U.S. patent number 3,696,379 [Application Number 05/094,441] was granted by the patent office on 1972-10-03 for apparatus for article theft detection.
This patent grant is currently assigned to Knogo Corporation. Invention is credited to Arthur J. Minasy.
United States Patent |
3,696,379 |
Minasy |
October 3, 1972 |
APPARATUS FOR ARTICLE THEFT DETECTION
Abstract
In combination with article theft detection apparatus which
employs a signal generator coupled to an antenna at a checkpoint
and means for detecting and indicating the change in signal energy
caused by the presence of a resonant circuit tuned to the signal
frequency adjacent the antenna, a second antenna adjacent the
checkpoint, a second detecting system connected thereto and means
controlled by the second detecting system for disabling the
indicating means when the energy change is due to spurious
radiation, line voltage changes, etc., or due to the presence of
such a resonant circuit at a different checkpoint to prevent false
or ambiguous indications.
Inventors: |
Minasy; Arthur J. (Woodbury,
NY) |
Assignee: |
Knogo Corporation (Westbury,
NY)
|
Family
ID: |
22245221 |
Appl.
No.: |
05/094,441 |
Filed: |
December 2, 1970 |
Current U.S.
Class: |
340/572.4;
340/505; 340/572.5 |
Current CPC
Class: |
G08B
13/2471 (20130101); G08B 13/2488 (20130101) |
Current International
Class: |
G08B
13/24 (20060101); G08b 021/00 () |
Field of
Search: |
;340/280,258R,258C,195
;343/6.5SS |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Caldwell; John W.
Assistant Examiner: Mooney; Robert J.
Claims
What is claimed is:
1. In a system for detecting the unauthorized removal of articles
from an enclosure comprising means for producing electromagnetic
waves in the vicinity of a limited egress facility from said
enclosure including first antenna means at said facility, signal
generating means connected to said first antenna means, and means
coupled to said generating means for indicating the passage of a
resonant circuit tuned to the frequency of said signal past said
facility, second antenna means located adjacent said facility,
disabling means having an input connected to said second antenna
means, said disabling means being responsive to variation of the
electromagnetic energy within the field of said second antenna
means to produce a disabling output and means applying the
disabling output from said disabling means to said indicating means
for disabling said indicating means when said energy varies.
2. A system as set forth in claim 1 wherein said second antenna
means is coupled to signal generating means.
3. A system as set forth in claim 1 wherein said second antenna
means is coupled to said signal generating means and is so located
with respect to said facility that the field thereof is affected by
the passage of said resonant circuit past said facility to an
extent less than that required to operate said disabling means.
4. A system as set forth in claim 1 wherein said second antenna
means is coupled to second signal generating means and is so
located with respect to said facility that the field thereof is
affected by the passage of said resonant circuit past said
first-mentioned antenna means sufficiently to cause operation of
said disabling means.
5. In a system for detecting the unauthorized removal of articles
from an enclosure having first and second closely adjacent egress
facilities comprising first and second protecting systems, one for
each facility, each protective system comprising means for
producing electromagnetic waves in the vicinity of its associated
facility including antenna means and signal generating means and
means including pulse generating means coupled to said generating
means for indicating the passage of a resonant circuit tuned to the
frequency of said signal past either of said facilities, the pulse
generated by the pulse generating means of one said system being
different from the pulse generated by the pulse generating means of
the other system when said resonant circuit is nearer to the egress
facility associated with said pulse generating means of said one
system than to the egress facility associated with said pulse
generating means of said other system and vice versa, the
combination therewith of first gate means having two states, one of
which permits and the other of which prevents operation of the
indicating means of said first system, second similar gate means
for permitting and preventing operation of the indicating means of
said second system, first pulse discriminating means coupled to the
pulse generating means of both said systems and to said first gate
means for controlling the state of the latter and permitting
operation of said indicating means of said first system when the
pulses generated by said pulse generating means have a first
predetermined difference but preventing operation thereof when said
pulses have a second predetermined difference, second pulse
discriminating means coupled to the pulse generating means of both
said systems and to said second gate means for controlling the
state of the latter and permitting operation of said indicating
means of said second system when the pulses generated by said pulse
generating means have said second predetermined difference but
preventing operation thereof when said pulses have said first
predetermined difference.
