US3530450A - Fire alarm systems with monitoring device for fire alarms connected in groups to a central station - Google Patents

Fire alarm systems with monitoring device for fire alarms connected in groups to a central station Download PDF

Info

Publication number
US3530450A
US3530450A US636173A US3530450DA US3530450A US 3530450 A US3530450 A US 3530450A US 636173 A US636173 A US 636173A US 3530450D A US3530450D A US 3530450DA US 3530450 A US3530450 A US 3530450A
Authority
US
United States
Prior art keywords
fire
fire alarm
alarm
fire alarms
alarms
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
US636173A
Other languages
English (en)
Inventor
Beat Walthard
Max Kuhn
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Cerberus AG
Original Assignee
Cerberus AG
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Cerberus AG filed Critical Cerberus AG
Application granted granted Critical
Publication of US3530450A publication Critical patent/US3530450A/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

Links

Images

Classifications

    • G—PHYSICS
    • G08—SIGNALLING
    • G08B—SIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
    • G08B29/00—Checking or monitoring of signalling or alarm systems; Prevention or correction of operating errors, e.g. preventing unauthorised operation
    • G08B29/12—Checking intermittently signalling or alarm systems
    • G08B29/14—Checking intermittently signalling or alarm systems checking the detection circuits
    • G08B29/145—Checking intermittently signalling or alarm systems checking the detection circuits of fire detection circuits

