U.S. patent number 3,766,540 [Application Number 05/139,049] was granted by the patent office on 1973-10-16 for appliance removal alarm system for motels.
This patent grant is currently assigned to HEC Corporation. Invention is credited to Walter S. Schopfer, Dieter Wuerth.
United States Patent |
3,766,540 |
Schopfer , et al. |
October 16, 1973 |
APPLIANCE REMOVAL ALARM SYSTEM FOR MOTELS
Abstract
A system for the prevention of the theft of televisions sets and
other appliances from motels and the like requires the modification
of the appliance by connecting a quartz crystal resonator across
its terminals. A frequency-modulated oscillator connected to a
transmission line linking all of the appliances is employed to
stimulate the crystals in sequence. A transmit-receive switch
operating at 100 herz frequency and phase detection between the
oscillator and the echoes from the crystals improve selectivity,
while a counter keeps track of the crystals heard from. An alarm
and a visual display of a number indicate the time and place of a
theft.
Inventors: |
Schopfer; Walter S. (Harrison,
NY), Wuerth; Dieter (West Boyleston, MA) |
Assignee: |
HEC Corporation (West
Boyleston, MA)
|
Family
ID: |
22484881 |
Appl.
No.: |
05/139,049 |
Filed: |
April 30, 1971 |
Current U.S.
Class: |
340/505;
340/13.33; 340/518; 340/523; 340/524; 340/533; 340/538; 340/568.2;
340/691.8 |
Current CPC
Class: |
G08B
13/1418 (20130101); G08B 26/002 (20130101) |
Current International
Class: |
G08B
26/00 (20060101); G08b 025/00 (); H04q
009/00 () |
Field of
Search: |
;340/280,276,191,216,310,408,152T,412,413,223,415,171A ;310/8.1,8.2
;343/6.5SS,6.8,6.5 ;325/31 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Caldwell; John W.
Assistant Examiner: Partridge; Scott F.
Claims
I claim:
1. A theft detection system for remote detection of the removal
from a transmission line of any of a plurality of appliances, each
of appliances having a pair of electrical terminals for connection
to said transmission line, the combination of,
a. a plurality of crystal resonators, each of said resonators being
resonant at a frequency which is one of an ordered set of
frequencies and different from the resonant frequency of the others
of said plurality, each of said resonators being connected between
a pair of said terminals to be set to ringing by application of a
voltage at said one frequency to said pair, and
b. an alarm set remote from said appliances connected to said
transmission line, said alarm comprising
i. transmitter means including a variable voltage controlled
oscillator for generating sequential electrical signals having
substantial energy components at each of the resonant frequencies
of said plurality of resonators,
ii. receiving means connected to said transmission line for
detecting signals at each of said resonant frequencies,
iii. transmit-receive isolation means for connecting said
transmitter means to said transmission line so that the energy
components at said resonant frequencies generated by said
transmitter means flow into said transmission line and are
substantially prevented from flowing directly into said receiving
means.
iv. multiplexing means for rendering said receiving means sensitive
to said resonant frequencies according to a predetermined program
of intervals and order,
v. alarm means connected to said receiver means responsive to a
departure from said program, and
vi. counting means connected to said multiplexing means for
counting signals corresponding to each detected resonant
frequency.
2. A theft detection system for remote detection of the removal
from a transmission line of any of a plurality of appliances, each
of said appliances having a pair of electrical terminals for
connection to said transmission line, the combination of,
a. a plurality of resonators, each of said resonators being
resonant at a frequency which is one of an ordered set of
frequencies and different from the resonant frequency of the others
of said plurality, each of said resonators being connected between
a pair of said terminals to be set to ringing by application of a
voltage at said one frequency to said pair, and
b. an alarm set remote from said appliances connected to said
transmission line, said alarm comprising
i. transmitter means for generating an electrical signal having
substantial energy components at each of the resonant frequencies
of said plurality of resonators,
ii. receiving means connected to said transmission line for
detecting signals at each of said resonant frequencies,
iii. transmit-receive isolation means for connecting said
transmitter means to said transmission line so that the energy
components at said resonant frequencies generated by said
transmitter means flow into said transmission line and are
substantially prevented from flowing directly into said receiving
means.