6. A system as set forth in claim 5 wherein each of said gate means
is normally in a state which prevents operation of the indicating
means controlled thereby and each of said pulse discriminating
means comprises means for comparing the amplitudes of the pulses
and changing the state of the associated gate, said first
discriminator changing the state of said first gate when the
amplitude of the pulse generated by the pulse generating means of
said first system is greater than the pulse amplitude generated by
the pulse generating means of said second system and said second
discriminating means changing the state of said second gate when
the pulse amplitude relationship is the opposite.
7. A system as set forth in claim 5 wherein each of said gate means
is normally in a state which permits operation of the indicating
means controlled thereby and each of said pulse discriminating
means comprises means for comparing the amplitudes of the pulses
and changing the state of the associated gate, said first
discriminator changing the state of said first gate when the
amplitude of the pulse generated by the pulse generating means of
said first system is greater than the pulse amplitude generated by
the pulse generating means of said second system and said second
discriminating means changing the state of said second gate when
the pulse amplitude relationship is the opposite.
8. In a system for detecting the unauthorized removal of articles
from an enclosure having first and second closely adjacent egress
facilities comprising first and second protecting systems, one for
each facility, each protective system comprising means for
producing electromagnetic waves in the vicinity of its associated
facility including antenna means and signal generating means and
means including pulse generating means coupled to said generating
means for indicating the passage of a resonant circuit tuned to the
frequency of said signal past either of said facilities, the
combination therewith of a first and second control antenna means
located respectively adjacent said first and second egress
facilities, means coupling said first control antenna means to said
signal generating means of said first system, means connecting said
second control antenna means to said signal generating means of
said second system, first means responsive to variation of the
electromagnetic energy within the field of said first control
antenna means, first disabling means connected to said first
responsive means and to the indicating means of said second system
for disabling the latter when said energy varies, second means
responsive to variation of the electromagnetic energy within the
field of said second control antenna means and second disabling
means connected to said second responsive means and to the
indicating means of said first system for disabling the latter when
the energy within the field of said second control antenna means
varies, said first control antenna also being so located with
respect to said first and second egress facilities that the field
thereof is affected by the passage of said resonant circuit past
said first facility to an extent sufficient to cause operation of
said first disabling means but is affected by the passage of said
resonant circuit past said second facility to an extent less than
that required to operate said first disabling means and said second
control antenna means being so located with respect to said first
and second egress facilities that the field thereof is affected by
the passage of said resonant circuit past said second facility to
an extent sufficient to cause operation of said second disabling
means but is affected by the passage of said second resonant
circuit past said first facility to an extent less than that
required to operate said second disabling means.
Description
This invention relates to detection systems and more particularly
it concerns novel arrangements for reliably indicating the passage
of articles past given checkpoints.
Various techniques have been developed in the past for monitoring
checkpoints, such as the exits of stores, in order to prevent the
unauthorized taking of articles of merchandise out of the store or
other protected area. Some of these techniques utilize radiating
electromagnetic energy which is reflected, absorbed, or otherwise
transformed by miniature electronic circuits embedded in, or
otherwise affixed to, the "protected" articles. The effect which
the miniature electronic circuit produces on the transmitted energy
is monitored continuously, and when a change occurs due to the
movement past a checkpoint of an article bearing the electronic
circuit, an alarm is sounded. One example of such a system is shown
and described in U.S. Pat. No. 3,500,373, and in such system a
simple resonant circuit is used as the electronic circuit and is
attached to a "protected" article.
If the system relies upon a change in energy within the field of
the radiating coil or antenna, such as in the system shown in said
U.S. Pat. No. 3,500,373, it may frequently happen that the alarm
will be activated by events which do not represent the unauthorized
removal of an article out of the protected area. Thus, in order to
obtain proper operation and protection, the detection equipment is
adjusted so that it is very sensitive to movement of an article
bearing a lable containing a properly tuned resonant circuit past
the egress facility, but as a result, the system becomes responsive
to energy changes caused by other nearby electrical equipment, line
voltage changes, spurious electrical energy received over the power
supply lines and the passage of a resonant circuit carrying label
through another nearby egress facility protected by another
protection system. Accordingly, false alarms, with the accompanying
problems, will occur or an unnecessary number of alarms will be
activated making it difficult to determine the location of the
facility involved.
