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Publication numberUS3623087 A
Publication typeGrant
Publication dateNov 23, 1971
Filing dateNov 21, 1968
Priority dateNov 21, 1968
Publication numberUS 3623087 A, US 3623087A, US-A-3623087, US3623087 A, US3623087A
InventorsGallichotte John H, Terrell Russell L
Original AssigneeMosler Safe Co
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Alarm monitoring system
US 3623087 A
Abstract  available in
Images(7)
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Claims  available in
Description  (OCR text may contain errors)

United States Patent [72] Inventors John H. Galllchotte Newtown; Russell L. Terrell, New Milford, both of Conn. [211 App]. No. 777,726 [22] Filed Nov. 21,1968 [45] Patented Nov. 23, 1971 [73] Assignee The Mosler Safe Company Hamilton, Ohio [54] ALARM MONITORING SYSTEM 12 Claims, 10 Drawing Figs.

[52] US. Cl 340/412, 340/2 I 3, 340/285 [51] Int. Cl ..G08b 19/00 [50] Field of Search 340/412, 164, 147, 213.1, 213, 215, 253, 255, 256, 285, 292,181, 220, 276; 317/7, 235 324/51 [56] References Cited UNlTED STATES PATENTS 3,174,143 3/1965 Akin 340/276 2,821,639 1/1958 Bright et al. 317/7 X 3,029,421 4/1962 Beguin 340/213.1 3,470,554 9/1969 Corbell 340/213 X OTHER REFERENCES Millman, J. & Taub, H. Pulse, Digital, and Switching Waveforms N.Y., McGraw-Hill Book Co., 1965, p. 650, Diagram 17- 24 (d). Tk 7835 M55P Lytel, A. ABC 5 of Silicon Controlled Rectifiers N.Y., Howard W. Sams & Co., lnc., 1965, p. 45, Diagram A. Tk2798Lg Primary Examiner-John W. Caldwell Assistant Examiner-Glen R. Swann, lll Attorney-Wood, Herron & Evans ABSTRACT: An alarm-monitoring system including a central station having a plurality of fire alarm indicating and control panels and a plurality of security alarm indicating and control panels, each panel having a plurality of zone sections individually responsive to a remote located alarm-condition responsive device or termination unit. Each zone section includes a sensor which generates an alarm signal at the central station when its associated fire or police alarm condition responsive device detects a fire or police alarm condition at its associated remote protected premise. Each zone section also includes an alarm condition storage device for storing the fact that an alarm condition has occurred, and an alarm condition indicator responsive to the storage device for providing an intermittent visual indication when an alarm condition occurs. Each zone section further includes a sensor for detecting circuit faults at its associated alarm condition responsive device or termination unit, a storage device for storing the fact that a circuit fault has occurred, and a circuit fault indicator for providing an intermittent indication of the detection of such a circuit fault. Each fire and security panel includes means for converting an intermittent indicating alarm signal to a continuous indicating signal. The signal-converting means of each panel is common to all zones of the panel. Each of the zones also includes a printer interface capable of generating, each time one of the zone storage devices changes state, a binary signal indicating the nature of the change and the identity of the zone. Associated with all of the panels and common to each of them is a printer which provides, in response to successive changes in the status of the zones, successive printed records reflecting the nature of the status change, the time and date there0f,'and the identity of the zone in which the status change occurs.

PATENTEmmv 23 mm SHEET 7 BF 7 -l- Hz BACKGROUND OF THE INVENTION This invention relates to systems which monitor, from a central station, a number of remotely located condition-responsive alarm reporting devices, and which, in response to the occurrence of an alarm condition at one or more of the remote locations, provide visual and/or audible alarm indications at the central station.

The alarm-monitoring systems of the general type to which this invention relates typically include a plurality of remotely located protected premises, and a central station to which it is desired to report the occurrence of alarm conditions at the remote stations. Each remote station includes an alarm condition responsive device. The alarm conditions responsive device, in the case of security reporting, may take the form of an intrusion switch or tamper switch. Such a switch is adapted to change between open circuit and closed circuit states in response to the occurrence of an alarm condition at the protected premise. Alternatively, the alarm condition responsive device may take the form of a thermal switch, as would be appropriate for fire reporting. in such case, the switch is adapted to change between open circuit and closed circuit states in response to an occurrence of a fire at the protected premise. In a typical system the alarm condition responsive devices are connected by wires to central station monitoring equipment which detects changes in the states of the remotely located condition responsive devices, and in response to such changes provides provides some form of indication for advising central station operating personnel that the alarm responsive device at a given remote station has gone into an alarm state.

The alarm-monitoring systems heretofore proposed have exhibited, from both an operational and structural viewpoint, a number of disadvantages. For example, the systems proposed have not provided a permanent and complete record of the activities of the alarm devices and their associated alarm indicators. Permanent and complete records of this type are useful in evaluating the effectiveness of the system insofar as the detection and reporting of alarm conditions is concerned, as well as in evaluating the efiectiveness ofthe personnel charged with responding and remedying the alarm conditions as they are detected and reported.

The previously proposed systems have also not been capable of detecting, transmitting and indicating, in addition to the fire or security alarm condition, a wide range of circuit fault conditions which in practice often occur at the remote station, such as open circuits, short circuits, grounding, and the like. Where circuit fault sensing and reporting capability has existed in the proposed systems, the capability has been limited, and in no case accomplished with equipment which is simple in design and operation.

Another disadvantage of the proposals made in the past is that they have provided no simple and convenient method of selectively disabling an alarm condition responsive device, such as an intrusion switch, from the central station. in prac tice, it is frequently desirable to periodically disable an intrusion switch, to permitfree access to a premise protected without the report and indication of an intrusion to the central station, and yet not disable other types of security devices such as tamper switches. For example, in a department store, it is desirable to disable, from a central location, the intrusion switches protecting store entrances during periods that the store is open for business without disabling the tamper switches which protect the equipment from compromise during the period the intrusion switch is disabled, The systems which have been proposed heretofore have not permitted such selective intrusion switch control from the central station with any degree of simplicity and still permit monitoring of other security-responsive devices, such as tampering switches, which may not be disabled.

Many of the proposed monitoring systems have also required, for ill intents and purposes, two separate monitoring systems where two different types of conditions, such as fires and intrusions, are to be detected and reported. The reporting and indicating equipment associated with one type of alarm condition responsive device, such as the fire-detecting thermal switch, has not been compatible with the other type of indicating and reporting equipment such as that designed for detecting intrusions. This absence of compatibility between the two types of indicating and reporting equipment has not resulted in an optimum reduction in the number and styles of components needed in a multiple alarm-type system.

SUMMARY OF THE INVENTION It has been a fundamental objective of this invention to provide an alarm-monitoring system which is capable of reporting and indicating the status of a large number of alarm responsive devices, not all of the same type, which eliminates the disadvantages or the proposals outlined above. This objective has been accomplished in accordance with various principles of this invention by providing a unique system which includes a control console located at a central station which monitors a plurality of fire and security condition responsive devices or termination units respectively associated with different remotely located zones or premises. Incorporated in the control console are at least one fire panel and one security panel, each of which includes a plurality of zone sections individually responsive to different alarm condition responsive devices located at difi'erent remote premises or zones.

Each fire panel includes a plurality of fire zone sections each associated with a different remotely located fire responsive device, that is, with a fire responsive device located in a different remote zone. Preferably, the remotely located fire responsive device takes the form of thermal switches adapted to switch from an open circuit to a closed circuit condition in response to a fire at the protected premise or zone.

Each security panel includes a plurality of security zone sections each associated with a different remotely located security responsive device, that is, with a security device located in a different remote zone. The remotely located security responsive devices, in a preferred form, are tamper and/or intrusion switches associated with doors, windows, and the like, which are adapted to switch between open circuit and closed circuit conditions in response to tampering and/or unauthorized intrusion through the protected door, window, etc., at the protected premise or zone.

The fire zone sections of each fire panel are connected to their associated remotely located fire responsive devices by two pairs of wires or lines, the wires of each pair having a remote station end and a central station end. Each pair of wires has its remote ends connected together, the connected ends of the pairs being coupled to different sides of the normally open fire-responsive thermal switch. At the central station one line of each pair is connected to a different side of a fire-sensing resistor, while the other line of each pair is capaci-- tively coupled to both an AC source and a DC source, with one of the lines being coupled to the DC source via a circuit fault sensing resistor.

Each central station fire zone section includes a fire sensor. The fire sensor monitors the AC potential across its associated fire resistor. Should this AC potential drop to zero, as occurs when the the fire resistor is short circuited by closure of the thermal switch in response to a fire at its associated remote premise, an alarm signal is provided at the output of the fire sensor, herein termed the fire-sensing point. A fire storage device, preferably a bistable multivibrator, is responsive to the fire alarm sensing point and, in response to an alarm signal at the fire alarm sensing point, switches to store the fact that a fire has been detected at the remote premise and reported to the central station. The fire storage device once switched in response to a fire alarm signal at the fire alarm sensing point, does not automatically reset when the alarm signal at the firesensing circuit disappears in response to termination of the fire alarm condition at the protected premise.

Each fire zone section also includes a circuit fault sensor. The circuit sensor monitors the DC potential across the circuit fault resistor. Should this potential drop, as occurs when one line of a pair is grounded or open circuited, a circuit fault signal is provided at the output of the circuit fault sensor. herein termed the circuit fault sensing point. A circuit fault alarm storage device, preferably a bistable multivibrator, is responsive to the circuit fault sensing point, and in response to an alarm signal thereat, switches to store the fact that a circuit fault has been detected. The circuit fault storage device, once switched in response to a circuit fault alarm signal at the circuit fault sensing point, does not automatically reset upon termination of the circuit fault signal when the circuit fault condition no longer exists.

Coupled to the fire alarm and circuit fault alarm storage devices are fire alarm and circuit fault alarm indicators. The fire alarm and circuit fault indicators each provide an intermittent visual signal and an audible signal when a fire alarm and a circuit fault alarm condition occur, respectively. Associated with the fire panel and common to all the fire zone sections thereof is a silencer. The panel silencer, when actuated, converts existing intermittent visual signals to continuous visual signals, and terminates any audible signals.

