U.S. patent number 3,662,371 [Application Number 04/877,173] was granted by the patent office on 1972-05-09 for ultrasonic intrusion detection system signal processing circuit.
This patent grant is currently assigned to Minnesota Mining and Manufacturing Company. Invention is credited to Thomas E. Collins, John H. Lee.
United States Patent |
3,662,371 |
Lee , et al. |
May 9, 1972 |
ULTRASONIC INTRUSION DETECTION SYSTEM SIGNAL PROCESSING CIRCUIT
Abstract
An electronic device for processing the amplitude modulations of
a received ultrasonic carrier wave to produce an alarm signal when
the pattern of the amplitude modulations is characteristic of an
alarm condition. The device produces an electrical signal which is
representative of the amplitude modulations of a received wave.
When the electrical signal has a frequency within a predetermined
pass-band, is of at least a predetermined amplitude, and persists
for a minimum time interval, an alarm signal is produced.
Inventors: |
Lee; John H. (Township of
Woodbury, Washington County, MN), Collins; Thomas E. (East
Oakdale, MN) |
Assignee: |
Minnesota Mining and Manufacturing
Company (St. Paul, MN)
|
Family
ID: |
25369411 |
Appl.
No.: |
04/877,173 |
Filed: |
November 17, 1969 |
Current U.S.
Class: |
367/93;
425/405.2; 367/112 |
Current CPC
Class: |
G01N
29/348 (20130101); G08B 13/1627 (20130101); G01N
29/4436 (20130101); G01N 29/032 (20130101); G01N
29/42 (20130101); G01N 2291/102 (20130101) |
Current International
Class: |
G01N
29/42 (20060101); G01N 29/032 (20060101); G01N
29/02 (20060101); G01N 29/36 (20060101); G01N
29/34 (20060101); G01N 29/44 (20060101); G08B
13/16 (20060101); G08b 013/00 () |
Field of
Search: |
;340/258,258A,261 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Caldwell; John W.
Assistant Examiner: Slobasky; Michael
Claims
What is claimed is:
1. An ultrasonic motion detector device which receives an
ultrasonic acoustic wave radiated into a space to be protected at
an essentially constant carrier frequency and amplitude and which
produces an alarm signal when the modulations of a received wave
are characteristic of an alarm condition, comprising:
A. means for producing an electrical signal which is representative
of the amplitude modulations of a received ultrasonic wave;
B. means for producing an alternating signal in response to said
electrical signal, said alternating signal having a frequency
corresponding to the frequency of said electrical signal but the
difference between the high and low amplitudes of an excursion of
said alternating signal being a first value when the absolute value
of the electrical signal amplitude is greater than a predetermined
reference amplitude and being another value less than the first
value when the absolute value of the electrical signal amplitude is
less than the predetermined reference amplitude;
C. means for passing said alternating signal as an output signal
when the frequency of said alternating signal is within a
predetermined passband;
D. means for producing an alarm signal in response to an output
signal which corresponds to a train of a predetermined number of
alternating signal excursions of said first value occurring within
a predetermined time.
2. An ultrasonic motion detector device according to claim 1
further comprising means for effectively varying said predetermined
reference amplitude in direct proportion to the time average of the
output signal amplitude.