One object of the invention is to minimize the number of false
alarms in systems of the type hereinbefore described.
Another object of the invention is to limit the operation of an
alarm to that alarm controlled by the system protecting the egress
facility nearest to the article bearing a resonant circuit, i.e.
the "protected" article, and being removed from the protected area
without authorization.
In one preferred embodiment of the invention intended to reduce the
number of false alarms due to radiation from sources other than the
protecting system, a second radiation energy change detecting
system, substantially identical to the detection system used to
operate the alarm, is coupled to the radiation source of the
protecting system and to a control antenna located adjacent to the
protecting antenna at the egress facility or checkpoint but in a
position such that its radiation field is substantially unaffected
by the movement of a resonant circuit past the egress facility and
preferably, in a position such that its field cannot be affected
appreciably by normal movement in the protected area of such
resonant circuit.
In another preferred embodiment where there are two closely
adjacent egress facilities or checkpoints with protecting antennas,
the fields of which are affected by the passage of a resonant
circuit past either of them, each detecting system is provided with
a pulse discriminator and a gate circuit and interconnections
therebetween so that the alarm of the protecting system which
detects the greater energy change will be operated whereas the
alarm of the other protecting system will not. In such embodiment,
the alarm which is operated will indicate the egress facility
nearest the resonant circuit.
In a further embodiment of the invention where there are two
closely adjacent egress facilities with protecting antennas, the
fields of which are affected by the passage of a resonant circuit
past either of them, a pair of control antennas, connected to
detecting systems, are located adjacent to the protecting antennas,
and their associated detecting systems are cross-connected with the
alarms of the detecting systems so as to permit operation of the
alarm of the protecting system having its protecting antenna
nearest the resonant circuit on an article being removed without
authorization and so as to prevent operation of the other alarm.
The control antennas are located so that the fields thereof are
significantly affected by the movement of a resonant circuit past
one of the protecting antennas but not past the other. In such
embodiment, false alarms will be kept to a minimum and ambiguity
with respect to the location of the resonant circuit will be
substantially eliminated.
Other objects and advantages of the invention will be apparent from
the following description of presently preferred embodiments
thereof, which description should be considered in connection with
the accompanying drawings in which:
FIG. 1 is a block diagram of an embodiment of the invention useful
in minimizing false alarms;
FIG. 2 is a partial block diagram of an embodiment of the invention
useful in restricting alarm operation to the system protecting the
egress facility nearest the "protected" article and to some extent,
in reducing false alarms; and
FIG. 3 is a block diagram of an embodiment of the invention useful
in minimizing false alarms and restricting the operation of an
alarm to that of the system protecting the egress facility nearest
the "protected" article.
In FIG. 1, the apparatus included within the dotted rectangle
designated by the reference numeral 1 corresponds to the protecting
system shown in FIG. 1 of U.S. Pat. 3,500,373, and as described in
such patent, the system comprises a coil or antenna 10 which is
located in the vicinity of the checkpoint or egress facility to be
monitored and protected. The antenna 10 may be the single coil
illustrated in FIG. 1 or it may include secondary coils as
described in said patent.
The antenna 10 receives energized current from a main oscillator
11, the output energy of which is periodically shifted in frequency
by means of the tuning circuit 12 connected to a frequency control
oscillator 13 through an amplifier 14.
The output energy from the main oscillator 11 is also fed to a
detecting system comprising a first signal detector 15 which
monitors the level of the energy at the junction 16. The output of
the first signal detector 15 is connected to the radio frequency
filter 16 which in turn is connected to a notch filter 17. The
output of the notch filter 17 is connected to a pulse detector 18
through an amplifier 18a, and when pulses appear at the output of
the pulse detector 18, a relay 19 operates which energizes an alarm
20, provided that the connection between the relay 19 and the alarm
20 is not interrupted as set forth hereinafter. As described in
said patent, a reduction in the energy level at the junction 16
such as by reason of the movement of a properly tuned resonant
circuit past the antenna 10, causes the appearance of pulses at the
output of a pulse detector 18. In this way, the passage of a
"protected" article bearing such a resonant circuit through or past
the antenna 10 is detected, and the alarm 20 is operated.