A manually actuated reset circuit is included in each fire zone section to reset the fire and circuit fault storage devices. The fire and circuit fault sensors provide an inhibit input to the reset circuit when either a fire or circuit fault exists, preventing resetting of the fire and circuit fault storage devices should a fire or circuit fault, as the case may be, still exist when the reset circuit is actuated.

A printer interface is also included in each fire zone section. The printer interface provides, in response to changes in state of the tire and circuit fault storage devices, a binary output identifying the zone and the nature of the change, that is, setting or resetting of the fire or circuit fault storage device. The output of the printer interface of each fire panel is input to a high-speed printer. The printer is common to all fire zone sections, as well as to all security zone sections.

The security zone sections of each security panel are connected via a pair of wires, to their associated remotely located termination units, in this case, to security responsive devices such as tamper or intrusion switches. in a preferred form, the security termination unit includes a resistor, and a normally closed intrusion switch shunting the resistor which is adapted to open circuit, placing the resistor in series with the pair of wires, in response to an intrusion. The security termination unit also includes an electrical polarity responsive switch connected across the wires in parallel with the intrusion switch. The polarity responsive switch changes between open circuit and closed circuit conditions in response to polarity reversals of the wires, alternatively enabling and disabling the intrusion switch. When he intrusion switch is disabled and enabled, the security zone section is respectively in the access and secure mode. in the access mode, wherein the intrusion switch is shunted by the polarity responsive switch, free entry through an area otherwise protected by the intrusion switch is possible without altering the resistance of the security termination unit. in the secure mode, wherein the intrusion switch is not shunted by the polarity responsive switch, an unauthorized entry into a protected area opens the normally closed intrusion switch, placing the resistor in series circuit with the wires, and thereby altering the resistance of the termination unit.

The security zone section, which is connected to the remotely located security termination unit by a pair of wires, monitors the resistance of the remote unit to provide an alarm if it changes, and controls the state of the polarity responsive switch to change the system between the access and secure mode. To accomplish these functions the security zone section includes a balanced DC bridge having connected in one leg thereof, via a bipolar switch operable to change the system mode, the security termination unit. Police alarm sensing circuitry responsive to the bridge balance condition provides a police alarm signal at a police alarm sensing point when the resistance is altered a predetermined amount due to an intrusion or tampering occuring when the system is in the secure mode. Responsive to the police alarm sensing point is a police alarm storage device, preferably a bistable multivibrator, which switches to store the fact that a police alarm condition, such as an intrusion or tampering, has occurred. The police alarm storage device does not automatically reset when the police alarm condition terminates.

A circuit fault sensor also responsive to the bridge balance condition is provided. The circuit fault sensor in response to increases or decreases in resistance of the security termination unit of magnitude other ethan that which accompanies an intrusion, such as resistance changes occasioned by open circuits or short circuits in the lines, provides a circuit fault alarm signal at its output, herein termed the circuit fault sensing point. A circuit fault storage device, preferably a bistable multivibrator, is connected to the circuit fault sensing point, and in response to a circuit fault alarm signal switches to store the fact that a circuit fault has occurred. Like the police alarm storage device, the circuit fault storage device does not automatically reset upon termination of the circuit fault condition.

To prevent switching of the police alarm storage device as a consequence of large increases in resistance of the security termination unit characteristic of circuit fault alarm conditions, the circuit fault sensing point is connected to the police alarm storage device. By reason of such connection, the circuit fault sensor inhibits switching of the police alarm storage device from its normal nonalarm condition when a circuit fault alarm signal is present.

A manually actuated reset circuit is connected to both the police alarm storage device and the circuit fault alarm storage device for resetting these storage devices. The reset circuit is connected to the police alarm sensing point and the circuit fault sensing point to inhibit operation of the reset circuit should an attempt be made to reset either or both of the storage devices when the alarm condition giving rise to the switched condition of the storage device still exists.

Each security zone section includes a printer interface which is responsive to both the police alarm and the circuit fault alarm storage devices. The security zone section printer interface provides a binary signal output each time the condition of the police alarm or circuit fault alarm storage device changes. The binary output identifies the nature of the change, that is setting or resetting of the police alarm or circuit fault alarm storage device, as well as identifies the zone in which the change occurs.

Also, responsive to the circuit fault and police alarm storage devices are police alarm and circuit fault indicators which, upon the occurrence of a police alarm or circuit fault condition, each provide an intermittent visual signal and an audible signal. Each security panel includes a silencer which is common to all the security zones of the security panel. The silencer, when actuated, changes intermittent police alarm or circuit fault visual signals to continuous visual signals, and terminates existing audible alarms.

The system printer, which is connected to the outputs of the printer interface of each fire zone section and each security zone section, includes time and date imprinting means, zone identification imprinting means, and zone alarm status change imprinting means. These imprinting means provide a printed record of the time and date of a zone status change, the nature of the zone status change, such as the occurrence of an alarm or the resetting of an alarm storage device, and the identity of the zone experiencing the status change.

The system of this invention provides a number of vary unobvious advantages. For example, the capability of a security responsive device, such as an intrusion switch, to transmit an alarm when entry is made into a protected premise can be controlled from a central monitoring station, thereby enabling the security responsive device to be selectively placed in an enabled or disabled condition. This result has been accomplished by providing a polarity responsive switch in parallel with the security responsive intrusion switch. The polarity responsive switch can be selectively placed in an open circuit or a closed circuit condition to selectively enable or disable the security responsive switch, respectively. By reason of the polarity responsive nature of the selective enabling and disabling switch, the state of the switch and, hence the capability of the intrusion switch to respond to an entry into the protected premise, can be controlled extraordinarily easily. Specifically, by merely reversing, via a bipolar switch, the interconnection of the lines connecting the security termination unit and its associated security zone monitoring section, the polarity responsive switch can be actuated and the operational mode changed between access and intrusion. Thus, by reversing the connection of the lines, the polarity responsive switch is changed between open circuit and closed circuit conditions, in turn enabling and disabling the security responsive device.

Another advantage of this system is that the fire termination unit permits simultaneous and independent detection of both circuit alarm conditions and fire alarm conditions at the protected premise. This result has been accomplished in a very simple manner by energizing the fire termination unit with both AC and DC potential. The AC potential provides an AC voltage across the fire-sensing resistor which can be monitored to detect the occurrence of a fire alarm condition. The DC potential provides a DC voltage across the circuit fault sensing resistor which can be monitored to detect the occurrence of a circuit fault, such as an open circuit or a short circuit condition at the termination unit.

The system is capable of reporting a fire alarm condition to the central station even though the wires interconnecting the central station and remotely located fire condition responsive device are partially severed. For example, the system is capable of reporting a fire alarm condition when a single ground and/or a single open circuit condition exists in the wires connecting the remote and central stations. Furthermore, under certain conditions, multiple open and short circuit conditions do not prevent reporting a fire alarm condition.

A further and very important advantage of this invention is that it provides with a single printer, successive printed records of successive changes in status of a large number of fire and security zone monitoring sections. These records identify the nature of the status change such as a fire or police alarm or a reset, the time and date of the change, and the identity of the zone in which the status change occurred. Such records enable the activity of a large number of security responsive and fire-responsive devices to be permanently and completely recorded, facilitating future evaluations and effectiveness studies.

Another important feature of this invention is the use of bistable storage devices which switch in response to an alarm condition for storing the fact that an alarm has occurred, but which are incapable of being reset so long as the alarm condition which caused the storage device to be switched in the first instance still exists. With a bistable storage device which can not be reset until the alarm condition which caused it to switch terminates, successive reactivations of the alarm, and consequently, successive printed records of status changes, do not occur should an attempt be made to prematurely reset the storage device.

Another advantage of this invention is that a single silencer can be utilized per panel to change the flashing nature of a visual signal to a continuous signal. Thus, only a single silence switch need be provided for controlling a plurality of zone section indicators. Thus, duplication of components of a multiunit system is minimized.

BRIEF DESCRIPTION OF THE DRAWINGS Other objectives and advantages of this invention will be more readily apparent from a detailed description of the invention taken in conjunction with the accompanying drawings in which:

FIG. 1 is a perspective view of a central station console suitable for monitoring and controlling a plurality of fire and security termination units associated with and located in remotely located zones or protected premises.

FIG. 2 is a segment of the printed record provided by the console of FIG. 1 showing successive printed records of successive status changes in certain zone monitoring sections.

FIG. 3 is a perspective view of a fire control section showing the various indicators and control means associated therewith.

FIG. 4 is a perspective view of a security control panel showing the various indicators and control means associated therewith.

FIG. 5 is a schematic circuit diagram of a system having a plurality of security and fire termination units, a plurality of associated security and fire zone sections, and a common printer. I

FIGS. 60 and 6b are schematic circuit diagrams of the security tennination unit and security zone section.

FIGS. 7g and 7b are schematic circuit diagrams of the fire termination unit and security zone section.

FIG. 8 is a schematic circuit diagram of an alternate form of security termination unit.

DESCRIPTION OF THE PREFERRED EMBODIMENT With reference to FIG. 1, the system is seen to include a control console I, which is located at a central station, having a plurality of alarm-indicating and control panels 2. The alarm indicating and control panels 2 include fire indicating and control panels 3 and security indicating and control panels 4, as shown more particularly in FIGS. 3 and 4, respectively. Each alarm indicating and control panel 2 includes a plurality of zone sections 5 each uniquely associated with a different remotely located fire or security termination unit to be described. Each of the zone sections 5 of an indicating and control panel 2, if the panel is of the fire alarm type depicted in FIG. 3, is adapted to indicate and control the state of a fireresponsive device, such as a thermal switch, located at the remote location or zone with which the zone section is associated. Each of the zone sections 5 of the indicating and control panel 2, if the panel is of the security type depicted in FIG. 4, is adapted to indicate and control the condition of a security device, such as a tamper switch or intrusion switch, located at the remote station or zone with which the zone section is associated. The zones 5 of the indicating and control panels 2 are also operative to provide indications of the occurrence of circuit fault alarms, such as open circuit conditions and short circuit conditions, occurring in the remotely located fire or security termination unit with which the zone is associated. Also located at the central station and forming part of the console l is a high-speed printer 6. The printer 6 is responsive to the zones 5 of the indicating and control panels 2 for providing a printed record (see FIG. 2) of the type, time and date of the occurrence of alarm conditions, such as fires, intrusions, tampering or circuit faults, and the identity of the particular zone in which the alann condition is present.

