US3832678A - Fire alarm system - Google Patents

Fire alarm system Download PDF

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Publication number
US3832678A
US3832678A US00196045A US19604571A US3832678A US 3832678 A US3832678 A US 3832678A US 00196045 A US00196045 A US 00196045A US 19604571 A US19604571 A US 19604571A US 3832678 A US3832678 A US 3832678A
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Prior art keywords
fire
voltage
current conducting
resistor
polarity
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US00196045A
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English (en)
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K Nilsson
G Nilvid
B Gysell
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Individual
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    • G—PHYSICS
    • G08—SIGNALLING
    • G08B—SIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
    • G08B25/00—Alarm systems in which the location of the alarm condition is signalled to a central station, e.g. fire or police telegraphic systems
    • G08B25/01—Alarm systems in which the location of the alarm condition is signalled to a central station, e.g. fire or police telegraphic systems characterised by the transmission medium
    • G08B25/018—Sensor coding by detecting magnitude of an electrical parameter, e.g. resistance

Definitions

  • a fire alarm system including a plurality of individual alarm devices connected to a two-wire electrical loop, each alarm device including a unidirectional current conducting means, a resistive impedance, and a switch adapted to move to an actuated position in response to fire detection.
  • a bidirectional voltage source a passive load having a predetermined value, and a resisitve impedance element also of a predetermined value, said plurality of alarm devices and the passive load forming one portion of a voltage divider, the other portion of the voltage divider being formed by the resistive impedance element.
  • a fire alarm signal can be distinguished from all other signals generated by the system, in that under normal operation, the voltage drop across the resistive impedance element is not altered in response to the application of a first polarity voltage and then a second polarity voltage, while in response to the detection of a fire, a switch in an alarm device assumes its actuated position, whereby the voltage drop across the resistive impedance element assumes a first value in response to a first polarity voltage and a second value different from the first value in response to a second polarity voltage.
  • the potential drop across the resistive impedance element remains the same for both polarity voltages.
  • This invention relates to a fire alarm system having a plurality of individual alarm devices connected to a two-wire electrical loop having a definite inpedance, said individual alarm devices being adapted in actuated position to allow current to flow in only one direction and said electrical loop being connected to a voltage sourc adapted to generate a voltage having a first polarity and a second polarity.
  • this invention relates to a fire alarm system comprising a two-wire electrical loop terminatingwith a load having a definite impedancy, a plurality of individual alarm devices connected to said electrical loop, each of said individual alarm devices comprising a uni-directional means, an impedance and a switch adapted in case of fire to be changed over from a rest position into an actuated position, said alarm devices being adapted in their actuated state to allow current to pass in one direction only and said electrical loop being connected to a voltage source devised to generate a voltage having a first polarity and a second polarity, and a resistive impedance connected to said loop and disposed together with the load to constitute a voltage divider and a voltage measuring means connected across said resistive impedance.
  • a central station which in the following will be called the measuring instrument, shall receive signals which are indicative of various states, which can appear in the loop.
  • states to which the measuring instrument should be sensitive are the normal state, the state of fire signal, the state of short circuit, the state of interruption of the circuit and the state of ground connection.
  • the signal indicating fire is unique and thereby prevents a fire alarm to be emitted for example, when a connection to ground appears in the loop.
  • the individual alarm devices become relatively expensive and include e.g., two uni-directional current conducting means to render possible conduction of current in two directions. Therefore, said systems become relatively complicated and expensive.
