U.S. patent number 3,573,620 [Application Number 04/733,693] was granted by the patent office on 1971-04-06 for security system with inductive to rf communications links.
Invention is credited to John Raymond Ashley, Coling Grahame Douglas.
United States Patent |
3,573,620 |
Ashley , et al. |
April 6, 1971 |
SECURITY SYSTEM WITH INDUCTIVE TO RF COMMUNICATIONS LINKS
Abstract
In a location system a radio transmitter carried by a security
guard or watchman includes a loop aerial and a loop demodulator,
and loop carrier frequency generators each generating a loop
carrier frequency modulated by a different modulating frequency are
installed at different points to be visited by the guard, so that
as the guard reaches each point the loop carrier is demodulated and
the modulating frequency is used to modulate the transmitter
carrier. The transmitted signals are picked up at a distant
monitoring point, demodulated, and the modulating frequency is
identified with the point visited.
Inventors: |
Ashley; John Raymond (Somerset,
EN), Douglas; Coling Grahame (Wiltshire,
EN) |
Family
ID: |
10223838 |
Appl.
No.: |
04/733,693 |
Filed: |
May 31, 1968 |
Foreign Application Priority Data
|
|
|
|
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May 31, 1967 [GB] |
|
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25199/67 |
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Current U.S.
Class: |
340/525; 340/306;
340/567; 340/658; 340/539.1; 455/41.1; 340/539.13 |
Current CPC
Class: |
G07C
1/20 (20130101) |
Current International
Class: |
G07C
1/00 (20060101); G07C 1/20 (20060101); H04b
001/50 (); G08b 025/00 () |
Field of
Search: |
;325/4,7,16,51,53,64,111,113,118 ;340/224,306,152 (TR)/
;340/286,287,311,312 ;343/226 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Griffin; Robert L.
Assistant Examiner: Brodsky; James A.
Claims
We claim:
1. A security system comprising signal receiving and transmitting
means to be carried by a watchman or security guard, a plurality of
inductive frequency generating means for generating a loop carrier
frequency and a predetermined location frequency for modulating the
loop frequency, said generating means being located at selected
points in the area to be patrolled by the watchman or security
guard, said signal receiving and transmitting means comprising a
loop aerial for receiving both the loop carrier frequency and the
location frequency generated by said generating means as the said
guard nears said generating means and a loop demodulator for
demodulating the received signal, said signal receiving
transmitting means being adapted to transmit the said demodulated
signal to a second receiving means for receiving said signal, said
second receiving means including a plurality of filters by which
the particular location frequencies may be recognized, and
indicating means for indicating the receipt of each particular
location frequency by said second receiving means.
2. A system as claimed in claim 1 in which the radio transmitter is
a V.H.F. transmitter.
3. A system as claimed in claim 1 in which the indicating means
comprises an indicator panel having a number of windows each
corresponding to one of the locations, a lamp behind each window,
and means responsive to the recognition of the respective
modulating frequency to cause the lamp to be illuminated.
Description
This invention relates in general to security systems, and more
particularly to a system by which the movements of a watchman or
security guard may be automatically indicated at a remote point on
a monitoring system which may, for example, be located at the
headquarters of a Security Service or in a Police Station.
In order to protect property and maintain continual watch for the
development of fires, it is quite usual to employ a night watchman
or security guard whose duty it is to patrol the property or
premises in question. To ensure that this officer carries out his
duties correctly it is common practice to provide a number of check
points all of which the officer is required to visit at
predetermined intervals. In one system the officer is provided with
a clock device into which he can insert any one of several keys
mounted at discrete locations in the premises in order to record
each visit to each location on a paper tape within the clock
device. However, it is possible for an officer to be attacked by
unauthorized persons lurking on the premises and in such a case the
fact that after being attacked the officer has not visited any of
the check points would not be known until the following morning and
the information would then be useless. If the officer should be
attacked he will, of course, desire to summon assistance but this
may involve giving the alarm by such means as blowing a whistle or
getting to an emergency pushbutton, and he may be prevented from
doing either of these things. The object of the invention is to
provide a system by which it is possible to monitor at a remote
location the movement of the officer so that if he fails to reach a
particular check point at a particular time this fact is indicated
at once.