iv. multiplexing means for rendering said receiving means sensitive
to said resonant frequencies according to a predetermined program
of intervals and order, and
v. alarm means connected to said receiver means responsive to a
departure from said program,
c. said transmitter means comprising an oscillator adapted for
frequency modulation over a band of frequencies,
d. said receiving means comprising filter means selective of said
band, a detector, and a low-pass circuit,
e. said resonant frequencies being uniformaly spaced within said
band,
f. said multiplexing means comprising a linear modulator for
advancing the frequency of said oscillator regularly from one end
of said band to the other slowly enough to excite in each of said
resonators an unambiguous response,
g. said oscillator being a voltage-controlled oscillator having a
center frequency of the order of 300 kiloherz,
h. said resonators being quartz crystals having resonant
frequencies spaced by uniform intervals of substantially two
kiloherz,
i. said filter having a pass band from 200 kiloherz to 400,
j. said detector being a phase detector responsive to changes in
amplitude and phase as said ocsillator is swept past one of said
resonant frequencies, and a low pass circuit,
k. said transmit-receive isolations means comprising a switch and a
multivibrator means for driving said switch alternately between a
first state and a second state, said switch being arranged so that
in its said first state, energy passes freely between said
oscillator and said transmission line and transmission of signals
through said filter is blocked, and in its said second state
signals pass freely from said transmission line through said filter
and flow of energy from said oscillator to said transmission line
is blocked,
l. said modulator comprising a ramp generator to supply a
modulating voltage to sweep said oscillator at a rate of the order
of four kiloherz per second, and
m. said alarm means comprising
i. a first trigger circuit for producing a counter-activating pulse
at each time of crossing of said oscillator frequency and the
resonant frequency of one of said resonators.
ii. a counter for accumulating the number of such crossings,
iii. a timer to mark the interval between said pulses, responsive
to a delay significantly in excess of the programmed interval
between said pulses to sound an alarm, stop the sweep of the ramp,
and read out the accumulated number in said counter, and
iv. means for resetting said ramp generator upon said counter
accumulating the cardinal number of resonators connected to said
transmission said number being the sum of the number of said
plurality and of control resonators part of said alarm set.
3. A theft detection system for remote detection of the removal
from a transmission line of any of a plurality of appliances, each
of said appliances having a pair of electrical terminals for
connection to said transmission line, the combination of,
a. a plurality of resonators, each of said resonators being
resonant at a frequency which is one of an ordered set of
frequencies and different from the resonant frequency of the others
of said plurality, each of said resonators being connected between
a pair of said terminals to be set to ringing by application of a
voltage at said one frequency to said pair, and
b. an alarm set remote from said appliances connected to said
transmission line, said alarm comprising
i. transmitter means for generating an electrical signal having
substantial energy components at each of the resonant frequencies
of said plurality of resonators,
ii. receiving means connected to said transmission line for
detecting signals at each of said resonant frequencies,
iii. transmit-receive isolation means for connecting said
transmitter means to said transmission line so that the energy
components at said resonant frequencies generated by said
transmitter means flow into said transmission line and are
substantially prevented from flowing directly into said receiving
means.
iv. multiplexing means for rendering said receiving means sensitive
to said resonant frequencies according to a predetermined program
of intervals and order, and
v. alarm means connected to said receiver means responsive to a
departure from said program,
c. said transmission means being a voltage controlled oscillator
variable in frequency over a band about a center frequency of the
order of 300 kiloherz,
d. said resonators being quartz crystals having resonant
frequencies spaced by uniform intervals within said band,
e. said receiving means comprising an amplifier, a filter, for
selectively passing said resonant frequencies and a phase detector
responsive to changes in amplitude and phase as said oscillator is
swept past one of said resonant frequencies, and a low pass
circuit,
f. said transmit-receive isolation means comprising a switch and
multivibrator means for driving said switch alternately between a
first state and a second state, said switch being arranged so that
in its said first state energy passes freely between said
oscillator and said transmission line and transmission of signals
through said filter is blocked, and in its said second state
signals pass freely from said transmission line through said filter
and flow of energy from said oscillator to said transmission line
is blocked,
g. said multiplexing means comprising a ramp generator to supply a
modulating voltage to sweep said oscillator at a rate of the order
of four kiloherz per second, and
h. said alarm means comprising,
i. a first trigger circuit for producing a counter activating pulse
each time of crossing of said oscillator frequency and the resonant
frequency of any of said resonators,
ii. a counter for accumulating the number of such crossings,
iii. a timer to mark the interval between said pulses, responsive
to an interval significantly in excess of the programmed interval
between said pulses to sound an alarm, stop the sweep of said ramp
generator, and read out the accumulated number in said counter,
and
iv. means for resetting said ramp generator upon said counter
accumulating the cardinal number of resonators connected to said
transmission line, said number being the sum of the number of said
plurality and the number of control resonators part of said alarm
set.