  • One main object of the invention is thus to provide a fire alarm system which, inspite of complying with the stated requirements on distinguishing various signal states, contains one uni-directional current conducting means only in each individual device and consequently becomes cheaper and, nevertheless, more reliable in operation.
  • Another object of the invention is to provide such a fire alarm system that depending on the type of detector used each individual alarm device is capable of operating with either a closing contact or an opening contact connected in series to the uni-directional current conducting means in contradiction to previously known systems which comply with the above stated requirements and which can operate only with a circuit closing contact in the detector signaling the state of fire.
  • FIG. 1 is a more or less diagrammatic representation of a system made according to the invention and having alarm devices connected in parallel to one another between the conductors or an electrical loop,
  • FIG. 2 is the equivalent diagram for the system shown in FIG. 1 in its normal condition of operation
  • FIG. 3 is the equivalent diagram of the system upon detection of fire
  • FIG. 4 is the equivalent diagram of the system on connection to ground
  • FIG. 5 is a schematical representation of a modified alarm system and FIG. 6 is a representation of a system having alarm devices connected in series to one another.
  • FIG. 1 a fire alarm system constructed according to the invention is represented highly diagrammatically.
  • the system comprises a closed electrical loop with conductors l and 2 which are connected to a resistive load R having high resistance such as 5 Kohm, for example, and which in the simplest case consists of a resistor.
  • the closed loop is fed with voltage from a voltage source 3.
  • a resistor R Connected to the loop and a point common to the terminals of the loop is a resistor R having a low ohm value of e.g. 200 ohms, across which resistor is connected a measuring instrument 4 which measures the voltage Vm across the resistor R
  • the closed loop thus together with the resistor R forms a voltage divider.
  • Each individual alarm device such as Al, for example, consists of a resistor R which is connected in series with a unidirectional current conducting means suchas a diode 5, and a normally open switch 6 adapted to close in case of fire.
  • the voltage source 3 is adapted to generate continuously or at a selectable moment a DC-voltage Vin, the polarity of which alternates with a frequency of e.g., 1 Hertz.
  • a DC-voltage having an arbitrary frequency can also be employed, but a DC-voltage is preferred because of the field of disturbances developed around the loop when AC-voltage is supplied.
  • Vml Vin'R /R +R It is easily understood that on supply to the circuit of a periodically alternating DC-voltage or an AC-voltage the absolute value for Vml will remain unchanged and that only the electric sign is changed.
  • a state similar to fire is a ground connection in the loop and this state must not result in the generation of a fire alarm.
  • a connection to ground of the conductors l and 2 means that a resistance is connected in parallel to R This resistance is illustrated in the equivalent diagram of FIG. 4 by the resistor R Since no switch 6 has been closed, no diode 6 has been switched in and the voltage Vm3 measured by the measuring instrument 4 will be independent of the polarity of the voltage from the voltage source 3 which means that -Vm3 will become equal to Vm3.
  • the voltage source 3 On short circuiting of the conductors 1 and 2 in the diagram of FIG. 1 and when disregarding the resistance of the conductors, the voltage source 3 will be connected directly across the resistor R and therefore the measuring instrument 4 will be supplied with the whole voltage Vin irrespective of the polarity thereof. This signals indicating a fault is also easily distinguishable from the fire indicating signals and therefore no fire alarm will be started.
  • the measuring instrument 4 may consist of a voltage meter adapted to transfer to the alarm emitting conductor signals according to the equations (2) and (3), or an analogue-digital converter or some other suitable device.
  • the voltage source 3 may be a DC-voltage source devised continuously to feed a DC-voltage to the loop and equipped with a polarity inverter which becomes operative when an abnormal voltage appears across the resistor R or some other resistive means and which periodically reverses the current direction of the DC- voltage supplied to the conductors 1 and 2. If desired, the current direction may be reversed all the time during the normal conditions of operation of the system. As mentioned above, the voltage source 3 may also be adapted to generate an AC-voltage having an arbitrary frequency.
