U.S. patent number 3,707,708 [Application Number 05/098,588] was granted by the patent office on 1972-12-26 for muting circuit for a security alarm system providing a sonic alert.
This patent grant is currently assigned to Multra-Guard, Inc.. Invention is credited to Carlo Dan.
United States Patent |
3,707,708 |
Dan |
December 26, 1972 |
MUTING CIRCUIT FOR A SECURITY ALARM SYSTEM PROVIDING A SONIC
ALERT
Abstract
An electronic circuit enabling an operator at a central station
to mute a sonic alarm device energized in the event of an emergency
condition occurring at a remote station under surveillance at any
time from the moment the alarm is heard and identified at the
central station to the time when a normal condition is restored.
The circuit additionally includes means which reenergizes the sonic
device automatically as soon as the normal condition is restored to
remind the operator that muting had previously occurred and further
requiring the operator to manually reset the circuit to deactivate
the reenergized sonic alarm device.
Inventors: |
Dan; Carlo (Bethesda, MD) |
Assignee: |
Multra-Guard, Inc. (Rockville,
MD)
|
Family
ID: |
22270002 |
Appl.
No.: |
05/098,588 |
Filed: |
December 16, 1970 |
Current U.S.
Class: |
340/503; 340/327;
340/328; 340/509; 340/521; 340/533; 340/550; 340/574; 379/44 |
Current CPC
Class: |
H04M
11/04 (20130101) |
Current International
Class: |
H04M
11/04 (20060101); G08b 007/06 (); G08b
013/22 () |
Field of
Search: |
;340/213.1,213.2,326,327 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Trafton; David L.
Claims
I claim as my invention:
1. A muting circuit for a sonic alarm device in a security alarm
system and being powered by an electrical supply voltage applied
thereto, comprising in combination: input signal means;
first circuit means coupled to said input signal means and said
sonic alarm device, being responsive to an input signal of a first
and a second type coupled to said input means to become operative
for energizing said sonic alarm device and remaining operative to
supply electrical voltage to said sonic alarm device until
reset;
reset means coupling said electrical supply voltage to said first
circuit means and selectively rendering said first circuit means
inoperative after being rendered operative by said input signal by
interrupting said electrical supply voltage coupled thereto;
second circuit means coupled across said sonic alarm device, being
normally inoperative but being rendered selectively operative in
accordance with a first control voltage applied thereto for short
circuiting said sonic alarm device and thereby muting said alarm
device;
third circuit means including normally open electrically controlled
switch means coupled to said second circuit means, being rendered
closed to generate said first control voltage upon the application
of a second control voltage fed thereto as well as a power voltage,
and muting switch means coupled to said controlled switch means for
selectively applying said second control voltage thereto and
rendering said controlled means closed whereupon said controlled
switch means remains closed as long as said power voltage is
applied;
fourth circuit means coupled from said input means to said third
circuit means, being responsive to said first type of input signal
for applying said power voltage thereto for the duration of said
first type of input signal; an
fifth circuit means coupled from said input means to said third
circuit means being responsive to said second type of input signal
for supplying said power voltage thereto for the duration of said
second input signal, said second and said third circuit means
however becoming inoperative upon the termination of said first and
second input signal due to the absence of said power voltage
whereupon said sonic alarm device again is rendered operative by
means of said first circuit means, remaining energized until said
first circuit means is rendered inoperative by said reset
means.
2. The invention as defined by claim 1 and additionally including
visual indicator means coupled to and energized by said first
circuit means providing a visual indication of the presence of said
first or second type of input signal at said input means.
3. The invention as defined by claim 1 wherein said first circuit
means comprises:
a controlled rectifier having a first and a second current
conducting electrode and a control electrode, and additionally
including circuit means coupling said reset means to one current
conducting electrode, the sonic alarm device to the other current
conducting electrode, and said control electrode to said input
means.
4. The invention as defined by claim 1 wherein said first circuit
means comprises:
a semiconductor controlled rectifier having an anode, a cathode and
a gate electrode including circuit means coupling said anode
electrode to said reset means, said cathode electrode to said sonic
alarm device and said gate electrode to said input means.
5. The invention as defined by claim 1 and additionally including
current limiting means coupled between said first circuit means and
said sonic alarm device.
6. The invention as defined by claim 1 wherein said second circuit
means comprises a semiconductor switch and said electrically
controlled switch means comprises a controlled rectifier having a
first and a second current conducting electrode and a control
electrode and including circuit means coupling one of said current
conducting electrodes to a circuit terminal for the application of
said power voltage, the other current conducting electrode to said
semiconductor switch, said control electrode to said muting switch
means, and said fourth and fifth circuit means to said circuit
terminal whereupon said muting switch means is adapted to render
said controlled rectifier conductive upon the application of said
power voltage to said circuit terminal upon the appearance of
either said first or second input signal at said input means and
whereupon said other current conducting electrode couples said
first control signal to said semiconductor switch.
7. The invention as defined by claim 1 wherein said fourth circuit
means comprises diode means coupling said first type of input
signal to said electrically controlled switch, said input signal
thereby comprising said power voltage.
8. The invention as defined by claim 1 wherein said fifth circuit
means comprises:
capacitive means coupled to said input means and being responsive
to said second type of input signal to be charged thereby, and
amplitude sensitive circuit means, coupled to said capacitance
means, being responsive to the amplitude of the voltage across said
capacitive means and coupling said supply voltage to said
electrically controlled switch when the voltage across said
capacitor exceeds a predetermined amplitude, said supply voltage
thereby comprising said power voltage.
9. The invention as defined by claim 8 wherein said amplitude
sensitive circuit means comprises a Schmitt trigger circuit.
10. A muting circuit for a sonic alarm device adapted to be powered
by a supply potential coupled from a power source comprising, in
combination:
a first controlled rectifier coupled to said sonic alarm system and
including circuit means for being rendered conductive upon the
application of a steady state and a pulsating alarm signal coupled
thereto to couple said supply potential therethrough to said sonic
alarm;
reset means coupling said power source to said first controlled
rectifier for supplying power thereto and for selectively rendering
said first control rectifier non-conductive when actuated;
normally open switch means coupled to said sonic alarm device and
being adapted to be rendered closed to short circuit said sonic
alarm;
second controlled rectifier means coupled to said normally open
switch means and additionally including circuit means for applying
a control signal to said switch means when either said steady state
or said pulsating alarm signal is coupled to said first controlled
rectifier, and being adapted to be selectively rendered conductive
only during the presence of said steady state or said pulsating
alarm signal to close said switch means; and
muting switch means coupled to said second controlled rectifier for
selectively rendering said second control rectifier conductive only
during the presence of said alarm signals to cause said normally
open switch means to short circuit said sonic alarm device, said
second controlled rectifier automatically becoming non-conductive
upon the disappearance of said steady state or said pulsating alarm
signal and removing said control signal from said switch means
causing said switch means to become open whereupon said first
controlled rectifier reactivates said sonic alarm until said first
controlled rectifier means is rendered non-conductive by said reset
means.
11. The invention as defined by claim 10 wherein said first and
second controlled rectifier means comprises a semiconductor
controlled rectifier and said normally open switch means comprises
a transistor.
12. The invention as defined by claim 11 wherein each said
semiconductor controlled rectifier has a first and second current
conducting electrode and a gate electrode and additionally
including input circuit means coupling said steady state and said
pulsating alarm signal to the gate electrode of said first
semiconductor controlled rectifier, and circuit means coupling said
muting switch means to the gate electrode of said second controlled
rectifier whereby said muting switch means couples a trigger signal
thereto when actuated.