Definitions

  • a fire alarm system including a plurality of individual fire alarms arranged in groups and connected to a central station. In response to a condition test signal, the fire alarms sequentially produce signals indicative of their condition which signals are counted in a system evaluation means which determines which fire alarm of a group is defective.
  • the present invention relates to an improved fire alarm system comprising a central signal station to which electric fire alarms are connected in groups, wherein the number of conductors between the central signal station and the fire alarms is independent of the number of fire alarms. Furthermore, the inventive fire alarm system additionally includes an apparatus for producing electrical test signals by means of which alarm-simulating conditions are produced at the fire alarms which, in turn, bring about an electrical change in condition at an intact fire alarm, and further, the inventive system includes an apparatus for evaluating such changes and conditions.
  • a monitoring device in which the number of conductors leading from the central station to the fire alarms is independent of the number of connected fire alarms.
  • all of the fire alarms are simultaneously caused to respond from the location of the central station.
  • a current measuring device at the central station which is provided at one of both current delivery conductors of the fire alarm, the response of all fire alarms is monitored, whereby there is checked the coincidence of the total current with some predetermined reference value.
  • this arrangement is limited to groups having relatively few fire alarms.
  • the present invention is characterized by the features that means are provided at the fire alarms which, during the checking operation, bring about a response of the individual fire alarms which is staggered in time. Further, the apparatus for evaluating the response conditions of the individual fire alarms determines by means of a counting operation if all fire alarms of a group have responded.
  • the fire alarm 17 depicted in FIG. 2 consists of two ionization chambers 1 and 2, the air content of which can be rendered completely or partially conductive by radioactive preparations as is known in the art. Further, this fire alarm 17 comprises a switch element 3, which in this instance is formed by a field-effect transistor 3. Ionization chamber 1 functions as a measuring chamber, whereas ionization chamber 2 is employed as. a reference chamber and can also be replaced by a high-ohm resistor or an equivalent high-ohm element. Likewise, it is possible to use instead of the field-effect transistor 3, a different switch element with high-ohm input resistance, for instance another semiconductor device or a cold cathode tube.
  • the ionization chambers 1 and 2 are connected in series with respect to one another and are coupled via the conductors 10 and 20, respectively, with the central station 18 and, at such location, are connected with the voltage source 100*.
  • the gate of the field-effect transistor 3 is disposed at the point of juncture or connection of both ionization chambers 1 and 2. Its anode is coupled via a resistor 5 with the negative feed conductor 20, and its cathode via a resistor 5a with a positive feed conductor 10.
  • the resistor 5a is, at the same time, a part of a voltage divider circuit incorporating the resitor 5a and the Zener diode 4, wherein the Zener voltage and the potential at the gate of the field-effect transistor 3 is selected in such a manner that this field-effect transistor 3 blocks during the normal operating condition.
  • the anode of the field-effect transistor 3 is coupled with the control gate of a control rectifier 6 (SCR), the cathode of which is connected to the negative feed conductor 20 and the anode of which is connected to the positive feed conductor 10 through the voltage divider incorporating the resistor 13 and the resistor 14.
  • SCR control rectifier 6
  • the indicating lamp 12 is arranged parallel to the resistor 13, and a Zener diode is connected parallel to the resistor 14.
  • the displacement of the potential at the gate of the field-effect transistor 3 which is brought about by the entry of combustion gases into the measuring chamber 1 also can be realized for checking or monitoring purposes in that, the potential of the supply conductor 10 is appropriately reduced.
  • Such can be, for instance, realized by introducing a Zener diode '8 in the supply conductor within the central station 18, whereby the Zener diode 8 during normal operation is short-circuited by means of a switch 7.
  • the primary winding of a transformer 11 is connected in the supply conductor 10, and the secondary winding of the transformer is coupled to the input of the evaluation circuit 19.
  • pulse-shaped signals appear at the input of the evaluation circuit. 19*, which characterize in binary form the response condition of a fire alarm (impulse: fire alarm has responded; no impulse: fire alarm has not responded).
  • the evaluation of the binary signals takes place digitally in the form of a counting operation, whereby after a certain period of time the counting condition of the evaluation device 19 is read and compared with a reference value.
  • the capacitor 9 arranged in parallel to the reference chamber 2 assures that it is possible to freely select a staggering or sequencing of the periods of response time of the individual fire alarms.
  • This sequencing occurs as follows.
  • the potential of the conductor 10 is lowered by opening the switch 7, but the potential at the gate of the field-effect transistor 3 remains contsant for a moment.
  • the period of time in which the capacitor 9 discharges to the new lower potential via the high-ohm ionization chambers and via the gate-anode path of the field-effect transistor is adjustable and can be selected by suitable dimensioning of the value of capacitor 9.
  • Each capacitor in the individual fire alarms can be selected to have a graduated capacitance thus effecting a true sequential response through all fire alarms of a group.
  • the checking operation in each instance can be carried out two or more times in succession.
  • the switch 16 which interrupts the current supply for a short period of time only serves to reset or return the fire alarm after a checking or monitoring operation has been completed.