  • the shown switch 6 may be a mechanical contact which in case of fire is closed by means not shown here, or a transistor or a controlled silicon rectifier which receives a control signal from a smoke detector or the like or some other conventional detecting device.
  • a controlled rectifier said rectifier also replaces the separately shown rectifier 5 as is illustrated in FIG. 5 which shows a modification of the alarm device A].
  • the silicon controlled rectifier 5 replaces both the diode 5 and the switch 6 of FIG. 1.
  • the control electrode 7 of the silicon rectifier is normally dead, but connected to a detector not shown here such as e.g., a flue gas detector which as soon as flue gas or smoke appears generates a signal to the control electrode 7 whereby the silicon rectifier is made capable of conducting current in one direction, i.e., in the illustrated case when the conductor 2 is at a higher potential than the conductor 1.
  • FIG. 6 shows a system according to the invention intended for fire alarm systems with a normally closed switch 6', which is opened in case of fire and consists e.g., of a simple fuse.
  • the switch 6' is connected in parallel with the diode 5 and the resistor R; in each alarm device, e.g., the alarm device Al.
  • the alarm devices Al A'n are in this case connected in series with one another in the simple loop consisting of the conductor 1', the load resistance R, and the conductor 2.
  • the voltage source 3 which is of the same kind as the source described hereinbefore is with its one pole connected to the conductor 1' and with its other pole to one end of the resistor R the other end of which is connected to the conductor 2'.
  • the measuring instrument 4' which is of the same kind as the measuring instrument 4 described above is connected over the resistor R' and provided with a conductor 7' for the generation of fire alarm signal.
  • the measuring instrument 4 will under the conditions set out above measure the voltage This deviation from the normal value means that the voltage source is subjected to current reversion as earlier described, and hereby the loop will be closed over the diode and the measuring instrument 4' will measure the voltage whereby it is confirmed that the case of fire actually is at hand.
  • the signals 'Vm5 and Vm6 differ from the signals generated by other possible conditions in the circuit such as short circuiting, connection to ground or conductor breaks.
  • a fire alarm system comprising a pair of common conductors (1, 2; 1', 2) terminating with a load resistor (R,; R',) having a predetermined resistance, a plu-,
  • each of said individual alarm devices comprising a single unidirectional current conducting means (5; 5') in series with a resistive element (R R;,) and a switch (6; 6'; 5a) adapted in case of fire to be changed over from a rest position into an actuated position, said switches being arranged in their rest positions to prevent current from flowing through the respective unidirectional current conducting means and the series connected resistive element, and in their actuated positions to allow current to flow in one direction only through said unidirectional current conducting means and the series connected resistive element, and a measuring resistor R R' connected with its one end to one of the conductors and with its other end to one terminal of a voltage source (3; 3'), the other terminal of said voltage source being connected to the input end of the other conductor, and said voltage source being devised to generate a voltage having a first and a second polarity, the measuring resistor being disposed together with the load resistor to
  • each alarm device includes a resistor (R which is connected in series to a uni-directional current conducting element (5) and to a normally open switch (6) said alarm devices being connected in parallel with the load.
  • each alarm device includes a resistor (R;,) serially connected to a uni-directional current conducting element (5') and a normally closed switch (6) connected in parallel to said resistor and said element, said alarm devices being connected in series with one another and the load.
  • said uni-directional current conducting element (5, 5') and the associated switch (6, 6') are constituted by a single controlled silicon rectifier (5a) the control electrode (7) of said controlled rectifier being diislposed in the case of fire to receive an actuating sign 9.
  • said uni-directional current conducting element and the associated switch consists of a transistor disposed in the case of fire to receive actuating signal vfrom a detector.