13. The invention as defined by claim 12 wherein said reset means
is coupled to one current conducting electrode of said first
controlled rectifier and additionally including diode means coupled
between said second current conducting electrode of said first
controlled rectifier and said sonic alarm device; and
circuit means coupling a voltage to one current conducting
electrode of said second controlled rectifier during the presence
of either said steady state or pulsating alarm signals and the
other current conducting electrode to said transistor.
14. The invention as defined by claim 13 wherein said last recited
circuit means includes:
a capacitor responsive to said pulsating alarm signal and being
charged thereby, a normally non-conductive transistor coupled
between said power source and said one current conducting electrode
of said second controlled rectifier, and an amplitude discriminator
circuit coupled between said capacitor and said transistor, said
transistor being rendered conductive by said amplitude
discriminator when the charge across said capacitor exceeds a
predetermined amplitude level to couple said supply potential to
said one current conducting electrode of said second controlled
rectifier; and
a semiconductor diode responsive to said steady state alarm signal,
coupled to said one current conducting electrode of said second
controlled rectifier and being selectively poled to apply said
steady state alarm signal to said one current conducting electrode
of said second controlled rectifier.
Description
CROSS REFERENCE TO RELATED APPLICATION
The present application is related to U.S. Patent Application Ser.
No. 59,413, entitled "Security Alarm System," filed on July 30,
1970 in the names of Carlo Dan, the inventor of the present
invention, and James F. Pinkham. Said related application is also
assigned to the assignee of the present invention.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to supervised alarm systems and more
particularly to a system wherein one or more remote stations under
surveillance can respectively communicate with a central monitor
station via a two wire telephone line to provide an emergency
warning or other type signal thereto comprising, inter alia, a
sonic alarm to indicate at the central station that an alarm
condition is present. This invention is particularly adapted to be
utilized as a burglary or unwanted intrusion alarm, a robbery or
"hold-up" alarm, and even a fire alarm system.
2. Description of the Prior Art
Security alarm systems typical of the prior art presently in use
are simple in construction and normally comprise a single closed
series loop circuit, including a perimeter protection circuit,
extending between the central monitoring station and the protected
premises. The perimeter circuit is adapted to include frangible
resistive tapes, trap wires, etc. A break in the perimeter circuit
thus breaks the closed loop circuit to the central station and
initiates an alarm.
The power supply for such systems consists of a battery or other
constant voltage power supply located either in the central
monitoring station or at the protected premises. With either
arrangement, the system is easily compromised or defeated because
the specifications for such systems, as dictated by the industry
and consumer testing facilities such as the Underwriter's
Laboratories, presently require that the systems merely give an
indication if the resistance in the total circuit loop in the
system varies .+-. 50 percent. Where telephone lines are utilized
to interconnect the protected premises to the central station, the
resistance of the lines themselves is in the range of 3000 ohms.
Where a 100 ohm perimeter circuit is connected in series to the
3000 ohms of the telephone lines, an alarm will not be given until
the resistance in the entire loop varies by approximately .+-. 1500
ohms. It can be seen, therefore, that the resistance in the
perimeter circuit can be tampered with over a considerably wide
margin and in some cases entirely removed without interrupting the
tolerance built into the system sufficient to sound an alarm.
In order to defeat such a series system where the battery or power
supply providing energy for the system is located in the protected
premises, it is merely necessary for one attempting to defeat the
system to take a voltage measurement across the phone line entering
the protected premises that constitutes the circuit to the central
station. This will provide information on the size of the battery
that must be substituted across the lines for the battery inside of
the protected premises and by connecting the battery of the correct
potential across the line and then cutting the line into the
premises, the premises is removed from the circuit to the central
station without interrupting the loop which then can be entered at
will without an alarm being indicated at the central station.
Where the battery or power supply is located at the central station
as opposed to being in the protected premises, one attempting to
compromise the system must first determine the proper resistance to
connect across the line going into the premises that connects the
protected premises with the central station, but does not have to
determine the supply potential. In the first example, one must also
determine the substitute resistance for the protected premises and
this is done in the same manner as will now be outlined.
A burglar or intruder, for example, must first place a ammeter in
one of the lines entering the premises, then cut the line so that
the circuit is completed through the ammeter and obtain information
as to the current in the line. The line is then spliced together
and then the ammeter removed. A voltage measurement is then taken
across the two lines into the premises with a volt meter and with
this information and using a simple Ohms law calculation, the
resistance in the perimeter circuit of the premises can be
determined knowing that a substantial portion of the resistance in
the loop circuit is in the phone line itself. A resistance of the
value calculated is shunted across the two lines entering the
premises and the two lines into the premises are then cut since it
is removed from the surveillance loop to the central station
without interferring with the loop or initiating an alarm at the
central station.
The burglar or intruder does not have to be accurate in determining
the store resistance and normally if a resistance in the amount of
200 ohms is shunted across the line, this will defeat the system
without sounding an alarm because it is well within the tolerance
range of the permissible resistance change in the entire loop
before the alarm is sounded. In the system where the power supply
is in the protected premises, the substitute resistance is placed
in series with the substituted battery. In cases where the
protected premises is extremely far from the supervising central
station the lines into the premises can be jumpered together
without any substitute resistance whatsoever without sounding an
alarm because the resistance in the store is less than the
resistance range tolerated by the system before initiating an
alarm.
Realizing these deficiencies, the above cross-reference related
application is directed to a system wherein a constant current DC
generator powers a communication link including a pair of telephone
lines coupled between a protected premise and a central monitor
station. The communications link includes means for reversing the
DC polarity of the constant current from a predetermined polarity
indicative of a normal condition to an opposite polarity in
response to a detected alarm condition which occurs in response to
a change in the operating parameters of a separate supervisory
circuit located at the protected premises. The change in polarity
is sensed at the central station and an indication of the alarm
condition is presented by means of indicator lights and a sonic
alarm. DC signalling of the alarm condition as well as the normal
condition is thus provided by means of constant current control and
DC polarity sensing. Signalling back to the protected premises from
the central station is achievable by interrupting the continuity of
the communication link and causing the constant current DC
generator to sense the open circuit condition.
In addition to security alarm systems per se, the prior art also
includes teachings of alarm monitoring systems of which U.S. Pat.
No. 3,452,345 issued to G. E. Kinsey is an illustrative example as
well as automatic alarm enunciator circuits of which the following
are illustrative examples: U.S. Pat. No. 3,525,988, K. C. Linder;
U.S. Pat. No. 3,480,938, M. E. Martin; and U.S. Pat. No. 3,381,286,
R. R. Walsh. The Kinsey patent is generally illustrative of a
system wherein the monitoring units contains an indicating unit
which when placed in the alarm condition remains in that condition
until it is reset, even through the protection circuit it monitored
is restored to its normal condition. The other patents are
generally illustrative of circuits which require an acknowledgement
of a supervisor having noted an alarm condition. Also a typical
muting type switch arrangement for an audible aLarm is disclosed in
U.S. Pat. No. 2,971,186, issued to T. Ripepi.
SUMMARY
The subject invention is directed to an improvement in alarm
monitoring systems and more particularly to a muting circuit for a
sonic alarm device utilized in connection with a security alarm
system and comprises: first circuit means coupled to the sonic
alarm for activating said sonic alarm device in response to a first
or steady state and a second or pulsating type of alarm signal and
being operable to maintain said sonic alarm activated in absence of
said alarm signals once having been applied; second circuit means
coupled to said sonic alarm system, being normally inoperative but
becoming operative upon the application of a control signal fed
thereto which then provides a shunt across said sonic alarm and
thereby render it non-operative; third circuit means, including a
muting switch, coupled to said second circuit means becoming
operable by the closing of said muting switch to couple said
control signal to said second circuit means only during the
presence of either of said two alarm signals; fourth circuit means
coupled to said third circuit means supplying power thereto only in
response to the first alarm signal; and fifth circuit means coupled
to said third circuit means supplying power thereto only in
response to said second alarm signal, said second circuit means
under the control of said third circuit means being adapted to
deactivate the sonic alarm device when the muting switch is closed;
but upon the cessation of the first or second alarm signal the
shunt provided by said second circuit means is removed due to the
removal of power supplied to said third circuit means whereupon
said first circuit means again reactivates the sonic alarm device.