  • the point of connection of these two ionization chambers 104 and 106 is conducted or lead to the starter electrode of a cold-cathode tube 108.
  • the cold-cathode tube 108 (switch triode) in this case replaces the field-effect transistor 3 of FIG. 2.
  • the cathode of the cold-cathode tube 108 is connected by a diode 110 to one current conductor 112, whereas the anode is coupled via a resistor R, to the other supply conductor 114.
  • the cathode of the cold-cathode tube 108 is furthermore con ditionally connected by means of a capacitor 116 directly with the supply conductor L.
  • the ionization chamber 104 functioning as a reference chamber, is situated between the starter electrode and anode of the cold-cathode tube.
  • Each measuring ionization chamber 106 is connected via a separate conductor 118 with the cathode of the previous tube 108.
  • all of the fire alarms are of identical construction. The only exception is the first fire alarm M in which the measuring chamber MK is directly connected to the supply conductor 112.
  • the switch 120 in the central station SZ of the supply line 112 is closed, so that the fire alarms M M M are directly connected to the supply voltage 122.
  • the capacitors 116 are charged via the diode 110 to the supply voltage.
  • the coldcathode tubes are in the blocked condition. Now, if combustion gases enter one of the measuring chambers 106, there appears at the starter electrode of the corresponding cold-cathode tube 108 an increased potential whereby the tube responds and draws a current via the resistor 124 and the supply conductor 114. This current causes an alarm-triggering device at the central station SZ to respond, for instance, a relay. Only a minimum voltage increase appears across the diode 110 of the fire alarm M which has responded, so that the subsequent fire alarms M remain in the rest condition.
  • the checking operation is initiated by Opening the switch 120.
  • the potential of the supply conductor 112 which now appears at the tap of a voltage divider circuit, namely, the resistor 126 and the resistor 128, is increased in such a manner that the cold-cathode tube 108 ignites because of the appropriate increase of the starter potential.
  • the individual diodes 110 of each alarm are prebiased in the blocking direction.
  • the increase in the potential of the conductor 112, in the first instance does not have any effect upon the remaining fire alarms M M
  • a current flows in the closed circuit of the fire alarm M which comprises the capacitor 116, the conducting cold-cathode tube 108, and the resistor 124. This current discharges the capacitor 116 to the operating voltage of the tube 108.
  • the potential at the cathode of the cold-cathode tube 108 reaches the potential of the conductor 112, so that the diode 110 conducts and draws a current through the primary winding of a transformer 130 provided in the central station SZ at the supply conductor 114.
  • the evaluation device 19 contains a digital counter at which the numeral 1 appears upon the current of the first impulse.
  • the potential of the supply conductor 112 is supplied via the conductor 118 to the one electrode of the next measuring chamber 106.
  • the corresponding increase in potential at the starter electrode of the cold-cathode tube 108 causes such to conduct whereby after discharge of the capacitor 116 via the transformer 130, a second impulse appears at the input of the evaluation device 19.
  • the count condition at the evaluation device 19 achieve a prescribed digital reference value.
  • a further indication that all fire alarms of a group have responded resides in connecting a relay 132 in series with the capaci- 6 tor C of the last fire alarm M,,.
  • This relay 132 is energized for a short interval upon response of the last fire alarm and closes a work contact 134.
  • This work contact 134 can be, for instance, employed for triggering an appropriate indicating device at the central station.
  • the resistor 128 is dimensioned in such a manner to be large enough so that the short-circuit current no longer brings about energization of the relay 136, then an increase of the voltage at the test point or location 140 can be used as the criterion for the response for the relay 132 and, therefore, the last fire alarm M In this instance, the voltage increase at point 140 simultaneously brings about switching-off of the responsive fire alarm, so that after termination of the checking operation, only the switch has to be closed in order to again place the installation in normal operation.
  • the transformer 130 and the relay 132 can also be combined with one another.
  • the checking operation which can last for up to several seconds, is repeated at appropriate time intervals.
  • a fire alarm system comprising:
  • said fire alarms including means responsive to said electric test signal to produce alarm-simulating conditions in a time sequential manner;
  • means for evaluating said alarm-simulating conditions of each of said plurality of fire alarms said means for evaluating including a counting means for counting said sequence of alarm-simulating conditions to determine whether all fire alarms of a group have responded.
  • a reference ionization chamber connected to said measuring ionization chamber
  • a cold-cathode tube having anode, cathode and starter electrode; a resistor; a capacitor; a diode;
  • means including said capacitor connecting said cathode electrode to said positive supply conductor
  • a capacitor connected in parallel with said reference ionization chamber, the capacitance of said capacitor in each fire alarm being graduated; a field-effect transistor means coupled across said powe supply and including a gate electrode;
  • said means for generating an electric test signal includes means at said central signal station for dropping said supply voltage during the checking operation, whereby the response times of said fire alarms to said electric test signal is caused to be staggered.
  • fire alarms further include means for transforming said alarm-simulating conditions into binary signals comprising stepwise current increases at said central signal station, said central signal station including means for differentiating said current increases into impulsespsaid means for evaluating includinga digital counter.
  • a fire alarm system comprising:
  • counting means included at said central signal station for counting each said sequential condition response signal and producing a system evaluation signal in response thereto.

