US3550111A - Security alarm system - Google Patents

Description

Dec. 22, 1970 4 H. R I 3,550,111

SECURITY ALARM SYSTEM Filed m. 16, 1966 4 Sheets-Sheet 1 22 20 24 26 ALARM 1- CONTROL 4 CENTRAL TRANSMITTER STATION ,30 /34 fail ROBBERY EQUIPMENT FIGURE l r342 g l LT (344 "j; n J II n FIGURE 2 r348 "'W 0 T 350 I I F L o 352 f 0 .lllllH llllll INVENTOR. HARQLD ERVIN FIGQRE 6 Dec. 22, 1970 H. D. ERVIN SECURITY ALARM SYSTEM Filed Aug. 16, 1966 FIGURE 3 4 Sheets-Sheet 2 M l. N 4 l .I WE O 1 3 u .I N 3 D O D 7 ||||I m N E m m m m A Y S F H B U 0 R 8 T IIIII W Dec. 22, 1970 'H. D. mm 3,550,111

SECURITY ALARM SYSTEM Filed Aug. 15, 1966 4 Sheets-Sheet 5 J6 i a 238 i 1 7 -22o FF|GuRE 4 i E r I INVENTOR. il l HAROLD o. ERVIN 1970 H. D. ERVIN SECURITY ALARM SYSTEM Filed Aug. 16, 1966 4 Sheets-Sheet 4 FIRE CONTROL M 2 .y M M m U T I I A HW m m H R IH mlls 8 m FIGURE 5 v INVENTOR HAROLD D, ERVIN nited States Patent 3,550,111 SECURITY ALARM SYSTEM Harold D. Ervin, 7020 Quakertown Ave., Canoga Park, Calif. 91306 Filed Aug. 16, 1966, Ser. No. 572,767 Int. Cl. G08b 19/00 US. Cl. 340-276 9 Claims ABSTRACT OF THE DISCLOSURE A security alarm system where one ormore identifiable signals can be generated at a local station upon the happening of a predetermined occurrence at the local station, and selectively transmitted to an alarm means at the local station, and further transmitted to a central station which is responsive to the identifiable signal. System check signals can be exchanged between the local station and the central station. Where more than one signal is generated at the local station, a predetermined signal, e.g., a signal identifiable at the central station as a fire signal, takes precedence over the other generated signals. The system further limits operating current, signals the loss of circuit continuity, and permits central station monitoring of the local station.

BACKGROUND OF THE INVENTION Security alarm systems are designed to eliminate the need for continuous human surveillance of a protected building or property. An alarm is usually sounded whenever a closed circuits is broken, i.e., opened; or vice versa. Additionally, the alarm can be received as an identifiable signal at a central station if desired, usually over conventional telephone wires. While many types of security alarm systems are known and used, each alarm system has one or more features which minimize its usefulness. Among the several undesirable features are conventional relays, which are mechanical in part and can develop pitted and open contacts; excessive power requirements, particularly where an alarm is signalled at a central station over many miles of telephone line; and, damage to the system from an overloaded or short-circuit condition. Additionally, the initial cost and operating expense are prohibitive to all but the large industrial user.

OBJECTS OF THE INVENTION Accordingly, it is an object of the invention to provide a new and improved security alarm system.

Another object of the invention is to provide a security alarm system that has no relays or similar devices.

Likewise, it is an object of the invention to provide a security alarm system using reliable solid state components.

A further object of the invention is to provide a security alarm system that extends battery life.

Yet another object of the invention is to provide a security alarm system that sharply limits an operating current and can be overloaded or short circuited without damage to the system.

A further object is to provide a new and improved security alarm system that increases signal voltage without an additional power supply.

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Still another object of the invention is to provide a security alarm system that can signal a central station from a monitored premise over conventional telephone lines.

It is also an object to provide a security alarm system that generates identifiable signal pulses corresponding to the happening of dilferent unwanted occurrences at a monitored premise.

Another object is to provide a security alarm system that accepts and displays signal pulses transmitted from a local station to a central station as identifiable signals.

Still another object is to provide a security alarm system wherein one signal pulse takes precedence over all other signal pulses.

It is also an object to provide a security alarm system that enables signalling between a central station and a local station.

A further object of the invention is to provide an improved security alarm system that can accurately measure battery voltages at a monitored premise from a central station regardless of line resistance.

Another object is to provide a security alarm system that indicates loss of circuit continuity between a monitored premise and an alarm indicator.

Yet another object is to provide a security alarm system having predeterminable delayed and instantaneous detector loops.

Still another object is to provide a security alarm system that is expandable from a local station system to a central station system having one or more plug-in modules at the local station.