The fire indicating and control panel 3, as shown more particularly in FIG. 3, includes l5 fire zone sections 3-1, 32...3- 15; each associated with a different fire responsive device, such as a thermal switch, located at a remote premise. The fire zone sections 3-1 to 3-15 each include a fire indicator 390-1 to 390-15, such as a lamp, which becomes intermittently illuminated upon the detection of a fire by the fire responsive device or termination unit with which the fire zone section is associated. Each of the fire zone sections 3-1 to 3-15 also includes a circuit fault indicating device 400-1 to 400-15 adapted to become intermittently illuminated upon the detection of a circuit fault, such as a short circuit or open circuit, at the fire-responsive device or termination unit with which the fire zone section is associated. Additionally, each fire zone section 3-] to 3-15 includes a reset switch 383-1 to 383-- 15 which, upon actuation is adapted to reset the zone section should the alarm condition, whether it be'a fire alarm or a circuit fault alarm, no longer exist. A test swltch 444, 445 is also included in each fire zone section 3-1 to 3-15 for simulating a fire alarm condition, and thereby testing the fire alarm indicating lamps 390-1 to 390-15. Associated with each fire control panel 3 is a single lamp test switch 405, common to all zones 3-1 to 3-15, which upon actuation illuminates the lamp 390-1 to 390-15 and 400-1 to 400-15 of each zone. Also associated with each fire panel 3, and common to all zones 3-1 to 3-15, is a silence switch 396, 413 which upon actuation is adapted to change an intermittently flashing lamp 390 or 400 to a continuously illuminated state.

The security indicating and control panels 4 include a plur'ality of security zone sections 4-1, 4-2...4-15, each associated with a different remotely located security responsive device or termination unit, such as a tamper switch, intrusion switch, or the like. The security zone sections 4-1 to 4-15 each include a police lamp 215 adapted to flash in response to the sensing of a police alarm condition, such as an intrusion or tempering, by the security termination unit with which the zone section is associated. Also included in each security zone section 4-1 to 4-15 is a circuit fault indicator lamp 210 which, like the police alarm indicator 215, is adapted to become intermittently energized upon the sensing of a circuit fault condition at the security termination unit with which the security zone section is associated.

To change the status of the remotely located security device, such as an intrusion switch, between disabled and enabled conditions, each security zone panel 4-1 to 4-15 is provided with mode switches 151-1 to 151-15. Actuation of the mode switch 151-1 to 151-15 changes the condition of the termination unit. Each security zone section 4-1 to 4-15 includes a secure lamp 200-1 to 200-15 and an access lamp 205-1 to 205-15 which are illuminated alternatively to indicate whether the remotely located security device, such as an intrusion responsive switch, associated with each zone section, is disabled or enabled, respectively. Reset switches 234-1 to 234-15 are included in each of the security zone sections 4-1 to 4-15. Upon actuation, these reset switches function to reset the zone section 4-1 to 4-15 providing the alarm condition, whether it be a police alarm or a circuit fault alarm, no longer exists.

Associated with each security control panel 4 and common to all the'zone sections 4-1 to 4-15 is a silence switch 231, 219 which upon actuation changes an intermittently flashing plice alarm lamp 215 or a circuit fault lamp 210 to a continuously energized condition. Also associated with each security control panel 4 and common to all the lamps 215-l to 214-15, 210-1 to 210-15, 205-1 to 205-15, and 200-1 to 200- of each panel is a lamp test switch 225 which upon actuation momentarily energizes all lamps in the security control panel 4.

The system, considered in more detail and with reference to FIG. 5, includes a plurality of security indicating and control panels 4, only one of which is shown, each including a plurality of security zone sections 4-1 to 4-15 individually responsive to a remotely located security termination unit 100-1 to 100-15, and a plurality of tire indicating and control panels 3, only one of which is shown, each including a plurality of fire zone sections 13-! to 3-15 individually responsive to remotely located fire termination units 300-] to 300-15. A printer 6 is responsive to each of the security zone sections 4-1 to 4-15 and to each of the fire zone sections 3-1 to 3-15.

The security termination unit 100 includes resistance means 105 shunted by a normally closed switch 108, such as an intrusion switch. Connected in parallel with the intrusion switch 108 is a polarity responsive switch 106 adapted to disable the switch 108 when in its closed position, herein termed the access" mode, and enable the switch 108 when in its open position, herein termed the secure mode.

Each security zone panel 4-1 to 4-15 includes a balanced DC bridge 110, having one leg DC thereof connected, via a bipolar switch 122, 127, 128 and 130, to its associated security termination unit 100. Responsive to the balance condition of the bridge H00 is a police and circuit fault sensor 160, 161 and 162 adapted to provide inputs to a security or police alarm storage device and a circuit fault storage device upon occurrence of police and circuit fault alarm conditions, respectively, for storing information indicative of the occurrence of a police alarm condition or a circuit fault alarm condition. By reason of a connection between the police sensing portion of the sensor 160, 161 and 162 and the circuit fault storage device 185, no information is stored in the circuit fault storage device 185 if a circuit fault occurs simultaneously with a police alarm condition.

Responsive to the police storage and circuit fault storage devices 170 and 185 are police alarm and circuit fault indicators 215 and 210, respectively, which provide intermittent visual and audible indications upon the occurrence of police and circuit fault conditions at the security termination unit 100. Also responsive to the police alarm and circuit fault storage devices 170 and 185 is a printer interface 240 adapted to provide a binary coded input to the printer 6 representing the type of alarm condition occurring in the security termination unit 100, as well as the zone in which the alarm condition occurred.

A reset circuit 182 is also provided which is responsive to momentary closure of a reset switch 234 for resetting the police alarm and circuit fault storage devices 170 and 185. A mode control circuit 134 responsive to momentary closure of a mode switch 151 is provided for actuating the bipolar switch 122, 127, 128, and 130, and thereby reversing the interconnection of the security termination unit 100 and corners D and C of the bridge 110, to switch the zone between secure and access states.

Associated with the indicators 215 and 210 of security zone sections 4-1 to 4-15 is a silence switch 231, 219 for terminating an audible alarm indication and changing, upon actuation, an intermittent visual alarm indication to a continuous visual alarm indication.

The fire termination unit 300 includes a normally open switch 303, such as a thermal switch, which in response to a tire alarm condition in the zone is operative to close and thereby short circuit lines 305 and 306 interconnecting the fire termination unit 300 and its associated fire zone section 3-1. The fire zone sections 3-1 to 3-15 each include a fire sensor 335 and a circuit fault sensor 360. The tire sensor 355 in response to short circuiting of the lines 305 and 306 provides an output to a tire alarm storage device 345 for storing information indicating the existence of a fire alarm condition in the zone. The circuit fault alarm sensor 360 is responsive to the existence of a circuit fault, such as an open circuit, short circuit or grounding of the lines 305 and 306, for providing an output to a circuit fault storage device 370 representing the existence of a circuit fault in the zone. Associated with the fire alarm and circuit fault storage devices 345 and 370 are fire alarm and circuit fault indicators 390 and 400 which provide, upon the occurrence of a fire or circuit fault, intermittent visual and audible alarm indications. A reset circuit 351, 385 responsive to momentary closure of reset switch 383 is provided to reset the fire alarm and circuit storage devices 345 and 370 providing the tire alarm and circuit fault alarm conditions no longer exist. A printer interface 415 is also provided for providing to the printer 6 a binary coded signal indicating the type of alarm condition occurring, and the zone in which the alarm condition occurs. Associated with the indicators 390-1 to 390-15 and 400-1 to 400-15 of the tire zone sections 3-1 to 3-15 is a silence switch 396, 413 for terminating an audible alarm indication and changing an intermittent visual alarm indication to a continuous visual alarm indication.

SECURITY TERMINATION UNIT The security termination unit 100 includes a pair of terminals 101 and 102 connected to one side of resistors 103 and 104, respectively, the other sides of which are connected to opposite sides of a resistor 105. Resistor 105, for reasons to be described later, is adapted to be selectively short-circuited by a transistor switch 106 which is biased through a resistor 107 connected between the transistor base and terminal 101. A normally closed intrusion switch 108 is connected in shunt with resistor 105. The intrusion switch 108 may take a variety of forms, for example, a magnetic reed switch which is adapted to open should an unauthorized entry be made through a protected, normally closed door. A normally closed tamper switch 109 is connected in shunt with the resistor 104. The tamper switch 109 may also take a variety of forms, for example, a strip of conducting foil placed on a protected window which is adapted to be broken, and thereby electrically interrupted, should an unauthorized entry be made through the protected window.

in the absence of intrusion and tamper conditions, resistors 105 and 104 are shunted by normally closed intrusion and tamper switches 108 and 109, respectively, and accordingly, the effective resistance of the security termination unit 100 is determined by the resistance of resistor 103. intrusions and tampering, as well as circuit faults such as open circuits or high impedance conditions approaching an open circuit and short circuits or low impedance conditions approaching a short circuit in the security termination unit 100 cause the resistance of unit 100 to change from that set by the resistance of resistor 103. Such changes in resistance are sensed by a balanced DC bridge to be described. Should the normally closed tamper switch 109 be opened as, for example, by an unauthorized entry through a protected window, the resistance of the security termination unit 100 is modified by the inclusion therein of the resistor 104 in series with the resistor 103. Opening of the intrusion switch 108 as, for example, by an unauthorized entry through a protected door, may or may not, depending upon the conductive state of the transistor 106 vary the resistance of the security termination unit 100. If the transistor switch 106 is in its conducting condition, herein defined as the access" mode, the resistor 105 is shunted. With the resistor 105 shunted, opening of the intrusion switch 108 is ineffective to alter the resistance of the security termination' unit 100. Accordingly, when the security termination unit .100 is in the access mode, the entry means protected by the intrusion switch 108 may be used without altering the resistance of the security termination unit 100. When the transistor switch 106 is in the nonconducting state, herein termed the secure mode, resistor 105 is short circuited by only the normally closed intrusion switch 108. Accordingly, should an unauthorized entry be made through the entry means protected by the intrusion switch 108, the intrusion switch is opened placing the resistor 105 in series with resistor 103 thereby altering the resistance of the security termination unit 100.