Landscapes

  • Engineering & Computer Science (AREA)
  • Computer Security & Cryptography (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Fire Alarms (AREA)
  • Alarm Systems (AREA)
US636173A 1966-05-09 1967-05-04 Fire alarm systems with monitoring device for fire alarms connected in groups to a central station Expired - Lifetime US3530450A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
CH670366A CH473431A (de) 1966-05-09 1966-05-09 Verfahren zur Betriebsüberwachung von Feuermeldern

Publications (1)

Publication Number Publication Date
US3530450A true US3530450A (en) 1970-09-22

Family

ID=4313718

Family Applications (3)

Application Number Title Priority Date Filing Date
US636173A Expired - Lifetime US3530450A (en) 1966-05-09 1967-05-04 Fire alarm systems with monitoring device for fire alarms connected in groups to a central station
US636174A Expired - Lifetime US3564524A (en) 1966-05-09 1967-05-04 Fire alarm system having a diode coupled checking circuit means
US78127A Expired - Lifetime US3678510A (en) 1966-05-09 1970-10-05 Fire alarm systems equipped with circuit monitoring devices

Family Applications After (2)

Application Number Title Priority Date Filing Date
US636174A Expired - Lifetime US3564524A (en) 1966-05-09 1967-05-04 Fire alarm system having a diode coupled checking circuit means
US78127A Expired - Lifetime US3678510A (en) 1966-05-09 1970-10-05 Fire alarm systems equipped with circuit monitoring devices

Country Status (11)

Country Link
US (3) US3530450A (forum.php)
AT (2) AT278599B (forum.php)
BE (1) BE698199A (forum.php)
CH (1) CH473431A (forum.php)
DE (1) DE1281321B (forum.php)
DK (1) DK136839B (forum.php)
ES (1) ES340611A1 (forum.php)
GB (1) GB1140294A (forum.php)
IL (1) IL27907A (forum.php)
NL (1) NL162763C (forum.php)
SE (2) SE365327B (forum.php)

Cited By (16)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3702468A (en) * 1970-08-10 1972-11-07 Nittan Co Ltd Fire alarming system
US3713128A (en) * 1970-08-07 1973-01-23 Systron Donner Corp Vault alarm system and method
US3714433A (en) * 1970-09-28 1973-01-30 Nittan Co Ltd Ionization smoke detector
US3728703A (en) * 1970-10-12 1973-04-17 Edward Co Inc Fire detector stabilizer circuit
US3778796A (en) * 1970-03-31 1973-12-11 Nittan Co Ltd Fire alarming system
US3866195A (en) * 1973-05-07 1975-02-11 Fire Alert Company Combustion product detector and method of calibrating
US3886534A (en) * 1973-01-08 1975-05-27 Polar Corp Security system
US3909815A (en) * 1973-06-01 1975-09-30 Gamma Electronic Detector for fumes and combustion gases
US4168497A (en) * 1976-03-15 1979-09-18 Cerberus Ag Fire and smoke sensing system
US4224611A (en) * 1977-03-25 1980-09-23 Muenstedt Wolfgang Smoke alarm station
US4481502A (en) * 1982-03-26 1984-11-06 Dawson N Rick Central smoke alarm and annunciator
US4595914A (en) * 1983-04-11 1986-06-17 Pittway Corporation Self-testing combustion products detector
US4916432A (en) * 1987-10-21 1990-04-10 Pittway Corporation Smoke and fire detection system communication
US5708414A (en) * 1993-08-19 1998-01-13 Sentrol, Inc. Sensitivity fault indication technique implemented in smoke detector system with self-diagnostic capabilities
US6396405B1 (en) 1993-08-19 2002-05-28 General Electric Corporation Automatic verification of smoke detector operation within calibration limits
CN112735110A (zh) * 2020-12-29 2021-04-30 深圳市安室智能有限公司 智能报警器测试系统、方法及装置