The first circuit means additionally includes a reset switch
coupling power thereto which when manually opened is adapted to
render said first device circuit means inoperable and thereby
deactivates the sonic alarm once more. This circuit thus enables an
operator to mute the sonic alarm any time from the moment an alarm
signal is detected to the time when the normal condition is
restored; however, as soon as the normal condition is restored, the
sonic alarm device will again sound and will remain thus until the
operator depresses the reset switch.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of the security alarm system contemplated
for use in combination with the subject invention;
FIG. 2 is an electrical schematic diagram of a constant current DC
generator and current sensing circuit utilized by the system shown
in FIG. 1;
FIG. 3 is an electrical schematic diagram illustrating the current
polarity reversing circuit, the perimeter-intrusion circuit, the
"hold-up" circuit, and audio surveillance circuit located at the
protected premises for the system shown in FIG. 1;
FIG. 4 is a schematic diagram illustrating an audio receiver
amplifier and squelch circuit located at the central monitor
station for the system shown in FIG. 1;
FIG. 5 is an electrical schematic diagram of the supervisory logic
circuit located at the central station for providing supervisory
indications of the condition of the protected premises for the
system shown in FIG. 1; and
FIG. 6 is an electrical schematic illustrative of the preferred
embodiment of the subject invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to the drawings and more particularly to FIG. 1,
there is disclosed in block diagrammatic form an overall system
diagram wherein a plurality of protected premises 10.sub.1,
10.sub.2 and 10.sub.n are monitored at a remote central station 12
including a respective plurality of supervisory circuits 14.sub.1,
14.sub.2 and 14.sub.n which are coupled back to the protected
premises by means of respective pairs of telephone lines 16.sub.1,
16.sub.2 and 16.sub.n. Each protected premises, for example, is
provided with signalling circuitry for providing an indication,
both visual and sonic, at the central station 12 of various alarm
conditions such as burglary and/or unwanted intrusion, robbery or
"hold--up" as well as audio surveillance of the premises under
specified conditions, e.g. "night" operation or during a "hold-up"
etc.
More particularly, each protected premises contains a constant
current DC generator 18 which is adapted to transmit a relatively
small DC current (1.5 ma. or 3.0 ma.) over an ungrounded or
floating two wire telephone line 16 to a supervisory logic circuit
20 forming part of the supervisory circuit 14. The DC current is
made to pass through a current polarity reverse circuit 22 which is
inserted in the current path to the telephone line 16 to provide a
polarity reversal in the event of an attempt to compromise a
perimeter-intrusion circuit 24 or a "hold-up" circuit 26 is
manually actuated. The current polarity is sensed by the
supervisory logic circuit 20 providing an indication thereof by
indicating lights generally shown by reference numeral 28. As will
be described in greater detail in the subsequent description, the
perimeter-intrusion circuit 24 provides a steady state current
reversal in the polarity reverse circuit 22 whereas the "hold-up"
circuit 26 is adapted to provide a continuous alternating reversal
whereupon the indicator lights 28 provide a coded indication of
which condition is occurring. A sonic alert device 27 and a muting
circuit 29 therefor which comprises the subject invention is also
coupled to the supervisory logic circuit 20 to provide a controlled
sonic alarm indication as will be explained subsequently in
detail.
Additionally, the perimeter-intrusion circuit 24 when compromised,
either intentionally or otherwise, activates an indicator light 30
at the protected premises 10. Audio communication or surveillance
is provided by an audio transformer 32 coupled into the DC current
communication link including the two wire telephone line 16. An
audio amplifier 34 coupled to one or more microphones 36 located in
the protected premises forming an audio surveillance circuit 37 is
connected to the audio transformer 32 so that audio signals picked
up by the microphone 36 are transmitted to the respective
supervisory circuit 14 which also includes a corresponding audio
transformer 38 coupled to the telephone lines at that end. The
output of the audio transformer 38 is then coupled into an audio
amplifier 40 which also has a squelch circuit 41 coupled thereto so
that an output to a loud speaker 42 will only be provided when the
audio level back at the protected premises exceeds a predetermined
value. The squelch circuit 41 also contains a "reset" switch not
shown which is adapted, inter alia, to control the operation of the
muting circuit 29.
A current sensor circuit 44 at the protected premises 10 is coupled
to the constant current DC generator 18 to sense a current
interruption of the DC current flowing between the DC generator 18
and the supervisory logic circuit 20 located at the central station
12. An indicator light 46 is coupled to the current sensor circuit
44 to provide an indication of the DC current failure which may be
caused for example by: (1) an accidental break in the telephone
line 16, (2) an attempt to insert a device such as a dummy load
into the system for defeating the alarm circuitry, (3) or an
intentional momentary opening of the circuit to provide a
signalling back to the protected premises from the central monitor
station 12. A push button switch 48 or the like contained in the
supervisory circuit 14 at the central station 12 can provide the
third operating mode. Additionally, the supervisory circuit 20 also
contains means, as will be subsequently illustrated, to also sense
an open circuit condition or a failure of the constant current DC
generator 18 and provide an indication of such a condition by means
of the indicator lights 28 as well as by the sonic alert device
27.
The use of the constant current DC generator 18 located at the
protected premises 10 as disclosed in FIG. 1 is capable of
employing currents at a relatively low value considering prior art
relay type signalling circuits which necessarily employ currents as
high as 30 or 40 milliamps. These higher currents produce circuit
problems with extremely small gauge telephone line pairs presently
available for leasing. As wire gauges get smaller, practical
signalling distances become even shorter. As noted above, with a
constant voltage variable current system a foreign potential of the
right voltage and polarity can accidentally or intentionally be
substituted for the signalling source without giving a false alarm.
The latter condition occurs when a sophisticated or knowledgeable
burglar for example defeats the system. The use of a constant
current DC generator on the other hand makes it considerably more
difficult to compromise the system because in order to do so a
constant current generator must be substituted into the
communication link externally of the protected premises while at
the same time disconnecting the constant current generator 18
without interrupting the current flow in the telephone lines 16 or
varying its predetermined magnitude either of which would be sensed
by the supervisory logic circuit 20 whereupon an alarm condition
would be indicated.
Considering now the subject system in greater detail, reference now
is made to FIG. 2 wherein reference numeral 50 designates a
regulated DC power supply of conventional design for providing a
+12 volt supply voltage. A 117 volt/60Hz AC line potential is
applied to the terminals 52 and 54 which is then coupled to the
power supply 50 by means of a power transformer 56. The 12 volt
supply voltage appears across the positive (+) supply buss 58 and
the negative (-) supply buss 60. FIG. 2 additionally discloses a
schematic representation of the preferred embodiments of the
constant current DC generator 18 referred to in FIG. 1 as well as
the current sensor circuit 44. The constant current DC generator
basically comprises a feedback controlled DC to DC voltage
converter capable of providing two magnitudes (1.5 milliamps and
3.0 milliamps) of constant DC current. The DC TO DC converter
comprises a well known DC to AC chopper circuit including
transistor switches 62 and 64 coupled to transformer 66 and driven
by means of a free running multivibrator 68 including transistors
70 and 72. The action of the multivibrator 68 causes mutually
opposite conductive states to alternately occur in transistors 70
and 72 for equal durations of time so that a square wave output
signal appears at their respective collector electrodes. These
square wave outputs are respectively coupled to the base electrodes
of transistors 62 and 64 by means of resistors 74 and 76 so that
transistors 62 and 64 are driven "on" and "off" accordingly. For
example where transistor 62 is in an 'on" state, transistor 64 is
in an "off" state, and vice versa. Moreover when either of
transistors 62 or 64 is "on", the +12 volt supply potential is
applied to one end of the primary winding 78 of the transformer 66.