3. An ultrasonic motion detector device which receives an
ultrasonic acoustic wave radiated into a space to be protected at
an essentially constant carrier frequency and amplitude and which
produces an alarm signal when the modulations of a received wave
are characteristic of an alarm condition, comprising:
A. means for producing an electrical signal which is representative
of the amplitude modulations of a received ultrasonic wave;
B. a saturation amplifier for producing an alternating signal in
response to said electrical signal, said alternating signal having
a frequency corresponding to the frequency of said electrical
signal but the difference between the high and low amplitudes of an
excursion of said alternating signal being a first value when the
absolute value of the electrical signal amplitude is greater than a
predetermined reference amplitude and being another value less than
the first value when the absolute value of the electrical signal
amplitude is less than the predetermined reference amplitude;
C. an active filter for passing the alternating signal as an output
signal having a pass-band of from about 50 Hz. to 200 Hz.; and
D. means for producing an alarm signal in response to an output
signal which corresponds to a train of a predetermined number of
alternating signal excursions of said first value occurring within
a predetermined time, which means comprises an integrator having a
charge time constant and a discharge time constant greater than
said charge time constant, which integrator is responsive to
one-half of each output signal corresponding to one-half of an
alternating signal excursion to store a charge at a rate determined
by said charge time constant and responsive to the other one-half
of each output signal to reduce the stored charge at a rate
determined by said discharge time constant and an amplitude
detector responsive to the stored charge reaching a predetermined
level to produce an alarm signal
4. An ultrasonic motion detector according to claim 3, wherein the
saturation amplifier comprises
a first common emitter amplifier which receives the electrical
signal as its input,
a second common emitter amplifier coupled in series with the first
common emitter amplifier, and
wherein the means for effectively varying the predetermined
amplitude comprises a feedback network for time-averaging the
charge stored in said integrator and for loading the output of said
first common emitter in direct proportion to said time-averaged
charge.
5. An ultrasonic motion detector according to claim 4, wherein said
feedback network loads the output of said first common emitter
amplifier relatively lightly when said first integrator is storing
less than a predetermined charge but abruptly changes to load said
output relatively heavily when the charge stored in said first
integrator exceeds a predetermined charge.
6. An ultrasonic motion detector according to claim 4, wherein said
feedback network is a current sink which draws current from the
output of said first common emitter amplifier in direct proportion
to the charge stored in said first integrator.
7. An ultrasonic motion detector according to claim 5, wherein said
active filter comprises
a third common emitter amplifier having its input coupled to the
output of said saturation amplifier;
an emitter follower having its input coupled to the output of said
third common emitter amplifier; and
a twin-T filter having its input coupled to the output of said
emitter follower and having its output fed back to the input of
said third common emitter amplifier.
8. An ultrasonic motion detector device which receives an
ultrasonic acoustic wave radiated into a space to be protected at
an essentially constant carrier frequency and amplitude and which
produces an alarm signal when the modulations of a received wave
are characteristic of an alarm condition, comprising:
A. means for producing an electrical signal which is representative
of the amplitude modulations of a received ultrasonic wave;
B. a saturation amplifier for producing an alternating signal in
response to said electrical signal, having a frequency
corresponding to the frequency of said electrical signal, the
excursions of which have a first amplitude whenever said electrical
signal exceeds a predetermined reference amplitude and have a
second amplitude less than said first amplitude whenever said
signal is less than said predetermined reference amplitude;
C. an active filter for passing said alternating signal as an
output signal having a frequency, the periodicity of which is
within a predetermined pass-band, said pass-band having a lower
limit which will reject turbulence type signals and an upper limit
which will reject environmental signals like those of a ringing
telephone; and
D. an alarm and indicator circuit for producing an alarm in
response to said output signal, corresponding to a train of said
first amplitude alternating signal excursions occurring within a
predetermined time.
Description
BACKGROUND OF INVENTION
Systems for detecting conditions corresponding to a fire or an
intruder within a protected space by sensing for changes in
ultrasonic acoustic waves radiated into the space are well known in
the art. In such systems, ultrasonic acoustic energy of a fixed
frequency (the carrier frequency) is radiated into the space to be
protected. An acoustic energy receiver is stationed in the space.
When there is no movement within the space, the radiated acoustic
energy exists as a standing wave pattern. Disturbances within the
space, such as those caused by an intruder, a fire, or
environmental noise such as the ringing of a telephone and air
turbulences caused by exhaust fans, vehicular traffic passing near
the protected space or even vibrating window blinds or water pipes
will disturb the standing wave pattern to cause a variation in the
energy sensed by the receiver.