The invention consists of a location system comprising a radio
transmitter to be carried by a watchman or security guard, the
radio transmitter including a loop aerial and a loop demodulator, a
plurality of frequency generating means, hereinafter called loop
carrier frequency generators each generating a loop carrier
frequency and a location frequency by which the loop carrier
frequency is modulated, the generators being located at selected
points in the area to be patrolled by the watchman or security
guard, each location frequency being different and being indicative
of the location of the associated generator, means for installation
at a monitoring point to receive the transmitted demodulated
carrier wave including filters by which the particular location
frequencies may be recognized, and means by which the receipt of
each particular frequency is indicated.
To promote a full understanding of the invention one embodiment
thereof will now be described, by way of example with reference to
the accompanying schematic drawings, in which:
FIG. 1 shows the apparatus carried by the officer and two inductive
loop frequency generators;
FIG. 2 shows the apparatus at the receiving or monitoring
point;
FIG. 3 shows the panel of a suitable indicating device.
Referring first to FIG. 1, there is shown an ordinary mobile pocket
radio transmitter (less microphone) indicated by a dotted rectangle
11. The rectangle 11 contains a block representing the radio
transmitter with a transmitting aerial 12a and having connected to
it the transmitter modulator 13. This mobile transmitter may be
very small and may be a pocket V.H.F. transmitter of the kind
carried by policemen who are on ordinary patrol duties covering
different beats. In addition to the transmitting apparatus 11 the
officer carries further apparatus indicated by the block 14
together with a loop aerial 15 connected to the block 14 by means
of a rod or cable. The block 14 contains a loop detector and a loop
demodulator.
At different points in the area to be patrolled by the officer is a
plurality of conventional inductive generators for generating both
a carrier frequency and a location frequency, two of which are
indicated at 16 and 17. Each of these inductive loop frequency
generators is arranged to generate a main or carrier frequency and
a location frequency by which the carrier frequency is modulated.
The carrier frequencies are identical but each of the location
frequencies is different so that the location of each particular
loop frequency generator may be identified by the unique location
frequency.
The loop aerial 15 carried by the officer is designed to receive
the loop carrier frequency from each of the inductive loop
frequency generators and this loop carrier is applied to the loop
detector and demodulated by the loop demodulator contained in the
block 14. The modulation frequency, which is, of course, the
location frequency, is then applied to the modulator 13 in the
officer's transmission equipment 11.
As the officer patrols the area in his charge the transmitter
transmits a continuous carrier frequency and each time he passes
near one of the inductive loop frequency generators, as represented
by 16 and 17, the particular location frequency is transmitted for
a short period.
At a location remote from the area being patrolled by the officer
is a monitoring apparatus consisting of a receiver 18 having a
receiving aerial 18a and tuned to the particular carrier frequency
which the radio transmitter carried by the officer is transmitting.
The output of the receiver 18 is passed to a demodulator 19 and the
demodulated output is passed through a series of filters 20 each
one of which responds to one of the location frequencies. Whenever
one of the location frequencies is received the particular
frequency is recognized by one of the filters and is caused to
provide an indication of its presence, for example, by operating a
relay which lights a lamp on an indicator 21.
FIG. 3 shows a suitable form of indicator 21 which may consist of a
front panel 22 having 10 circular bezels each of which contains a
glass window 23, which may be colored if desired. The 10 indicators
are numbered and a lamp is provided behind each window. It may be
arranged that once one of the lamps behind a window 23 has been
illuminated by the receipt of one location frequency it will remain
illuminated until another location frequency is received, when the
indicator corresponding to the location of the new frequency is
illuminated and the previously illuminated indicator is
extinguished. This mode of operation may conveniently be achieved
by the use of relays.
The indicator shown in FIG. 3 in only exemplary and indicating
means suitable for any desired number of different locations may
easily be provided.
It will be evident from the foregoing description that the system
according to the invention offers many advantages. In the first
place it is possible continuously to monitor the movements of the
officer. If he does not arrive at a particular place by a
particular time then it is known that something is not as it should
be, which may be due either to a failure of duty on the part of the
officer or to some other cause. Not only does the invention make it
possible to detect quickly the kind of condition which the officer
is intended to detect, i.e., the presence of intruders or fire, but
the monitoring system will also give an indication if the officer
should have an accident or be taken ill so that he is unable to
continue his patrol.
* * * * *