Depending upon the magnitude of the voltage appearing at the center
tap 80 of the primary winding 78, a corresponding AC voltage will
appear across the secondary winding 82 for the combined switching
of transistors 62 and 64. Where for example the frequency of
operation of the multivibrator 68 is in the order of 2500 to 3000
cycles per second, a corresponding frequency AC output will appear
across the secondary winding 82. A smoothing capacitor 84 is
connected directly across the winding 82. The AC output voltage
appearing across the secondary winding 82 is applied across
opposite terminals 86 and 88 of a full wave rectifier bridge 90 so
that a DC voltage appears across terminals 92 and 94.
A current sensing feedback control circuit for maintaining a
predetermined constant current value at terminals 92 and 94 of the
output of the rectifier bridge 90 is included which maintains the
voltage at the center tap 80 at a predetermined voltage level so
that either a 1.5 or 3.0 ma output is constantly provided. This is
effected by means of a current sensing transformer 96 the primary
winding 98 of which is coupled in series between one end of the
secondary winding 82 and the input terminal 86 of the rectifier
bridge 90. The magnitude of the AC current flowing through the
primary winding 98 is sensed across the secondary winding 100 which
is then rectified by means of the semiconductor diodes 102 and 104
and applied across one side 106 of capacitor 108 which has its
opposite side 110 coupled to the center tap 112 of the secondary
winding 100. The magnitude of the voltage across capacitor 108 then
is proportional to the AC current flowing in the output circuit of
the transformer 66. A voltage divider circuit including fixed
resistors 114, 116, 118 and thermistor 120 connected in parallel
with resistor 116 is connected across capacitor 108. The voltage
appearing at the junction between resistor 116 and 118 is applied
as one input to a differential amplifier including transistors 122
and 124. It should also be noted that the + side 106 of capacitor
108 is also coupled to the +12 volt supply buss 58 through resistor
126 thereby providing a substantially constant voltage at circuit
junction 127. The input signal applied to transistor 122 which is
proportional to the DC to DC converter output current is compared
against a fixed voltage reference provided by the diodes 128 and
130 as well as resistor 132 which is commonly connected to chassis
ground in combination with the base of transistor 124.
Chassis ground is adapted to be at a +6 volt level provided by the
perimeter-intrusion circuit 24 which will be subsequently
considered. This +6 volt voltage is applied at terminal 134. One
section A of a three pole two position "Day-Night" switch 136 is
connected by means of its normally closed contacts between chassis
ground and the common connection between diodes 128 and 130. The
normally closed position of switch section 136-A referred to as the
"day" position D, provides a fixed voltage reference to the other
input of the differential amplifier including transistors 122 and
124 to produce a constant DC current of 1.5 ma. out of the
rectifier bridge at terminals 92 and 94. The open position of
switch section 136-A is referred to as the "night" position N and
provides a voltage reference which is adapted to cause a constant
DC current of 3.0 ma. from the rectifier bridge 90 output.
The differential amplifier output provided at the collector of
transistor 122 is directly coupled to the base of transistor 138
which in turn is coupled by means of its collector electrode and
resistor 140 to the base of transistor 142. Transistor 142 is
shunted across capacitor 144 which is directly connected between
the center tap 80 of primary winding 78 and the negative side of
the 12 volt supply appearing at the supply buss 60. Transistors 138
and 142 are controlled by the differential output of transistors
122 and 124 to cause transistors 142 to act as a variable resistive
impedance across capacitor 144 to control the electrical charge on
capacitor 144. If for example transistor 142 is fully conductive,
it acts as a virtual short circuit across capacitor 144 whereupon
it fully discharges and the center tap 80 is directly connected to
the - supply buss 60. When this condition occurs, a full 12 volt
square wave is alternately impressed across each half of the
primary winding 78. In the condition where transistor 142 is only
partially conductive, capacitor 144 accumulates a charge whereupon
the potential at the center tap 80 rises to a value so that the
amplitude of the square wave impressed across the primary of the
transformer 66 is decreased. Thus, the negative feedback provided
by the current transformer 96, the differential amplifier including
transistors 122 and 124 as well as the transistors 138 and 142 in
combination with capacitor 144 will change the voltage at center
tap 80 to effectively control the magnitude of the DC current flow
out of terminals 92 and 94 of the rectifier bridge and maintain it
at a value as determined by the position of the day-night switch
section 136-A.
Completing the consideration of the constant current generator 18
one or more stages of RC filter circuitry 146 is coupled across the
output terminals 92 and 94 of the rectifier bridge 90 in order to
remove any undesired ripple or other noise present from being
transmitted to the current polarity reverse circuit shown in FIG.
3.
In the event that circuit interruption for current flow from the
secondary winding 82 of the transformer 66 occurs, the current
transformer 96 will sense the current interruption and the voltage
appearing across capacitor 108 will fall whereupon transistors 148
and 150 in the current sensor circuit 44 will become conductive
since junction 110 is coupled to the base of N-P-N transistor 148
by means of resistor 152. Since the emitter of transistor 148 is
coupled to the +12 volt supply buss 58 by means of resistor 126, it
will become conductive as the voltage at junction 110 falls. The
conduction of transistor 148 causes transistor 150 to become
conductive, due to the coupling of the resistors 154 and 156. When
transistor 148 becomes conductive, a signal is coupled to the base
of transistor 150 by means of resistor 154 which renders it
conductive. The conductive transistor 150 acts like closed switch
and applies the +12 volts appearing on supply buss 58 across the
green indicator lamp 46 which is connected between the collector of
transistor 150 and the - supply buss 60. Thus for any discontinuity
of the predetermined DC constant current, the indicator light 46
will be turned "on" and an indication of this condition will be
displayed at the protected premises 10.
Now referring to FIG. 3 attention is directed to the constant
current polarity reverse circuit 22 which includes a pair of
circuit leads 160 and 162 which are coupled to the filter circuit
146 connected across the output terminals 92 and 94 of the
rectifier bridge 90 shown in FIG. 2. Leads 160 and 162 are
respectively connected to sets of relay contacts 164 and 166 of a
double pole electromagnetically actuated relay 168 which
constitutes a current reversing relay energizable by means of the
relay coil 170. The circuit leads 160 and 162 are selectively
coupled to a pair of output circuit leads 172 and 174 by means of
the current reversing relay 168 and the secondary windings 176 and
178 of the audio transformer 32 shown in FIG. 1 which has its
primary winding coupled to the audio amplifier 34. The circuit lead
160 is connected to the output lead 174 through contacts 164 and
the secondary winding 178 when relay 168 is in its normally
deenergized position while circuit lead 162 is connected to the
output lead 172 through contacts 166 and the secondary winding 176.
When the current reversing relay 168 is energized, however, relay
contacts 164 and 166 will operate to reverse the connections.
The purpose of the audio transformer 32 is to couple the microphone
36 and amplifier 34 when energized to the output leads 172 and 174.