4. A theft detection system for remote detection of the removal
from a transmission line of any of a plurality of appliances, each
of said appliances having a pair of electrical terminals for
connection to said transmission line, the combination of,
a. a plurality of resonators, each of said resonators being
resonant at a frequency which is one of an ordered set of
frequencies and different from the resonant frequency of the others
of said plurality, each of said resonators being connected between
a pair of said terminals to be set to ringing by application of a
voltage at said one frequency to said pair, and
b. an alarm set remote from said appliances connected to said
transmission line, said alarm comprising
i. transmitter means for generating an electrical signal having
substantial energy components at each of the resonant frequencies
of said plurality of resonators,
ii. receiving means connected to said transmission line for
detecting signals at each of said resonant frequencies,
iii. transmit-receive isolation means for connecting said
transmitter means to said transmission line so that the energy
components at said resonant frequencies generated by said
transmitter means flow into said transmission line and are
substantially prevented from flowing directly into said receiving
means,
iv. multiplexing means for rendering said receiving means sensitive
to said resonant frequencies according to a predetermined program
of intervals and order, and
v. alarm means connected to said receiver means responsive to a
departure from said program,
c. said transmitter means being an oscillator variable in frequency
over a band about a center frequency,
d. said resonators having resonant frequencies spaced by uniform
intervals within said band,
e. said multiplexing means sweep the frequency of said oscillator
at uniform rate across said band, and
f. said alarm means comprising,
i. a first trigger circuit for producing a counter incrementing
pulse each time of crossing of said oscillator frequency and the
resonant frequency of any of said resonators,
ii. a counter for accumulating the number of such crossings,
and
iii. a timer to mark the interval between said pulses, responsive
to an interval significantly in excess of the programmed interval
between said pulses to sound an alarm, stop the sweep, and read out
the accumulated number.
5. A system as defined by claim 4 wherein
c. said transmitter means comprises an oscillator adapted for
frequency modulation over a band of frequencies,
d. said receiving means comprise filter means selective of said
band, a detector, and a low-pass circuit,
e. said resonant frequencies are uniformaly spaced within said
band, and
f. said multiplexing means comprise a linear modulator for
advancing the frequency of said oscillator regularly from one end
of said band to the other slowly enough to excite in each of said
resonators an unambiguous response.
6. A system as defined by claim 5,
g. wherein said resonators are quartz crystals.
7. A system as defined by claim 5,
g. wherein said transmit-receive isolation means comprise
i. a switch having a first and a second state, connected to said
transmitter means, said receiving means, and said transmission
line, aranged so that in its first state energy passes freely
between said transmitter means and said transmission line and is
substantially barred from passing from said transmission line and
from said transmitter means through said receiver means, and in its
second state signals pass freely between said receiver means and
said transmission line,
ii. together with driving means for periodically oscillating said
switch between its said two states at intervals which are
substantially briefer than the ringing time of said resonators, and
substantially longer than the response time of said filter
means.
8. A system as defined by claim 6,
h. wherein said transmit-receive isolation means comprise,
i. a switch having a first and a second state, connected to said
transmitter means, said receiving means, and said transmission
line, arranged so that in its first state energy passes freely
between said transmitter means and said transmission line and is
substantially barred from passing from said transmission line and
from said transmitter means through said receiver means, and in its
second state signals pass freely between said receiver means and
said transmission line,
ii. together with driving means for periodically oscillating said
switch between its said two states at intervals which are
substantially briefer than the ringing time of said resonators, and
substantially longer than the response time of said filter
means.
