U.S. patent number RE29,082 [Application Number 05/612,883] was granted by the patent office on 1976-12-14 for intrusion detector.
This patent grant is currently assigned to Barnes Engineering Company. Invention is credited to Frank Schwarz.
United States Patent |
RE29,082 |
Schwarz |
December 14, 1976 |
Intrusion detector
Abstract
A simple optical system collects and applies radiation from a
predetermined field of view onto a thermopile detector. The
thermopile detector has a plurality of rows of thermocouples having
all active junctions with alternate polarity which are aligned in
columns of the same polarity, whereby in response to an object
moving across the thermopile an output signal is produced of
alternately changing polarity. Logic circuitry is provided for
processing the signals from the thermopile in a predetermined
polarity sequence to discriminate against false alarms and for
indicating the presence of an intruder and sounding an alarm.
Inventors: |
Schwarz; Frank (Stamford,
CT) |
Assignee: |
Barnes Engineering Company
(Stamford, CT)
|
Family
ID: |
26904360 |
Appl.
No.: |
05/612,883 |
Filed: |
September 12, 1975 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
Reissue of: |
209660 |
Dec 20, 1971 |
03760399 |
Sep 18, 1973 |
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Current U.S.
Class: |
340/555;
250/338.1; 250/342; 250/DIG.1 |
Current CPC
Class: |
G08B
13/19 (20130101) |
Current International
Class: |
G08B
13/189 (20060101); G08B 13/19 (20060101); G08B
013/18 () |
Field of
Search: |
;340/258B,258D,228R,228S
;250/338,342 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Trafton; David L.
Attorney, Agent or Firm: Levinson; Joseph Norton; Robert
Ames
Claims
I claim:
1. An intrusion detector for generating alternating signals as a
result of thermally varying patterns of objects moving across the
field of view of the detector comprising
a. a layer of thermal insulating material,
b. a thermopile detector mounted on said layer of insulating
material comprised of a plurality of thermocouples of dissimilar
metals with all junctions being constantly exposed to the field of
view of said detector,
c. said thermocouples being serially connected in rows with
adjacent thermocouples in said rows being of alternate polarity
d. said rows of thermocouples being serially interconnected and
aligned to form columns of the same polarity thermocouples and
adjacent columns of alternate polarity thermocouples, and
e. output terminals connected across said thermopile detector which
provides thereat a changing polarity output signal in response to
an object moving across said thermopile detector.
2. The structure set forth in claim 1 having optical means for
collecting and applying radiation from a predetermined field of
view on all junctions of said thermopile detector.
3. The structure set forth in claim 2 wherein said optical means
comprises a wide angle lens.
4. The structure set forth in claim 2 wherein said optical means
includes a wide angle spherical reflector.
5. The structure set forth in claim 1 including
a. optical means for collecting and applying radiation from a
predetermined field of view on all junctions of said thermopile
detector, and
b. circuit means coupled to the output terminals of said thermopile
detector for processing signals from said thermopile detector in a
predetermined polarity sequence for indicating the presence of an
intruder and discriminating against false alarms.
6. The structure set forth in claim 5 wherein said circuit means
includes a plurality of signal processing channels which respond to
said predetermined polarity sequence and generate signals of fixed
duration, the coincidence of which provides an output indicating
the presence of an intruder.
Description
BACKGROUND OF THE INVENTION
This invention relates to an intrusion detector, and more
particularly to a motion detection system utilizing a simple wide
field of view optical system with a thermopile detector which is so
constructed as to produce opposite polarity output signals as an
object in the field of view of the optical system moves across the
thermopile to produce a sequence of motion which with proper
processing and logic circuitry indicates the presence of an
intruder.
Many intrusion detector systems have been proposed, both active and
passive in nature. The active systems generally require a source of
radiant energy in the form of light or other radiation which is
projected into or covers a predetermined area which, when crossed
by the intruder, interrupts or alters the radiation to cause an
alarm. Since all active systems require a source of radiation or a
transmitter, additional equipment is needed and is a source of
failure as well as being more easily detected by the intruder. The
passive type system utilizes the radiation in the form of infrared
which is generated by the intruder and picked up by a suitable
infrared detector and processed to give an alarm. Noise spikes and
other forms of interference in many of these systems generate
unwanted alarms. Various passive systems have been suggested which
provide a plurality of detector elements viewing separate or
overlapping fields of view in an attempt to overcome these
problems. The present invention is a passive system which has a
simple optical system covering a wide field of view which utilizes
a single thermopile detector device directed to the solution of
these problems.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an intrusion
detector utilizing a new detection approach for indicating the
presence of an intruder in the field of view of the system.