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  • Business, Economics & Management (AREA)
  • Emergency Management (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Fire Alarms (AREA)
  • Fire-Detection Mechanisms (AREA)
  • Alarm Systems (AREA)
US00196045A 1970-11-12 1971-11-05 Fire alarm system Expired - Lifetime US3832678A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
SE7015288A SE402660B (sv) 1970-11-12 1970-11-12 Brandalarmanleggning

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US3832678A true US3832678A (en) 1974-08-27

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US00196045A Expired - Lifetime US3832678A (en) 1970-11-12 1971-11-05 Fire alarm system

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US (1) US3832678A (enrdf_load_stackoverflow)
BE (1) BE775169A (enrdf_load_stackoverflow)
CH (1) CH540539A (enrdf_load_stackoverflow)
DE (1) DE2154537A1 (enrdf_load_stackoverflow)
DK (1) DK129069B (enrdf_load_stackoverflow)
FI (1) FI53762C (enrdf_load_stackoverflow)
GB (1) GB1338690A (enrdf_load_stackoverflow)
NL (1) NL7115165A (enrdf_load_stackoverflow)
NO (1) NO131693C (enrdf_load_stackoverflow)
SE (1) SE402660B (enrdf_load_stackoverflow)

Cited By (22)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3991413A (en) * 1975-06-23 1976-11-09 Berger Philip H Constant current detector system
US4110683A (en) * 1977-07-08 1978-08-29 The United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration Apparatus including a plurality of spaced transformers for locating short circuits in cables
US4161727A (en) * 1976-09-15 1979-07-17 Siemens Aktiengesellschaft Process for generating and transmitting different analog measured values to a central control from a plurality of fire alarm circuits which are arranged in the form of a chain in an alarm loop
US4162489A (en) * 1976-08-24 1979-07-24 Siemens Aktiengesellschaft Fire alarm system comprising a plurality of alarms which may be operated by way of an alarm loop
US4287515A (en) * 1979-04-27 1981-09-01 Baker Industries, Inc. Fire detection system with multiple output signals
EP0072187A1 (en) * 1981-02-06 1983-02-16 Institute For Industrial Research And Standards Method and apparatus for identifying the location of a change in state of a part of an electrical circuit
US4568923A (en) * 1982-02-04 1986-02-04 Nittan Company, Limited Fire alarm system
EP0224819A1 (de) * 1985-11-26 1987-06-10 Siemens Aktiengesellschaft Gefahrenmeldeanlage
WO2013052622A3 (en) * 2011-10-06 2013-06-20 Microchip Technology Incorporated Differential current measurements to determine ion current in the presence of leakage current
US8847802B2 (en) 2011-10-06 2014-09-30 Microchip Technology Incorporated Microcontroller ADC with a variable sample and hold capacitor
US8884771B2 (en) 2012-08-01 2014-11-11 Microchip Technology Incorporated Smoke detection using change in permittivity of capacitor air dielectric
US8902760B2 (en) 1998-04-10 2014-12-02 Chrimar Systems, Inc. Network system and optional tethers
US9071264B2 (en) 2011-10-06 2015-06-30 Microchip Technology Incorporated Microcontroller with sequencer driven analog-to-digital converter
US9176088B2 (en) 2011-12-14 2015-11-03 Microchip Technology Incorporated Method and apparatus for detecting smoke in an ion chamber
US9189940B2 (en) 2011-12-14 2015-11-17 Microchip Technology Incorporated Method and apparatus for detecting smoke in an ion chamber
US9207209B2 (en) 2011-12-14 2015-12-08 Microchip Technology Incorporated Method and apparatus for detecting smoke in an ion chamber
US9252769B2 (en) 2011-10-07 2016-02-02 Microchip Technology Incorporated Microcontroller with optimized ADC controller
US9257980B2 (en) 2011-10-06 2016-02-09 Microchip Technology Incorporated Measuring capacitance of a capacitive sensor with a microcontroller having digital outputs for driving a guard ring
US9467141B2 (en) 2011-10-07 2016-10-11 Microchip Technology Incorporated Measuring capacitance of a capacitive sensor with a microcontroller having an analog output for driving a guard ring
US9823280B2 (en) 2011-12-21 2017-11-21 Microchip Technology Incorporated Current sensing with internal ADC capacitor
US10210747B1 (en) * 2018-05-25 2019-02-19 Stephen David Ainsworth Fire alarm testing device and method
EP3573033A2 (en) 2018-05-25 2019-11-27 Stephen David Ainsworth Fire alarm testing device and method