9. A system as defined by claim 8 wherein,
i. said ringing time is of the order of one-tenth second,
j. said response time is of the order of one-tenth of a
millisecond,
k. said switching intervals are of the order of 10 milliseconds,
and wherein
l. said oscillator frequency is advanced from one of said resonant
frequencies to the next in the order of one second,
m. whereby a complete scanning cycle is completed in the order of
one minute.
10. A system as defined by claim 8 wherein,
i. said ringing time is more than 10 milliseconds,
j. said resonse time is less than one-tenth of a millisecond,
k. said switching intervals are between two and 50 milliseconds,
and wherein
l. said oscillator frequency is advanced from one of said resonant
frequencies to the next in less than one second.
11. A system as defined by claim 8 wherein said oscillator is a
voltage-controlled oscillator.
Description
This invention relates to theft detection devices and more
particularly to apparatus for the detection of the removal of a
television set or other electrical appliance from a remote location
where it is installed.
In the preferred embodiment of the invention each of the television
receivers in a motel is connected to a common antenna system to
which is also connected detection equipment so that upon removal of
any set, an alarm is sounded and the room number of the removal is
displayed at a central monitoring location.
It is an object of the invention that no substantial changes need
be made in either the television receiver or in the wiring of a
motel to install a system. It is a further objective that the mode
of operation of the detection system should not be readily
observable or readily disabled by a thief. It is a further
objective that the system be fail-safe and reliable.
A feature of the invention by which the above objects are realized
is the installation of a simple quartz crystal resonator of
predetermined frequency across the input terminals of each set, the
frequencies of successive crystals differing in convenient steps of
1000 herz or so.
A further feature of the invention is a voltage controlled
oscillator and saw-tooth modulator by which the oscillator
frequency is swept from one crystal frequency to the next to check
on each set every minute or less.
A still further feature of the invention is a transmit-receive
switch by which transmission from the oscillator is interrupted
periodically so that the monitoring apparatus may listen for the
ringing of the crystals; and it is a feature of the invention that
the failure of the apparatus to hear a return echo at the
predetermined time corresponding to the frequency of a particular
resonator, generates an alarm and a display of the missing
response.
Other objects and features of the invention will be apprehended
from the following specification taken in conjunction with the
annexed figures of which
FIG. 1 is a simplified block diagram of the invention,
FIG. 2 is a block diagram of the invention in its preferred
embodiment,
FIG. 3 is a detail of the end-point decode matrix of FIG. 2,
and
FIG. 4 is a detail of the transmit-receive gate of FIG. 2.
FIG. 1 is illustrative of the invention in its broadest context.
There is a plurality n of appliances A.sub.1,A.sub.2. . .A.sub.n to
be protected. They are all connected to a transmission line 100.
Inside each appliance is a resonator X.sub.1,X.sub.2,. . .X.sub.n.
Each of these resonators is tuned to respond to a different
frequency.
At a central location is a multi-frequency generator 110 which is
designed to transmit signals having frequency components to match
the frequencies of each of the n resonators (generically designated
X.sub.i) It may be convenient to include two test resonators
X.sub.0 and X.sub.(n.sub.+1) bracketing the frequency band of the
resonators.
Transmission of these frequencies casues the resonators X.sub.i to
"sing" and this singing may be detected by a receiver 120,
especially if there is a transmit-receive isolator 130 to interrupt
transmission while the receiver "listens".
The disappearance of the singing of any resonator is evidence of
the removal of the appliance. The singing of the resonators might
be detected by including in the receiver a detector corresponding
to each of the resonators X.sub.i ; but this is seen to be
unnecessary when multiplexing means 140 are provided so that the
same receiving circuits may be used sequentially to listen in turn
for the singing of the several resonators X.sub.i according to some
prearranged program. As singing of the resonators is detected,
these events each increment a register 150 according to a
prearranged pattern until all of the resonators are accounted for.
The failure of the register to conform to the prearranged pattern
of counts, triggers an alarm 160.
There are various means well known in the art to produce a
plurality of frequencies sequentially or simultaneously whereby to
stimulate the resonators; and there are various means by which the
receiver may be tuned to respond to one after the next of the
resonators. Frequency synthesizers, or example, may be programmed
to switch from frequency to frequency in accordance with any
predetermined pattern. The use of such sophisticated equipment may
be justified in some cases, but a much simpler preferred embodiment
has been found to be satisfactory for motel television protection,
as shown in FIG. 2.
