U.S. patent number 3,781,859 [Application Number 05/245,535] was granted by the patent office on 1973-12-25 for controlled wave pattern ultrasonic burglar alarm.
Invention is credited to Albert L. Hermans.
United States Patent |
3,781,859 |
Hermans |
December 25, 1973 |
CONTROLLED WAVE PATTERN ULTRASONIC BURGLAR ALARM
Abstract
A burglar alarm employs ultrasonic sound to protect a plurality
of rooms. Each protected room contains a transmitter which emits an
ultrasonic signal in a controlled wave pattern. The signal is
received, filtered, and detected to determine if a doppler shift in
the ultrasonic signal of a particular amplitude and frequency
characteristic of human movement is present. If so, an alarm is
given.
Inventors: |
Hermans; Albert L. (San
Leandro, CA) |
Family
ID: |
22927063 |
Appl.
No.: |
05/245,535 |
Filed: |
April 19, 1972 |
Current U.S.
Class: |
340/507; 340/529;
367/94; 340/514; 342/28; 367/112 |
Current CPC
Class: |
G08B
13/1627 (20130101) |
Current International
Class: |
G08B
13/16 (20060101); G08b 013/16 () |
Field of
Search: |
;340/258A,1R ;343/7.7
;310/8.7 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Caldwell; John W.
Assistant Examiner: Swann, III; Glen R.
Claims
I claim:
1. A burglar alarm system for detecting intrusion into a protected
enclosure comprising:
oscillator means to generate an ultrasonic signal of predetermined
frequency;
a directional, wide-beam transmitter means, connected to said
oscillator means and located inside said protected enclosure with
its transmitting axis directed toward the floor of said enclosure,
to emit an ultrasonic sound at said predetermined frequency in a
beam toward said floor;
directional receiver means, located inside said protected
enclosure, with its sensitive axis directed toward said floor of
said enclosure to receive and convert said ultrasonic sound to an
electrical signal, the communication path between said transmitter
means and said receiver means being other than the line of sight,
such that said sound emitted from said transmitter means must be
reflected a plurality of times between said floor and the ceiling
of said enclosure before it can be received by said receiver
means;
decoupler means, connected to said receiver means, to present an
input impedance to said electrical signal;
filter means, connected to said decoupler means, to filter
extraneous electrical noise from said electrical signal;
phase detector means, connected to said filter means and said
oscillator means, to mix said electrical signal and said ultrasonic
signal, and to generate a doppler signal from the phase difference
between said electrical signal and said ultrasonic signal;
intrusion detection means, connected to said phase detector means,
to generate an alarm actuating signal upon reception of a doppler
signal of predetermined frequency and amplitude indicative of human
movement inside the protected enclosure;
alarm means, connected to said intrusion detection means, to render
an alarm upon receipt of said alarm actuating signal;
fail safe means, connected to said oscillator means and said alarm
means, to generate an alarm actuating signal upon failure of said
oscillator means to generate said ultrasonic signal of
predetermined frequency;
turbulence circuit means connected to said phase detection means
and said intrusion detection means to remove from said doppler
signal electrical noise due to random noise and air turbulence in
said protected enclosure;
memory logic means to delay rendering of said alarm; and
a walk test switch causing any alarm to be controllably rendered
instantly, so that installation and adjustment of said system is
facilitated.
2. A burglar alarm system according to claim 1, wherein said
turbulence circuit means consists of an integrated circuit
amplifier which receives said doppler signal as an input, and whose
output is connected to a clipping circuit to remove background
noise, said clipping circuit consisting of two parallel diodes of
predetermined forward breakdown voltage, each aligned in a
conductive direction opposite the other, the output of said
clipping circuit being connected in series to a series combination
of a resistor, a filter capacitor, and a half-wave rectifier, the
output of said half-wave rectifier being connected to said
intrusion detection means; said turbulence circuit further
including a feedback circuit to remove voltage peaks connected
between said input and said output of said integrated circuit
amplifier, said feedback circuit consisting of a plurality of
diodes of predetermined forward breakdown voltage, a first number
of said plurality of diodes connected in series in the same
conductive direction, the remainder of said plurality of diodes
connected in series and arranged in parallel connection with said
first number of diodes, said remainder of diodes aligned in
conductive direction opposite to said first number of diodes.
3. A burglar alarm system according to claim 1, wherein said
decoupler means comprises capacitive impedance means, connected
between said receiver means and said filter means, to increase the
voltages of said electrical signal.
