U.S. patent number 3,696,359 [Application Number 05/109,866] was granted by the patent office on 1972-10-03 for intrusion alarm system.
This patent grant is currently assigned to Sperry Rand Corporation. Invention is credited to Hugh C. Maguire, Gerald F. Ross.
United States Patent |
3,696,359 |
Ross , et al. |
October 3, 1972 |
INTRUSION ALARM SYSTEM
Abstract
A wireless point of entry intrusion alarm system having a
central monitor and alarm cooperates with magnetically actuable
entry detectors placed at potential entry locations. Each sensor is
automatically reset by the same magnetic means upon reclosure of
the guarded entry.
Inventors: |
Ross; Gerald F. (Lexington,
MA), Maguire; Hugh C. (Westford, MA) |
Assignee: |
Sperry Rand Corporation
(N/A)
|
Family
ID: |
22329975 |
Appl.
No.: |
05/109,866 |
Filed: |
January 26, 1971 |
Current U.S.
Class: |
340/539.14;
340/547; 455/67.7; 335/205; 455/127.1 |
Current CPC
Class: |
G08B
13/08 (20130101); G08B 13/22 (20130101) |
Current International
Class: |
G08B
13/22 (20060101); G08B 13/08 (20060101); G08B
13/02 (20060101); G08b 013/08 () |
Field of
Search: |
;340/224,274
;325/105,115,169,185 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Trafton; David L.
Claims
We claim:
1. An intrusion alarm system for detecting relative motion between
first and second parts comprising:
magnetic field generating means affixed to one of said parts,
first switch means having first and second states with respect to
first and second magnitudes of said magnetic field,
respectively,
charging circuit means operative in series circuit relation only
when said first switch means is in said first state comprising:
electrical current source means,
first resistor means, and
capacitor storage means,
alarm actuator circuit means operative in series circuit relation
only when said first switch means is in said second state
comprising:
said capacitor storage means,
voltage sensing means for providing an output signal when the
voltage stored on said capacitor storage means exceeds a
predetermined value, and
said electrical current source means,
second switch means responsive to said output signal by changing
from a non-conducting to a conducting state, and
alarm circuit means operative in series relation with said second
switch means only when in said conducting state comprising:
said electrical current source means,
multivibrator means, and
oscillator means for transmitting an alarm signal.
2. Apparatus as described in claim 1 wherein said oscillator means
is responsive to said multivibrator means for producing a train of
pulsed radio frequency signals for space transmission.
3. Apparatus as described in claim 2 wherein said multivibrato
means is adapted to produce an audio frequency semi-square wave
output with rise times sufficiently slow for substantially limiting
the harmonic content of the output of said radio frequency
oscillator means.
4. Apparatus as described in claim 1 wherein said first switch
means comprises single pole, double throw reed switch means having
first, second, and third electrical terminal means,
said first terminal means supports said double throw reed, and
said reed supports contact means for contacting said first or
second terminal means with respect to the magnitude of said
magnetic field.
5. Apparatus as described in claim 4 wherein:
said first terminal means is connected to said capacitor storage
means,
said second terminal means is connected to said first resistor
means, and
said third terminal means is connected to said second resistor
means.
6. Apparatus as described in claim 4 wherein said second switch
means comprises:
magnetically actuatable single pole, single throw reed switch means
connected to said electrical source means, and
solenoid magnetic field generating means connected to said
electrical source means for actuating said magnetically actuatable
single pole, single throw reed switch means.
7. Apparatus as described in claim 6 wherein said voltage sensing
means comprises transistor switch means for controlling current
flow through said solenoid magnetic field generating means when
said voltage drop across said second resistor exceeds a
predetermined value.
8. Apparatus as described in claim 1 including remotely located
receiver means indicating reception of said pulsed radio frequency
space transmitted signals for alarm purposes.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention pertains to means for providing protection of
buildings or other elements of property from forced entry or
unauthorized treatment and more specifically relates to
magnetically actuable radio signal transmission devices for
detecting the unauthorized entry of buildings or for detecting
unauthorized access to or movement of guarded property.