Many analyses have been made to determine the characteristic
variations of the different types of disturbances. A long sought
after objective of these analyses has been to unambiguously
distinguish between variations characteristic of a fire or an
intruder and variations characteristic of environmental noise.
Many such analyses, and systems predicated upon the conclusions of
these analyses, considered the frequency composition of the
received wave to be the criteria for unambiguously identifying
different types of disturbances. Such a prior art system shall
hereafter be referred to as a "frequency demodulated" system, i.e.,
one in which an electrical signal corresponding to a received
acoustic wave is frequency demodulated.
Such frequency demodulated systems are disclosed in U.S. Pat. Nos.
2,655,645; 2,794,974; and 3,111,657. An objective of each of the
latter two of these patents is to solve the problem of false
alarms. A premise of both patents is that the amplitudes of the
different frequency components of valid alarm signals (caused by a
fire or an intruder) are essentially the same whereas the
corresponding amplitudes of turbulence signals vary inversely with
frequency. These patents thus each include circuits for separating
a received signal into a low frequency component and a high
frequency component together with additional circuitry for
comparing the amplitudes of the two signals. A circuit is included
for attenuating the low frequency component so that the comparison
produces a difference signal only for valid alarm signals. The two
components of a turbulence signal, after attenuation of the low
frequency component, are approximately equal and thus do not
produce a difference signal when compared. U.S. Pat. No. 3,111,657
also includes additional circuitry for preventing false alarms when
the composition of a turbulence signal does not simultaneously
include both a high and a low frequency component as is sometimes
the case. This additional circuitry comprises integrators for
time-averaging the high and low frequency components and will
prevent a turbulence signal having only a high or a low frequency
component from producing a false alarm for those cases when the
time-average of the high and low frequency components over a
pre-selected period is approximately equal.
We have discovered that it is not necessary to frequency demodulate
the received signal. We thus are able to eliminate all of the
circuitry for separating a received signal into two components and
for comparing and otherwise processing these components. Instead,
we merely amplitude demodulate received signals. We have found that
the frequency, duration, and amplitude of the amplitude
demodulation signal of a received wave is a reliable criteria for
distinguishing between environmental noise and valid alarm
condition disturbances. Specifically, we have found that signals of
relatively low frequency correspond to turbulence disturbances
whereas a higher frequency signal is characteristic of a valid
alarm disturbance, i.e., both fire and intrusion type disturbances.
We have also found that environmental noises other than turbulence,
e.g., the ringing of a telephone, are characterized by amplitude
modulations of still higher frequencies.
In a preferred embodiment, the ultrasonic motion detector device of
the present invention comprises a circuit for producing an
electrical signal corresponding to amplitude modulations of a
received ultrasonic wave. The received waves comprise reflections
of a wave both radiated into a space to be protected and modulated
according to disturbances within the area. The electrical signal is
applied to another circuit which produces an alternating signal.
The alternating signal is produced to have a first value (i.e. the
difference between the high and low amplitudes of a signal
excursion) when the absolute value of the electrical signal
amplitude is greater than a predetermined reference amplitude and
to have another value less than the first value when the absolute
value of the electrical signal amplitude is less than the
predetermined reference amplitude. The alternating signal is
applied to a further circuit which passes the alternating signal as
an output signal when the frequency of the alternating signal is
within a predetermined pass-band. Another circuit receives the
output signal and produces an alarm signal when the output signal
corresponds to a train of alternating signal excursions of the
first value occurring within a predetermined or minimum time. By
blocking passage of alternating signals of low and high frequency
and by requiring that an alternating signal which is passed persist
for a minimum time, the signal processing circuit of the present
invention avoids false alarms while reliably indicating valid alarm
conditions.
In another embodiment, an additional circuit is provided for
effectively varying the predetermined reference amplitude in direct
proportion to changes in the time average of the output signal
amplitude to compensate for changes in the ambient level of
environmental noise signals.