Yet another object is to provide a security alarm system that is expandable having low power requirements with a relatively long operating life with substantially no maintenance requirements.

Likewise, an object is to provide a security alarm system that is inexpenesive yet reliable.

SUMMARY OF THE INVENTION Briefly, in accordance with the preferred form of my invention, a new and improved security alarm system is provided wherein at least one identifiable signal is generated at a local station upon the happening of an unwanted occurrence at the local station or portion thereof being monitored, and transmitted to an alarm means at the local station which is selectively responsive to the generated signal, and further transmitted as an improved signal to a central station which is responsive to the generated signal. At least one identifiable signal that does not signal the happening of an unwanted occurrence can be generated at the local station and transmitted to the central station which is responsive thereto. In a similar manner, the local station is responsive to an identifiable signal generated at the central station. When more than one identifiable signal is generated at the local station, a predetermined signal takes precedence over other signals that can be generated. The security alarm system further limits operating current, signals the loss of circuit continuity, and permits the monitoring of an electrical power supply such as a local station battery from the central station.

Further objects, features, and the attending advantages of the present invention will be apparent when the following description is read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of the invention;

FIG. 2 is an electrical schematic of a simplified security alarm system functionally similar to the preferred security alarm system illustrated by FIGS. 3, 4 and FIG. 3 is an electrical schematic of a portion of the preferred security alarm system of the invention;

FIG. 4 is an electrical schematic of another portion of the preferred security alarm system of the invention;

FIG. 5 is an electrical schematic of another portion of the preferred security alarm system of the invention; and

FIG. 6 is a plot of several wave signals generated by the preferred security alarm system of FIGS. 3, 4 and 5.

DESCRIPTION OF THE INVENTION Referring to the drawings, and particularly to FIG. 1, a simplified block diagram of the security alarm system of my invention is shown in a specific operating arrangement. A local station alarm and control module and a local station bell and wiring protection module 22 are electrically connected in a conventional manner. The local station control module 20 is the basic module in my new and improved security alarm system. The local station control module can be used to detect an unwanted intrusion of the premises or any part thereof that is monitored, to detect a fire, to monitor equipment, and the like.

It is contemplated that the local station control module can be used with an existing local station alarm device such as an alarm bell located on the premises. It is also contemplated that the bell and wiring protection module 22 can be used with an existing local station alarm device. These will be described hereinafter in more detail.

In the preferred form of my invention, the local station control module 20 is connected to a local station alarm transmitter module 24 that is connected, preferably by conventional telephone lines, to a central station 26.

When the local station premises are monitored at a central station 26 as shown by FIG. 1, suitable detector circuits or loops in the local station control module 20 preferably monitor the local premises for the happening of an unwanted occurrence such as an intrusion, and send an identifiable signal to the central station 26 where it is accepted and displayed or otherwise indicated. Other occurrences are monitored by enlarging the simplified portion of the security alarm system, i.e., the local station control module 20 and the bell and wiring protection module 22, through one or more plug-in modules 28. The plug-in modules 28 can include, for example, fire alarm module 30, an equipment monitoring module 32, a robbery alarm module 34, and a timer module 36. It is contemplated that the station occurrences monitored by each of the plug-in modules 28, except the timer module 36, can be other than those as defined. For example, several locations at the local station could be monitored and identified by using a separate one of the modules 30, 32 and 34 for each local station monitoring position.

SIMPLIFIED ALARM SYSTEM FIG. 2 shows one circuit for a simplified alarm system functionally similar to the local station control module 20 and bell module 22. The simplified alarm system has a suitable source of electrical power such as a conventional battery 40 that is connected through a switch 42 to one or more detector means schematically illustrated as a switch 44. The detector means 44 can be a continuous conductor such as a conventional metal foil commonly used on windows for indicating an unwanted intrusion when the foil is broken. The detectorm eans 44 can also be a temperature sensitive member that opens the circuit when the temperature exceeds a predetermined limit. The detector means 44, thus, can have a variety of forms; however, it normally provides a current path that is opened with the happening of the unwanted occurrence. When the detector means 44 is opened, current from the battery no longer flows through diode 46. This allows the voltage to increase at point 48, Which causes control transistor to conduct and turn on switch transistor 52. Voltage is thus applied to a suitable indicator means such as a conventional bell 54 which signals the happening of the unwanted occurrence such as an intrusion to the premises or part thereof, a fire, and the like.

In the simplified alarm circuit of FIG. 2, the alarm bell 54 will continue to sound or ring even if the detector means 44 is again closed to complete the current path. Diode 46 is reverse biased and cannot conduct so that the bell 54 will continue to ring. Switch 42 can be used to stop the alarm bell 54 from ringing, and can also be used to deenergize the alarm circuit.