2. Description of the Prior Art
Prior art intrusion devices of many types have served
advantageously in the protection of lives and property from
intruders, but generally have been complex, expensive, and
difficult to install and maintain. There has been an unfulfilled
need for inexpensive and easily installed and easily operated
intrusion sensing apparatus which has the reliability of such prior
devices, but which offers greater economy of ownership and
flexibility of use. Many prior devices require relatively large
batteries and charging installations for their successful
operation. Others use permanent wiring which is complex to install
even in a building while under construction. Sensing systems that
depend on the physical breaking of electrical contacts have not
afforded great reliability, as well as being difficult to install
and to conceal. For example, the kind of alarm sensor using
conductive tapes fastened to the glass of windows is expensive and
difficult to install and maintain. Further, it is particularly
sensitive to development of high false alarm rates as the condition
of the building degrades and causes misalignment of electrical
contacts. False alarm rates are high where sensors are used that
notice disturbances in sonic or electromagnetic standing wave
fields.
SUMMARY OF THE INVENTION
The present invention relates to a wireless alarm system for
providing protection of buildings or of other property from
unauthorized entry or removal. The intrusion system utilizes a
centrally located radio receiver and alarm system cooperating with
magnetically actuable radio transmitters placed at points of
possible entry. Each transmitter is furnished with a magnetically
actuated condenser charging circuit having a very low current drain
demand on an associated miniature battery. Further, each
transmitter is magnetically actuated upon the event of an intrusion
to transmit a short, low energy level signal to the centrally
located receiver for actuating an alarm. No further transmission is
made by the affected transmitter until it is magnetically reset,
for instance, by the manual closing of the associated entry.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1A and 1B are respective elevation views of two situations
showing a representative installation of the novel intrusion
sensor.
FIG. 2 is a circuit diagram illustrating the electrical connection
of components of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
FIG. 1A illustrates one manner of use of the novel intrusion sensor
1 with its associated antenna 3 when affixed to a stationary part
or frame 5 of a window 4, that window 4 to be monitored against
unauthorized entry. Closely associated with intrusion sensor of
detector 1, when the movable part of window or barrier 4 is in its
normal closed position, is a small bar magnet or other source of
magnetic field 2 affixed to window 4 by an adhesive or other
conventional fastening means. The intrusion sensor 1 and magnet 2
may be installed permanently or temporarily by untrained personnel
and may readily be shifted from one location to another since no
electrical wiring is required. In such a manner, sensors may be
installed to detect the opening of a window, door, sky light, or
roof hatch or to detect an unauthorized act causing relative
movement between a magnet placed on an expensive object of art
relative to a sensor affixed to the wall from which the object is
supported.
Opening of an entry such as the window 4 of FIG. 1A is illustrated
in FIG. 1B. It is seen that by raising the frame of window 4,
magnet 2 is removed from the proximity of sensor 1, and sensor 1 is
no longer affected by the magnetic field of magnet 2. Sensor 1 is
thereby caused to transmit a short duration alarm signal via
antenna 3 to a central receiver 51 yet to be described in
connection with FIG. 2.
The general disposition of sensor 1 and magnet 2 in FIGS. 1A and 1B
is intended to be illustrative of one of many ways of using the
apparatus. If desired, elements 1, 2, and 3 may be mounted in a
completely concealed manner. Various other alternative
configurations will be apparent to those skilled in the art, all
permitting sensor 1 to sense a characteristic of an element in a
normal position (open or closed) and to sense a change of the
element from its normal position induced by the removal of the
normal magnetic field from proximity to sensor 1.
Referring now to FIG. 2, details of the intrusion sensor 1 of FIGS.
