U.S. patent number 3,683,352 [Application Number 05/127,276] was granted by the patent office on 1972-08-08 for alarm system for sensing smoke and intruders.
This patent grant is currently assigned to Winslow Technology. Invention is credited to Frederick Gans, Henry W. West.
United States Patent |
3,683,352 |
|
August 8, 1972 |
ALARM SYSTEM FOR SENSING SMOKE AND INTRUDERS
Abstract
An alarm system using a laser generated light beam which extends
through a plurality of isolated detectors and ends at a control
station. Each detector includes two light-to-electric transducers,
one for detecting smoke by scattering and the other to detect an
intruder by the temporary blocking of the beam. There is no
electrical wiring connecting the detector stations. A signal
denoting smoke or an intruder is sent over the laser beam in the
form of an amplitude or polarization modulation at a characteristic
frequency. This signal is received at the control station, its
frequency of modulation is determined and an alarm is
activated.
Inventors: |
Henry W. West (Red Bank,
NJ), Frederick Gans (Jamaica, NY) |
Assignee: |
Winslow Technology (Inc.,
Gatontown)
|
Family
ID: |
22429257 |
Appl.
No.: |
05/127,276 |
Filed: |
March 23, 1971 |
Current U.S.
Class: |
340/557; 340/630;
340/870.28; 340/870.09; 359/240; 359/246 |
Current CPC
Class: |
G08B
13/183 (20130101); G08B 19/00 (20130101) |
Current International
Class: |
G08B
13/183 (20060101); G08B 19/00 (20060101); G08B
13/18 (20060101); G08b 013/18 () |
Field of
Search: |
;340/228S,258B,237R,189
;350/161 ;356/211 ;250/199 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: David L. Trafton
Attorney, Agent or Firm: Albert F. Kronman
Claims
Having thus fully described the invention, what is claimed as new
and
1. An alarm system for sensing the presence of a light barrier
comprising: a source of light collimated into a narrow parallel
beam; a first polarizing means for making the light beam plane
polarized; a plurality of sensor stations positioned at places
where it is desired to detect a light barrier, each of said
stations including a container having an entrance and an exit
opening for the passage of the light beam, each of said stations
also including a photo-transducer adapted to sense the reduction in
intensity of the light beam; an oscillator coupled to each sensor
station for generating a distinctive frequency; coupling means
between the photo-transducer and the oscillator in each station for
starting the oscillator only when the transducer detects a light
barrier; a crystal modulator controlled by the oscillator for
modulating the light beam as it passes through the sensor
container; a control station for receiving the light beam and for
interpreting its modulated information, said station including a
second polarizing means set at an angle to the first polarizing
means for converting the modulated light beam into a variable
intensity beam; a photo-transducer for converting the variable
intensity beam into an alternating current; a plurality of filter
circuits respectively tuned to pass a frequency corresponding to
the frequency of one of the oscillators; and an alarm coupled to
each of said filter
2. An alarm system as claimed in claim 1 wherein said source of
light is a
3. An alarm system as claimed in claim 1 wherein the light from
said source
4. An alarm system as claimed in claim 1 wherein at least one light
filter is positioned in the path of the light beam for eliminating
ambient light
5. An alarm system as claimed in claim 1 wherein a photo-detector
in a sensor station is arranged for detecting an intruder and
normally receives
6. An alarm system as claimed in claim 1 wherein a photo detector
in a sensor station is arranged for detecting smoke, said
photo-detector positioned to one side of the beam and receiving
light only when smoke
7. An alarm system as claimed in claim 1 wherein the crystal
modulator is
8. An alarm system as claimed in claim 1 wherein the crystal
modulator includes two plate electrodes for creating an A.C.
electric field in the
9. An alarm system as claimed in claim 1 wherein each alarm coupled
to a filter is designated by a symbol to indicate the location of
the sensor
10. An alarm system as claimed in claim 8 wherein the capacity
created by the two crystal electrodes causes resonance with an
inductance in the oscillator output circuit.
Description
There are many smoke detectors and intruder alarms available today
for the protection of property. These systems work on various
principles, some using radar, some ultra-sonic beams and some using
light beams. All these prior systems have some disadvantages. Radar
systems are difficult to contain in the area to be protected and
disturbances outside the area may trigger the alarm. Ultrasonic
beam systems require a separate generator and detector for each
room since the beams cannot penetrate walls. Light beams offer the
best protection but focusing problems limit their range and, again
separate and complete installations must be made for each room or
protection area.
The present invention has none of the above listed disadvantages. A
single laser generator and a single control sensor are all that are
necessary for an entire building. A laser beam is sent through each
room in the building at places where an intruder is sure to be
found. The beam is reflected by a plurality of mirrors until it
reaches a control center where the alarm annunciator is installed.