The mode in which the security termination unit 100 is operated, as indicated, depends upon the state of conduction of transistor switch 106. Control of the state of conduction of transistor switch 106, and, hence, control of the mode of operation of the security termination unit 100, is effected by reversing the polarity of terminals 101 and 102. When terminals 101 and 102 are positive and negative, respectively, the security termination unit 100 is placed in the access mode with the transistor 106 conducting, the resistor 105 short circuited. With the polarity of terminals 101 and 102 negative and positive, respectively, the security tennination unit 100 is in the secure mode with the transistor switch 106 in a nonshunting relation to the resistor 105.

BALANCED DC BRIDGE The balanced DC bridge 110 has four vertices designated A, B, C, and D which respectively define fixed resistance legs AB, BC, and AD and a variable resistance leg DC in which is connected the security termination unit 100 in a manner to be described in detail hereafter, Across vertices A and B is connected a source of regulated DC voltage which includes a resistor 114 connected between point A and positive line 115, and a Zener diode 113 having its cathode connected to point A and its anode connected to point C which is grounded via a line 112. Vertex points D and B constitute the tap points of the bridge and under normal or nonalarm conditions are at the same voltage. By normal" or nonalarm is meant the absence, in the termination unit 100, of intrusions, tamperings, or circuit faults such as open circuits or short circuits.

Considering the bridge 110 in more detail, leg AB is seen to include a resistor 116 and a resistor 117. Leg BC includes a resistor 118 and a resistor 119. Resistor 117 and resistor 118 are of equal value and in combination with a diode 120 shunting resistors 117 and 118 constitutes a center tap voltage divider with bridge vertex point B at the center thereof. Bridge leg AD includes resistor 111 which can be varied in value to balance the bridge, that is, to equalize the voltage at bridge tap point D and B.

Variable resistance bridge leg DC includes two parallel circuit paths, each of which incorporates the security termination unit 100. The first circuit path, herein termed the access" path, includes the emitter-collector path of a transistor switch 122, a resistor 123, line terminal 124, the security termination unit 100, line terminal 125, a resistor 126, and the emitter-collector path of a transistor switch 127. The access circuit path, which includes the security termination unit 100, is connected between bridge vertex points A and C by rendering conductive transistor switches 122 and 127 in a manner to be described.

The other variable resistance circuit path connected between bridge vertex points A and C, herein termed the secure" path, includes the emitter-collector path of a transistor switch 128, the resistor 126, the line terminal 125, the security tennination unit 100, line terminal 124, resistor 123, and the emitter-collector path of a transistor switch 130. The secure path is connected between bridge vertex points A and C by rendering conductive the transistors 128 and 130 in a manner to be described.

Transistor switches 122 and 127 in the access path and transistor switches 128 and 130 in the secure path provide, in combination, a bilateral switch which functions to selectively reverse the polarity of terminals 124, 101, and 125, 102 thereby switching the transistor 106 to change the mode of the security termination unit 100 between access and secure modes. When transistor switches 122 and 127 are conducting, and the secure path is conductively connected between bridge vertex points A and C, terminals 101, 124 and 102, 125 are positive and negative, respectively, placing the security termination unit 100 in the access mode. With the security termination unit 100 in the access mode, the transistor 106 is conducting and the intrusion switch 108 is short circuited, thereby enabling free access through entries normally protected by the intrusion switch 108. When transistor switches 128 and 130 are conducting, the secure path is conductively connected between bridge vertex points A and C, rendering terminals 102, 125, and 101, 124 positive and negative, respectively, placing the security termination unit 100 in the secure mode. With the security termination unit 100 in the secure mode, the transistor 106 is nonconducting, rendering the security termination unit 100 sensitive to changes in the condition of intrusion switch 108.

BRIDGE CIRCUIT OPERATION Secure Mode-As previously indicated, the bridge 110 is placed in the secure mode by rendering conductive transistor switches 128 and 130 and rendering nonconductive transistor switches 122 and 124. Under such conditions of transistor switch conduction and nonconduction, terminals 102, 125 and 101, 124 are rendered positive and negative, respectively. With the terminals so polarized, transistor switch 106 is nonconductive rendering the resistance of the security termination unit 100 sensitive to the condition of the intrusion switch 108.

No Alarm-1n the secure mode if neither the intrusion switch 108 nor the tamper switch 109 is open by an unauthorized entry through a protected passage or window, the resistance of the security termination unit 100 is substantially equal to the resistance of resistor 103. With the resistance of the security termination unit 100 substantially termination to the resistance of the resistor 103, bridge tap points D and B are substantially equal in potential and no alarm is produced by the alarm-sensing circuitry described.

intrusion Alarm-Should an intrusion alarm occur in the secure mode, the switch 108 is opened, placing resistor 105 in series with resistor 103. The increased resistance of the security termination unit 100 increases the resistance of bridge leg DC, raising the potential at tap point D relative to the potential of tap point C, causing a police alarm to be produced in a manner to be described.

Tamper Alarm-Should a tamper alarm condition occur in the secure mode, the normally closed switch 109 opens, placing resistor 104 in series with resistor 103, increasing the resistance in bridge leg DC. The increase in resistance in bridge leg DC increases the potential of tap point D relative to the potential of tap point C, causing the police alarm to be produced.

Short Circuitlf, in an attempt to compromise the security termination unit 100 when in its secure mode, terminals 101 and 102 are short circuited, the resistance of bridge leg DC is substantially reduced from its normal condition, lowering the potential at tap point D relative to the potential of tap point B, producing a circuit alarm in the manner to be described.

Open Circuitlf, in attempting to compromise the security termination unit 100 when in its secure mode, the terminals 101 and 102 are open circuited, the resistance of bridge leg DC becomes very large, causing the potential of tap point D to substantially increase relative to the potential of tap point B, producing a circuit alarm.

Access Mode-The system is placed in the access mode by rendering conductive transistor switches 122 and 127 and rendering nonconductive transistor switches 128 and 130. With the transistor switches in such states of conduction and nonconduction, terminals 101, 124 and 102, 125 are rendered positive and negative, respectively, placing transistor 106 in conductive state to shunt the intrusion switch 108. Accordingly, the resistance of the security termination unit 100 is rendered insensitive to changes in the condition of intrusion switch 108.

No Alarmln the absence of an alarm condition in the security termination unit 100, tap points D and B are at substantially equal potential. Accordingly, no alarm is produced.

Intrusion AlarmShould entry be made through a passage protected by intrusion switch 108 when the security termination unit 100 is in its access mode, the switch 108 is placed in its open circuit condition. However, the resistance of the security termination unit 100 remains unchanged by reason of the short circuit placed across resistor 105 by conducting transistor switch 106. Since the resistance of the security termination unit 100 does not change, the resistance in bridge leg DC is unchanged and the potential of tap points D and B is substantially equal, producing no alarm.

Should the terminals 101 and 102 be short-circuited or open circuited, or the tamper switch 109 switched to its open circuit condition, when the system is in its access mode, a circuit fault alarm or a police alarm, respectively, is produced in the manner described previously in connection with. operation in the secure mode.

MODE-SWITCHING CIRCUIT The mode-switching circuit includes the four transistor "switches 122, 127, 128 and 130, constituting the previously noted bilateral switch, and a system mode bistable multivibrato'r or flip-flop 134. The mode flipflop 134 includes a pair of cross-coupled transistors 135 and 136 having their emitters connected in common to grounded line 112, and their collectors connected to positive line via resistors 137 and 138. respectively. The bases of transistors and 136 are connected to the collectors of transistors 136 and 135, respectively, via resistor 140 and 141, respectively. A capacitor 142 is connected between the transistor bases and resistors 140 and 141 to increase immunity to transient noise. The bases of transistors 13S and 136 are also connected, via diodes 146 and 147 and capacitors 148 and 149, to a line 150 selectively groundable via a normally open mode switch 151. Line 150 is connected to a capacitor 152, the other side of which is grounded, and to the midpoint of a voltage divider formed by resistors 153 and 154 interconnected between the positive line 115 and the grounded line 112.

The mode flipdlop 134 is bistable and can be switched from one state to another by momentary actuation of mode switch 151. As defined herein, the mode flip-flop 134 is in the secure" mode when transistors 135 and 136 are conducting and nonconducting, respectively. With transistor 13$ conducting, the transistor collector potential is at a relatively low value, causing transistors 127 and 122 of the bilateral switch to be rendered nonconductive, which in turn renders transistors 12B and 130 of the bilateral switch conductive. With transistors 122 and 127 nonconductive and transistors 128 and 130 conductive, the secure path is conductively connected between bridge vertex points D and C, placing the system in the secure mode. When transistors 135 and 136 are nonconducting and conducting, respectively, the mode flipflop is herein defined as residing in the access mode. With transistor 135 nonconducting, the collector potential is at a relatively high level, switching transistor 127 to the conducting state, which in turn switches transistor 122 to the conducting state. With both transistors 122 and 127 conducting, transistors 128 and 130 are rendered nonconductive, conductively connecting the access path between bridge vertex points D and C, placing the system in the access mode. The bistable condition of the mode flip-flop 134 can be switched from one condition to another to thereby change the system mode, by momentary closure of the mode switch 151. Closure of mode switch 151 drops the potential on the bases of transistors 135 and 136 switching the state of the base triggered mode flipflop in a manner well-known to those skilled in the art, and accordingly not described in detail herein.

ALARM SENSING CIRCUIT The alarm-sensing circuit 159 includes transistors 160, 161, 162, 163, 164, 165, and 166 suitably biased to be rendered nonconductive in the absence of an alarm condition at the security termination unit 100, and a transistor 167 suitably biased to be rendered conductive in the absence of an alarm condition. The collector of transistor 164 is herein termed the police alarm sensing point. in a manner to become evident hereafter, the potential of the police alarm sensing point increases above a normal nonalarm point in response to either an intrusion or a tamper condition in the security termination unit 100. The collector of transistor is herein termed the circuit alarm sensing point." The potential of the circuit alarm sensing point increases above a normal value in response to the existence across terminals 101 and 102 of the security termination unit 100, of either a short circuit condition or an increase of line current greater than a predetermined amount, or an open circuit condition or a decrease of line current greater than that necessary to produce a police alarm.