1A and 1B will be described; it will be understood that the
intrusion sensor 1 is normally placed adjacent an avenue of
possible entry so that its element 10 sensitive to the position of
magnet 2 is close to magnet 2 when the window, door, or other entry
barrier is in a normal position, such as a closed position.
Sensitive element 10 is a conventional single pole, double throw,
dry reed switch, though other reed switches or other switches
capable of changing state according to the presence or absence of a
magnetic field of predetermined level may alternatively be
employed. In a preferred embodiment, reed switch 10 has
contact-bearing leads 11 and 12 supported in generally parallel
relation at one end 13 of a hermetic envelope 14. At the opposite
end 15 of switch 10 is a lead 16 similarly sealed within envelope
14 and supporting a contact-bearing switch blade spring 17. Lead 16
is coupled through low internal leakage condenser 20 to ground.
Lead 11 is connected through charging resistor 21 to the positive
terminal of battery or other electrical source 22. The second
terminal of battery 22 is grounded. On the other hand, lead 12 of
switch 10 is coupled through resistor 23 to ground and also to the
gate electrode of field effect transistor 24. The source electrode
of transistor 24 is grounded, while its drain electrode is
connected through solenoid 31, in which a second switch 30 is
immersed, to the positive terminal of battery 22.
Switch 30 may be generally similar to switch 10 in that it may be a
conventional dry reed switch, but having a single pole, single
throw characteristic whose conductivity state is determined by the
presence or absence of a magnetic field generated by the
surrounding solenoid or coil 31. For example, switch 30 may
comprise a hermetic envelope 32 with leads 33 and 34 projecting
through its ends to support the respective internal contact-bearing
switch blade springs 35 and 36. Switch 30 is connected at its lead
33 to a positive pole of battery 22 and at lead 34 to a transmitter
device yet to be explained that comprises, in series relation,
multivibrator 40, oscillator 41, and antenna 3.
In one form of the apparatus, the sensor 1 employed a 9 volt
battery 22, the charging resistor 21 was 1 megohm, resistor 23 was
82,000 ohms, and condenser 20 was 10 microfarads; subminiature
elements are used throughout.
The output of switch 30 on lead 34 is the input to a conventional
multivibrator circuit 40. Multivibrator 40 is a free running
circuit, when supplied with the input signal, whose output serves
as a modulation signal, as will be seen. Multivibrator 40 is
preferably of the simple conventional type producing a semi-square
low audio frequency wave output with a comparatively slow rise
time, the wave having a frequency, for example, of 1 KHz. On the
other hand, either amplitude, frequency or pulsed modulation may be
employed.
Multivibrator 40 serves as a modulator for oscillator 41, in effect
turning it on and off. Oscillator 41 may be an inexpensive
crystal-controlled oscillator operating, for example, at a 100
milliwatt level at a suitable carrier radio frequency, such as
27.255 MHz. Modulator 40 produces 100 per cent modulation of the
carrier radio frequency within oscillator 41, and its limited rise
time characteristic satisfactorily limits the harmonic content of
the output radio frequency signal. The output of oscillator 41 is
radiated into space by antenna 3, which may comprise a simple
conventional un-tuned wire antenna. The duration of the output or
pulse burst is minimized for the purpose of preserving the life of
battery 22. However, it is also desired to prevent false alarms,
such as may be triggered by electrical storms. Thus, an optimum
duration when using amplitude modulation may be on the order of 1
second.
FIG. 2 illustrates the situation arbitrarily defined as normal for
purposes of explanation, when window 4 is closed, so that magnet 2
is at its closest proximity to sensor 1; i.e., window 4 is in the
position shown in FIG. 1A. In this condition, switch blade spring
17, being constituted of magnetic material, is held by the magnetic
field of magnet 2 against the contact-bearing lead 11 of switch 10,
as illustrated in FIG. 2. In this same normal situation, switch 30
is non-conducting, their spring characteristics holding switch
blade springs 35 and 36 apart. In this state, condenser 20 has
normally been charged from battery 22 through a path including
charging resistor 21, lead 11, switch blade spring 17, lead 16, and
ground. Charging of condenser 20 is slow, since the time constant
of the R-C circuit comprising resistor 21 and condenser 20 is quite
large. Thus, the maximum current drain to which battery 22 is
subjected is very low, and battery 22 has a life substantially
equal to its normal shelf life.