The multi-frequency generator is a voltage-controlled oscillator
(vco) 210 controllable between 200 kiloherz and 400 kiloherz. The
resonators X.sub.0,X.sub.1. . . .X.sub.n,X.sub.(n.sub.+1) are tuned
at frequencies such as 250,000 herz, 252,000, 254,000 etc. up to
352,000 herz if there are 50 appliances to protect (n=50)
The transmit-receive isolator is a gate circuit 232 operated with
switches S.sub.1 and S.sub.2 by a 100 herz multivibrator 234.
Multiplexing is achieved by modulating the vco 210 with a ramp
generator 242 which linearly sweeps the frequency of the vco 210
across the band including all of the resonators in less than a
minute.
Since the Q of quartz crystal resonators at these frequencies is
typically 30,000, and Q is a measure of the ratio of the energy of
vibration to the amount of that energy dissipated in a cycle of
free oscillation, ringing time of such crystals is of the order to
a tenth of a second. The energy decays by a constant factor over
each interval of time. If we term the "half-life" as the time
required for half of the energy of vibration to decay, then, for
purposes of this specification "ringing time" is defined as two
half lives. The dynamics of quartz crystal oscillators are well
described in the literature; and need not be repeated here since
details are unimportant to the practice of the invention wide
variations in all parameters being permissible. It has been found
that so-called DT cut crystals do not exhibit objectionable modes
of oscillation and are, therefore preferred.
In the embodiment of FIG. 2, the alarm set is connected to the
common antenna transmission line 100 for all of the TV sets of a
motel through a VHF trap 244 which prevents the system frequencies
and harmonics from interfering with television reception. The
crystals X.sub.1,X.sub.2. . .X.sub.n are connected between terminal
pairs t.sub.1,t.sub.2,. . .t.sub.n which are the antenna terminals
of the television sets installed in the n suites to be protected.
There must be an isolating impedance in the branch to each
applicance so that a thief could not disable the whole system by
shorting out the cable in one room, and isolation (not shown) may
also be needed to protect television reception from too close
coupling to the system.
The band pass of the receiving circuits is determined by a filter
248 (at the output of the amplifier 246) which need not have sharp
skirts but which excludes broadcast radio signals above 400
kiloherz (kh) and power system noises below 200 kh. This filter
also determines the response time of the receiving system which can
be readly much less than a millisecond. The ringing time of the
crystals and the response time bracket the switching period of the
transmit-receive isolation circuitry. The multivibrator 234 has a
frequency of about 100 herz transmitting for 2 milliseconds, and
receiving for 8 milliseconds in each period. The output of the
oscillator 210 is passed by the "and" gate 232, while the passage
of ringing signals through the receiving circuitry is interrupted
by switches S.sub.1 and S.sub.2 at the intput and output
respectively of the filter 246.
It is a property of the crystal oscillators at resonance both the
magnitude and phase angle of the impedance change markedly with a
change of only about 30 herz in frequency. Thus the freely decaying
crystal oscillations will tend to either lag or lead the driving
oscillator as the oscillations are being built up or diminished.
Thus, although the amplitude of the ringing signals responds to the
oscillator, a detector based on both phase and amplitude produces a
larger, sharper, and more characteristic response.
The phase detector 250 comprises a phase-splitting amplifier 252 to
produce opposite phases of the amplified ringing signal which are
applied to the collectors of the transistors Q.sub.1 and Q.sub.2.
Opposite reference phases are supplied directly from the oscillator
210 to the bases of the transistors Q.sub.1 and Q.sub.2. The
detected output from the two transistors will undergo a full
excursion from minimum to maximum amplitude in the space of two
sampling times. The output is smoothed by the low-pass circuit
comprising the amplifier 258 with feedback capacitance C.sub.1 and
resistance R.sub.1 which is down 3 db. at 100 herz.
The smoothed output of the low pass circuit is applied to the
One-shot trigger circuit 260 by connection 261.