4. A burglar alarm system according to claim 3, wherein said memory
logic means comprises a first transistor normally biased in the off
condition, with a base connection to said intrusion detection
means, and switchable to the on condition when said base connection
receives said alarm actuation signal; a second transistor normally
biased in the on condition, with a base connection to the collector
of said first transistor and switchable to the off condition when
said first transistor switches to the on condition, the emitter of
said second transistor being connected in series with the first
terminal of the operating coil of an alarm relay, the second
terminal of said operating coil being connected to ground; a diode
connected in parallel relationship with said operating coil to
protect said second transistor from the inductive surge of said
operating coil; and a timing circuit comprising a charging resistor
connected to a first terminal of a capacitor, the second terminal
of said capacitor being connected to ground, said timing circuit
being connected to said emitter of said second transistor in
parallel relationship with said operating coil, and a second
resistor connected to said first terminal of said capacitor and to
ground, whereby reception of an alarm actuating signal will turn on
said first transistor, causing said second transistor to turn off,
and causing said capacitor to discharge, through said charging
resistor, to a voltage insufficient to operate said operating coil
of said alarm relay, thereby rendering a delayed alarm.
5. The burglar alarm system according to claim 4, wherein said walk
test switch is connected between said second terminal of said
capacitor and ground, to selectively remove said capacitor from
said timing circuit, thereby causing any alarm to be controllably
rendered instantly.
6. The burglar alarm system according to claim 5, wherein said
receiver means comprises a plurality of ultrasonic receivers, each
of said receivers containing a metal plate, each said plate having
a resonant frequency equal to said predetermined frequency at which
said transmitter means emits said ultrasonic sound.
7. The burglar alarm system according to claim 6, further including
a piezoelectric crystal affixed to each said metal plate to convert
the vibrations of each said plate to an electrical signal, each
said crystal being connected in parallel with the primary winding
of a variable transformer, the secondary winding of each said
transformer being connected in parallel with a variable
potentiometer for adjusting the sensitivity of each said
receiver.
8. The burglar alarm system of claim 5 wherein said transmitter
means comprises at least one ultrasonic transmitter containing a
metal plate having a resonant frequency equal to the predetermined
frequency at which said transmitter means emits ultrasonic sound,
and a piezoelectric crystal, affixed to said plate, which receives
said ultrasonic signal from said oscillator means to vibrate said
plate at said resonant frequency.
Description
BACKGROUND OF THE INVENTION
Many burglar alarm systems have attempted to use ultrasonic sound
to detect unauthorized intrusion, but have met with only qualified
success. In attempting to maximize sensitivity to human intrusion,
these systems have been too susceptible to false alarms, rendering
them commercially undesirable. These false alarms are usually
caused by electrical interference, from power lines, electrical
equipment, etc., and particularly in the case of ultrasonic alarms,
to random background noise such as jet planes, auto traffic, etc.,
and to non-intrusive movement, such as air turbulence, hanging
decorations, draperies and the like.
Another problem encountered by former ultrasonic systems was the
difficulty, and therefore high cost, of installation. This was due
to the unbalancing of the central alarm system as new rooms were
added to the system requiring repetitive rebalancing of each room
receiver with the central system as installation progressed.
It is therefore an object of this invention to provide an
ultrasonic burglar alarm system which optimally is sensitive to
intrusion while giving no false alarms.
It is another object of this invention to employ a controlled wave
pattern of ultrasonic radiation in an ultrasonic burglar alarm to
increase the sensitivity of the alarm system.
It is a further object of this invention to provide an ultrasonic
burglar alarm which is simple and inexpensive to install and
maintain.
It is a further object of this invention to provide an ultrasonic
burglar alarm which employs transducers which are not affected by
air turbulence.
THE DRAWING
FIG. 1 is a block diagram of the circuitry of the present
invention.
FIG. 2 is a representation of the controlled wave pattern of
ultrasonic sound employed in the present invention.
FIG. 3 is a schematic diagram of the limiter amplifier section of
the circuitry shown in FIG. 1.
FIG. 4 is a schematic diagram of the memory logic section of the
circuitry shown in FIG. 1.
FIG. 5 is a schematic diagram of a receiver transducer and
decoupler connected to the central alarm system.
FIg. 6 is a partially cut-away side view of a receiver
transducer.
FIG. 7 is a perspective view of the receiver transducer of FIG. 6,
shown with the top removed.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The alarm system, shown in block diagram in FIG. 1, is powered by a
regulated power supply 1, which includes a standby battery to
provide power during a blackout and to defeat any attempt to unplug
the system. The oscillator 2 generates an ultrasonic tone, at
approximately 20,000 Hz, which is fed to the transmitting
transducers 3 which are installed in the areas to be protected. The
oscillator signal is sampled by the fail safe circuit 4, which is
connected to the alarm circuit relay 17. If the oscillator 2 should
fail to operate, either through malfunction or an attempt to
disrupt the system, the fail-safe circuit 4 will sense the
diminished output of the oscillator 2, and will actuate the alarm
circuit relay 17. The oscillator signal is also sampled by the
phase detector 13.