A capacitor 184 is coupled between opposite ends of the secondary
windings 176 and 178 so that relay operation does not interfere
with the operation of the audio amplifier 34 when energized. In
this respect, the audio amplifier 34 is energized by the
application of the +12 volt supply voltage thereto either by means
of resistor 186 which is connected to the night terminal N of the
second section B of the "day-night" operation switch 136 or circuit
lead 188 coupled back to the "hold-up" circuit 26. In the present
system, therefore, the audio amplifier is energized when the switch
136-B is manually switched to "night" operation or whenever the
"hold-up" circuit is energized.
The perimeter-intrusion circuit 24 and the hold-up circuit 26
operate to energize the relay coil 170 in the following manner.
Considering first the perimeter-intrusion circuit 24, a frangible
resistive tape circuit of well known construction is generally
illustrated by the fixed resistance 190. The value of this
resistance is in the order of 25-100 ohms, depending upon the kind
and length of tape and wiring utilized. It is applied to the
perimeter of glass windows and doors etc. and is coupled in series
between chassis ground and the +12 volt supply potential through a
perimeter interlock switch 192, the third section C of the
day-night operation switch 136, a variable resistor 194 and a fixed
resistor 196. The +12 volts is coupled to the circuit by means of
terminal 197 and supply buss 199 which is adapted to be connected
to supply buss 58 shown in FIG. 2. The resistive tape 190 is
coupled in series with perimeter interlock switches 192 to the
night terminal N of the switch 136-C while a variable resistance
198 is connected between the day terminal D and resistive tape 190,
to chassis ground so that during day operation a resistance may be
substituted for the perimeter interlock switch circuit. The
variable resistor 194 is adapted to adjust the value of the
potential applied across both the perimeter or protection circuit
resistance 190 and the substitute resistance 198.
The voltage divider potential appearing across resistance 190 and
the rheostat 198 is coupled to one input of a differential
amplifier circuit 200 comprised of transistors 202 and 204. This
input is applied through resistor 206 to the base of transistor
202. The other input to the differential amplifier 200 consists of
a reference voltage applied to the base of transistor 204 by means
of the fixed resistors 208 and 210 in combination with the
adjustable resistance 212 all coupled in series between circuit
junction 213 and the +12 volt supply voltage appearing in supply
buss 199. The variable resistor 212 provides a means of adjusting
the value of the reference potential applied to the base of
transistor 204 to a predetermined value. Junction 213 is connected
to chassis ground which in the embodiment of all the circuitry
included at the protected premises 10 is made to be at a value of
+6 volts. This is provided by the action of P-N-P transistor 214
which has its emitter directly connected to junction 213. The base
of transistor 214 is connected to a voltage divider consisting of
fixed resistors 218, 220 and 222 which are connected in series
across the 12 volt supply potential. The negative pole f the supply
potential is provided by supply buss 223 which is connected to
terminal 216 which in turn is adapted to be connected to the buss
60 shown in FIG. 1. The common connection between resistors 220 and
222 is made to have a value of +6 volts so that the connection of
the collector of transistor 214 to the negative buss 223 causes
transistor 214 to become conductive and apply the +6 volts directly
to chassis ground through junction 213. This +6 volt potential is
also connected to terminal 221 which is common to terminal 134
shown in FIG. 2. The reason for this condition to exist is in order
to allow the output signal voltages of the differential amplifier
200 appearing at circuit junctions 224 and 226 respectively to
swing both upwardly and downwardly from the preset operating point.
This is established by making the value of the variable resistance
198 substantially identical to the perimeter wiring and interlock
switch 192 resistance and then with the switch section 136-C in the
night position N, the variable resistance 194 is adjusted to
provide an input in the order of 60 millivolts to the base of
transistor 202, at which value the differential amplifier 200 will
respond to .+-. 30 percent change in the perimeter tape resistance
190. Any deviation of the resistance 190, e.g. by breaking the tape
or attempting to defeat system, from the .+-. 30 percent value as
established by the variable resistance 194 will cause one or the
other of transistors 228 or 230 to become conductive.
The collectors of both P-N-P transistors 228 and 230 are coupled to
the base of N-P-N transistor switch 234 by means of respective
collector load resistors 236 and 238 such that when either
transistor becomes conductive transistor 234 receives a signal
which will render it conductive also. Since the emitter of
transistor 234 is directly connected to the negative side of the
supply potential appearing on buss 223 and whereas the collector is
coupled to one side of the relay coil 170 through diode 240 the
conduction of transistor 234 causes the relay coil 170 to energize
because the other side of relay coil 170 is directly connected to
the +12 volt supply buss 199. Relay contacts 164 and 166 switch
upon energization of coil 170 and reverse the polarity of the
current flow of the constant current in output leads 172 and
174.
A tunnel diode 242 is coupled across the base-emitter junction of
transistor 234 in order to provide a more positive actuation of the
relay coil 170 since the tunnel diode 242 will effect a much faster
turn-on of the transistor 234 whenever either of the transistors
228 or 230 is rendered conductive. The turn-on of transistor 234
also energizes a red indicator lamp 30 which has one side connected
to +12 volt supply providing an indication at the protected
premises 10 of a compromise of the perimeter-intrusion circuit
24.
Whereas prior art apparatus in some cases utilizes differential
relay circuitry which is directly actuated by a change in either
the perimeter circuit resistance alone or the combination of the
perimeter circuit resistance plus the resistance in the
transmission line, the disclosed system is adapted to provide a
greater sensitivity in the protection circuit due to the fact that
the current reverse relay 168 is not directly controlled by the
perimeter resistive tape circuit resistance 190 but acts in
response to a change only in the perimeter circuit resistance which
is sensed by the differential amplifier 200. It is the highly
sensitive differential amplifier 200 including the transistors 202
and 204 which control the relay coil 170 through the turn-on of
transistor 234 which is in series with the relay coil across the
+12 volt supply potential. In other words, most resistive sensing
circuits employ sensitive relays. These relays necessarily have
wide tolerance between pull-in and drop-out current. Furthermore,
in "direct wire" alarm systems utilizing telephone lines, the line
resistance is a part of the overall circuit and compromise
protection is not what it should be over relatively long high
resistance lines. Also most conventional circuits will not measure
minute changes in current.
In the present embodiment, however, the alarm condition threshold
of the perimeter-intrusion circuit 24 is adjusted by means of
rheostat 194 until the current flow through the perimeter
resistance 190 equals a voltage input to the differential amplifier
200 which will not trigger the turn-on of transistor 234. When the
voltage drop across the perimeter resistance which is applied to
the base of transistor 202 drops below or increases above the
reference voltage appearing at transistor 204 by a predetermined
percentage indicative of an alarm condition, the developed error
signal operates to turn-on transistor 234 causing the current
reverse relay 168 to operate and maintain its new state until the
alarm condition is corrected and provide an alarm signal back to
the central station. While not specifically shown, the perimeter
resistance 190 may when desirable include a positive or a negative
temperature coefficient thermistor to compensate for environmental
resistance changes.
In addition to the perimeter intrusion circuit 24 being operable to
operate the current reverse relay 168 for a sensed change in the
perimeter resistance 190, the hold-up circuit 26 is also adapted to
activate the current reverse relay 168 but in a slightly different
mode of operation. Whereas a detected change in the perimeter
resistance 190 will cause a steady state actuation of the current
reverse relay 168, the hold-up circuit 26 will cause a continuous
alternating reversal of the current relay 168 to constantly cause
the current to reverse back and forth and provide a flashing type
of visual indication at the central station 12 as well as a
pulsating sonic "beep".