Another object of this invention is to provide a new and improved
intrusion detector having a simple wide-angle field of view and a
single thermopile detector for indicating the presence of motion
within the field of view of the detector.
Still a further object of this invention is to provide a new and
improved intrusion detector which decreases the probability of
false alarms.
In carrying out this invention in one illustrative embodiment
thereof, a simple wide field-of-view optical collecting system
directs radiation from its field of view onto a thermopile detector
having an all-active junction construction. The thermopile detector
is made up of rows of a plurality of thermocouples with alternate
polarity which are aligned in columns having the same polarity.
Circuit means are coupled to the thermopile detector for processing
signals therefrom in a predetermined polarity sequence such that an
object moving across the field of view of the thermopile produces a
changing polarity output signal which indicates the presence of an
intruder in the field of view of the thermopile and discriminates
against false alarms.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an isometric view of one form of novel thermopile
structure, broken for ease of illustration, which may be employed
in the present invention.
FIG. 2 is an optical and electrical schematic of an illustrative
embodiment of the intrusion detector of this invention.
FIG. 3 is an optical schematic of another form of optical system
which may be employed in the present invention.
FIGS. 4-7 represent waveforms which will be useful in illustrating
the operation of one form of electronic processing and circuit
logic which may be employed in the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to FIG. 1, an unusual thermopile detector 10 is shown
which is a key element in the present invention. The thermopile 10
is formed of a series of thermocouples of dissimilar metals 14 and
16, forming a junction 15 which is blackened to enhance the
thermocouple response. It should be appreciated that the drawing of
the thermopile is considerably out of scale for ease of
illustration. The metals 14 and 16 are very thin and are
considerably narrowed between junctions. The dissimilar metals 14
and 16 may be bismuth and antimony, or any other suitable
thermocouple material. The thermopile 10 is formed using
conventional vacuum evaporation techniques on a substrate 12 of
material which is a fairly good insulator, for example,
polystyrene, plexiglass, polyethylene terephthalate, etc. The
illustrated construction of thermopile 10 differs from conventional
thermopile construction in that all junctions are active, with no
reference junctions. With such a construction, alternating
polarities are set up across a row of thermocouples. The thermopile
10 is also arranged such that columns 1, 2, 3 and 4 are formed,
with the thermocouples making up the columns being of the same
polarity. All of the thermocouple junctions 15 are serially
connected between a pair of output leads 18 and 19, such that the
signals are additive and therefore an object appearing across one
column provides an additive signal output of greater amplitude than
could be achieved by a single thermocouple. With the construction
shown, an object moving across columns 1, 2, 3 and 4 will generate
a sinusoidal output across the output leads 18 and 19, which signal
can be processed to detect the presence of an intruder. A
thermopile operating in the conventional mode would generate a DC
signal, which would require a reticle or moving chopper to provide
the AC signal generated in the present invention without any
additional moving elements. The thermopile 10 is also quite useful
as the intrusion detector, since it operates in the far infrared
region of the electromagnetic spectrum with a long wavelength
filter placed before the detector, and therefore would be immune to
flashing lights, automobile headlights, or other types of signals
which would produce false alarms in other active or passive types
of alarm systems.
FIG. 2 illustrates one type of spherical reflecting concentric
optical system which provides a wide field of view, on the order of
90.degree. .times. 60.degree., with sufficient sensitivity for
ranges of about 30 feet, which could be utilized to guard an entire
room. The optical system is essentially a spherical reflecting
mirror 20 which applies radiation collected from a field of view
through aperture stops 22 onto the thermopile 10 which is mounted
on a concentric spherical support 21. Instead of mounting the
thermopile 10 on a curved support 21, concentric with the spherical
reflector 20, a flat mounting base may be utilized as in FIG. 3,
utilizing a wide-field-of-view lens 24, or with the spherical
reflector 20, as illustrated in FIG. 2 by utilizing an oval window.