Mounted in each protected area in association with each
transmitting transducer 3 are the receiving transducers 5,
connected to the system by high impedance decouplers 6. The
receivers 5 receive the ultrasonic signal emitted by the
transducers 3, and the received signal is passed through the
decoupler 6 to the noise filters. The electrical noise filter 7,
the radio frequency filter 8, and the lightning filter ]remove
extraneous noise which could cause a false alarm. The filtered
signal then goes to the amplifier 10, and the sensitivity control
11. The sensitivity is adjusted to pass the maximum signal strength
without causing a false alarm. The signal then goes to the
amplifier 12, and the phase detector 13. The phase detector mixes
the received signal with the sampled signal from the oscillator 2,
and produces a doppler signal which is amplified by the band pass
amplifier 14, which senses and amplifies a frequency component of
approximately 35 Hz, produced by that of an intruder moving within
the protected areas. The amplified doppler signal is then fed
through the turbulence circuit 16 to the intruder circuit 15 which
sends an alarm signal to the alarm circuit relay 17. The alarm
signal is delayed, however, by the memory logic circuit 18, which
receives the signal through the normally closed walk test switch
19. The memory logic 18 delays the alarm signal once for a short
time, approximately one second, to provide a further safeguard
against false alarms. The delay does not reset for a period of
time, approximately one minute, so that a slow stepping burglar
will still actuate the alarm. After the time delay, the alarm
signal actuates the alarm relay 17 which operates an automatic
police call, siren or other alarm device desired.
The schematic diagram of FIG. 3 shows the limiter amplifier and the
level amplifier circuit that makes up the turbulence circuit 16,
and the intruder circuit 15 of FIG. 1. Amplfier 26 receives the
doppler signal through conductor 27, and puts out an amplified
signal through conductor 28. Line 29 provides positive operating
voltage, line 30 provides negative operating voltage, and line 31
is ground. Connected from line 27 to line 28 is a diode bridge 32
in a feedback arrangement. There are four series diodes in one
direction in parallel with four diodes in the reverse direction.
Each diode 33 has a forward breakdown voltage of 0.6 volts, so that
the feedback effect takes place whenever the doppler signal is
greater than .+-. 2.4 volts. Thus all booming sounds picked up by
the receivers 5 are limited in amplitude so that the large signals
cannot blast their way through to the intruder circuit 15. The
signal is then conducted by line 28 to the parallel back to back
diodes 34.
Again each diode has a forward breakdown voltage of 0.6 volts. Thus
the first 0.6 volts of the doppler signal excursion in either the
positive or negative direction is clipped eliminating the low
voltage component of the doppler signal which results from random
background noise. The signal then goes through the limiting
resistor 35 and the coupling capacitor 36, to the half wave
rectifier 37. The rectifier 37 conducts the negative portion of the
doppler signal to ground, and the remaining signal, lying between
0.6 volts and 2.4 volts, then passes through resistor 41 to
conductor 42 and to the amplifier 48 which is part of the intruder
circuit 15. A threshold level is formed by resistor 43 and diode 44
at conductor 49. When the D.C. level at conductor 42 exceeds the
set level at conductor 49, amplifier 48 passes the signal to
conductor 50 which is considered an alarm condition. The positive
voltage for amplifier 48 is provided at line 45, negative voltage
at 46 and ground at 47.
The intruder circuit 15 prevents false alarms due to falling
objects or short wall or building movements due to earthquakes,
sonic booms and the like, and provides an approximate delay of 0.15
seconds.
The circuits shown in FIG. 4 are the memory logic 18 and walk test
19 as shown in FIG. 1. It consists of transistor 53 biased normally
off and transistor 54 biased normally on. Transistor 53 receives
the alarm actuating signal from the fail safe circuit 4 or from the
intruder circuit 15 through balancing resistor 52. When an alarm
signal comes from intruder circuit 15 through conductor 50 of FIG.
3, it enters through resistor 52 of FIG. 4 to the base of
transistor 53 which causes it to conduct. The bias voltage from
resistor 55 which normally holds transistor 54 in the conducting
condition is removed and transistor 54 stops conducting. Resistor
56 and resistor 61 in series with relay 62 are current limiting
devices. When transistor 54 ceases to conduct, the voltage normally
holding relay 62 engaged disappears and an alarm condition exists.