POLICE ALARM ClRCUlT The police alarm circuit is in the form of a bistable multivibrator or flip-flop 170 which includes a pair of cross-coupled transistors 171 and 172 having their collectors connected to the positive line 1 15 via resistors 173 and 174. The bases of transistors 171 and 172 are connected to the collectors of transistors 172 and 171, respectively, via resistors 175 and 176, The base of transistor 171 is also connected to the collector of transistor 167 via a diode 177 and a resistor 178, rendering the police alarm flip-flop 170 responsive to the state of transistor 167 of the alarm-sensing circuit 159, and more particularly -to the police and circuit alarm sensing points. The base of transistor 172 is connected via a resistor 180 to the output line 181 of a reset circuit 182 to be described, rendering the transistor 172 responsive to the output of the reset circuit. The police alarm flip-flop 170 is in its alarm condition as herein defined when transistors 171 and 172 are conducting and nonconducting. The police alarm flip-flop 170 is in its nonalarm condition as herein defined when transistors 171 and 172 are nonconducting and conducting, respectively. The police alarm flip-flop 170 switches from a nonalarm to an alarm condition in response to an intrusion or tamper condition in the security termination unit 100 when in the secure mode, and a tamper condition when in the access mode.

ClRCUlT FAULT ALARM CIRCUIT The circuit fault alarm circuit includes a bistable multivibrator or flip-flop 185 having a pair of cross-coupled transistors 186 and 187, the collectors of which are connected via resistors 188 and 189 to the positive line 115. The bases of transistors 186 and 187 are connected to the collectors of transistors 187 and 186, respectively, via resistors 190 and 191. The base of transistor 186 is also coupled to the circuit alarm sensing point 165 via a diode 192, a resistor 193 and a resistor 194, rendering transistor 186 responsive to the voltage at the circuit alarm sensing point. The base of transistor 187 is also connected to the output line 181 of the reset circuit 182 rendering transistor 187 responsive to the output of the reset circuit. The circuit alarm flip-flop 185 is in the circuit alarm condition as defined herein when transistors 186 and 187 are conducting and nonconducting, respectively, and is in the nonalarm condition as herein defined when transistors 186 and 187 are nonconducting and conducting, respectively. The flip-flop 185 switches from a nonalarm to an alarm condition in response to a circuit fault, that is, a short circuit or open circuit, in the security termination unit 100.

OPERATION OF ALARM SENSING CIRCUIT Police Alarm Condition-As previously noted, when an intrusion condition (secure mode) or a tamper condition (secure or access mode) is present at the security termination unit 100 by reason of switch 108 or switch 109 being placed in its open condition, the potential of tap point D of the bridge 110 increases relative to that of tap point B by a specified magnitude. The increase of potential at tap point D of the balanced bridge is input via a coupling resistor to the base of normally nonconducting transistor 162 switching this transistor to its conducting state. Switching of transistor 162 to a conducting state in turn switches normally nonconducting transistor 164 to a conducting state. With transistor 164 conducting, the emitter-collector current of this transistor increases, raising the potential of the collector thereof which constitutes the police alarm sensing point. The increased potential at the police alarm-sensing point is input via a coupling resistor to the base of normally nonconducting transistor 166, switching this transistor to a conducting state. The increased flow of current in the emitter-conductor path of conducting transistor 166 lowers the potential on the collector of this transistor which is input via a coupling resistor to the base of normally conducting transistor 167 switching transistor 167 to a nonconducting state. With transistor 167 nonconducting, the potential of the collector increases and is coupled via diode 177 and resistor 178 to the base of transistor 171 of police alarm flip-flop 170, which in its nonalarm state is nonconductive, rendering this transistor conductive. The switching of transistor 171 to the conductive state switches the state of the police alarm flip-flop 170, causing the transistor 172 to be rendered nonconductive. Thus, in response to either an intrusion alarm (secure mode) or a tamper alarm (secure or access mode) occurring at the security termination unit 100, the police alarm flip-flop is switched and placed in its alarm condition. Once placed in the alarm condition, the police alarm flip-flop remains in such condition until reset or switched by a positive pulse output from the reset circuit 182 on reset line 181.

Open Circuit Conditionln response to an open circuit condition produced across terminals 101 and 102 of the security termination unit 100. the potential at tap point D of the balanced bridge increases by a magnitude in excess of the increase of potential which occurs for either an intrusion or a tamper alarm condition. The substantial increase in potential at point D occasioned by an open circuit condition across terminals 101 and 102 switches normally nonconducting transistor to its conductive state. The increased current flow in the emitter-collector path of conducting transistor 160 lowers the potential at the base of normally nonconducting transistor 165, placing this transistor in its conductive state. With transistor rendered conductive, an increased current flows in its collector-emitter path raising the potential at the circuit alarm sensing point. The increased potential at the circuit alarm sensing point is input via resistors 194 and 193 and diode 192 to the base of normally nonconducting transistor 186 of the circuit alarm flip-flop 185, switching the transistor 186 to its conducting state. Switching of transistor 186 to a conducting state switches normally conducting transistor 187 to its nonconductive state. Thus, the circuit alarm flip-flop is switched to its alarm condition by the presence of an open circuit across terminals 101 and 102 of the security termination unit 100, and remains in such alarm state until reset by a positive pulse input into the base of transistor 187 from output line 181 of reset circuit 182.

The increased potential at the circuit alarm sensing point, in

addition to being input to the base of transistor 186 of the circuit alarm flip-flop for switching the state of this flip-flop, is also input to the base of normally nonconducting transistor 167, switching this transistor to its conducting state. The increased current flowing in the emitter-collector path of conducting transistor 167 lowers the collector potential thereof. The lowered collector potential of transistor 167 is coupled to the base of transistor 171 of the police alarm flip-flop via diode 177 and resistor 178 preventing the police alarm flipflop from being switched from its nonalarm condition to its alarm condition. Short Circuit Condition-The presence of a short circuit across terminals 101 and 102 of the security termination unit 100 lowers the potential at tap point D of the balanced bridge. The decreased potential at tap point D is resistively coupled to the base of normally nonconducting transistor 161, switching this transistor to a conductive state. The switching of transistor 161 to a conducting state is effective to raise the potential input to the base of normally nonconducting transistor 163, switching this transistor to a conducting state. The increased current flow in the emitter-collector path of conducting transistor 163 raises the potential of the base of normally nonconducting transistor 165, switching this transistor to a conducting state. The conduction of transistor 165 produces an increase in the collector potential thereof, raising the potential of the circuit alarm sensing point. The increase of potential at the circuit alarm sensing point is coupled via resistor 194, resistor 193 and diode 192 to the base of transistor 186 of the circuit alarm flip-flop 185, switching this flip-flop in a manner similar to that described with respect to the open-circuit condition. Thus, in response to a short-circuit condition across terminals 101 and 102 of the security termination unit 100, the circuit alarm flip-flop 185 is switched to an alarm condition. The circuit alarm flip-flop 185 when switched remains in the switched condition until reset by a positive signal from the reset circuit 182 on line 181.

The increased potential at the circuit alarm sensing point occasioned by the short circuit condition across terminals 101 and 102 of the security termination unit 100, in addition to being input to the circuit alarm flip-flop 185 to switch this flipflop to the alarm condition, is also resistively coupled to the base of normally nonconducting transistor 167, switching this transistor to a conductive state. With transistor 167 conducting the collector potential thereof is lowered. This decreased potential is coupled to the base of police alarm flip-flop transistor 171 via diode 177 and resistor 178 preventing the police alarm flip-flop 170 from 'being switched to its alarm condition.

If the police alarm flip-flop 170 (or the circuit alarm flipflop 185) is in its alarm storage condition, a subsequent circuit alarm condition (or police alarm condition) cannot operate to switch the circuit alarm flip-flop (or police alarm flip-flop) to store a circuit alarm (or police alarm). Specifically, if a circuit alarm is stored in flip-flop 185, the collector of conducting transistor 186 is at a low potential, forward biasing diode 196. With diode 196 forward biased a police alarm signal at the collector of transistor 167 is shunted past the base of transistor 171 of the police alarm flip-flop 170, preventing this flip-flop from switching to store a police alarm. If a police alarm is stored in flip-flop 170, the collector of conducting transistor 171 is low, rendering diode 197 susceptive of being forward biased by circuit alarm signal coupled thereto via resistor 193. With diode 197 susceptive of being forward biased, a circuit alarm signal coupled to diode 197 via resistor 193 forward biases the diode, shunting the circuit alarm signal from the base of circuit alarm flip-flop transistor 186, preventing storage of a circuit alarm therein.

SYSTEM MODE AND ALARM CONDITION lNDlCATORS Secure Mode-To indicate that the system is in the secure mode, a secure lamp 200 is provided. The secure lamp is connected between a source of positive potential 201 and the grounded line 112 via the emitter-collector path of a transistor switch 202, the base of which is resistively coupled to the collector of transistor 136 of the mode flip-flop 134. In operation, when the mode flip-flop 134 places the system in the secure mode, transistor 136 is nonconductive and its collector is at a relatively high potential. The relatively high potential of the collector of transistor 136 of the mode flip-flop 134 is resistively coupled to the base of transistor switch 202 placing this transistor in its conductive state and in turn providing an energization path for the secure lamp 200.

Access ModeTo indicate that the system is in the access mode, an access lamp 205 is provided. The access lamp 205 is connected between a source of positive potential 206 and the grounded line 1 12 via the emitter-collector path of a transistor switch 207, the base of which is resistively coupled to the collector of transistor 135 of the mode flip-flop 134. In operation, when the mode flip-flop places the system in the access mode, transistor 135 is nonconductive and its collector is at a relatively high potential. The relatively high collector potential of transistor 135 is resistively coupled to the base of transistor switch 207 placing this transistor in its conductive state to provide an energization circuit for the access lamp 205.

Circuit Alarm-To indicate that a circuit alarm condition exists, a circuit alarm lamp 210 is provided. The circuit alarm lamp 210 has one side thereof connected to the grounded line 112 via the emitter-collector path of a normally nonconductive transistor switch 211, the base of which is direct coupled to the emitter of transistor 186 of the circuit alarm flip-flop 185. The other side of the circuit lamp 210 is connected via a pair of diodes 212 and 214 to a source of intermittent positive potential 213. in operation, when the circuit alarm flip-flop 185 is placed in its alarm condition, the transistor 186 is rendered conductive. This switches transistor 211 from its normally nonconducting state to a conducting state completing an energization circuit for the lamp 210, enabling the lamp to be energized from the source of intermittent positive potential 213. With the lamp 210 intermittently energized, the circuit lamp flashes, indicating the occurrence of a circuit alarm. Police Alarm-To indicate the occurrence of a police alarm, a police lamp 215 is provided. The lamp 215 has one side thereof connected to the grounded line 112 via the emittercollector path of a normally nonconducting transistor switch 216, the base of which is connected to the emitter of transistor 171 of the police alarm flip-flop 170. The other side of the police alarm lamp 215 is connected via a diode 217 and a diode 214 to the source of intermittent positive potential 213. In operation, when a police alarm occurs, the police alarm flipflop switches. This causes transistor 171 to be rendered conductive. With transistor 171 conductive, the normally nonconducting transistor switch 216 is rendered conductive, completing an energization path for the police lamp 215, causing this lamp to flash.