However, it has also been found that when there are energy changes
due, for example to spurious radiations from nearby electrical
equipment which are received by the antenna 10 and which are within
the frequency range detected by the first signal detector 15, when
there are rapid changes in the supply line voltage or when spurious
signals of the proper frequency enter the apparatus within the
rectangle 1, such as by way of the power supply lines connected
thereto, pulses will be produced at the output of the pulse
detector 18 under certain circumstances. Such pulses will similarly
activate the relay 19 and energize the alarm 20 thereby causing
operation of the alarm 20 even when a "protected" article is not
within the effective range of the antenna 10. Such false alarms are
undesirable not only from the standpoint of causing unnecessary
investigation and possible embarrassment, but also if there are
frequent false alarms, the apparatus is considered less reliable
and the attendants will pay less attention thereto, sometimes
permitting the unauthorized removal of "protected" articles.
In one preferred embodiment of the invention for reducing the
number of false alarms, a control detecting system which is a
duplicate of the detecting system described hereinbefore is
connected to the main oscillator 11 and to a control antenna 21
which may have the same in construction as the antenna 10. In FIG.
1, the control detecting system is enclosed within the dotted
rectangle 2 and comprises a first signal detector 22, the output of
which is connected to a radio frequency filter 23. The output of
the radio frequency filter 23 is connected to a notch filter 24,
and its output is fed to the pulse detector 25 through an amplifier
26. Whenever a pulse is present at the output of the pulse detector
25, a relay 27 is operated which opens the circuit between the
relay 19 and the alarm 20 by opening the contacts 28, and such
opening of the contacts 28 prevents operation of the alarm 20 by
the relay 19.
Although a separate oscillator could be used, preferably the main
oscillator 11 of the protecting system 1 is coupled to the junction
point 29 of the control detecting system through a driver 30 and an
amplifier 31 so that energy of the frequency radiated by the
antenna 10 is also radiated by the control antenna 21 and is
received by the first signal detector 22. Accordingly, if a
"protected" article carrying a resonant circuit were placed
adjacent to the antenna 21, pulses would be produced at the output
of the pulse detector 25 which would operate the relay 27 and
prevent operation of the alarm 20. However, the antenna 21 is not
located at an egress facility or checkpoint but is located in a
position with respect to the antenna 10 such that the field thereof
is either unaffected by the movement of a resonant circuit past the
antenna 10, or is affected to a substantially smaller degree than
the field of the antenna 10. In the latter event, the control
detecting system is adjusted in a well-known manner so that the
change in the field of the antenna 21 must exceed a predetermined
level before the relay 27 will operate. Preferably, the antenna 21
is located in a position such that within the normal area of
movement of the "protected" article the field of antenna 21 will be
substantially unaffected by a resonant circuit carried by a
"protected" article.
From the foregoing, it will be apparent that when a "protected"
article is moved past the antenna 10, the relay 27 will not be
energized by such movement, thereby maintaining the continuity of
the relay and alarm circuits 19 and 20, and the alarm 20 will be
operated. However, the antenna 21 is located in a position with
respect to the antenna 10 so that it will be affected by spurious
radiation from nearby electrical equipment in essentially the same
manner as antenna 10. Similarly, the control detecting system 2 is
connected to the same power supply lines as the protecting system 1
so that it will be affected by spurious radiation on the power
supply lines or by line voltage changes in the same manner as the
protecting apparatus 1. Accordingly, whenever one of these events
occurs which will affect the protecting system 1 so as to produce a
pulse or pulses at the output of the pulse detector 18, a similar
pulse or pulses will be produced by the output of the pulse
detector 25, causing operation of the relay 27, opening the
contacts 28 and thereby preventing operation of the alarm 20.
Accordingly, false alarms will be reduced.