The preferred simplified alarm circuit of FIG. 2 has a meter 56 that normally indicates loop current which is an indication of the voltage in battery 40. Since the loop current passes through the circuit to the bell 54, any failure of the circuit will be reflected by a zero reading at meter 56. It is contemplated that the meter 56 can "be omitted if desired.

CONTROL MODULE Referring now to FIG. 3, the control module 20 employed in this invention comprises basically the functions of the simplified alarm as shown in FIG. 2.

A conventional source of direct current such as premises battery 60 is connected to the security alarm system of the invention through ganged switch 62 that has a first or off position 64, a second position 66 that is preferably associated with a day loop, and a third position 68 that is preferably associated with a night loop. Current from the battery 60 passes through a meter 70 that again monitors the condition of the battery. Meter 70 also indicates whether switch 62 is in either the first, second, or third positions '64, 66, *68, respectively. A rheostat 72 in series with the meter 70 adjusts the meter to read full scale or any desired scale reading.

When switch 62 is in the third position 68 as illustrated by FIG. 3, which for purposes of description will be referred to as the night position, current from the battery 60 passes through a first detector loop schematically indicated by switch 74 and through a second detector loop schematically indicated by switch 7 6. The first loop or switch 74 can be a continuous conductor such as a conventional metal foil commonly used on windows for indicating an unwanted intrusion when the foil is broken. The first loop as well as the second loop normally provide a current path that is opened with the happening of an unwanted occurrence. The second loop or switch 76 is preferably associated with windows or doors that are normally opened and closed throughout a normal business day. However at night, the locked windows and doors must be monitored to provide complete protection to the local premises. The battery current passes through the first loop 7 4 to an indicator means such as an alarm bell 7 8 in the alarm module 22. The control module 20 is generally located within the monitored premises and electrically connected by suitable conductors to the alarm module 22 that is usually located on an external wall of the premises. Thus, the conductors normally will have an exposed length, schematically indicated at 80, which is frequently accessible so that one or more of the wires could be in tentionally cut or accidentally broken.

Operatively, the first loop 74 provides an instantaneous detector loop. When the switch 62 is in the third position 68 and both the first and second loops schematically illustrated as switches 74 and respectively, are current carrying, the happening of an unwanted occurrence such as an intrusion to the monitored premises at the local station interrupts the current flow through loop 74 from the premises battery 60. This increases the applied voltage at point 82 and causes control transistor 84 to conduct and turn on switch transistor 86. Voltage is then applied from battery 60 to the alarm bell 78 in alarm module 22. The

sounding of alarm bell 78 signals the happening of the unwanted occurrence. Switch transistor 86 will continue to be turned on even if switch 74 is subsequently closed because voltage from the battery 60 is applied across resistor 87 to point 82 so that control transistor 84 is turned on until switch 62 is placed in the first or off position 64.

If the conductors to the alarm bell 78, such as at 80, are short circuited, the drive of transistor 86 is limited to protect both transistor 86 and the control module 20. The voltage drop across resistor 88 increases as the demand for load current in the short circuited conductors 80 increases. When the voltage drop reaches the threshold value of the series-connected emitter-to-base of transistor 89 and diode 90, current passes through the transistor 89 and diode 90, and then through control transistor 84 to ground. This limits the drive of transistor 86 to a predetermined value dependent upon the value of resistor 88.

The short-circuit condition for example, across the conductor wires between the control module 20 and the alarm module 22 is indicated at the local premises or station. Transistor 89 is turned-on when the threshold value of the series-connected emitter-to-base of transistor 89 and diode 90 is reached and each conducts. When transistor 89 is turned-on, voltage from the premises battery 60 is applied to a suitable indicator means such as bell or buzzer 91. This signals the short circuit condition.

The second loop 76 provides a delayed detector loop. \Vhen the switch 62 is in the third position 68 as described above, transistor 92 is turned on and has essentially equal voltages at the collector and emitter. Since the second loop 76 is preferably used for windows and doors that can be opened, the possibility occurs that a conductor switch (not shown but schematically illustrated as switch 76) on a window or a door could be opened when the window or door is momentarily opened and then closed, for example, by a gust of wind that could rattle the window or door. When the second loop is momentarily opened, transistor 92 is turned off and the collector voltage starts increasing. However, capacitor 94 begins to charge through resistor 96 and retard the rate at which the collector voltage of transistor 92 is increasing. If the second loop is closed before the collector voltage of transistor 92 reaches the threshold value of series-connected diodes 98 and 100, as would be the case if a gust of wind momentarily opened and then closed switch 76, transistor 92 will again be turned on and the collector voltage will return to a voltage essentially equal to the emitter voltage.