Considering now the hold-up circuit 26, it is comprised of a
normally deenergized free running multivibrator circuit 244
including transistors 246 and 248 which receive the +12 volt supply
potential on supply buss 199 through a silicon controlled rectifier
(SCR) 250 coupled to the +12 volt supply buss 199 over circuit lead
252. The actuation of a normally open push-button switch 254 causes
a positive trigger voltage to be coupled to the gate of SCR 250 by
means of resistors 256 and 257 and the diode 258 to turn the SCR
250 "on". When SCR 250 IS "on", i.e. in its conductive state, the
+12 volt supply potential appears at circuit junction 260 which is
at the cathode electrode of SCR 250, and which then applies the +12
volt supply potential to the multivibrator 244 by means of resistor
262. The application of the +12 volt supply potential to the
multivibrator 244 causes a square wave voltage output signal to be
applied to the base of transistor 264 which in turn is coupled to
transistor 266. Transistor 266 is alternately rendered conductive
and non-conductive thereby which momentarily returns one side of
the relay coil 170 to the negative supply buss 268. In this manner
the current reverse relay 168 is operated in a flip-flop fashion
having a frequency of operation determined by the operating
frequency of the multivibrator 244 which may be, for example, one
pulse per second.
In addition to energizing the multivibrator 244, the turn-on of SCR
250 by means of the hold-up switch 254 also couples the +12 volt
supply potential to the audio amplifier 34 in the audio
surveillance circuit by means of the diode 268 and resistor 186 in
order to provide a "listening-in" capability of the protected
premises at the central station 12. In this manner, this capability
provides an advantage in that not only can the sounds and voices
surrounding the hold-up situation be heard, but a description of
the robbers can immediately be transmitted to the central station
for relay to the police department, etc. providing greater speed in
apprehension.
A silicon controlled rectifier characteristically operates such
that when its gate electrode is selectively triggered to turn the
device "on", it will remain in an "on" condition until it is
deactivated. This is provided in the subject circuit by means of a
normally open "reset" push-button switch 270 which is coupled
across the device through capacitor 272 which charges up when the
"reset" switch 270 is closed to render the SCR 250 non-conductive.
When SCR 250 is turned "off" the hold-up circuit 26 again reverts
to its normal "stand by" state and the +12 volt supply voltage is
removed both from the multivibrator 244 and the audio amplifier
34.
Completing the description of the hold-up circuit 26, the operation
of the multivibrator 244 does not activate or turn-on the red
indicator light 30 in the perimeter-intrusion circuit 24 due to the
polarity coupling of diode 240 between the lamp 30 and one side of
the relay coil 170 which is common to the collector of transistor
266. The present embodiment of the circuitry thus described also
has for its objective an override capability over the
perimeter-intrusion circuit 24 in the event of the hold-up circuit
26 is simultaneously activated. This priority is provided by
transistor 274 coupled across the base and emitter of transistor
234 in the perimeter-intrusion circuit 24. When the +12 volt supply
voltage is applied to the multivibrator circuit 244 the +12 volts
supply potential is also applied to the base of the transistor 274
by means of circuit lead 276 and resistors 277 and 279 which will
render transistor 274 conductive and apply a virtual short circuit
across transistor 234 so that it cannot be activated and cause the
red indicator lamp 30 to be energized notwithstanding the fact that
the perimeter circuit resistance 190 has been compromised and a
control signal indicative thereof has been coupled to either
transistor 228 or 230 from the differential amplifier 200.
What has been described thus far is the circuitry contained at the
protected premises where in a normal "stand by" state the constant
current DC generator 18 shown in FIG. 2 applies a relatively minute
DC current (1.5 or 3.0 ma. ) in a predetermined polarity direction
over a two wire telephone line 16 which is preferably ungrounded,
i.e. floating, to a supervisory logic circuit 20 at the central
station 12. In the event of the compromise of the perimeter circuit
resistance 190 only, the current reversal relay 168 is actuated in
response to a control signal provided by a highly sensitive
electronic differential amplifier 200 to cause a steady state
polarity reversal of the constant current DC current in the
telephone line 16. If a hold-up for example occurs, the hold-up
circuit 26 is actuated whereupon the current reversal relay is
caused to alternate continuously at a rapid rate causing the
polarity of the DC current to switch back and forth as long as the
hold-up circuit is initiated. Additionally, the hold-up circuit
also causes the audio surveillance circuit including the microphone
36 and audio amplifier 34 to be actuated so that audio signals can
additionally be transmitted from the protected premises 10 to the
central station 12. Under certain conditions the audio surveillance
circuit can be actuated independently such as for night operation
by switch 136-B (FIG. 3) whereupon a continuous audio surveillance
can be provided over the two wire telephone lines.
Bearing the foregoing in mind, it becomes necessary that the
supervisory circuitry 14 located at the central station 12 respond
to the coded signalling respectively provided by the audio
surveillance circuit 37, the hold-up circuit 26 and the
perimeter-intrusion circuit 24. Referring now to FIGS. 4 and 5, the
other end of the two wire telephone line 16 at the central station
12 is coupled into a pair of input circuit leads 278 and 280 as
shown in FIG. 4 which are connected to the audio transformer 38
shown in FIG. 1 which is identical to the transformer 32 located in
the polarity reverse circuit 22 shown in FiG. 3. Circuit leads 278
and 280 are connected to one end of the windings 284 and 286
respectively which at this end of the communication link act as
primary windings. The opposite ends of windings 284 and 286 are
directly connected to the supervisory logic circuit 20 shown in
FiG. 5 by means of circuit leads 288 and 290. In the event that an
audio signal is sent over the two wire telephone line 16, it will
appear across winding 292 of transformer 38 which is then coupled
to a conventional transistor audio amplifier including transistors
294, 296, and 298. The audio signal is capacitively coupled from
the transformer winding 292 by means of the capacitor 300 which is
connected to a "volume" adjust potentiometer 302 which is adapted
to couple only a selected amount of the signal amplitude appearing
across transformer 292 to the amplifier. Ordinarily, any audio
signal coupled to the transformer 282 from the protected premises
10 would be amplified and heard at the central station 12 by means
of a loudspeaker 304 coupled to the common emitter connection
between transistors 296 and 298 by means of the capacitor 306.
In the embodiment shown in FIG. 4, a squelch circuit 41 is employed
to normally render the audio amplifier 40 deenergized until a
certain predetermined signal level appears across the winding 292.
The squelch circuit 41 is adapted to eliminate unwanted background
noise from being constantly monitored. This circuit consists of a
"sensitivity" potentiometer 310 coupled between one end of
transformer winding 292 and chassis ground. The slider portion of
the potentiometer 310 is capacitively coupled to a two stage
transistor amplifier including transistors 312 and 314 which has
for its objective the coupling of a triggering signal to the gate
of SCR 316 which is coupled across a +12 volt power supply
potential appearing on supply buss 317 and chassis ground, across
terminals 319 and 321, by means of the series circuit combination
of a normally closed push-button "reset" switch 318, a
semiconductor diode 320 and a yellow indicator lamp 322. A normally
unenergized supply buss 324 is coupled between the SCR 316 and the
collector of transistor 296 in the audio amplifier 40. When the
audio signal amplitude exceeds the predetermined level as set by
the potentiometer 310, SCR 316 is rendered conductive at which time
the +12 volt supply potential supplied through the "reset" switch
318 is applied simultaneously to the supply buss 324 and through
the diode 320 to the yellow indicator lamp 22. Once activated, the
squelch circuit 41 will remain in continuous operation with the
yellow indicator lamp 22 remaining "on" until such time that the
"reset" switch 318 is manually opened at the central station 12
whereupon SCR 316 will be turned "off" and the entire audio
amplifier 40 and squelch circuit 41 will revert back to a "stand
by" state.