Families Citing this family (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS595955B2 (ja) * 1979-07-27 1984-02-08 ホーチキ株式会社 火災報知機
DE2935335C2 (de) * 1979-08-31 1985-08-08 Siemens AG, 1000 Berlin und 8000 München Gleichstrommeldeanlage
DE3043357C2 (de) * 1980-11-17 1985-01-17 Siemens AG, 1000 Berlin und 8000 München Verfahren und Vorrichtung zur Widerstandsmessung an einer Meldeleitung
DE3719988A1 (de) * 1987-06-15 1988-12-29 Total Feuerschutz Gmbh Einzelidentifikation

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US3268881A (en) * 1963-08-01 1966-08-23 Alfred W Vasel Detection device
US3603949A (en) * 1967-06-26 1971-09-07 Cerberus Ag Fire alarm installation
US3611362A (en) * 1969-03-19 1971-10-05 Gen Signal Of Canada Ltd Alarm sensing and indicating systems
US3626403A (en) * 1968-04-29 1971-12-07 Goodwin Alfred George Ive Protective systems and apparatus therefor
US3653025A (en) * 1969-08-04 1972-03-28 Caswell Equipment Co Inc Signalling system
US3676877A (en) * 1970-04-18 1972-07-11 Mittan Co Ltd Fire alarm system with fire zone locator using zener diode voltage monitoring
US3711854A (en) * 1971-10-19 1973-01-16 Federal Sign And Signal Corp Parallel alarm circuit having series supervision
US3716834A (en) * 1971-10-07 1973-02-13 H Adams Data transmission system with immunity to circuit faults

Patent Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3268881A (en) * 1963-08-01 1966-08-23 Alfred W Vasel Detection device
US3603949A (en) * 1967-06-26 1971-09-07 Cerberus Ag Fire alarm installation
US3626403A (en) * 1968-04-29 1971-12-07 Goodwin Alfred George Ive Protective systems and apparatus therefor
US3611362A (en) * 1969-03-19 1971-10-05 Gen Signal Of Canada Ltd Alarm sensing and indicating systems
US3653025A (en) * 1969-08-04 1972-03-28 Caswell Equipment Co Inc Signalling system
US3676877A (en) * 1970-04-18 1972-07-11 Mittan Co Ltd Fire alarm system with fire zone locator using zener diode voltage monitoring
US3716834A (en) * 1971-10-07 1973-02-13 H Adams Data transmission system with immunity to circuit faults
US3711854A (en) * 1971-10-19 1973-01-16 Federal Sign And Signal Corp Parallel alarm circuit having series supervision