When the second loop 76 is opened for a period of time greater than the time delay introduced by capacitor 94, as would be the case if an intruder gained entry through a window or door, the collector voltage of transistor 92 increases to the threshold value of series-connected diodes 98 and 100 which will then conduct. Even where the switch 76 is eventually closed, battery current is applied through resistor 87 and diode 100. The applied voltage at point 82, therefore, increases and control transistor 84 conducts and turns on switch transistor 86 which energizes alarm bell 78.

When the switch 62 is in the second position 66, the first loop 74 is conducting current. However, the second loop 76 is deenergized in the preferred embodiment as illustrated by FIG. 3 because the windows and doors are usually opened and closed throughout a normal business day, for example, at the local premises. The base-temitter current of transistor 92 can not be interrupted when switch 62 is in the second position 66. Therefore, diodes 98 and 100 can not conduct and alarm bell 78 will not be energized by the second loop.

When the first loop 74 is opened during the normal business day by the happening of an unwanted occurrence, such as an intrusion to the monitored premises, the applied voltage at the base of control transistor 102 increases and causes control transistor 102 to conduct. Transistor 102 turns on transistor 89 which applies voltage from the premises battery 60 to the indicator means such as alarm bell or buzzer 91. Alarm bell 91 signals the happening of the unwanted occurrence, preferably at the control module 20. Since it is generally preferred not to signal the happening of the unwanted occurrence outside the local premises, alarm bell 78 is not energized. In the second switch position 66, control transistor 84 is not turned on and thus switch transistor 86 is not turned on. It is contemplated that both alarm 91 and alarm bell 78 can be energized if desired, although in the preferred security alarm system as illustrated, this is not possible.

The alarm bell 91 will also be energized in the second switch position 66 whenever the connecting wires between the control module 20 and the alarm module 22 are accidentally or intentionally opened; for example, by cutting one or all of the exposed wires schematically shown at by FIG. 3. The opened wires cause an increase in applied voltage at point 82 which causes control transistor 102 to conduct. The contacts and bell coil in alarm bell 78 of alarm module 22 are part of the circuit and if either the contacts or bell coil should open, transistor 102 will also conduct. Alarm bell 91 is energized in a manner similar to that described hereinbefore to signal these open circuits.

ALARM MODULE The alarm module 22 as shown by FIG. 3 not only provides an indicator means such as alarm bell 78 to selectively signal the happening of an unwanted occurrence, but also senses the continuity of the connecting wires between the control module 20 and the alarm module. Thus, if the connecting wires are accidentally or intentionally opened, the alarm bell 78 signals the open circuit.

Battery 106 is connected to alarm bell 78 through a silicon controlled rectifier (SCR) switch 108. If one or more of the exposed wires 80 are opened, SCR switch 108 is turned on and the alarm bell 78 sounds. An SCR driver transistor 110 is controlled by transistor 112 if the pair of wires 113 are broken, and by transistor 114 if the pair of wires 115 are broken. Transistors 112 and 114- are normally biased 01f; however, if any wire is broken, base current will pass through either resistor 116 or 117 and cause either transistor 112 or 114 to turn on. SCR driver transistor 110 then conducts, turns on SCR switch 108, and thereby energizes alarm bell 78. SCR switch 108 provides a self-latching feature in the alarm module 22 and, when turned on, can only be turned off by positioning switch 62 in control module 20 to an adjacent switch position.

Fuse 118 protects SCR switch 108 if the exposed wires 80 are shorted rather than opened.

TRANSMITTER MODULE Referring to FIG. 4, the transmitter module 24 is connected to the local premises battery 60 through battery lead 120, and to the control module 20 through control module leads 122, 124 and 126. In the security alarm system as illustrated, lead 128 connects the transmitter module 24 to the equipment module 32 and the robbery module 34. When the control module 20 is connected through the transmitter module 24 to the central station 26, a local alarm bell such as alarm bell 78 as shown by FIG. 3 is generally not desirable. However, it is contemplated that a local alarm bell can be used for certain occurrences to indicate the happening of an unwanted occurrence while a similar signal is transmitted from the control module through the transmitter module to the central station. For purposes of description, the voltage applied to the alarm module 22 from battery 60 as a voltage signal of the happening of an unwanted occurrence is applied through lead 122 to the transmitter module 24. A bias voltage is applied through lead 126 to the transmitter module 24.

The incoming signal voltage passes to a unijunction oscillator circuit 130 which increases the signal voltage.

The unijunction oscillator circuit 130 develops stepped voltage pulses that are fed through diode 132 and added to the signal voltage passing through diode 134 at summing point 136. Capacitor 138 has a finite decay time and can only discharge a relatively small amount before another stepped voltage pulse is developed by the unijunction oscillator circuit and passed through diode 132 to summing point 136. The voltage at summing point 136 is thus increased.