The essential feature of the optical system is that it be as simple
as possible and yet perform the function of covering a wide fiew of
view and applying radiation therefrom onto the thermopile
detector.
Signals from the thermopile 10 are applied to a preamplifier 26. At
this point it should be remembered that the thermopile detector 10
is designed so that a person moving horizontally across the
sensor's field of view, and thus crossing columns 1, 2, 3 and 4
successively, causes a succession of thermocouples to be heated up
and in consequence generate output signals. With such an
occurrence, the output from the preamplifier 26 is shown in FIG. 3
as waveform 46 with alternately positive- and negative-going
signals being generated as the object moves across the various
columns formed by the thermocouples of the thermopile 10. The
preamplifier 26 is coupled to a voltage comparator 28 having a
reference voltage 30 applied thereto, and voltage comparator 28 is
connected to a monostable multivibrator 32. The preamplifier 26
boosts the signals represented by waveform 46 in FIG. 4 to a
sufficient level so that the voltage comparator 28 switches state
when the signal 46 exceeds the reference voltage 30. This activates
multivibrator 32, which sets up an output voltage of fixed value
represented by the waveform 48 in FIG. 5, which is held for a fixed
period, for example 5 seconds. The preamplifier 26 is also
connected to another channel which includes an inverter 34, another
voltage comparator 36 having a reference voltage level 38, and a
multivibrator 40. Accordingly, if the signal 46 is due to an
intruder in the field of view, the person would have moved so as to
heat up column 2 of the thermopile detector 10. This generates a
negative-going signal that will be sensed by the voltage comparator
36 after having the signal polarity changed by inverter stage 34.
If the threshold level set by the reference voltage level 38 is
exceeded, the voltage comparator 36 changes state and activates
monostable multivibrator 40 to generate a fixed amplitude pulse for
a given duration, for example 5 seconds, as shown by the waveform
50 on FIG. 6. Multivibrators 32 and 40 are both connected to an AND
gate 42, which is connected to an alarm 44. When the output pulses
of multivibrators 32 and 40 coincide, the AND gate 42 is enabled,
generating a signal 52 as shown in FIG. 7, and the alarm 44 is
activated. The alarm 44 may take any suitable form, visual,
audible, or can be used to actuate other devices, such as telephone
lines, etc. If the single monostable multivibrator 32 has been
triggered on by a false signal, such as a noise spike or RF
interference, etc., only one output pulse will have been initiated.
Lacking confirmation from a second, opposite polarity pulse, there
would be no output signal from the AND gate, and no alarm, so that
false alarms would be avoided. Although only two logic channels
have been illustrated in the electronic processing, for simplicity
in explanation and ease of illustration, the same logic could be
extended to a sequence of three or more alternating polarity pulses
that may be made mandatory before a final output alarm is
generated. Imposition for a requirement for additional output
pulses enormously decreases the probability of false alarms that
may be generated by the intrusion system.
The intrusion alarm system of the present invention, being passive
and small, is not readily detectable, and may easily be concealed
if it is desired to have it operate surreptitiously. Since the
optical system is simple and covers a wide field of view, an entire
room may be covered to detect intrusion, no matter where the
intruder enters the covered area. Since the detector is all active
junctions, producing a varying polarity signal as an intruder
traverses the field of view of the detector, no moving parts are
necessary to detect the intrusion, making the system simple, with
long operating life. The optics and detector portion of the system
may be mounted conveniently in the desired location which has an
unobstructed view of the entire area to be covered, while the
electronics may be positioned elsewhere, inside or outside the
protected area. The sinusoidal voltage pattern generated by the
thermopile detector of the present invention, which is produced by
the motion of an intruder, provides an ideal output for logic
circuitry for sensing two opposite polarity pulses and thus being
able to recognize the signal pattern of interest to generate an
alarm only on that pattern, and thus prevent false alarms.
Since other modifications and changes, varied to fit particular
operating requirements and environments, will be apparent to those
skilled in the art, the invention is not considered limited to the
examples chosen for purposes of disclosure, and covers all changes
and modifications which do not constitute departures from the true
spirit and scope of this invention .
* * * * *