Families Citing this family (22)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3717862A (en) * 1969-10-16 1973-02-20 Nittan Co Ltd Fire detecting system and testing means therefor
US3753258A (en) * 1970-03-31 1973-08-14 Nittan Co Ltd Fire alarming system
US3806921A (en) * 1972-04-18 1974-04-23 Aboyne Pty Ltd Detector device
US3755799A (en) * 1972-07-31 1973-08-28 Pyronics Inc Ultraviolet flame detector
US3842409A (en) * 1972-12-13 1974-10-15 Unitec Inc Ionization detector apparatus
US4003039A (en) * 1973-07-19 1977-01-11 Pyrotector, Incorporated Optical fire detection system
DE2454196C3 (de) * 1974-06-14 1985-02-07 Cerberus AG, Männedorf, Zürich Brandmeldeanlage
US3983548A (en) * 1975-02-19 1976-09-28 Tufts Howard L Fire detection system
USRE30117E (en) * 1975-07-25 1979-10-16 Cerberus Ag Ionization-type fire or smoke sensing system
US3987423A (en) * 1975-12-22 1976-10-19 The United States Of America As Represented By The United States Energy Research And Development Administration Ionization-chamber smoke detector system
US4097850A (en) * 1976-11-01 1978-06-27 Pittway Corporation Means for adjusting and for testing a detecting device
DE2754746C3 (de) * 1977-12-08 1981-10-15 Preussag Ag Feuerschutz, 2060 Bad Oldesloe Meldeeinrichtung
DE2857333C2 (de) * 1978-10-24 1984-08-23 Preussag Ag Feuerschutz, 2060 Bad Oldesloe Meldeeinrichtung
DE3050185A1 (de) * 1980-02-08 1982-12-02 Hartwig Dipl.-Ing. 2409 Scharbeutz Beyersdorf Brandmeldeeinrichtung
DE3004753C2 (de) * 1980-02-08 1983-12-22 Hartwig Dipl.-Ing. 2409 Scharbeutz Beyersdorf Brandmeldeeinrichtung
GB8515774D0 (en) * 1985-06-21 1985-07-24 Mckenna F E Fire hazard detection systems
US5019805A (en) * 1989-02-03 1991-05-28 Flash-Alert Inc. Smoke detector with strobed visual alarm and remote alarm coupling
US5416391A (en) * 1992-07-31 1995-05-16 Correa; Paulo N. Electromechanical transduction of plasma pulses
US5233707A (en) * 1992-11-05 1993-08-10 Ladd Furniture Co., Inc. Stackable bunk beds forming a modular furniture assembly
DE102009060418A1 (de) * 2009-12-22 2011-06-30 Minimax GmbH & Co. KG, 23843 Prüfeinrichtung für Gefahrenmeldeanlagen
US9564045B2 (en) * 2014-04-14 2017-02-07 Stephen D. Ainsworth Alarm system testing device
CN110533895A (zh) * 2019-09-29 2019-12-03 赛特威尔电子股份有限公司 一种火灾报警器的检查方法及火灾报警装置

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2697824A (en) * 1953-06-26 1954-12-21 Petcar Res Corp Test circuit for flame detector systems
US3438019A (en) * 1965-10-11 1969-04-08 Us Navy Data gathering system

Family Cites Families (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2667630A (en) * 1950-12-22 1954-01-26 Jorgensen Asger Lars Automatic fire alarm system
DE966199C (de) * 1952-12-13 1957-07-11 Telefonbau & Normalzeit Gmbh Pruefeinrichtung fuer Empfangszentralen von Meldeanlagen, insbesondere solchen, die mit Morsesicherheitsschaltung ausgeruestet sind
DE1067708B (de) * 1956-05-09 1959-10-22 Siemens Ag Anordnung zur Kennzeichnung des Herkunftsortes von Signalen in wechselstromgespeisten Meldeleitungen
US2917731A (en) * 1958-05-23 1959-12-15 George H Rodgers Multiple indicator system with resettable warning signal
US3064245A (en) * 1959-05-25 1962-11-13 Jr John E Lindberg Heat detection device
US3192506A (en) * 1960-03-04 1965-06-29 Sargrove Electronics Ltd Electronic indicator system more particularly for use in mines
CH380594A (de) * 1960-11-02 1964-07-31 Securiton Ag Ionisations-Brandmeldeanlage
US3134970A (en) * 1961-05-31 1964-05-26 American District Telegraph Co Alarm system

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2697824A (en) * 1953-06-26 1954-12-21 Petcar Res Corp Test circuit for flame detector systems
US3438019A (en) * 1965-10-11 1969-04-08 Us Navy Data gathering system