The increased signal voltage passes from the transmitter module 24 to the central station through suitable conductors such as conventional telephone wires 140 and 142. A current limiting circuit 150 in the transmitter module 24 sharply limits the current if an over-load or short circuit condition should occur in the telephone wires 140 and 142. The current limiting circuit 150 includes transistor 152, resistor 154, and diode 156 connected in a standard manner.

TRANSMITTER MODULE AND CENTRAL STATION Referring again to FIG. 4, the security alarm system of my invention enables the central station 26 to accurately measure the voltage of premises battery 60 (see FIG. 3) even when the line resistance of telephone wires 140 and 142 is great.

A current regulating circuit 160 in the transmitter module '24 cooperates with meter 162 in the central station 26. In the current regulating circuit 160, transistor 164 is forward biased by current flowing through resistor 166, through the base-to-emitter junction of transistor 164, through resistor 168, and through the base-to-emitter junction of transistor 170, to ground. A voltage divider, resistors 172 and 174, provides a voltage to the emitter of transistor 176; this voltage will decrease as the premises battery 60 ages. The voltage at the emitter of transistor 176 is compared to the voltage drop across resistor 168 and transistor 170. The voltage drop across resistor 168 is a function of the line current in telephone wires 140 and 142 which is regulated by transistor 164. If the line current should increase, the base of transistor 176 becomes more positive causing transistor 176 to conduct more heavily and reduce the base voltage of transistor 164. This holds the collector current of transistor 164 constant so that the line current is sharply regulated regardless of the line resistance of telephone wires 140 and 142, at least to approximately 25,000 ohms in one operatin g embodiment of the security alarm system.

The emitter bias voltage of transistor 176 preferably regulates the line current in telephone wires 140 and 142 t at 60 a. If the voltage of the premises battery 60 decreases, for example, from 6 volts to volts, the emitter bias voltage of transistor 176 regulates the line current at 50 ,ua. Meter 162 is preferably scaled to read ,ua. for each volt at the premises battery 60. Thus, meter 162 will read 60 ya. when the premises battery 60 is at 6 volts. Similarly, meter 162 will read ya. when the premises battery is at 5 volts. It is contemplated that other voltage ranges can be used with the security alarm system of my invention. Resistor 178 is added to the current regulating circuit 160 so that meter 162 sees 10 ,ua. for each volt. Resistor 174 is adjusted and set so that 60 a. of line current is fed to meter 162 with 6 volts at the premises battery 60.

It can be seen, therefore, that meter 162 will indicate the battery voltages of premises battery 60 so that separate service calls to check the premises battery voltage at the local station or premises are not necessary.

A signal generating circuit 180 in the transmitter module 24 generates an identifiable signal when switch 182 is closed. Current from the premises battery 60 (see FIG. 3) passes through the closed switch 182 and charges capacitor 184. Capacitor 184 will discharge through unijunction transistor 186 when the capacitor voltage exceeds the intrusion standoff ratio of the unijunction transistor.

The discharge through unijunction transistor 186 causes control transistor 188 to conduct and turn on switch transistor 190. Switch transistor 190 is turned on for a finite length of time as determined by the discharge rate of capacitor 184 through unijunction transistor 186 and control transistor 188. This finite signal pulse passes through the unijunction oscillator circuit in a manner similar to that as disclosed hereinbefore, and then to the central station over telephone wires and 142 as an identifiable signal. When capacitor 184 has discharged, switch transistor 190 is turned off and remains off until capacitor 184 again charges to the intrusion standoff ratio of the unijunction transistor 186, and the cycle repeats until switch 182 is opened.

CENTRAL STATION Referring again to FIG. 4, the increased signal voltage from the transmitter module 24, as described hereinbefore, passes through telephone wires 140 and 142 to the central station 26. The signal passes through meter 162 and through resistor 194 to turn on transistor 196. When transistor 196 is turned on, the voltage at point 198 is decreased which turns on transistors 200 and 202.

A visual indicating means such as lamp 206 is turned on when transistor 202 conducts. Lamp 206 will remain lit as long as the signal voltage is applied across transistor 196. The signal voltage across transistor 196 is limited to a predetermined voltage by diode 208 on line 204. A conventional power supply 210 which includes power inverter 212 and battery 214 provides a source of electrical power for the central station 26.