Should magnet 2 be moved so that its magnetic field no longer
influences reed switch 10, the spring nature of switch blade spring
17 forces it to break the circuit between resistor 21 and condenser
20. Instead, a circuit between condenser 20 and lead 12 is
established; thus, a voltage is developed across resistor 23. Such
an event causes field effect transistor 24 to conduct and current
from battery 22 is allowed to flow through coil 31 and transistor
24 to ground. The magnetic field generated by coil 31 consequently
causes switch blade springs 35 and 36 of reed switch 30 to come
into contact with one another. The modulating multivibrator 40 is
then caused to supply its semi-square wave output wave to high
frequency oscillator 41. Pulsed radio frequency carrier energy is
thereby transmitted by antenna 3.
Transmission from antenna 3 continues for a short time, for
example, about one second and is ended when the charge stored on
condenser 20 is dissipated. Thus, the voltage across resistor 23
fails to maintain field effect transistor 24 in its conducting
state, reed switch 30 is opened, and the supply of an excitation
signal to multivibrator 40 ends, ending operation of oscillator 41.
Thus, if window 4 remains open, no further drain is imposed on
battery 22. However, sensor 1 is automatically in condition to be
recycled by shutting window 4 and thus reestablishing a charging
circuit for condenser 20 from battery 22 through charging resistor
21 and reed switch 10. The sensor thereafter operates each time its
associated window or other entry barrier is opened, radiating one
short train of radio frequency energy pulses once for each such
opening event, and being reset for the next opening event by each
successive closure of the entry barrier.
It will be understood that a plurality of sensors 1 may be used in
a dwelling or business building or other location, one at each
door, window, or other potential entry. Each may be provided with
an identifying radiation characteristic merely by adjustment of the
relative modulating frequency of the corresponding free running
multivibrator. In a simple form of the system, all modulation
frequencies may be substantially the same. The radiated carrier
train, when received by an antenna 50 of a central monitor receiver
51, may be demodulated therein for the purpose of supplying the
audio signal to an alternating current sensitive relay within
receiver 51. Operation of the relay may supply power to a device 52
for producing a sustained visual or audible alarm within the
building or outside of it. Receiver 51 and alarm 52 may be supplied
from a common power source if desired. Operation of receiver 51 may
alternatively or additionally supply an alarm signal via telephone
lines to a conventional alarm device at a central police station or
detective agency. Where discrete modulation frequencies
characterize the several sensors used in a building, the several
different-frequency signals provided by sensors with adjustable
frequency multivibrators may be demodulated by receiver 51 and
supplied through corresponding audio frequency filters to activate
relays which light tell-tale lamps (not shown). Such relays would
preferably latch in the activated position so that a display
indicating the location of the disturbed entry is readily afforded.
Unauthorized movement of a safe, a display case, valuable painting,
or the like may be similarly signalled locally or at a police
headquarters. Where the system supplies alarm signals to a remote
headquarters, the owner has the option of disabling receiver 51
when present in the protected building by operating switch 54 and
observing the state of indicator lamp 55. He may similarly disable
the connection to alarm 52 in his presence so that police
headquarters will not be subjected to false alarms when the
building entries are permissibly used. Receiver 51 may be adapted
to handle inputs from other conventional sensor devices, such as
smoke or fire detectors.
While the invention has been described in its preferred embodiment,
it is to be understood that the words which have been used are
words of description rather than of limitation and that changes
within the purview of the appended claims may be made without
departure from the true scope and spirit of the invention in its
broader aspects.
* * * * *