Cited By (18)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3778796A (en) * 1970-03-31 1973-12-11 Nittan Co Ltd Fire alarming system
US3713128A (en) * 1970-08-07 1973-01-23 Systron Donner Corp Vault alarm system and method
US3702468A (en) * 1970-08-10 1972-11-07 Nittan Co Ltd Fire alarming system
US3714433A (en) * 1970-09-28 1973-01-30 Nittan Co Ltd Ionization smoke detector
US3728703A (en) * 1970-10-12 1973-04-17 Edward Co Inc Fire detector stabilizer circuit
US3886534A (en) * 1973-01-08 1975-05-27 Polar Corp Security system
US3866195A (en) * 1973-05-07 1975-02-11 Fire Alert Company Combustion product detector and method of calibrating
US3909815A (en) * 1973-06-01 1975-09-30 Gamma Electronic Detector for fumes and combustion gases
US4168497A (en) * 1976-03-15 1979-09-18 Cerberus Ag Fire and smoke sensing system
US4224611A (en) * 1977-03-25 1980-09-23 Muenstedt Wolfgang Smoke alarm station
US4481502A (en) * 1982-03-26 1984-11-06 Dawson N Rick Central smoke alarm and annunciator
US4595914A (en) * 1983-04-11 1986-06-17 Pittway Corporation Self-testing combustion products detector
US4916432A (en) * 1987-10-21 1990-04-10 Pittway Corporation Smoke and fire detection system communication
US5708414A (en) * 1993-08-19 1998-01-13 Sentrol, Inc. Sensitivity fault indication technique implemented in smoke detector system with self-diagnostic capabilities
US5821866A (en) * 1993-08-19 1998-10-13 Slc Technologies, Inc. Self-diagnosing smoke detector assembly
US5936533A (en) * 1993-08-19 1999-08-10 Slc Technologies, Inc. Method of automatic verification of smoke detector operation within calibration limits
US6396405B1 (en) 1993-08-19 2002-05-28 General Electric Corporation Automatic verification of smoke detector operation within calibration limits
CN112735110A (zh) * 2020-12-29 2021-04-30 深圳市安室智能有限公司 智能报警器测试系统、方法及装置

Also Published As

Publication number Publication date
GB1140294A (en) 1969-01-15
NL6706275A (forum.php) 1967-11-10
IL27907A (en) 1972-01-27
NL162763B (nl) 1980-01-15
DK136839C (forum.php) 1978-05-16
SE338527B (forum.php) 1971-09-06
NL162763C (nl) 1980-06-16
US3678510A (en) 1972-07-18
AT278599B (de) 1970-02-10
US3564524A (en) 1971-02-16
CH473431A (de) 1969-05-31
AT279431B (de) 1970-03-10
BE698199A (forum.php) 1967-10-16
DK136839B (da) 1977-11-28
ES340611A1 (es) 1968-06-01
DE1281321B (de) 1968-10-24
SE365327B (forum.php) 1974-03-18

Similar Documents

Publication Publication Date Title
US3530450A (en) Fire alarm systems with monitoring device for fire alarms connected in groups to a central station
US3603949A (en) Fire alarm installation
US4595914A (en) Self-testing combustion products detector
KR100228042B1 (ko) 분리된 표시기를 갖춘 고장회로 검지기
US3882476A (en) Alarm system with periodic test section
US3821734A (en) Fire alarm system with remote central station
US3676680A (en) Ionization fire alarm with insulation monitoring system
US4030095A (en) Pulsed alarm system
SE507139C2 (sv) Sätt och anordning för funktionskontroll av ljustända halvledarventilenheter i HVDC-ventilanläggningar
GB1584045A (en) Fire alarms
JPH0430699B2 (forum.php)
JPS64753B2 (forum.php)
GB1202760A (en) Improvements in or relating to alarm signal installations
US3160866A (en) Electric alarm system
US3621262A (en) Alarm device gas discharge tube
US3717862A (en) Fire detecting system and testing means therefor
US3562730A (en) Alarm control unit and test circuit therefor
US3491290A (en) Quick-response high voltage test system for locating and resolving faults in insulation of electrical cables
US2556363A (en) Alarm system with circuit integrity checking means
US3559196A (en) Fire alarm with bistable characteristics
US3750123A (en) Smoke sensing circuit with battery standby
US3550111A (en) Security alarm system
US4506255A (en) Operation test circuit for fire detectors
US3553674A (en) Theft alarm system utilizing a bridge having a capacitive voltage divider
US3795905A (en) Lamp failure detection system