Specific embodiments of the invention chosen for purposes of
illustration and description are shown in the accompanying drawings
wherein:
FIG. 1 is a block diagram of an ultrasonic intrusion detector
system employing the processing circuit of the present
invention;
FIG. 2 is a schematic circuit diagram of a preferred embodiment of
the signal processing circuit of the present invention;
FIG. 3 is a schematic circuit diagram of a circuit for use with the
processing circuit of FIG. 2 to compensate for variations in the
ambient environmental noise signal level.
With reference to the block diagram of FIG. 1 there is shown a
transmitter 10 which radiates ultrasonic waves 12 at an essentially
constant amplitude and frequency (a "carrier" frequency) into a
space to be protected. The transmitter 10 is not considered a part
of the present invention. Reflected waves 14 impinge upon and are
demodulated by a receiver 16. The output of the receiver is an
electrical signal which is a representation of the amplitude
modulations of the received wave. An illustrative representation of
the electrical signal produced by receiver 16 is illustrated as
waveform 18. The output of receiver 16 is shown to be applied to a
saturation amplifier 20 which converts the electrical signal 18 to
an alternating signal, shown as waveform 22. Waveforms 18 and 22
have the same time base. Thus it is apparent that the saturation
amplifier 20 provides a signal the excursions of which have a first
amplitude whenever the electrical signal of waveform 18 exceeds a
predetermined reference amplitude. Otherwise, for amplitudes of
waveform 18 less than a predetermined amplitude, the signal
excursion (i.e., the peak-to-peak amplitude) is less than the first
amplitude excursion. In the waveform 18, zero reference is
indicated by solid line 24 and the predetermined amplitude is
represented by the equidistant displacements of dashed lines 23 and
25. In waveform 22, the first amplitude excursions, corresponding
to waveform 18 signals greater than the predetermined amplitude
limits of dashed lines 23 and 25, are shown to occur between
reference lines 27 and 29. The alternating signal of saturation
amplifier 20 is applied to an active filter 26. Active filter 26
passes as an output signal, shown as waveform 28, those alternating
signals having a periodicity within a predetermined pass-band. The
lower limit of the pass-band rejects turbulence type signals; the
upper limit rejects environmental noise signals like those from a
ringing telephone. The output signal 28 from active filter 26 is
applied to an alarm and indicator circuit 30 which produces an
alarm signal in response to an output signal corresponding to a
train of first amplitude alternating signal excursions occurring
within a predetermined time. The foregoing describes a basic
embodiment of the present invention. A further improvement of the
device of FIG. 1 is shown in dashed lines as a feedback circuit 32.
Feedback circuit 32 effectively varies the predetermined reference
amplitude 23 and 25 in direct proportion to changes in the time
average of the output signal amplitude.
FIG. 2 is a schematic diagram of the basic embodiment of FIG. 1.
Receiver 16 is shown to comprise a transducer 34 which is
responsive to variations in the received acoustic wave to
correspondingly vary the base current applied to the base lead of
transistor 36. Transistor 36 is the amplifier of one stage of the
two stage common emitter amplifier shown generally as 38. The
combination of transducer 34 and amplifier 38 are tuned to the
carrier wave frequency, which for the present example shall be
assumed to be 40 KHz. The output of the two stage common emitter
amplifier 38 is applied to an emitter follower amplifier 40. The
emitter follower output is an electrical signal representative of
amplitude demodulation of a received wave. The emitter follower 40
output is shown to be applied as the input to saturation amplifier
20. Saturation amplifier 20 comprises a first common emitter
amplifier, shown generally as 42, and a second common emitter
amplifier, shown generally as 44. The combination of the amplifiers
42 and 44 provides an alternating signal representation of the
electrical signal output of receiver 16. This alternating signal is
provided as the input to active filter 26 which is shown to
comprise an active network, shown generally as 45, and a twin-T
network shown generally as 46. Active network 45 is shown to
comprise a common emitter amplifier 48 coupled in series with an
emitter follower 50 the output of which is the input to twin-T
network 46. The output of twin-T network 46 is fed back via
coupling capacitor 52 to the input of common emitter amplifier 48.