The system described in FIG. 1 will also provide substantial
reduction of false operation of the alarm even if the
interconnection between the main oscillator 11 and the junction 29
is omitted. Thus, by omitting the driver 30 and the amplifier 31
and their interconnections with the junction point 29 and the main
oscillator 11, the control detecting system 2 and the antenna 21
will not be energized by the main oscillator 11 and therefore, the
energization of the control detecting system will not be identical
to that of the protecting apparatus 1. Accordingly, the control
detecting apparatus may not be affected by spurious radiation etc.
in exactly the same manner as the protecting apparatus 1 is
affected thereby so that under some conditions the alarm 20 may be
operated because of the failure of the control detecting apparatus
2 to produce an inhibiting pulse. However, in many cases, the
spurious radiation, line voltage changes, etc. which will produce
an alarm operating pulse in the protecting apparatus 1 will also
produce an inhibiting pulse in the control protecting apparatus 2
even in the absence of the interconnection between the main
oscillator 11 and the junction point 29.
FIG. 2 represents the relevant portions of a pair of protecting
systems 3 and 4 including antennas 10 positioned at a pair of
checkpoints or egress facilities located closely enough normally to
cause operation in many instances, of the alarms of both protecting
systems whenever a "protected" article is moved past or through the
field of either of the antennas. For example, in some cases there
are two exit doors located within a few feet of each other and each
door is protected by a separate protecting system with the intent
of indicating which doorway the protected article is being moved
through. However, it has been found that in some instances the
movement of a "protected" article through one of the doorways which
will cause the operation of the alarm corresponding to such doorway
will also cause operation of the alarm corresponding to the other
doorway. This, of course, makes the indication of the doorway
through which the "protected" article is being removed ambiguous
and makes it difficult to ascertain the "protected" article being
removed without authorization.
In FIG. 2 each of the protecting systems 3 and 4 comprises an
amplifier 18a a pulse detector 18, a relay 19 and an alarm 20.
Protecting systems 3 is connected to an antenna 10 located at a
first doorway or checkpoint and protecting system 4 is connected to
an antenna 10 located adjacent a nearby doorway or checkpoint.
Normally it is desired that when a protected article is moved past
the first doorway, the alarm 20 of the protecting system 3 will be
activated and that when a protected article is moved past the other
doorway, the alarm 20 of the protecting system 4 will be activated.
However, it has been found that under some conditions the alarms 20
of both protecting systems 3 and 4 will be activated when a
protected article is moved through either the first doorway or the
other doorway. An examination of the output of the pulse detectors
18 shows that unless the alarms 20 are activated by the presence of
a protected article almost midway between the two doorways, the
pulse output of one pulse detector 18 will differ from the pulse
output of the other detector pulse detector 18. For example, if the
protected article is moved through the doorway protected by the
system 3, the pulse at the output of the detector 18 forming a part
thereof, will have an amplitude and shape different from the
amplitude and shape of the pulse at the output of the pulse
detector 18 forming part of the system 4 and vice versa. Thus, the
pulses can be differentiated on the basis of their amplitude, rise
time and wave shape. In the embodiment shown in FIG. 2 one or more
of the differences is utilized to cause operation of only the alarm
20 associated with the system 3 or 4 having its antenna 10 closest
to the protected article being removed without authorization.
Accordingly, in each of the systems 3 and 4, conventional gate
circuits 32 and 33 controlled by conventional pulse discriminators
34 and 35 are interposed between the pulse detectors 18 and the
relays 19. The outputs of the two pulse detectors 18 are also fed
to both of the pulse discriminators 34 and 35 so that, for example,
when the output of the pulse detector 18 of the system 3 has a
predetermined relationship with the pulse output of the pulse
detector 18 in the other system 4, the gate 32 will permit the
relay 19 associated therewith to operate and hence, will cause
operation of the alarm 20 of system 3. Similarly, when the output
pulse of the pulse detector 18 of the system 4 has a predetermined
relationship with the pulse output of the detector 18 of the other
system 3, the gate 33 will permit operation of the relay 19
associated therewith and hence, operation of the alarm 20 in the
system 4.