The flashing condition of either the police alarm lamp 215 or the circuit alarm lamp 210 may be modified or converted to a condition of continuous illumination by momentary closure of a normally open silence switch 219. Silence switch 219 is connected between a source of positive potential 220 and the control electrode of a normally nonconducting silicon control rectifier switch SCR 221 connected between the positive line 115 and the lamps 210 and 215 via diode 212 and diode 217. In operation, if either the circuit alarm lamp 210 or the police alarm lamp 215 is in its intermittent flashing condition, the respectively flashing lamp can be rendered continuously illuminated by momentary closure of the switch 219. Closure of switch 219 provides a triggering signal to the control electrode of SCR 221, rendering the SCR conductive. Conduction of SCR 21 connects the positive line 115 to the flashing lamp 210 or 215, as the case may be, continuously energizing the lamp.

Any attempt to reset, via reset circuit 182, either the police alarm flip-flop or the circuit alarm flip-flop while either the police alarm condition or a circuit alarm condition exists will be ineffective to switch either of the alarm flip-flops. So long as a police alarm condition exists placing the police alarm flip-flop 170 in its alarm condition, or a circuit alarm condition exists placing the circuit alarm flip-flop 185 in its alarm condition, the police alarm lamp 215 and circuit alarm lamp 210, whether flashing or continuously illuminated, cannot be extinguished.

A lamp test switch 225, which is normally, open, is provided to permit testing of the secure lamp 200, the access lamp 205, the circuit alarm lamp 210 and the police alarm lamp 215. The switch 225, when momentarily depressed, momentarily couples a source of positive potential 226 to the bases of secure mode lamp transistor switch 202, access mode lamp transistor switch 207, circuit alarm lamp transistor switch 211, and police alarm lamp transistor switch 216. With the source of positive potential 226 momentarily coupled to the bases of transistors 202, 207, 211 and 216, the transistors are momentarily rendered conductive, providing momentary energization paths for the secure mode lamp 200, the access mode lamp 205, the circuit alarm lamp 210 and the police alarm lamp 216, momentarily energizing these lamps. AnnunciatorAn annunciator device generally indicated by the reference numeral 228 is also provided to give an audible alarm when a circuit alarm condition or police alarm condition occurs. The annunciator 228 is connected between a source of positive potential 229 and the grounded line 112 by a normally nonconductive transistor switch 230. The base of transistor 230 is R-C coupled to the collector of transistor 187 of the circuit alarm flip-flop 185 and R-C coupled to the collector of the transistor 172 of the police alarm flip-flop 170.

In operation, if a police alarm condition should occur, the transistor 172 of the police alarm flip-flop 170 is rendered nonconductive, raising the potential of the collector thereof which in turn switches transistor 230 to its conducting state completing an energization circuit for the annunciator 228 thereby energizing the annunciator. The annunciator 228 is similarly energized by completion of an energization circuit through the emitter-collector path of transistor 230 in response to a circuit alarm condition. in this case, the transistor 230 is switched to its conductive state in response to the increased potential of the collector of transistor 187 of the circuit alarm flip-flop 185 when the latter is in its alarm condi- 7 tion. The annunciator 228 is preferably designed so as to remain latched in the annunciating condition once an energization circuit is completed thereto through the emitter-collector path of the transistor 230, until reset by momentary closure of a silence switch 231 which is ganged'with silence switch 219.

The annunciator could, for example, be an electric bell or buzzer (not shown) energized through the anode-cathode path of an SCR. In such case, the gate of the SCR is connected through a difierentiator to the collector of transistor 230 to render the SCR conductive, and the annunciator operative, upon transistor 230 being rendered conductive. The gate is also connected to ground through silence switch 231, enabling the SCR to be rendered nonconductive and the annunciator disabled, upon momentary closure of switch 231.

RESET CIRCUIT A reset circuit 182 responsive to momentary closure of a normally open reset switch 234 is provided to reset the police alarm flip-flop 170 and the circuit alarm flip-flop 185 should either of these flip-flops have been placed in an alann condition and the alarm condition is no longer existent. The reset circuit 182 includes a capacitor 235 adapted to charge to the polarity shown through a resistor 233 connected to a positive line 115. The reset circuit 182 also includes a nonnally conducting transistor 236 the base of which is resistively coupled to the negative side of the capacitor 235. The collector of the normally conducting transistor 236 is connected via a resistor 237 to the positive line 115. The emitter of transistor 236 is connected to grounded line 112. The line 181 connected to the collector of transistor 236 constitutes the output of the reset circuit 182.

In operation, the transistor 236 is normally conducting, producing a low level output on reset circuit output line 181 by reason of the voltage drop across resistor 237. When the reset switch 234 is momentarily closed, the positive side of the charged capacitor 235 is grounded, causing the negative side of the capacitor to assume a potential substantially below ground. With the negative side of the capacitor 235 below ground potential, the normally conducting transistor 236 is rendered nonconductive. The rendering of transistor 236 nonconductive terminates the current flow in the transistor emitter-collector path, in turn raising the potential of the transistor collector, providing a positive signal on the reset circuit output line 181. The positive signal on reset circuit output line 181 is resistively coupled to the base of transistor 172 of the police alarm flip-flop 170 and to the base of transistor 187 of the circuit alarm flip-flop 185 resetting these flip-flops (assuming they are in the alarm condition), placing them in the nonalarm condition. With the police alarm and circuit alarm flip-flops 170 and 185 placed in their nonalarm conditions, the police alarm lamp transistor switch 216 and the circuit alarm lamp transistor switch 211 are rendered nonconductive, terminating the energization of the police lamp 215 and the circuit alarm lamp 210 should any of these indicator devices have been energized.

The switching of the transistor 236 of the reset circuit 182 to the nonconducting state in response to momentary closure of the reset switch 234 to reset the police alann and circuit alarm flip-flops 170 and 185 and in turn extinguish the alarm lamps 210 and 215 cannot occur if either a police alarm condition or a circuit alarm condition exists. If a circuit alarm condition exists, the circuit alarm sensing point 165 is at an abnormally high potential. This abnormally high potential is resistively coupled to the base of transistor 236 maintaining this transistor in conduction. Consequently, even though the switch 234 is momentarily closed, depressing the negative side of the capacitor 235 to a below ground potential, the transistor 236 remains conductive and a positive reset signal cannot be provided on reset circuit output line 181 to reset the circuit alarm flip-flop 185. Ifa police alarm condition exists at the time of closure of reset switch 234, the transistor 236 is 185, and

similarly maintained conductive by vinue of a positive signal resistively coupled to the base of transistor 236 from the collector of transistor 167 which is placed in a nonconducting condition when the transistor 166 is switched to a conducting state by an abnormally high potential at the police alarm sensing point 164. Thus, the transistor 236 cannot provide a positive reset signal on line 181 to reset the police alarm flipflop in response to closure of the switch 234 when a police alarm condition exists.

PRINTER INTERFACE A printer interface 240 responsive to the mode flip-flop 134, the circuit alarm flip-flop 185, the police alarm flip-flop 170, and the reset circuit 182 functions to provide on printer interface output lines 243, 244, 245 a binary output signal representative of the changes in state of the flip-flops 134,

170 and of the reset circuit 182. The printer interface 240 includes a coding matrix 246 which functions to convert positive matrix input signals on reset line 248, circuit alarm line 249, police alarm line 250, secure mode line 251, and access mode line 252 into appropriate three-digit binary numbers on printer interface output lines 243, 244 and 245.

The coding matrix includes three normally nonconducting transistors 255, 256 and 257 each having their collectors connected through a resistor to a source of positive potential, and their emitters connected in common to ground lines 112. The collectors of transistors 255-257 are connected to printer interface output lines 243-245, respectively. The bases of transistors 255-257 are resistively coupled to the matrix input lines 248-251 in different combinations for reasons to become apparent hereafter. The bases of the output transistors 255-257 are also connected to ground line 112 via the emitter-collector path of normally conducting switching transistors 258, 259 and 260, respectively. The bases of transistors 258-260 are also connected to the matrix input line 248-252 indifferent combinations and to a strobe line 261 common to each transistor for reasons to become apparent hereafter. The transistors 258-260 are normally rendered conductive by a positive signal level existing on strobe line 261 generated in a manner to be described hereafter. With transistors 258-260 normally conductive, the output transistors 255-257 are held in nonconductive conditions by reason of the short circuit path existing between their bases and emitters established by the emitter-collector paths of conducting transistors 258-260.

With transistors 255-257 normally nonconducting, a positive signal level is provided on their collectors and hence a positive signal level appears on printer interface output lines 243-245. The existence of a positive signal level on output lines 243-245 is herein defined as a logical zero." A logical one" is provided on printer interface output lines 243-245 when transistors 255-257, respectively, are rendered conductive by the simultaneous switching of transistors 258-260, respectively, to their nonconductive states and the presence of positive input signals on lines 248-252 to the bases of transistors 255-257, respectively, rendering these latter transistors conductive which effectively grounds their collectors, providing a logical one on output lines 243-245, respectively.

A strobing monostable multivibrator 263 functions to normally provide on its output line 261 a positive signal level to hold transistors 258-260 in their conducting state, in turn grounding the bases of transistors 255-257 which holds these latter transistors nonconductive. With transistors 255-257 held nonconductive, positive signal levels or logical zeros are present on output lines 243-245. The strobing monostable multivibrator 263 also functions to provide on its output line 261 a negative strobe pulse in response to a positive trigger signal on its input line 264 produced by a trigger circuit 265. Such a positive trigger signal is provided on line 264 each time mode flip-flop 134, circuit alarm flip-flop 185, police alarm flip-flop 170, or reset circuit 182, changes state.

