great. In this manner the system may be made so sensitive
that the weaker side areas of another orientation may be uti-
lized. As a result, the marker cannot pass the area without
being detected irrespective of its orientation.
Furthermore, the system no longer depends on the shape
and orientation of the aerial.
The invention will be described below with reference to
the accompanying drawing, in which
Fig~ 1 is a diagrammatic view of the system according to
the invention,
Fig. 2 illustrates the use of the system,
Fig. 3 illustrates another possibility of using the
system, whereby the construction of the aerial is indicated,
and
Fig. 4 illustrates both the transmitted and the received
signals.
Fig. 1 illustrates how an aerial 1 is connected to a
transmitter 2 or a receiver 3, 4 through a change-over switch
5. This change-over switch is controlled by a synchronizing
unit 6 having an appropriately high frequency. At the trans-
mission of a short signal from the transmitter 2 at the fre-
quency of ~or instance 1 MHz, an alternating current is in-
duced in an oscillatory circuit in a marker 18, cf. Fig. 2,
when said marker is present within the electromagnetic area
; created by the transmitting aerial. When this transmission of
signals ceases, i.e. when the aerial 1 is connected to the
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receiver 3, 4 through the change-over switch 5, the oscilla-
tory circuit of the marker 18 emits a signal at the same fre-
quency until -the oscillations are quenched. This signal is
received by the aerial 1 and transmitted to a signal proces-
sor 7 through the receiver 3, 4. At th0 same time this signalprocessor 7 receives pulses from the synchronizing unit 6 and
is thereby permitted to count the signals received uninter-
ruptedly from a marker 18. This procedure is obtained by the
counter in question being zeroed when no signal is received
during the receiving period following immediately upon a
transmitting period. The signal processor 7 furthermore con-
trols whether the frequency of the signals received corre-
sponds to the frequency of the signals transmitted. As a re-
sult an additional security against false alarms is pro~ided.
Fig. 2 illustrates how a plurality of figure-of-eight
aerials 8 may be located in such a manner that a broad pas-
sage can be controlled. The system is built into a frame
stand, and the frame members 9, 10, 11, 12, 13, 14, 15, and
16 form the figure-of-eight aerial. The transmitter 2, the
receiver 3, 4, and the processor 7 have been built into a
box 17.
The figure~of-eight aerial, which preferably is located
in one plane, generates a toroidal area, which for the sake
of clarity only appears at one of the aerials. This procedure
implies within a predetermined range that the passing marker
is detectable almost irrespective of its orientation.
According to the invention it is, however, also shown
how the weaker side areas also may be utilized, said areas
only being indicated at one of the aerials too for the sake
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of clarity. They may be utilized in such a manner that a mar-
ker cannot pass therethrough either when itis parallel to the
direction (two directions) of the main area. This is accord-
ing to the invention obtained by the transmitting period last-
ing for instance 60 ~sec. and the following first receivingperiod lasting 20 ~sec. During this period, the number of
peaks is counted, and when the transmitter frequency is 1 MHz,
it corresponds to about 20 peaks or periods (or more when
noice signals are present too). Subsequently, a blank period
of for instance 40 ~sec. follows, and then a second receiving
period, cf. Fig. 4, in which the number of peaks is counted.
When a predetermined number of peaks is counted during a re-
ceiving period, a signal is transmitted. When another prede-
termined number of signals is uninterruptedly counted from
the first receiving perioa at the same time as the number of
signals from the second receiving period does not exceed a
predetermined number, the alarm is produced. In this manner
the system is so sensitive that the weaker side areas can be
utilized too. The side areas may thereby detect the marker 18
20 when said marker has not been detected by the main area, then
utilizing that the orientation of these weaker side areas
differs from the orientation of the main area, cf. Fig. 2.
An additional advantage of the system according to the
invention is that it does not depend on the form and location
~5 of the aerial. Furthermore, it is possible to use a multipole
aerial. In all cases it is, however, an advantage to shape
the aerial in such a manner that remote areas from the outside
are automatically compensated for, e.g. by the loops having
the same area.
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The system furthermore possesses the advantage that it
is not sensitive to shakings and is easy to mount.
The marker is preferably formed by a coil in connection
with a capacitor, the coil functioning as a receiving and
transmitting aerlal for the marker. The Q-value is preferably
greater than 50.
The system according to the invention may be varied in
many ways without thereby deviating from the scope of the
invention. According to an alterna-tive embodiment of the di-
gital high-pass filter, the signal to be filtrated is carried
through an A/D converter and subsequently to a digital com-
puter in the form of a microprocessor automatically perform-
ing the filtration.
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