The gates 32 and 33 and the pulse discriminators 34 and 35 may take
several conventional forms depending upon the type of operation it
is desired to obtain. In the preferred embodiment, the gates 32 and
33 are normally closed and require pulses of a predetermined
amplitude and polarity from the pulse discriminators 34 and 35 to
cause opening of the gates 32 and 33 and activation of the
associated alarms. For example, let it be assumed that positive
going pulses must be applied to the gates 32 and 33 to cause
opening thereof and hence, transmission of pulses from the pulse
detectors 18 to the relays 19 and activation of the alarms 20. Let
it also be assumed that the pulse discriminators 34 and 35 are
conventional pulse differential amplifiers which are connected to
the pulse detectors 18 so that when the pulse output of the pulse
detector 18 of the system 3 is greater than the pulse output of the
pulse detector 18 of the system 4, the pulse discriminator 34 will
provide a positive going pulse sufficient to open the gate 32.
Under the assumed conditions, this represents movement of a
protected article nearer to the antenna 10 connected to the system
3 and therefore, the alarm 20 of such system will be activated.
However, when the pulse outputs of the two pulse detectors 18 are
equal or the pulse output of the pulse detector 18 of the system 4
is greater in amplitude than the pulse output of the pulse detector
18 of the system 3, the pulse discriminator 34 will either produce
no output pulse or will produce a negative going pulse. Such
conditions represent either movement of a protected article
substantially midway between the two doorways protected by the two
systems or movement of a protected article nearer to the antenna 10
of the system 4. In such a situation, the gate 32 will not be
opened, and the alarm 20 will not be operated.
Assuming that gate 33 and the pulse discriminator 35 are similar to
and operate in the same way as gate 32 and pulse discriminator 34,
it will be seen that when the amplitude of the pulse at the output
of the pulse detector 18 of the system 4 is greater than the output
pulse of the pulse detector 18 of the system 3, the alarm 20 of the
system 4 will be operated indicating that the protected article is
nearer to the antenna 10 of the system 4. Similarly, if the pulse
outputs of the two detectors 18 are equal in amplitude or if the
output pulse of the pulse detector 18 in the system 3 is greater
than the output pulse of the detector 18 of the system 4, the alarm
20 of the system 4 will not be operated.
Therefore, in the embodiment shown in FIG. 2, only the alarm 20 of
the protecting systems 3 and 4 which has its antenna 10 nearest the
protected article being moved will be activated. Although, neither
of the alarms 20 will be operated if the protected article is
maintained substantially midway between the two doorways such
conditions will not persist if a person tries to move the article
through one or the other of the doorways. Also, the area midway
between the doorways can be obstructed so at to prevent the
presence of a protected article substantially midway between the
two doorways.
It will also be apparent from the foregoing description of the
embodiment in FIG. 2 that when both detecting systems are
substantially similarly affected such as by spurious radiation from
nearby electrical equipment, line voltage fluctuations etc., the
gates 32 and 33 will not be open thereby reducing false operation
of the alarms 20.
In the event that it is desired merely to prevent simultaneous
operation of both alarms 20 when a protected article is moved past
one of the doorways, the gates 32 and 33 may be conventional gates
circuits which are continuously open and which are turned off only
when a pulse of the proper polarity and amplitude is applied
thereto by one of the pulse discriminators 34 and 35. In this
situation the pulse discriminator 34 would turn off the gate 32
only when the output pulse of the detector 18 of the system 4 has
an amplitude greater than the output pulse of the pulse detector 18
of the system 3. Similarly, the pulse discriminator 35 would turn
off the gate 33 when the output pulse of the pulse detector 18 in
the system 3 is greater in amplitude than the output pulse of the
pulse detector 18 of the system 4. In this way, the alarm 20 of the
system 3 would not be activated when the protected article is
nearer the antenna 10 associated with the system 4 and the alarm 20
of the generating and detecting system 4 would not be activated
when the protected article is nearer the antenna 10 associated with
the system 3. However, if the output pulses of the detection 18 are
substantially equal, such as is the case when the protected article
is substantially midway between the doorways or when the systems
are affected by spurious radiation, both alarms 20 will be
activated.
Although the embodiment of FIG. 2 has been described on the basis
that the pulse discriminators 34 and 35 distinguish between the
pulse outputs on the basis of amplitude, it will be apparent to
those skilled in the art that the pulse discriminators may
differentiate between the pulses and activate or de-activate the
gates 32 and 33 on the basis of other characteristics of the
pulses, such as, rise time or wave shape.