The output of active filter 26 is provided through coupling
capacitor 54 as the input signal to alarm and indicator circuit 30.
The alarm and indicator circuit 30 is shown to generally comprise
an emitter follower 56 and integrator circuit 58, a Schmidt Trigger
60 and a relay output 61. The path for charging capacitor 62 of
integrator 58 is through transistor 64, and resistor 66. The
discharge path of capacitor 62 is through resistor 70. The charge
time constant of integrator 58 is chosen so that random, short
duration disturbances characteristic of environmental noise do not
cause an alarm. The discharge time constant is selected to be much
larger than the charge time constant so that a long duration
disturbance characteristic of a valid alarm condition will cause an
alarm. We have found a ratio of the discharge to charge time
constants of about 30 to be acceptable.
FIG. 3 illustrates a circuit which would provide compensation for
variations in the ambient level of turbulence signals. The
connection points A through E of the circuit of FIG. 3 would be
connected at the similarly identified points in FIG. 2. In addition
to providing a slightly different integrator circuit, shown
generally as 74, the circuit of FIG. 3 includes a feedback network
shown generally as 76. Integrator 74 is essentially the same as the
integrator 58 having a charge path through transistor 64 and
resistor 66 to capacitor 62. The integrator discharge path is
through resistors 80 and 82. The relationship between the charge
and discharge time constants of integrator 74 is the same as that
previously discussed for integrator 58. Feedback network 76, as
shown, may conveniently be a Miller integrator. The transistor 84
of the integrator is shown to have its collector lead coupled to
the output of the first common emitter amplifier of the saturation
amplifier 20. The Miller integrator of feedback network 76
time-averages the charge stored by capacitor 62 of integrator 74 to
sink current from, i.e., to load, the output of common emitter
amplifier 42 in direct proportion to the charge stored in capacitor
62.
Briefly, the operation of a circuit of FIG. 2 is as follows.
Transducer 34 receives reflected waves of the carrier waves
propagated into the space to be protected and varies the bias
current applied to the base of transistor 36 in a manner
corresponding to variations of the received wave. Emitter follower
40 strips the carrier frequency from the output signal of amplifier
38 to provide an electrical signal which is representative of the
amplitude modulation of the received wave. The amplifier 20
receives this electrical signal as its input and is driven into
saturation whenever the amplitude of the input signal exceeds a
predetermined reference amplitude. Returning to FIG. 1 momentarily,
it is seen that when the signal 18 exceeds the reference amplitude
indicated by dashed lines 23 and 25, an alternating signal is
produced having an excursion (a first excursion) extending between
reference lines 27 and 29. On the other hand, if the amplitude of
signal 18 is less than the reference amplitude of lines 23 and 25,
the excursion of the corresponding alternating signal of amplifier
20 is less than the first excursion. The alternating signal of
amplifier 20 is applied to the input of active filter 26 which has
a pass-band of from about 50 Hz. to 200 Hz. In FIG. 1, the portion
of waveform 22 corresponding to periods t.sub.0 and t.sub.2 of the
time scale corresponds to a frequency between 50 Hz. and 200 Hz.
and thus are passed by active filter 26 as an output signal.
Portions of the waveform 22 of period t.sub.1 and t.sub.3, however,
correspond to frequencies respectively below and above the
pass-band of filter 26 and thus their passage is essentially
blocked.