The strobing monostable multivibrator 263, considered in more detail, includes a pair of cross-coupled transistors 266 and 267, the emitters of which are grounded. The bases of transistors 266 and 267 are resistively and capacitively coupled. respectively, to the collectors of transistors 267 and 266, respectively. With the bases of the transistors 266 and 267 so intercoupled, transistor 266 is normally rendered. nonconductive, providing a high level positive signal on the strobing monostable output line 261. This signal holds transistor 258-260 in saturation, in turn holding transistors 255-257 nonconducting to provide relatively high level positive signals on output lines 243-245 corresponding to logical zeros.

in operation, when a positive trigger signal output from the trigger circuit 265 is input to the base of transistor 266, the normally nonconducting transistor 266 is switched to a conducting state, providing on its collector a low level signal which is output on strobe line 261. The low level signal on strobe line 261, in a manner indicated previously, switches transistors 258-260 to their nonconducting state, enabling transistors 255-257 to conduct and provide logical ones on output lines 243-245 if the appropriate positive signals are also present on their bases from different ones of the input lines 248-252. Since the multivibrator 263 is monostable, the transistor 266 remains conductive, providing the low level output on strobe line 261, only momentarily, the state of the strobing monostable multivibrator switching back to its normal condition, with transistor 266 nonconducting and transistor 267 conducting, after a short interval.

The trigger circuit 265 has a plurality of input lines 270, 271, 272, 273, 274, and 275 which are connected to the mode flip-flop 134, the circuit alarm flip-flop 185 and the police alarm flip-flop 170 for responding to changes in state of these flip-flops and, as a consequence thereof, producing a positive triggering signal on output line 264 to switch the strobing monostable and in turn produce the low level strobe signal on line 261 for strobing the coding matrix 246. Line 270 is connected to the collector of transistor 172 of police alarm flipflop 170 and by virtue of such connection provides a positive going change in signal level on line 270 when a police alarm condition causes police alarm flip-flop 170 to change to its alarm condition. The positive-going change in signal level on line 270 coincident with the switching of police alarm flip-flop 170 to the alarm condition is difierentiated by a capacitor 276 and a resistor 277, providing a positive trigger pulse on trigger output line 264.

Trigger input line 273 is connected to the collector of transistor 171 of police alarm flip-flop 170 and provides on line 273 a positive going signal when the police alarm flip-flop 170 is reset and switches from an alarm condition to a nonalarm condition. The positive-going signal on line 273 coincident with the resetting of the police alarm flip-flop 170 is differentiated by a capacitor 278 and a resistor 279 producing on trigger output line 264 a positive trigger pulse.

Trigger input line 272 is connected to the collector of transistor 187 of the circuit alarm flip-flop 185 and provides a positive-going signal on input line 27 2 when the circuit alarm flip-flop 185 switches from its nonalarm condition to its alarm condition. The positive-going signal input on trigger input line 272 coincident with the switching of circuit alarm flip-flop 185 to the alarm condition is differentiated by a capacitor 280 and a resistor 281, providing on output line 264 a positive trigger pulse.

Trigger circuit input line 271 is connected to the collector of transistor 186 of the circuit alarm flip-flop 185 and provides on input line 271 a positive going signal when the circuit alarm flip-flop 185 is reset and switched from an alarm condition to a nonalarm condition. The positive going signal on trigger alarm input line 271 is differentiated by a capacitor 283 and a resistor 284, providing on trigger output line 264 a positive trigger pulse.

Trigger circuit input line 274 is connected to a positive line 285 via the emitter-collector path of a normally nonconducting transistor 286, the base of which is capacitively coupled to Eli the collector of transistor of the mode flip-flop 134. In

operation, when the mode flip-flop switches from the access" state to the secure state, a negative going signal is provided at the collector of transistor 135 which is capacitively coupled to the base of transistor 2B6, momentarily providing a positive input signal to line 274 which is differentiated by capacitor 287 and a resistor 288, providing a positive pulse on trigger circuit output line 264.

Trigger circuit input line 275 is connected to the positive line 285 via the emitter-collector path of a normally nonconducting transistor 290 the base of which is capacitively coupled to the collector of transistor 136 of the mode flip-flop I34. When the mode flip-flop 134 switches from the secure mode to the access mode, a negative signal is provided on the collector of transistor 136 which is capacitively coupled to the base of transistor 29!), momentarily rendering transistor 290 conductive. The momentary conduction of transistor 290 produces a positive-going signal on trigger circuit input line 275 which is differentiated by a capacitor 291 and a resistor 292 providing on trigger circuit output line 264 a positive trigger signal.

OPERATION OF PRINTER INTERFACE Police Alarm Flip-flop Switched to Alarm ConditionWhen the police alarm flip-flop switches to an alarm condition in response to an intrusion (secure mode) or tampering (access or secure mode), the collector of transistor 172 goes positive. This provides a positive signal on police input line 250 to the code matrix 246, as well as a positive signal to the police input line 270 of the trigger circuit 265. The positive input of police line 250 is input to the bases of normally nonconducting transistors 256 and 257. This positive input enables transistors 256 and 257 to conduct and produce on output lines 244 and 245 low level signals corresponding to logical ones when the transistors 259 and 260 are switched to their conductive state by a negative signal on strobe line 261, the negative signal being produced by the monostable multivibrator 263, which is triggered by an output on line 264 produced by the input on line 270. Thus, in response to switching of the police alarm flip-flop 170 to the alarm condition, logical ones are produced on output lines 244 and 245 to provide the binary number Ol Police Alarm Flip-Flop Reset-When the police alarm flipflop is reset, a positive signal is input on reset line 248 from the reset circuit 182, enabling transistors 255 and 256 to be rendered conductive and produce logical ones on output lines 243 and 244 when transistors 258 and 259 are strobed by the monostable multivibrator 263 as a consequence of a positive signal being input to the trigger circuit 265 on line 273. Thus, when the police alarm flip-flop is reset to its nonalarm condition, logical ones are produced on output lines 243 and 244, providing the binary number l 10.

Circuit Alarm Flip-Flop Switched to Alarm Condition-When the circuit alarm flip-flop is switched to an alarm condition by either an open circuit or a short circuit across terminals 101 and 102 of the security termination unit 100, a positive signal is input on line 249 to the coding matrix 246. This provides a positive signal to the bases of transistors 255 and 257 enabling these normally nonconducting transistors to conduct and provide logical ones on output lines 243 and 245 when the normally conducting transistors 258 and 260 are strobed by the output from the strobing monostable multivibrator 263 produced as a consequence of the input on line 272 to the trigger circuit 265. Thus, in response to a switching of the circuit alarm flip-flop 185 from a nonalarm condition to an alarm condition, logical ones are produced on output lines 243 and 245, producing the binary number [01.

Circuit Alarm Flip-Flop Reset-When the circuit alarm flipflop 185 is reset by a positive reset signal on line 181 output from the reset circuit 182, a positive signal is input on line 248 of the code matrix 246. The positive input signal on line 248 is input to the base of transistors 255 and 256 enabling these transistors to conduct and provide logical ones on lines 243 and 244 when the normally conducting transistors 258 and 259 are strobed by the output from the monostable multivibrator 263 produced in response to the positive signal input to the trigger circuit 265 on line 271. Thus, when the circuit alarm flip-flop 185 is reset from the alarm condition to the nonalarm condition logical ones are provided on lines 243 and 244 producing the binary number 1 l representing the reset condition.

System Changes to the Secure Mode-When the system changes to the secure mode, the mode flip-flop 134 changes to the secure mode and a negative-going signal is produced at the collector of transistor 135. This signal is effective to momentarily switch transistor 286 to its conducting state, providing a positive-going signal to the base of transistor 256, enabling this transistor to conduct and thereby provide a logical one at terminal 244 when transistor 259 is rendered conductive by the output on strobe 261 from the monostable multivibrator 263 produced as a consequence of the positive-going input to the trigger circuit 265 on line 274. Thus, when the system switches from the access mode to the secure mode a logical one is provided at terminal 244, representing the binary output 010.

System Changes to Access ModeWhen the system changes to the access mode, the mode flip-flop 134 switches, producing a positive'going signal at the collector of transistor 135 which is efi'ective to momentarily switch transistor 290 to its conducting state and provide a positive-going signal on line 252. The positive signal on line 252 is input to the base of transistor 257 enabling this transistor to conduct and provide a logical one at terminal 245 when transistor 260 is strobed by the output on line 261 from the strobing monostable multivibrator 263 as a consequence of the input to the trigger circuit 265 on line 275. Thus, when the system switches to the access mode a logical one is provided at terminal 245, providing the binary number 001.

ZONE IDENTIFICATION CIRCUIT A zone identification circuit, including a transistor 295, provides on zone identification line 296 a negative pulse each and every time a binary number is provided on output lines 243-245. The transistor 295 has its emitter connected to ground line 112 and its collector connected bya resistor to a source of positive potential. The collector of transistor 295 is connected to zone identification line 296 and constitutes the output of the zone identification circuit. The base of the transistor 295 is connected to the collector of transistor 267 of the strobing monostable multivibrator 263. The transistor 295 is normally nonconducting by reason of the connection of its base to the collector of normally conducting transistor 267 of the strobing monostable multivibrator. With transistor 295 normally nonconducting, the collector of transistor 295 is at a relatively high potential providing a logical zero on zone identification line 296. When, however, the strobing monostable multivibrator is momentarily switched by the input from the trigger circuit 265, the transistor 295 is momentarily rendered conductive, lowering the potential of the collector thereof to approximately ground and providing a logical one on zone identification line 296. Thus, each time the system switches from either the secure state to the access state or the access state to the secure state, or the police alarm flip-flop R70 and circuit alarm flip-flop 185 switch to alarm conditions or are reset, an input is provided to the trigger circuit 265, which in turn switches the strobing monostable multivibrator 263. The monostable multivibrator 263, in turn, causes the transistor 295 to be momentarily rendered conductive, providing a logical one on zone identification line 296.