An audio indicating means such as an alarm bell 220 is energized simultaneously with the lamp 206. When transistor 202 is turned on as described above, transistor 222 conducts after a finite time delay while capacitor 224 charges. Transistor 222 turns on transistor 226 which passes a trigger pulse through diode 228 to turn on SCR 230. Current passes through SCR 230 to resistor 232 which turns on transistor 234 and thereby turns on switch transistor 236. Current is then applied through transistor 236 to the alarm bell 220.

The audio indicating means 220 is deenergized at the central station 26 by closing switch 238 which turns off SCR 230. When SCR 230 is extinguished, transistors 234 and 236 are turned off and current is no longer applied through switch transistor 236 to the alarm bell 220. However, the visual indicating means, eg lamp 206, will remain lit as long as the signal voltage from the transmitter module 24 is applied across transistor 196.

A signal from the central station 26 to the central module 20 in response, for example, to the identifiable signal generated by the signal generating circuit in the transmitter module 24, is initiated by closing ganged switch 240 in the central station. When switch 240 is closed, transistor 222 will not conduct and, therefore, the alarm bell 220 at the central station 26 is not energized. However, voltage is applied from the power supply 210 in the central station 26 over the conventional telephone wires 140 and 142 to the transmitter module 24. The voltage signal from the central station 26 experiences a relatively large voltage drop across a Zener diode 242 and resistor 244, and passes over line 124 to the control module 20 (see FIG. 3). The voltage signal causes control transistor 102 to conduct and turn on switch transistor 89. Current is applied to the alarm bell or buzzer at the local premises which completes the signal circuit from the control station 26 to the control module 20.

If the conventional telephone wires 140 and 142 are accidentally or intentionally shorted, lamp 206 is turned on to signal the shorted condition of the wires between the central station 26 and the transmitter module 24. The shorted wires draw from the power supply 210 which passes through resistor 194. As more current is applied through resistor 194, the voltage drop increases across resistor 194 and turns on transistor 250, which causes transistors 252 and thereby transistor 254 to conduct. Current from the power supply 210 is applied through transistor 254 and charges capacitor 256. Capacitor 256 will discharge through unijunction transistor 258 when the capacitor voltage exceeds the intrinsic standoff ratio of the unijunction transistor. The discharge through unijunction transistor 258 causes control transistor 260 to conduct and turn on transistors 200 and 202. Lamp 206 is thus turned on when transistor 202 conducts for a finite length of time as determined by the discharge rate of capacitor 256. When capacitor 256 has discharged, transistor 260 is turned off and remains off until capacitor 256 again charges to the intrinsic standoff ratio of the unijunction transistor 258. Alarm bell 220 is energized simultaneously with the lamp 206 as described hereinbefore.

If the conventional telephone wires 140' and 142 are accidentally or intentionally opened, transistor 248 will not conduct. However, voltage from the power supply 210 is then applied across the voltage divider network, i.e., resistors 262 and 264, and diode 266, which makes point 268 become more negative and cause transistor 254 to conduct. Lamp 206 and alarm bell 220' are energized simultaneously in a manner similar to that described hereinbefore with regard to the shorted telephone wires 140 and 142.

When a normal signal voltage from the transmitter module 24 passes through the telephone wires 140 and 142 to the central station 26 and turns on transistor 196, transistor 270 is also turned on since the voltage at control point 198 is decreased. This shorts out transistor 2 48 and prohibits the energization of lamp 206 and alarm bell 220 as described above.

FIRE MODULE Referring again to FIG. 3, a fire module 30 can be used with my security alarm system, preferably as a plugin module cooperating with the control module 20.

Temperature sensitive detectors 272 and 274 are suitably positioned at the local premises. When the temperature exceeds a predetermined limit, the particular detector closes; for example, detector 272. When detector 272 closes, the voltage applied from premises battery 60 increases at point 276 which turns on transistor 278. Transistor 278 passes a trigger pulse to turn on SCR 280 and cause control transistor 84 in the control module 20 to conduct and turn on switch transistor 86. Voltage is then applied from battery 60 to the alarm bell 78 in alarm module 22. Voltage is also applied to capacitor 282. Capacitor 282 charges and when the capacitor voltage exceeds the intrinsic standoff ratio of unijunction transistor 284, capacitor 282 discharges through the unijunction transistor to turn on transistor 286 in the control module 20. When transistor 286 conducts, control transistor 84 no longer conducts and switch transistor 86 is turned off, deenergizing alarm bell 7 8. Transistor 286 conducts for a finite length of time as determined by the discharge rate of capacitor 282 through unijunction transistor 284." When capacitor 282 has discharged, transistor 286 no longer conducts and control transistor 84 once again conducts. Transistor 286 remains off until capacitor 282 again charges to the intrinsic standotf ratio of the unijunction transistor 186. Alarm bell 78 is, therefore, energized and deenergized in a predetermined series of signal pulses to generate an identifiable signal. When a central station 26 is used with my security alarm system as described hereinbefore, the identifiable signal from the fire module 30 passes to the transmitter module 24 through lead 122 and then to the central station over telephone wires 140 and 142.