A plurality of sensors are positioned along the beam and are
provided with individual battery power but there is no wiring from
the sensor stations to the control station. The laser light beam
carries the intruder information to the control station and
indicates the room in which the intruder broke the beam. Each
sensor station is provided with a smoke detector in addition to the
intruder detection means.
One of the features of the invention is a single light generator
and a single control station, covering a large building having many
rooms.
Another feature of the invention is the transmission of
intruder-smoke information by means of a light beam, either
amplitude or polarization modulated.
Still another feature of the invention is the absence of signal
wiring between the sensor stations and the control station.
For a better understanding of the present invention, together with
other details and features thereof, reference is made to the
following description taken in connection with the accompanying
drawings.
BRIEF DESCRIPTION OF THE FIGURES
FIG. 1 is a schematic diagram of a building having two rooms
showing, the laser generator, six sensor stations and a control
station.
FIG. 2 is a perspective drawing of a sensor.
FIG. 3 is a cross sectional view of the sensor shown in FIG. 2 and
is taken along line 3--3 of that figure.
FIG. 4 is a cross sectional view of a sensor station having two
photoconductive cells, one for smoke and one to sense the blocking
of the laser beam.
FIG. 5 is a schematic diagram of connections of the sensor station
shown in FIG. 4.
FIG. 6 is a schematic diagram of the complete system showing the
laser generator, four polarizing crystals, four oscillators, a
control station which includes four filters and four
annunciators.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to FIG. 1, two rooms are indicated, one above the
other with a laser beam generator 10 positioned in the upper room.
The laser beam is directed to a first sensor 11, past a window 12,
to a first mirror 13. Mirror 13 sends the beam to several other
mirrors 14, 15, and 16, in the same room, the beam passing through
sensors 17 and 18. The last mirror 16 in the upper room directs the
laser beam through a hole in the floor and to mirrors 20, 21, 22,
and 23.
Three sensor stations 24, 25, and 26 are positioned in the path of
the beam which passes a door 27 and several other windows. The beam
is terminated at a control station 28. The detection system is not
limited to the number of mirrors shown nor to the number of sensor
stations. There is no theoretical limit to the number of mirrors
and sensors and the laser beam may be directed across the room
areas and is not confined to any particular range or angular
direction. The system may be used outside a building to detect
intruders and smoke in a restricted area.
Referring now to FIGS. 2, 3, and 4, the sensor detectors are
positioned in a light tight box 30 having an entrance tube 31 and
an exit tube 32. The preferred system includes light filters 33,
but these are not always necessary. The light filters are used only
in rooms where there is considerable ambient illumination that
might be reflected into the boxes 30 and give a false alarm. It is
well known that lasers can produce light beams in the near
infra-red region of the spectrum. Such beams are preferred since
there is almost no light of such wave length generated by modern
systems of area illumination. The boxes 30 are formed with louvers
34 in the top and bottom sides so that smoke can pass freely
through the box space.
Inside the sensor box 30 is a first photoconductive cell 35 for
detection of intruders. A second photoconductive cell 36 is
preferably mounted inside the sensor box 30 for detection of smoke.
However, sensor units may be constructed with only one cell to
detect either intruders or smoke if desired. A small piece of glass
37 is mounted in front of cell 35 and in the path of the laser beam
in order to reflect a portion of the beam to the cell and keep it
normally conductive. A plain piece of glass without silvering will
be sufficient to reflect about 6 percent of the light (if
unpolarized). By varying the angle of polarization, values ranging
from two percent to 10 percent can be obtained without an
additional reflective coating (u = 1.523). Since the laser beam is
concentrated and of small diameter, better results are obtained if
the reflecting surface is convex, as shown, thereby spreading the
reflected light over a large area and reducing the probability of
hot spots on the cell surface.
Photoconductive cell 36 is normally non-conductive and is designed
for detecting smoke. When the air is clear, the laser beam 38
passes through the box 30 without producing any action. When smoke
fills the box, the scattered light activates cell 36 and makes it
conductive.
In each sensor box, a light modulating means must be mounted. Light
modulators are of many types. There are slow moving shutters,
sectored wheels, polarizers, both electrostatic and
electromagnetic, and Kerr cells. While the invention is not limited
to any particular type of modulator, the electrostatic type of
polarizer is preferred since it requires less power than other
types and since there is no mechanical motion. One type, made of
crystal potassium dihydrogen phosphate, changes the angle of the
plane of polarization when under the influence of an electrostatic
field. This type of modulator together with other types is
described in the Proceedings of the IEEE for October 1966. Such a
crystal 40 with electrodes 41 is positioned so that the light beam
makes an angle of 45.degree. with the electric field produced by an
oscillator. A steady AC wave from the oscillator applies a
polarization angle shift to the light beam passing through the
crystal.