Cited By (31)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3991413A (en) * 1975-06-23 1976-11-09 Berger Philip H Constant current detector system
US4162489A (en) * 1976-08-24 1979-07-24 Siemens Aktiengesellschaft Fire alarm system comprising a plurality of alarms which may be operated by way of an alarm loop
US4161727A (en) * 1976-09-15 1979-07-17 Siemens Aktiengesellschaft Process for generating and transmitting different analog measured values to a central control from a plurality of fire alarm circuits which are arranged in the form of a chain in an alarm loop
US4110683A (en) * 1977-07-08 1978-08-29 The United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration Apparatus including a plurality of spaced transformers for locating short circuits in cables
US4287515A (en) * 1979-04-27 1981-09-01 Baker Industries, Inc. Fire detection system with multiple output signals
EP0072187A1 (en) * 1981-02-06 1983-02-16 Institute For Industrial Research And Standards Method and apparatus for identifying the location of a change in state of a part of an electrical circuit
US4568923A (en) * 1982-02-04 1986-02-04 Nittan Company, Limited Fire alarm system
EP0224819A1 (de) * 1985-11-26 1987-06-10 Siemens Aktiengesellschaft Gefahrenmeldeanlage
US9019838B2 (en) 1998-04-10 2015-04-28 Chrimar Systems, Inc. Central piece of network equipment
US8942107B2 (en) 1998-04-10 2015-01-27 Chrimar Systems, Inc. Piece of ethernet terminal equipment
US9812825B2 (en) 1998-04-10 2017-11-07 Chrimar Systems, Inc. Ethernet device
US9049019B2 (en) 1998-04-10 2015-06-02 Chrimar Systems, Inc. Network equipment and optional tether
US8902760B2 (en) 1998-04-10 2014-12-02 Chrimar Systems, Inc. Network system and optional tethers
CN103946703B (zh) * 2011-10-06 2017-02-22 密克罗奇普技术公司 用以确定存在漏电流时的离子电流的差动电流测量
US9805572B2 (en) 2011-10-06 2017-10-31 Microchip Technology Incorporated Differential current measurements to determine ion current in the presence of leakage current
US8847802B2 (en) 2011-10-06 2014-09-30 Microchip Technology Incorporated Microcontroller ADC with a variable sample and hold capacitor
US9071264B2 (en) 2011-10-06 2015-06-30 Microchip Technology Incorporated Microcontroller with sequencer driven analog-to-digital converter
WO2013052622A3 (en) * 2011-10-06 2013-06-20 Microchip Technology Incorporated Differential current measurements to determine ion current in the presence of leakage current
TWI580959B (zh) * 2011-10-06 2017-05-01 微晶片科技公司 用於判定離子腔室中之離子電流的方法及用於偵測煙霧之裝置
CN103946703A (zh) * 2011-10-06 2014-07-23 密克罗奇普技术公司 用以确定存在漏电流时的离子电流的差动电流测量
US9437093B2 (en) 2011-10-06 2016-09-06 Microchip Technology Incorporated Differential current measurements to determine ION current in the presence of leakage current
US9257980B2 (en) 2011-10-06 2016-02-09 Microchip Technology Incorporated Measuring capacitance of a capacitive sensor with a microcontroller having digital outputs for driving a guard ring
US9252769B2 (en) 2011-10-07 2016-02-02 Microchip Technology Incorporated Microcontroller with optimized ADC controller
US9467141B2 (en) 2011-10-07 2016-10-11 Microchip Technology Incorporated Measuring capacitance of a capacitive sensor with a microcontroller having an analog output for driving a guard ring
US9207209B2 (en) 2011-12-14 2015-12-08 Microchip Technology Incorporated Method and apparatus for detecting smoke in an ion chamber
US9189940B2 (en) 2011-12-14 2015-11-17 Microchip Technology Incorporated Method and apparatus for detecting smoke in an ion chamber
US9176088B2 (en) 2011-12-14 2015-11-03 Microchip Technology Incorporated Method and apparatus for detecting smoke in an ion chamber
US9823280B2 (en) 2011-12-21 2017-11-21 Microchip Technology Incorporated Current sensing with internal ADC capacitor
US8884771B2 (en) 2012-08-01 2014-11-11 Microchip Technology Incorporated Smoke detection using change in permittivity of capacitor air dielectric
US10210747B1 (en) * 2018-05-25 2019-02-19 Stephen David Ainsworth Fire alarm testing device and method
EP3573033A2 (en) 2018-05-25 2019-11-27 Stephen David Ainsworth Fire alarm testing device and method

Also Published As

Publication number Publication date
NO131693B (enrdf_load_stackoverflow) 1975-04-01
DK129069B (da) 1974-08-12
DE2154537A1 (de) 1972-05-18
SE402660B (sv) 1978-07-10
GB1338690A (en) 1973-11-28
BE775169A (fr) 1972-03-01
CH540539A (de) 1973-08-15
NO131693C (enrdf_load_stackoverflow) 1975-07-09
FI53762C (fi) 1978-07-10
NL7115165A (enrdf_load_stackoverflow) 1972-05-16
FI53762B (enrdf_load_stackoverflow) 1978-03-31

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