The function of transistor 286 as described hereinbefore ensures that the signal generated by fire module 30 takes precedence over a signal generated by or passed to the control module 20, for example, an unwanted intrusion to the local premises. The fire module 30 gen 10 erates a signal that is a series of alarm bell pulsations which are in direct contrast to the continuous ringing of the alarm bell for an unwanted intrusion.

ROBBERY MODULE Referring now to FIG. 5, a robbery module 34 can be used with my security alarm system, preferably as a plugin module.

An alerting switch 288 in the robbery module 34 is manually opened if a robbery occurs at the premises being monitored. This interrupts current flow from the premises battery 60 to ground through lead and transistor 290. Transistor 291 is then turned on and the emitter voltage of transistor 291 is applied to SCR 292 which fires and charges capacitor 294 until the intrinsic standoff ratio of unijunction transistor 296 is exceeded, whereupon transistor 298 conducts and turns on transistor 300. A signal pulse passes to the trasmitter module 24 for a finite length of time as determined by the discharge rates of capacitor 294 and capacitor 302. An identifiable signal is developed at the central station 26 by the charging and discharging effect of the capacitors 294 and 302.

EQUIPMENT MODULE Referring again to FIG. 5, an equipment module 32 can be used as a plug-in module where it is desirable to monitor the functioning of equipment such as laboratory furnaces, industrial freezers, and the like.

Equipment detectors such as switches 304 and 306 are suitably connected to the particular equipment that is monitored so that when there is a malfunction or the happening of a point in a lengthy cycle, switch 304, for example, is closed. It is possible with the equipment module 32 to have switch 306 open, for example, when there is a malfunction, a cycle point, and the like. Again in a manner similar to that previously described for the FIRE MODULE and the ROBBERY MODULE, a signal pulse having a finite period is developed and passes to the transmitter module 24. A series of similar pulses is generated by the equipment module 32 which are passed to the central station 26 as an identifiable signal by the transmitter module 24.

It is possible to utilize the signal generating characteristic of the previously described ROBBERY MODULE during those times when the robbery module 34 would not be used, such as after normal business hours. Additional equipment detectors such as switches 308 and 310 are again connected to the particular equipment that is monitored. The closing of switch 308, for example, will initiate the generation of a composite signal pulse by combining the signal pulse of the equipment module 32 with the signal pulse of the robbery module 34. The composite signal passes to the transmitter module 24 as previously described.

TIMER MODULE Referring again to FIG. 5, a timer module 36 can be used with my security alarm system, preferably as a plugin module. It is the purpose of the timer module 36 to limit the sounding of the local alarm 78 in the alarm module 22 (see FIG. 3) to a predetermined length of time.

When a voltage signal representing the happening of an unwanted occurrence is developed by the control module 20 (see FIG. 3), the voltage signal initiates the timing circuit 320 in the timer module 36 through lead 322. One example of a timer circuit that can be used is described and illustrated in the General Electric Transistor Manual, Seventh Edition (1964) by Figure 13.32 at page 322 and related text. After a predetermined length of time, as determined by the particular timing circuit 320, transistor 324 is turned on and current is applied through leads 326 and 328 to the control module 20. Current applied through lead 328 turns on transistor 286 in the control module 20 (see FIG. 3). When transistor 286 conducts, control transistor 84 no longer conducts and switch transistor 86 is turned oil, deenergizing alarm bell 78.

Current applied through lead 326 causes control transistor 102 in the control module 20 to conduct and turn on transistor 89 which applies voltage from the premises battery 60 to the indicator means such as alarm bell or buzzer 91.

In the preferred security alarm system as illustrated, a signal generated by fire module 30 takes precedence over a timing signal generated by the timer module 36. The fire module 30 generates a signal pulse over lead 330 that turns off transistor 324 and inhibits the passing of a timing signal over leads 326 and 328.

WAVESHAPES OF SIGNALS Referring now to FIG. 6, the waveshapes generated by the preferred security alarm system as illustrated and described hereinbefore are shown.

The control module 20 generates a continuous signal 340. The fire module 30 generates an identifiable signal 342 that is on proportionately longer than it is off. Closing switch 182 in the transmitter module 24 generates signal 344. An open or shorted wire between the transmitter module 24 and the central station 26 generates signal 346. The robbery module 34 generates signal 348. When switches 304 and 306 in the equipment module 32 are closed or opened, respectively, signal 350 is generated. When switches 308 or 310 are closed, signal 352 is generated.