FIG. 3 illustrates a further embodiment of the invention which may
also be used to minimize false alarms and at the same time prevent
ambiguity in alarm activation. The embodiment illustrated in FIG. 3
is in effect a combination of a pair of the systems shown in FIG. 1
with the control detecting system associated with one of the
protecting systems cross-connected with the protecting system
associated with an adjacent separate doorway or checkpoint.
In FIG. 3, a pair of protecting antennas 10 are located at closely
spaced doorways or checkpoints and are in positions such that the
fields of both are affected sufficiently by the passage of a
protected article past either checkpoint, or through either
doorway, to cause operation of the associated alarms 20. Thus, one
of the antennas 10 is connected to the generating and detecting
system 36 similar to the generating and detecting apparatus of
system 1 shown in FIG. 1, and the output thereof controls an alarm
20 through a pair of contacts 37 which may be open by a relay 38.
When the protected article is moved past the antenna 10 the system
36 operates the alarm 20 provided that contacts 37 are closed.
Similarly, the other antenna 10 is connected to a generating and
detecting system 39 similar to the generating and detecting
apparatus of system 1 shown in FIG. 1 and energizes the alarm 20
through the contacts 40 when the protected article is within the
field of the antenna 10 associated therewith. When relay 41 is
energized, contacts 40 open preventing operation of the alarm 20.
In the absence of energization of the relays 38 and 41 the alarms
20 of both protecting systems would be operated whenever a
protected article moves past either of the antennas 10.
The relay 41 is energized by the output of a control detecting
system 42 similar to the controlled detecting system 2 shown in
FIG. 1, and such system 42 is connected to a control antenna 21
which is located in a position such that the relay 41 is energized
by the system 42 whenever a protected article is moved past the
antenna 10 connected to the system 36, but is not energized when a
protected article is moved past the antenna 10 connected to the
detecting system 39. Similarly, the relay 38 is energized by the
control detecting system 43, which is similar to the control
detecting system 2 shown in FIG. 1 and to the control detecting
system 42. Whenever a protected article is moved past the antenna
10 connected to the detecting system 39, the relay 38 is energized
but it is not energized when a protected article is moved past the
antenna 10 connected to the detecting system 36. However, all the
antennas 10 and 21 may be located relatively close to each other so
that they are substantially equally affected by spurious radiation
from nearby electrical equipment, and all the detecting systems may
be connected to the same supply lines so that they will be
substantially equally affected by spurious radiation, line voltage
changes, etc.
Accordingly, when a protected article is moved past the antenna 10
connected to the detecting system 36 the relay 38 will not be
energized and the alarm 20 associated therewith will be sounded. At
the same time, the antenna 21 connected to the system 42 will cause
energization of the relay 41 preventing activation of an alarm 20
connected to the detecting system 39 even though pulses are
produced therein by virtue of the movement of such protected
article. Similarly, when a protected article is moved past the
antenna 10 connected to the detecting system 39 the alarm 20
associated therewith will be operated and the control detecting
system 43 will energize the relay 38 preventing operation of the
alarm 20 associated with the detecting system 36 even though there
is a pulse output from such system. In this way, only the alarm 20
of the detecting system past which the protected article is moved
and nearest thereto will be activated.
Also, since all antennas are substantially similarly affected by
spurious radiation, line voltage changes, etc. the relays 38 and 41
will both be energized at the time such radiation or changes occur
so that neither alarm 20 will be activated. In this way, false
alarms are reduced.
Although each of the embodiments hereinbefore described have been
described as activating and alarm 20, which may be an audible or
visible alarms, it will be apparent to those skilled in the art
that instead of such alarms, or in addition thereto, the detecting
systems may be used to activate automatic door closing mechanisms
which will close and lock the exit door associated with the
protecting system as a protected article is moved toward such door,
such closing and locking of the doors indicating the attempted
removal of a protected article and therefore, being indicating
means. Also, although in each of the embodiments the indicating
means is disabled subsequent to the pulse detector, i.e. either
before or after the relay which normally operates the alarm, it
will be apparent to those skilled in the art that the indicating
means may be disabled at an earlier or later point in the
protecting system.
* * * * *