The active filter output is applied to the base of emitter follower
56 the emitter current of which flows through resistor 66 and into
capacitor 62. Schmidt Trigger 60 is coupled between resistor 66 and
capacitor 62 as an amplitude detector to produce an alarm signal by
switching states when the charge stored in capacitor 62 reaches a
predetermined level, i.e., the trigger level of the Schmidt
Trigger. The trigger level is chosen to be sufficiently greater
than the quiescent charge of capacitor 62 that neither a half
excursion, nor even several successive full excursions, of the
output signal will raise the charge in capacitor 62 to the trigger
level for it has been found that environment noise can generate
several successive first amplitude excursions within the frequency
pass-band characteristic of valid alarms. Assuming a carrier
frequency of 40 KHz., a frequency of the amplitude demodulated
signal (corresponding to an intruder) of 100 Hz. and, to simplify
analysis, an idealized waveform, approximately 40 excursions would
be required to raise the quiescent charge (about 1.2 v.) on
capacitor 62 to the trigger voltage (1.5 v.) of Schmidt Trigger 60.
Feedback network 32 compensates for variations in the ambient noise
level which would change the quiescent charge of capacitor 62 (and
thus also change the differential charge required to reach the
trigger level). As the charge on capacitor 62 increases above the
quiescent level, the Miller integrator time-averages the charge and
sinks or draws current from the output of common emitter amplifier
42 in proportion to the time-averaged charge. The current drawn off
by Miller Integrator 76 is thus diverted from the input to common
emitter amplifier 44 which effectively increases the amplitude of
the input signal required to drive amplifier 20 into saturations,
i.e., it effectively increases the predetermined reference
amplitude.
Typical values of components of the circuits of FIGS. 2 and 3 are
given in the following table.
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TABLE I
I. FIG. 2 Resistor Capacitor R1 56 K.OMEGA. C1 10 .mu.f, 16 v R2
4.7 K.OMEGA. C2 .047 .mu. f R3 47.OMEGA. C3 .22 .mu.f R4 10
K.OMEGA. C4 .047 .mu.f R5 1 K.OMEGA. C5 .22 .mu.f R6 56 K.OMEGA. C6
.22 .mu.f R7 470.OMEGA. C7 .22 .mu.f R9 10 K.OMEGA. C8 125 .mu.f,
16 v R10 47.OMEGA. C9 10 .mu.f, 16 v R11 1 K.OMEGA. C10 .047 .mu.f
R12 3.3 meg..OMEGA. C11 125 .mu.f, 4 v R13 470 K.OMEGA. C12 .22
.mu.f R14 10 K.OMEGA. C13 .015 .mu.f R15 47 K.OMEGA. C14 125 .mu.f,
4 v R16 10 K.OMEGA. C15 125 .mu.f, 4 v R17 15 K.OMEGA. C18 .1 .mu.f
R18 22.OMEGA. C19 .1 .mu.f R19 3.3 K.OMEGA. C20 .22.mu.f R20 150
K.OMEGA. C52 10 .mu.f, 16 v R21 2.2 K.OMEGA. C54 .22 .mu.f R22 33
K.OMEGA. C62 125 .mu.f 4 v R23 22 K.OMEGA. all transistors GE
2N3394 R24 100.OMEGA. R25 4.7 K.OMEGA. Transducer 34 R26 56
K.OMEGA. 40 KHz ceramic transducer, R27 4.7 K.OMEGA. commercial
type number R28 10 K.OMEGA. MK-109 offered for sale by R29
47.OMEGA. MASSA DIVISION of R30 1 K.OMEGA. Dynamics Corporation of
R31 15 K.OMEGA. America R32 15 K.OMEGA. R33 15 K.OMEGA. R34 8.2
K.OMEGA. R35 47 K.OMEGA. R39 1.2K.OMEGA. R40 39.OMEGA. R41 820
K.OMEGA. R42 15 K.OMEGA. R66 680.OMEGA. R70 100 K.OMEGA. II. FIG. 3
Resistor Capacitor R80 27 K.OMEGA. C88 125 .mu.f 10 v R82 47
K.OMEGA. R86 2.2 K.OMEGA. Transistor 84 GE 2N3394
__________________________________________________________________________
it will be appreciated that, while certain specific embodiments
have been shown and described, various changes and modifications
may be resorted to without departing from the true spirit and scope
of the invention as defined in the appended claims.
* * * * *