FIG. 5 shows one manner of connecting the two photoconductive cells
to the oscillator and the crystal. A first relay 42 has a winding
43 connected in series with a battery 44 and the cell 35. The cell
35 is for detection of intruders and is normally illuminated by the
laser beam 38 reflected by the glass reflector 37 so that contacts
45 on relay 42 are normally closed. A second relay 46 has a winding
47 connected in series with the second cell 36 and the battery 44.
Cell 36 is for smoke detection and normally is not conductive so
that contacts 48 and 50 are open. Contacts 48 connect the battery
44 to an oscillator 51 when closed. Contacts 50 are locking
contacts and hold the relay in its operated condition once smoke
has been detected. The oscillator, which may be any suitable type,
delivers a predetermined frequency wave to the crystal 40. The
locking circuit through contacts 50 can be broken and the circuit
normalized by manually operating a switch 52. The circuit is
battery operated to make sure the system will continue in operation
even if the main AC supply lines are disconnected. However, to keep
the battery in good condition, a trickle charger circuit is
generally supplied. This circuit includes a step-down transformer
53 and a rectifier 54.
The operation of the above circuit is as follows: Relay 42 is
normally conducting and contacts 45 are open because cell 35 is
activated. Relay winding 47 is not receiving current because cell
36 is not receiving any light and contacts 50 and 48 are open. The
oscillator 51 also receives no current because contacts 48 are open
and the crystal 40 produces no modulation on the light beam. Now,
let it be assumed that an intruder steps in front of the laser
beam. The light from reflector 37 no longer makes cell 35
conductive and current is cut off from winding 43, closing
contacts. Current now flows from the positive battery terminal over
conductor, through contacts 45, over conductor 56, to winding 47 of
relay 46, then over conductor 57 to the negative terminal of the
battery. This current activates the relay 46, closing contacts 48
and 50 and delivering battery power to the oscillator 51 and a high
frequency wave to the crystal 40. Holding contacts retain the relay
46 in operation until an operator pushes switch 52 open. As long as
the intruder remains in front of the sensor, blocking the laser
beam, there will be no alarm indicated, but it is assumed that the
intruder moves to one side in the course of his operations and, as
soon as the beam is again established, a modulated light is
delivered to the control station 28 where it will be detected and
the alarm sounded.
Now let is be assumed that smoke enters the sensor box 30 and
causes scattering of the laser beam. Cell 36 is made conductive and
current from the battery 44 passes through the cell, then over
conductor 56 to winding 47 on relay 46, then back to the battery by
way of conductor 57. This current activates the relay, closing
contacts 48 and 50 sending DC current to the oscillator and AC
power to the modulating crystal. Again, holding contacts 50 retain
the relay in operated condition until switch 52 is opened manually
by an operator at the sensor. In this case, the laser beam
transmits a modulated light beam to the control circuit 28 as soon
as the oscillator is activated since the beam is concentrated
sufficiently to send light through the smoke.
FIG. 6 shows all the main components in the system in order to
explain the general operation. The laser 10 generates a beam of
light which first passes through a polarizing means 60 which may be
a Nicol prism. The polarized beam 38 then passes through all the
modulating prisms 40, to a second Nicol prism 61 which acts as an
analyzer and is preferably set at an angle of 45 degrees to the
first prism 60. The beam then moves to a photo transducer 62 which
may be a photoconductive or photoelectric cell. Again, a negative
lens 63 may be used to spread the concentrated laser beam over a
wide area to lower spot heating. An amplifier 64 is coupled to the
transducer but it is arranged to amplify only alternating currents
so its output is zero under normal conditions. The amplifier output
is connected to a plurality of filters 65 each tuned to pass a
frequency which matches the frequency of one of the oscillators. An
alarm, which may be audible or visual is connected to each filter
circuit and is labeled to indicate the location of the operated
sensor. If the second sensor detects an intruder or smoke, switch
48 is closed, the oscillator 51-2 sends high voltage to crystal
40-2 and the beam is modulated by a high frequence shift of the
polarization angle. The average intensity of the beam is not
changed. When the beam passes through the second Nicol prism 61,
the frequency variations and transformed into intensity variations
and the photocell 62 sends AC to the amplifier having a frequency
f.sub.2. This current is amplified and sent on conductors 66 to all
the filters 65 but only one 65-2 sends current to its output and
the alarm 67.
It should be noted that the system described above has quite a high
light efficiency. Each polarizing crystal cuts out about 55 percent
of the light but there are only two of these crystals, no matter
how many modulators are used and there is plenty of light left over
to operate the final phototransducer 62. It should also be noted
that if an intruder moves around and breaks several more light
beams, all of the modulating frequencies will be carried on the
same laser beam and a corresponding number of alarms will be set
off.
Any type of oscillator 51 can be used, as noted above. Since the
load is a capacitor and requires rather high voltage for its
operation, a resonant circuit can be set up, at the output
frequency, by the use of an output step-up transformer having
enough secondary inductance to resonate with the crystal load.
* * * * *