Referring now to the supervisory logic circuit 20 shown in FIG. 5,
it is adapted to sense: (1) the instantaneous polarity, both steady
state and alternating, of the constant DC current transmitted from
the constant current DC generator 18 shown in FIG. 2, (2) the value
of the constant DC current, and (3) the intermittent or continuous
loss of constant DC current, as well as providing indications of
these three conditions by means of indicator lights and an audible
alarm. The audible or sonic alarm is provided during alarm
condition as well as for a loss of constant DC current. The
constant current circuit loop between the constant current
generator 18 in the protected premises 10 and the supervisory
circuit 14 is provided by means of circuit leads 288 and 290 being
coupled together in the logic circuit 20 through a series
connection of a "signal back" push-button switch 323 and resistors
324 and 326. DC current flow in one polarity direction produces a
voltage across resistor 324 which is adapted to cause transistors
328 and 330 to become conductive or turn "on". A current in the
opposite polarity direction, however, will not turn transistors 328
and 330 "on" due to the way in which the base and emitter
electrodes of the transistor 328 is coupled across resistor 324 by
means of resistor 332. A current in the opposite direction,
however, causes a voltage drop to occur across resistor 326 which
is of a proper polarity to turn transistors 334 and 336 "on". It is
seen then that the base and emitter electrodes of transistor 334 is
coupled across resistor 326 by means of resistor 338 in an opposite
sense to that shown with respect to transistor 328.
These transistors are powered from a 12 volt power supply potential
produced by the full wave DC rectifier bridge 340 which has 117
volt, 60Hz AC line potential applied across terminals 342 and 344
by means of the transformer 346. Terminals 348 and 350 of the
rectifier bridge constitute the +12 volt and -12 volt terminals
respectively to which supply buss leads 352 and 354 are connected.
A capacitor 356 is coupled across terminals 348 and 350 for
providing a filter action of the +12 volt DC supply voltage.
Thus when a constant DC current of a first polarity direction flows
through circuit leads 288 and 290, transistor 328 and 330 will be
rendered conductive. Transistor 330 acts substantially as a closed
switch and the 12 volt DC power supply potential appearing across
busses 52 and 354 is applied across a green indicator light 358
providing an indication of this first current polarity which by
definition is made to indicate the "normal" steady state condition
of the alarm system. Upon energization of the current reverse relay
168 (FIG. 3) as described above, being indicative of an alarm
condition, the DC constant current polarity will cause the
transistor 336 to act as a substantially closed switch and apply
the 12 volt supply voltage across a red indicator lamp 360 through
the diode 362 providing an indication of an alarm condition. The
green indicator lamp 358 meanwhile is "off" due to the fact that
transistor 330 has become non-conductive. If for example the
perimeter-intrusion circuit 24 actuates the current reverse relay
168, a continuous red indication will be provided. On the other
hand, however, if the hold-up circuit 26 actuates the current
reverse relay 168 in the alternately mode previously described both
the green and red indicator lights 358 and 360 respectively will
alternately turn "on" providing a flashing indication.
In addition to operating the red indicator lamp 360, transistor 336
is coupled to SCR 364 and relay coil 366 through the diode 368. The
purpose of this circuit is to energize a sonic alarm device 27
which is energizable through the embodiment of the subject
invention shown in FIG. 6 through the relay contacts 372. Thus both
a visual and sonic alarm is provided during an alarm condition. The
purpose of the SCR 364 is to additionally provide a memory voltage
signal to the red indicator lamp 360 after the alarm condition has
subsided. As noted before, once a silicon controlled rectifier is
triggered conductive, it will remain conductive until the circuit
is interrupted. Accordingly, SCR 364 will provide a current path
for the red indicator lamp 360 from the +12 volt supply buss 352
through a normally closed "reset" push button switch 374, a diode
376 and a resistor 378. The resistor 378 limits the voltage applied
to the indicator lamp 360 so that it will light relatively dimly as
compared to the brightness provided for the previously described
alarm condition. The dim red indicator lamp thus designates that an
alarm condition has occurred but which has subsided. Pressing the
"reset" switch 374, however, will turn SCR 364 "off" and extinguish
the dim red light 360. The circuitry surrounding SCR 364 then
merely acts as a memory circuit.
In the event that the circuit loop completing the constant DC
current flow between the protected premises 10 and the central
station 12 is interrupted for any reason, transistor 380 in
combination with diodes 382 and 384 act as a logic NAND circuit
such that transistor 380 only becomes conductive when both
transistors 330 and 336 are non-conductive. When this occurs a blue
indicator lamp 386 is turned "on" by means of +12 volt being
applied thereto through diode 388 and circuit lead 390 coupled
thereto, since when transistor 380 is made conductive it acts as a
closed switch. Additionally, the collector of transistor 380 is
coupled to the relay coil 366 by means of the diode 392 so that
when current interruption occurs, the normally open relay contacts
372 close energizing the sonic alarm device 27 as will be
subsequently explained.
A second memory circuit including SCR 394 is coupled between the
NAND circuit transistor 380 and the "reset" switch 374 to provide
an indication of current interruption after this condition no
longer exists. The blue indicator lamp 360 then is lighted whenever
an open line condition occurs such as when a "signal back" is
desired from the central station 12 to the protected premises
merely by momentarily opening the push-button switch 323 which
would then be sensed by the current relay 96 (FIG. 2) in the
constant current generator 20. A loss of current such as would
occur for a malfunction of the constant current generator 20 would
also cause the blue indicator lamp 386 to light in the supervisory
circuit 14. a shorted telephone line 16 or open lines 172, 174 and
288 and 290 for example would by be indicated b6 the blue lamp 386.
SCR 294, however, is triggered "on" by the NAND circuit transistor
380 by means of the diode 395. After the current interruption
condition subsides, however, SCR 394 still conducts and provides a
current path to the blue indicator lamp 386 through the resistor
396 and diode 398. The resistor 396 limits the current through the
blue indicator lamp 386 so that it shines dimly in the same manner
as previously described with respect to the red indicator lamp 360.
A subsequent actuation of the normally closed "reset" switch 374,
however, will cause SCR 394 to become non-conductive whereupon the
dimly lit blue indicator lamp is turned off.
Finally, a DC constant current level measuring circuit is provided
which includes transistors 400, 402 and zener diode 404 in
combination with the diodes 406 and 408 which is operative to cause
transistors 400 and 402 to become conductive whenever a
predetermined level, for example, 2.5-3.0 ma. is being transmitted
from the constant current DC generator 18 at protected premises 10.
When this condition occurs relay coil 410 becomes energized closing
the relay contacts 412 whereupon the +12 volt supply potential on
supply buss 354 is applied across a yellow indicator lamp 414.
Section A of the day-night switch 136 controls the DC current level
so as to provide a 1.5 ma. current flow during day operation and
3.0 ma. during night operation as previously explained. Therefore,
the yellow lamp 414 at the central station 12 provides indication
at the supervisory circuit 14 when lit that the system is in the
night operating mode.
The supervisory circuit 14 then provides a coded indication both
visually and audibly of the condition of the respective
perimeter-intrusion circuit 24 and the hold-up circuit 26 located
at the protected premises to which it is connected as well as the
condition of the communication link between the protected premises
and the central station. The protected premises on the other hand
is adapted to provide a visual indication of the condition of the
perimeter-intrusion circuit 24 as well as a loss or substantial
reduction of the constant DC current flowing in the communication
link including the telephone transmission lines.