The signals illustrated by FIG. 6 are displayed in the preferred security alarm system as identifiable visual signals with an alerting audio signal, until muted, at the central station 26 by lamp 206 an alarm bell or buzzer 220, respectively. It is contemplated that other Wavesignals can be generated or can be used to identify other occurrences than those previously described and designated. It is also contemplated that additional signal lamps, such as lamp 206, can be used in the central station 26 to enlrage the security alarm system. Thus, several signal generating modules, control modules, and transmitter modules could be used at premises being monitored to enlarge the possible identifiable signals that could be generated at the premises and transmitted to the central station. For example, the telephone wire at the local or monitored premises could be shorted in a coded sequence causing transistors 250 and 252 at the central station 26 to conduct. If the coded signals were removed from the collector of transistor 250 and applied to another indicator, such as a lamp similar to lamp 206, a second set of signals could be transmitted over telephone wires 140 and 142. With minor circuit modifications, a third set of coded signals could also be transmitted over the same telephone wire by opening and closing the wire in a predetermined coded sequence.

As will be evidenced from the foregoing description, certain aspects of my invention are not limited to the par ticular details as illustrated and described, and it is contemplated that other modifications and applications will occure to those skilled in the art. It is, therefore, intended that the appended claims shall cover such modifications and applications that do not depart from the true spirit and scope of the invention.

I claim:

1. A security alarm system having a central station and at least one local station, the security alarm system comprising:

(a) power supply means providing a voltage source having a determinable level,

(b) transmission means electrically connecting said local station to the central station,

(c) local station switch means electrically connected to said power supply means and to said transmission means, said local station switch means having a plurality of switch positions,

((1) central station monitor means. electrically con- 1.2. nected to said transmission means monitoring the local station,

(e) local station signal means electrically connected to said local station switch means, said local station signal means includes a detector means responsive to the happening of a predetermined occurrence at the local station and generating a first signal voltage greater than said determinable voltage level of said power supply means, and identifiable as the happening of the predetermined occurrence,

(f) said detector means includes a first detector loop means electrically connected to at least one of said plurality of switch positions provided by said local station switch means and instantaneously generates said first signal voltage, and a second detector loop means electrically connected to at least a second of said plurality of switch positions provided by said local station switch means and selectively generates said first signal voltage after a predetermined period of time,

(g) central station indicator means responsive to said first signal voltage and generating an identifiable signal corresponding to the predetermined occurrence, and

(h) central station signal means electrically connected to said transmission means responsive to a decrease in electric current in said transmission means below a predetermined current level and generating a second signal voltage,

(i) said central station indicator means further responsive to said second signal voltage and generating an identifiable signal at the central station so that the integrity of said transmission means is monitored.

2. The security alarm system of claim 1 in which said power supply means includes a local station power supply means and a central station power supply means, said central station signal means being responsive to said decrease in electric current in said transmission means from said local station power supply means.

3. The security alarm system of claim 1 in which said detector means includes a plurality of detectors separately responsive to the happening of a predetermined unwanted occurrence and generating a selected waveshape identifiable as the predetermined unwanted occurrence.

4. The security alarm system of claim 3 in which a selected one of said detectors generates a waveshape identifiable as the predetermined unwanted occurrence that takes precedence upon the mutual happening of several unwanted occurrences so that said central station indicator means is responsive only to said selected signal voltage.

5. The security alarm system of claim 1 in which said local station signal means includes a signal generating circuit means electrically connected to said transmission means and generating a fourth signal voltage identifiable as a system check signal from the local station to the central station, said central station indicator means responsive to said fourth signal voltage and generating an identifiable signal corresponding to the system-check predetermined occurrence.

6. The security alarm system of claim 1 in which said local station signal means includes a local station indicator means selectively responsive to said first signal voltage, said selective response of said local station indicator means determinable by at least said local station switch means.

7. The security alarm system of claim 6 in which said local station signal means includes a local station timer means limiting actuation of said local station indicator means to a predetermined period of time.

8. The security alarm system of claim 6 in which said local station indicator means includes a local station indicator power supply means selectively energizing said local station indicator means when said local station indicator means is electrically disconnected from said power supply means.

9. The security alarm system of claim 1 in which said local station signal means includes current regulating means converting said first signal voltage input into a proportional regulated electric current output so that accurate transmission of an analog signal over said transmission means is possible without regard to the transmission means series resistance.

References Cited UNITED STATES PATENTS Byrne 340-276 Akin 340-409 Sadler 340276X Silliman et al. 340-276X Bristol 340276X THOMAS B. HABECKER, Primary Examiner D. L. TRAFTON, Assistant Examiner US. Cl. X.R.

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