FIRE TERMINATION UNIT The fire termination unit 300, which is located at the premises to be protected, includes a pair of terminals 301 and 302 between which is connected a normally open thermal switch 303. The thermal switch 303 is adapted to close upon the occurrence of a fire alarm condition at the protected premises. While a single thermal switch 303 is shown, those skilled in the art will understand that in practice a plurality of thermal switches may be connected in parallel between terminals 301 and 302. Terminals 301 and 302 are coupled to suitable fire and circuit fault sensing and indicating circuitry, located at a central monitoring station remote from the protected premises, to be described, by means of an AC and DC energized dual loop circuit 304. The AC energization of the dual loop circuit 304 facilitates detection, by the central station fire sensing circuitry, of the closing of thermal switch 303 at the protected premises, and the provision of an indication thereof at the central station. The DC energization of the dual loop circuit 304 permits circuit faults in the dual loop circuit, such as grounding or open circuiting, to be sensed by the central station fault circuit sensing devices and an indication thereof provided at the protected premise.

DUAL LOOP CIRCUIT The dual loop circuit 304 includes a first loop 305 and a second loop 306 respectively interconnecting points E and F and points G and H. Loops 305 and 306 have terminals 307 intermediate their end points E, F and G, H which are connectable in use to terminals 301 and 302 of the fire termination unit 300. Connected between points F and G of loops 305 and 306 is a fire-sensing resistor 309. The fire-sensing resistor 309, in the absence of a fire alarm condition at the protected premises which short circuits ten'ninals 307 and 308, is in series circuit arrangement with loops 305 and 306. The fire-sensing resistor 309 is adapted to be short circuited by the closing of thermal switch 303 when a fire condition exists at the protected premises.

A source of AC potential 310 having its output terminals 311 and 312 is included to provide an AC potential between loops 305 and 306. The AC supply terminal 311 is coupled to the loop 305 via capacitors 313 and 314 connected to points E and F. The AC supply terminal 312 is coupled to the loop 306 via capacitors 315 and 316 connected to points G and H. With AC supply terminals 311 and 312 coupled to loops 305 and 306 in the manner indicated, an alternating current potential exists across fire-sensing resistor 309 so long as the loops 305 and 306 are not short circuited by closure of thermal switch 303 as a consequence of a fire alarm condition at the protected premises. A change in this AC potential across resistor 309 due to the closure of thermal switch 303 is sensed to provide a fire alarm indication at the central station in a manner to be described.

Since AC supply terminal 311 is connected to both points E and F ofloop 305, grounding of the loop 305 and/or open circuiting of the loop 305 between either point E and terminal 307 or point F and terminal 307 is ineffective to alter the capability of the thermal switch 303 to short circuit the firesensing resistor 309 should a fire at a protected premises cause the thermal switch 303 to close. Likewise, since AC supply terminal 312 is connected to both points G and H of the loop 306, grounding of the loop 306 and/or open circuiting of the loop between point G and terminal 308 or point H and terminal 308 is ineffective to destroy the capability of the thermal switch 303 to short circuit the fire-sensing resistor 309 and provide a detectable fire alarm circuit condition should the thermal switch 303 be closed by the existence of a fire at the protected premises. By reason of the manner in which the AC source 310 is connected to the loops 305 and 306, the capability of the thermal switch 303 to short circuit the firesensing resistor 309 in response to a fire at the protected premises is also not destroyed by simultaneous open circuit conditions in both loops 305 and 306 so long as there is continuity in at least one of the loop sections E-307 or F-307 of loop 305 and continuity in at least one of the loop sections 6-308 or H308 of loop 306. The effectiveness of the thermal switch 303 to short circuit the resistor 309 in response to a fire at the protected premises can be destroyed if open circuits develop in both loop sections -307 and F-307 of loop 305, or in both loop sections 6-308 and H-308 of loop 306. If loops 305 and 306 are both grounded, resistor 309 is short circuited, simulating a fire at the protected premises.

The AC potential source 310 may take any suitable form, and preferably includes a conventional astable multivibrator having a pair of alternatively conducting transistors 317 and 318 suitably cross-coupled and biased to provide highfrequency alternations in their conductive states as required for astable operation. Preferably the frequency of operation of the astable multivibrator 310 is selected to be approximately 1,000 Hertz. A positive start circuit 319 is also provided to insure that the oscillator 310, when energized, initiates oscillation. The positive start circuit 319 includes a capacitor 320 and a resistor 322 connected between a source of positive potential 321 and ground, and a diode 323 connected between the collector of transistors 317 and the junction of capacitor 320 and resistor 322.

To facilitate detection of circuit faults in the loops 305 and 306, such as short circuits and open circuits, the series circuits combination of loop 305, fire-sensing resistor 309 and loop 306 is connected between a source of positive DC potential 330 and ground 329 via a pair of resistors 331 and 332. With the connection of the series circuit combination of loop 305, fire-sensing resistor 309 and loop 306 between the source of positive DC potential 330 and ground 329 in the absence of a circuit fault condition in the loops, such as an open circuit or short circuit, a steady state DC current level flows through the series circuit combination, providing a predetermined voltage at point H. The voltage at point H decreases from the specified voltage level existing under noncircuit alarm conditions if either or both of the lines 305 and 306 are grounded and/or open circuited. This decrease in potential at the point H is detected by circuit fault sensing means, to be described, providing an indication of the existence of a circuit fault in the dual loop circuit 304.

FIRE SENSING CIRCUIT A fire-sensing circuit 335 responsive to the AC potential across the fire-sensing resistor 309 is provided to detect the short circuiting of fire sensor resistor 309 occasioned by the closing of thermal switch 303 in response to a fire at the protected premises. The fire-sensing circuit 335 includes a normally nonconducting transistor 336. The transistor 336 has its base-collector conjunction connected across the fire-sensing resistor 309 via a full-wave rectifier 338, rendering the transistor 336 responsive to the AC potential across the firesensing resistor 309. The emitter of transistor 336 is clamped by a voltage divider formed by resistors 341 and 342. With the transistor 336 so connected, the transistor is normally held in nonconducting state. Coupling capacitors 339 and 340 connected between the full-wave rectifier 338 and the fire-sensing resistor 309 isolates the base circuit of the transistor 336 from the DC potential across the fire-sensing resistor which is produced by the DC current flowing therethrough utilized for circuit fault detectionpurposes. The collector of transistor 336, herein defined as the fire-alarm sensing point, constitutes the output of the fire-sensing circuit 335.

Under nonfire alarm conditions, that is, with the thermal switch 303 in the open condition, the AC voltage appearing across the fire-sensing resistor 309, when rectified, biases the transistor 336 into its nonconducting state, providing a relatively low potential at the collector of transistor 336 and, hence, at the fire-alarm sensing point. Should the thermal switch 303 close in response to a fire at the protected premises, short-circuiting loops 305 and 306 and, hence, the fire-sensing resistor 309, the rectified AC potential input to the base circuit of transistor 336 decreases to zero, causing the transistor 336 to switch to its conducting state. With the transistor 336 conducting, the collector potential rises, providing a relatively high signal level at the fire alarm sensing point indicative of the existence of a fire at the protected premises.

FIRE ALARM FLIP-F LOP A fire alarm flip-fiop 345 is provided which is switchable from a normal or nonalarm condition to an abnormal or fire alarm condition in response to an increased potential at the fire alarm sense point occasioned by the closure of thermal switch 303. The flip-flop or bistable multivibrator 345 includes a pair of cross-coupled transistors 346 and 347. The bases of the transistors 346 and 347 are coupled to the collectors of the transistors 347 and 346, respectively, via resistors 348 and 349. The base of transistor 346 is also resistively coupled to the fire alarm sense point, rendering the flip flop 345 responsive to the output of the fire-sensing circuit 335. The base of the transistor 347 is resistively connected to the output line 350 of a reset circuit 351, to be described, rendering the,

flipflop 345 responsive to the reset circuit. The collectors of the transistors 346 and 347 are connected to a source of positive potential 353 via resistors 354 and 355. The emitters of the transistors 346 and 347 are respectively connected to ground via a resistor and a diode.

The flip-flop 345 is in the normal or nonfire alarm condition when transistors 346 and 347 are nonconducting and conducting, respectively, and is in the abnormal or fire alarm condition when transistors 346 and 347 are conducting and nonconducting, respectively. Assuming the flip-flop 345 is in the normal or nonalarm condition, the flip-flop is switched to its fire alarm condition by the increase in potential at the fire alarm sense point, which is coupled to the base of the transistor 346 to switch this transistor from a nonconducting state to a conducting state, which in turn causes transistor 347 to switch from a conducting state to a nonconducting state. The flipflop 345 is switched from its alarm condition, wherein transistor 347 is nonconducting and transistor 346 is conducting, to its nonalarm condition, wherein transistor 346 is nonconducting and transistor 347 is conducting, by a relatively high potential signal on reset output line 350 which is coupled to the base of transistor 347.

ClRCUIT FAULT SENSING CIRCUIT A circuit fault sensing circuit 360 is provided to detect the decrease in potential at point H occasioned by a circuit fault, such as grounding or an open circuit in the loops 305 and/or 306. The circuit fault sensing circuit 360 includes a normally nonconducting transistor 361. The base of the transistor 361 is resistively coupled to point H to render the fault sensing circuit 360 responsive to the potential at point H. A capacitor 359 connected between the base of transistor 361 and ground serves as an AC bypass for the base circuit. The emitter of transistor 361 is connected to a voltage dividing network formed by resistors 363 and 364, which clamps the emitter. The collector of transistor 361 constitutes the output of the circuit fault sensing circuit 360 and is herein defined as the circuit alarm sensing point.

In operation, in the absence of a circuit fault in the loops 305 and 306, such as a ground condition and/or an open cir cuit condition, the DC potential at point H is at a specified, relatively high, normal level holding the transistor 361 of fault-sensing circuit 360 in a nonconducting state. With the transistor 361 in a nonconducting state, a relatively low potential is present at the collector of transistor 361 and, hence, at the circuit alarm sensing point. Should a circuit fault occur, such as by open circuiting and/or grounding loop 305 and/or loop 306, the potential at point H drops to ground potential, rendering the transistor 361 of the fault-sensing circuit 360 conductive. With transistor 361 conductive, the potential at the collector thereof, and hence at the circuit alarm sensing point, increases providing an output from the circuit fault sensing circuit 360 indicative of the existence of a fault in the loop circuit 304.

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Classifications
U.S. Classification340/509, 340/521, 340/518, 340/525
International ClassificationG08B25/14
Cooperative ClassificationG08B25/14
European ClassificationG08B25/14