Turning attention now to the subject invention and more
particularly to the preferred embodiment thereof which is shown
schematically in FiG. 6, there is disclosed a circuit which enables
a monitoring operator at the central monitor station 12 to mute the
sonic alarm device 27 any time from the moment that an alarm
condition as previously described is heard and identified by the
suitable indicator lights 28 to the time when the normal condition
is again restored. As soon as the normal operating condition is
restored, however, the circuit shown in FIG. 6 will automatically
cause the sonic alarm 27 to be sounded again to remind the operator
that he has previously muted the sonic alarm and subsequently
requiring him to manually reset the circuit in order to deactivate
the reenergized sonic alarm device 27.
Prior to considering FIG. 6 in detail, it should be observed that
the relay contacts 372 shown in FIG. 5 are adapted to apply the +12
volt supply potential appearing on buss lead 352 to terminal 373
when closed. Thus when, for example the perimeterintrusion circuit
24 is compromised, relay coil 366 will close relay contacts 372 in
a steady state mode as long as this condition exists and therefore
a continuous +12 volt signal will appear at terminal 373. If on the
other hand the hold-up circuit 26 is compromised, relay contacts
372 will be opened and closed at a relatively rapid rate (once per
second) as determined by the multivibrator 244 (FIG. 3) at which
time a pulsating +12 volt signal will appear at terminals 373. Both
the steady state and pulsating +12 volt signals constitute an input
signal to the muting circuit shown in FIG. 6 for initiating the
energization of the sonic alarm device 27. This input signal is
coupled to terminal 420 shown in FIG. 6. Additionally, a +12 volt
power supply potential is applied to terminal 422 from the squelch
circuit 41 shown in FIG. 4. More particularly, the +12 volt supply
potential applied to terminal 319 in FIG. 4 is coupled to terminal
325 through the manual "reset" switch 318. The reset switch 318 is
adapted to provide the manual reset for the muting circuit shown in
FIG. 6 as well as resetting the squelch circuit 41 as previously
explained.
The point of common reference potential illustrated as ground in
FiG. 6 is returned to circuit terminal 424 and is coupled to either
terminal 321 shown in FIG. 4 or 355 shown in FiG. 5 so that a
current return path is provided back to the negative terminal 350
of the diode bridge 340 shown in FIG. 5.
Considering now the circuitry shown in FiG. 6, first circuit means
including SCR 426 has its anode electrode directly connected to the
+12 volt supply potential applied to terminal 422 from the reset
switch 318 (FIG. 4). SCR 426 has its gate electrode coupled to
input terminal 420 by means of the diode 428 and resistor 430. The
cathode electrode of SCR 426 is returned to ground through resistor
432. Circuit junction 434 which is common to the cathode of SCR 426
and resistor 432 is coupled to the red indicator lamp 436 through
the diode 438 as well as the sonic alarm device 27 through the
diode 440 in combination with the common base transistor
configuration including transistor 442. Upon the appearance of
either the steady state or pulsing input signal (+12 volts) at
terminal 420, indicative of an alarm condition, this signal is
coupled to the gate of SCR 426 by means of diode 428 and resistor
430 which immediately becomes conductive i.e. turns "on" and
remains conductive until such time that the +12 volt power supply
potential is momentarily interrupted by means of the manual reset
switch 318 shown in FIG. 4. When SCR 426 turns "on", the +12 volt
supply potential appears at circuit junction 434 which then turns
the red indicator lamp 436 "on" as well as activating the sonic
alarm device 27. Transistor 442 merely acts as a current limiter
for the sonic alarm device 27.
If muting of the sonic alarm device 27 is desired upon the
translation of an alarm signal (either steady state or pulsating
+12 volts) to input terminal 420 second circuit means including
transistor 446 and third circuit means including a normally opened
mute switch 444 and SCR 448 is employed. In the event that a steady
state +12 input signal appears at terminal 420 it is coupled to
circuit junction 450 which is common to the cathode of SCR 446 by
means of fourth circuit means including diode 452. If on the other
hand a pulsating +12 input signal appears at terminal 420 it is
coupled to fifth circuit means including, inter alia, capacitor 454
by means of capacitor 456, resistor 458 and diode 460. The voltage
built up across capacitor 454 by the pulsating input signal is
applied to the base of transistor 462 which is one element of a
Schmitt trigger circuit including transistor 464. The Schmitt
trigger circuit is a voltage amplitude sensitive circuit such that
it is normally in a first operating state but when a voltage of a
predetermined amplitude appears at the base of transistor 462 it
switches to a second state whereupon a +12 volt output signal
appears at the collector of transistor 462. This output signal is
then coupled to the base of switch transistor 466 by means of
coupling resistor 468 which immediately becomes conductive to apply
the +12 volt supply potential at terminal 422 to circuit junction
450 by means of the diode 470. The fourth and fifth circuit means
then act to supply power to SCR 448 when a steady state and
pulsating input signal, respectively, appears at input terminal
420.
Upon depression of the mute switch 444, +12 volts applied to
terminal 445 is coupled to the gate of SCR 448 which turns "on" and
remains conductive as long as any +12 input signal indicative of an
alarm signal appears at terminal input 420. When SCR 448 turns
"on", +12 volts appears at circuit junction 472 which is common to
the cathode electrode of SCR 448 and resistor 474. The appearance
of the +12 volt potential at circuit junction 472 is coupled to the
base of transistor 446 by means of resistors 476 and 478. This
turns transistor 446 "on" which shunts the current heretofore
energizing the sonic alarm device 27 to ground due to the fact that
the collector of transistor 446 is coupled to the collector of
current limiting transistor 442 while the emitter of transistor 448
is connected directly to ground. Thus the sonic alarm 27 is
selectively muted during an alarm condition.
Upon the cessation or removal of the alarm condition and the system
returns to its normal operating state, relay contacts 372 shown in
FIG. 5 open, removing any +12 volt input signal at terminal 420.
The +12 volt potential heretofore appearing at circuit junction 450
as provided by either the fourth or fifth circuit means is removed
whereupon SCR 448 turns "off" due to the removal of power. This
also results in the turn-off of transistor 446. The non-conduction
of transistor 446 effectively removes the shunt from the sonic
alarm device 27. However, since SCR 426 is still in a conductive or
"on" state, the turn-off of transistor 448 will result in the
reapplication of the energizing current to the sonic alarm device
27 through the current limiting transistor 442 and the diode 440.
The sonic alarm 27 will then remain activated until such time that
SCR 426 is subsequently turned off by the manual resetting of the
reset switch 318.
Thus the present invention operates to sound the sonic alarm device
27 in the event of an alarm condition and provides means for muting
the sonic alarm device 27 in spite of the continuance of the alarm
condition; however the circuit will automatically operate to
reactivate the sonic alarm device 27 when the alarm condition is
removed and will remain activated until SCR 426 is turned off by
means of manually depressing the reset switch 318 in the squelch
circuit 41.
What has been shown and described, therefore, is a reliable fully
supervised bidirectional signalling system for use in alarm,
telemetry, remote control and other applications which is operable
in combination with relatively log wire circuits such as telephone
lines while utilizing extremely low currents and which will at the
same time indicate trouble and/or alarm conditions both visibly and
sonically at the introduction of foreign potential, loss of line
continuity or other detrimental circuit faults. The sonic alarm is
operated through a muting circuit which enables an operator to mute
the sonic alarm at any time from the moment the alarm is noticed to
the time when the normal condition is restored; however, as soon as
the normal condition is restored, the sonic alarm will sound again
to remind the operator to depress the reset button which will then
deactivate the sonic alarm until a new alarm condition exists.
Having thus described the present invention with what is at present
considered to be the preferred embodiment thereof,
* * * * *