Because of the integration time, the one-shot fires at about the
time the gate 232 is to reopen. Via connection 262 and inverter 264
the gate 232 is blocked for an instant. The output pulse of the
trigger circuit 260 is also applied to a second trigger circuit,
the timer 268, to the bistable circuit 270 and through the "or"
gate 272 to increment the two-stage binary-coded-decimal counter
273. The timer 268 occupies its "zero" condition for approximately
three-fourths of a second unless within that time it receives the
next pulse from the one-shot 260, in which case its zero is
extended for a further three-fourths second. Three-quarters of a
second is selected as being significantly greater than the time
required for the ramp generator 234 to sweep the oscillator 210 by
the two kh separation between crystals. Thus, in normal operation
the timer 268 is never permitted to set itself to "one." The
bistable circuit 270 is provided to hold the timer 268 at zero even
at the end of a scanning cycle. It is, therefore, necessary to
install at the alarm set,or elsewhere, crystals for any rooms that
do not have installed TV sets.
When a TV is removed, there is a gap in the pattern of pulses from
the one-shot 260, and the timer 268 switches itself back to "one."
This change of state triggers a second one-shot 274, which in turn
immediately triggers the latch circuit 276, turning on the alarm
280. Through connection 282, inverter 284, and gate 272, and
through normally closed switch S.sub.3 the one-shot 274 calls for
the decoders 286 and 287 to generate a display of the number of the
missing crystal on the display 290, and finally through connection
292 stops the sweep. After a predetermined delay of typically three
to ten seconds to allow an attendant to note the number, the
one-shot 273 resets, increments the counter 274 to correct the
count for the missing crystal, and the sweep resumes.
The sweep continues until the number (n+1) is accumulated on the
counter 273 at the time when the sweep reaches the frequency of the
crystal X.sub.(n.sub.+1), the upper end-point crystal. At that
point, the end-point decoder 300 (shown in detail in FIG. 3)
activates the reset one-shot 320, which produces a reset signal on
connection 322. This signal resets the ramp generator 242, the
counter 273, and through inverter 326, the bistable 270. Because
the ramp generator cannot be relied upon to reset to exactly the
same frequency each time, it is reset to some frequency safely
below the frequency of the resonator X.sub.0 and the timer is held
in its zero state until the first pulse from the one-shot 260 is
applied to the bi-stable to release the zero state maintained until
that time through connection 330 to the bistable 270.
It will be recognized that the invention may be constructed in many
equivalent ways using logic components available in commerce and
well-known in the art. The following parts are preferred: For the
BCD counter 273, two sections of Texas Instruments type 7490
integrated circuits; for the seven segment decoders 286 and 287,
type 7447; for the "ready" bistable 270, half of a type 7474. The
gate 232 is wired from standard parts as shown in FIG. 4.
The endpoint decoder is preferable made up of one part 331 of a No.
7400 nand gate, one No. 7460 dual four-input and gate 332, and two
No. 7400 gates 333 and 334 connected as inverters as shown in FIG.
3.
The outputs of the first section 333 supplies at terminals A and A
one BCD bit and its complement; similarly the other outputs B,B
,C,C & D,D are available for units and in the other section 334
A',A' ,B',B' ,C,C' & D,D' for tens.
Depending upon the selected value of (n+1) either A or A is
jumpered to terminal 1 of gate 335. Similarly selected jumpers are
made to terminals 2,3, and 4 of gate 335, and to terminals
1',2',3', and 4' of gate 336.
A significantly important use for the invention has been found in
the protection of television sets in motels. In this service, a
common antenna system is generally available, and this has been
found to supply a superior transmission line compared to the
electrical power wiring. Commonly there is so much noise of various
descriptions on the power lines that the simple system disclosed
herein may be unreliable. The circuitry may be made more selective
by using the superheterodyne principle in the receiving circuitry,
or by a more sophisticated frequency modulator permitting the
oscillator to "slew" between crystals so that more time may be
devoted to confirming signals.
Transmit-receive isolation may be achieved by other means such as
balanced bridge-like circuitry which would approximately balance to
exclude transmitter power from the receiver except where the phase
departs wildly as it does in the neighborhood of the
resonances.
It will thus be seen that the objects set forth above, among those
made apparent from the preceding description, are efficiently
attained. Since certain changes may be made in the constructions
set forth without departing from the scope of the invention, it is
intended that all matter contained in the above description shall
be interpreted as illustrative and not in a limiting sense.
It is also to be understood that the following claims are intended
to cover all of the generic and specific features of the invention
herein described, and all statements of the scope of the invention
which, as a matter of language, might be said to fall
therebetween.
* * * * *