However, after system has been set in the non-alarm condition for a
period of 60 seconds current flowing through the conducting
transistor 54 flows through resistor 56 to conductor 60 and through
resistor 58 which charges capacitor 57 to full charge. When
transistor 54 ceases to conduct, the current stored in capacitor 57
flows through diode 59 to conductor 60 through resistor 61 and
holds relay 62 engaged for a period of approximately 1 second.
The resistor 63 in parallel with capacitor 57 is selected at random
and changes the discharge time and charge time of the memory logic
circuit so that no one will know the actual time delay of the
circuit. The wall test jack switch 19 used during installation,
opened by plugging in an installer's walk test device, opens the
circuit at capacitor 57 from the circuit so that the relay will
respond instantly when transistor 54 switches off.
The sensitivity adjustment and system balancing can be accomplished
quickly and inexpensively.
The circuitry of FIG. 5 shows a schematic view of a receiver
transducer 5 connected to the central alarm system. The receiver 5
consists of a tuned metal plate 64, which is tuned to the ultra
sonic frequency at which the system operates. The plate receives
this frequency from transmitter 3. A piezoelectric crystal 65,
which is connected to the secondary winding 66 of the transformer
67, converts the received sound to electrical signals. The
transformer 67 adjusts the reaction of the receiver circuit to
provide optimum sensitivity at the operating frequency. The gain of
the signal induced in the primary winding 68 is controlled by the
variable resistor 69, which is a precision 20 turn potentiometer.
The signal then goes through terminal block 70 to the decoupling
capacitors 71. Conductors 72 connect to the two other decoupler
inputs. Isolation transformer 73 isolates the three decoupler
inputs from the electronics of the control unit and also works with
the electrical noise filter circuit.
FIG. 2 shows a typical installation of a transmitting transducer 20
and a receiving transducer 21 in a small room 22, and the
controlled wave pattern 23 that is used to detect intrusion. Both
transducers 20 and 21 are directional, and are mounted on the
ceiling 24 of the room 22 with their sensitive axes towards the
floor. The transmitter 20 directs a wide beam of sound toward the
floor, and that beam is reflected and re-reflected many times
before being received by the receiver 21. It can be seen that there
is no line of sight communication path between the transducers 20
and 21.
Therefore decorations hanging from the ceiling and tall decorative
plants moving in convection currents will not actuate the alarms.
This is due to the fact that the controlled wave pattern system is
much more sensitive to sustained movement through the
multireflected beam than to short movements directly between the
transducers 20 and 21.
It should be noted that because of the low profile of the sound
emitting tuned plate, the receiver 5 or transmitter 3 are not
readily effected by air currents blowing against them. Also, with
slight modification they can be flush mounted in any wall or
ceiling, permitting an unobstructive and effective
installation.
The tuned plate 64 (of FIGS. 6 and 7) has a flat surface, making it
economical to manufacture a true tuned ultrasonic emitting surface.
When tuned electrically to its operating frequency the plate acts
with a fly wheel effect making it possible to produce more
ultrasonic energy more efficiently.
FIGS. 6 and 7 are views of receiver 5. The receiver 5 consists of a
long rectangular metal box 74, with a cover 75 held on by screws 76
which fit through slots 77 of the box 74. The cover 75 has
double-sided foam adhesive tape 78 applied to it, to facilitate
easy installation to any smooth surface. In one corner of the box
74 is a small rectangular plastic box 79 in which the potentiometer
69 and the transformer 67 are imbedded in epoxy plastic. The hole
85 allows adjustment of the potentiometer 69 without removal of the
cover 74.
The tuned plate 64 is attached to the box 74 by bolts 81, which
extend through the bottom 80 of the box. The plate 64 is spaced
apart from the box 74 by bushings 82. The crystal 65 is soldered
and cemented to the tuned plate 64, to provide good electrical and
mechanical union. The crystal 65 converts the vibrations of said
plate 64 into electrical signals, as discussed above.
The transmitters 3 have the same outward appearance as the
receivers 5. Each transmitter is housed in a box of the same
dimensions as the box 74, and each employs the same tuned plate 64
-- piezoelectric crystal 65 combination to emit the ultrasonic
signal, the crystal 65 vibrating said tuned plate 64 to oscillate
at the correct ultrasonic frequency. The transmitters 3, however,
are not adjustable.
It should be noted that because of the low profile of the box 74,
the receiver 5 or transmitter 3 are not readily affected by air
currents blowing against them. Also, with slight modification they
can be flush mounted, in any wall or ceiling, permitting an
unobstructive and effective installation.
It should also be noted that there is ample room in the box 74 for
a thermal switch, and therefore the box 74 could also house a fire
sensor for a fire alarm system operated in conjunction with the
present burglar alarm system.
* * * * *