US3559196A - Fire alarm with bistable characteristics - Google Patents

Fire alarm with bistable characteristics Download PDF

Info

Publication number
US3559196A
US3559196A US693937A US3559196DA US3559196A US 3559196 A US3559196 A US 3559196A US 693937 A US693937 A US 693937A US 3559196D A US3559196D A US 3559196DA US 3559196 A US3559196 A US 3559196A
Authority
US
United States
Prior art keywords
alarm
transistor
condition
combustion
fire alarm
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
US693937A
Other languages
English (en)
Inventor
Andreas Scheidweiler
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 US3559196A publication Critical patent/US3559196A/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
    • G08B17/00—Fire alarms; Alarms responsive to explosion
    • G08B17/10—Actuation by presence of smoke or gases, e.g. automatic alarm devices for analysing flowing fluid materials by the use of optical means
    • G08B17/11—Actuation by presence of smoke or gases, e.g. automatic alarm devices for analysing flowing fluid materials by the use of optical means using an ionisation chamber for detecting smoke or gas

Definitions

  • a fire alarm device exhibiting bistable characteristics, the device comprising a detector element which provides an electric signal in response to a phenomenon accompanying combustion, and an amplifying device connected with said detector element in a feedback circuit in a manner such that the appearance of an electric signal produces a change in the condition of the amplifying device which, in turn, produces a change in the potential applied to the detector element resulting in the maintenance of the change in condition of the amplifying device until such time as a re-setting operation is performed on the circuit.
  • This invention relates to fire alarm devices consisting of at least one combustion sensitive element which responds to a phenomenon accompanying combustion by the production of an electric signal, the electric signal being then applied to an electronic circuit including a transistor which responds to the signal.
  • Combustion sensitive elements which respond to phenomenon accompanying combustion such as the development of smoke, a rise in temperature, the appearance of flames and the like, and which in response to these phenomena develop an electric signal, are known in numerous variations.
  • smoke-sensitive, light-sensitive and temperature-sensitive elements have already been employed for a long time in fire alarms to produce an electric signal indicative of combustion.
  • electronic circuits and components To amplify the voltage appearing across the sensitive element in a fire alarm, numerous electronic circuits and components have been employed.
  • the cold-cathode tube had proved particularly suitable for this amplification purpose, but the cold-cathode tube has since been successfully replaced by the field-effect transistor.
  • Both the field-effect transistor and the coldcathode tube have the advantage of a high input impedance and are preferably employed in conjunction with high-impedance combustion sensitive elements such as the smoke-sensitive ionization chamber.
  • high-impedance combustion sensitive elements such as the smoke-sensitive ionization chamber.
  • these amplification components can also be made to function as threshold level detectors, so that a substantial alteration in signal occurs at their output only when the potential at their input exceeds a predetermined value.
  • the output of the transistor which in the following description is employed generally to symbolize any amplifier element, is connected to an electronic circuit of which the primary pur- 3,559,196 Patented Jan. 26, 1971 pose is to pass on any alarm signal which arises to some remote central position.
  • the electronic circuit may contain elements which serve to supervise the complete operational readiness of the fire alarm.
  • the fire alarm itself may include an indicator device which indicates the condition of the system, that is, ready for operation, alarm or failure.
  • the combustion sensitive element, the amplifier device, and the electronic circuit form a signal chain; the electronic circuit thereby usually providing an alarm signal to the remote central position in response to an alarm signal initiated by the combustion sensitive elements so long as, and only so long as, the combustion sensitive element provides the corresponding signal voltage, that is, so long as the amplifier element is retained in its altered condition.
  • the electronic circuit includes a bistable circuit element which serves to store the alarm condition until the alarm is actually reset, usually from the remote central position.
  • bistable elements have primarily comprised controlled rectifiers and electromechanical relays.
  • controlled rectifiers have the disadvantage that they may easily be caused to ignite and change over into the alternative stable condition by external interference. If this disadvantage is to be avoided, aged and stabilized circuit elements such as capacitors and Zener diodes must be employed, the addition of which makes the alarm more expensive and moreover reduces the reliability of the system over the period considered.
  • a fire alarm device including a detector element which provides an electric signal in response to a phenomenon accompanying combustion, and an amplifying device connected with said detector element in a feedback circuit in a manner such that the appearance of an electric signal produces a change in the condition of the amplifying device which, in turn, produces a change in the potential applied to the detector element resulting in the maintenance of the change in condition of the amplifying device until such time as a re-setting operation is performed on the circuit.
  • the inventive system consisting of a combustion sensitive element, an amplifying device, and an electronic feedback circuit is, by these means, rendered bistable and accordingly differs in principle even from a further variety of the known fire alarms in which the two combustion sensitive elements are connected in series in a bridge connection with an electronic circuit, the bridge connection and the electronic circuit forming a feedback system having a monostable characteristic.
  • an alarm signal is given only so long as the bridge circuit is unbalanced, effective or only apparent diminution of the alarm-initiating condition thus returning the bridge into balance and suppressing the alarm signal.
  • FIG. 1 shows a circuit diagram useful for explaining the prior art
  • FIG. 2 is a circuit diagram of one embodiment of a fire alarm device according to the invention.
  • FIG. 3 is a circuit diagram of a modified form of the arrangement shown in FIG. 2;
  • FIG. 4 shows another modification of the arrangement described in relation to FIG. 2.
  • FIG. 1 a known arrangement of a fire alarm is depicted as including a combustion sensitive element 1 consisting of an ionization chamber with a resistance element 2 connected in series with it across a power supply represented only by negative and positive terminals 11 and 12.
  • the ionization chamber 1 is arranged such that the ambient air has almost unhindered access thereto. Because of the physical characteristics of the ionization chamber, its electrical resistance changes upon the entrance of smoke particles resulting in a corresponding change in the voltage appearing across the ionization chamber.
  • the magnitude of the electric current which flows in the absence of smoke aerosols within the ionization chamber is determined by the strength of the radioactive preparation associated with the chamber, the ionizing radiation therefrom making the air in the chamber conductive.
  • An amplifying device is depicted as a field-effect transistor 4, the grid of which is connected to the ionization chamber 1 in such a manner that the voltage across the chamber controls the current in the field-effect transistor. Accordingly, the voltage across resistor 6 is then a measure of the voltage across the combustion sensitive element 1.
  • An electronic circuit controlled by the amplifier element consists of a controlled rectifier 8a which is connected in series with a meter 9 across the supply.
  • the trigger or control electrode of rectifier 8a is returned to the positive line of the supply by way of a resistor 26 and is connected to the emitter of transistor 4 by means of a Zener diode 25.
  • the rectifier 8 is triggered so that current passes through meter 9. This condition is maintained until the circuit is re-set by removing the supply.
  • the meter 9 serves to indicate the occurrence of an alarm condition.
  • FIG. 2 shows a first embodiment of an alarm device constructed in accordance with the invention.
  • an ionization chamber 1 is connected in series with a resistor 2 which may comprise a second ionization chamber and the junction of these components is connected to the grid of a field-effect transistor 4.
  • the cathode or source electrode of the field-effect transistor is connected to a tapping of a voltage divider formed by a fixed resistor and a variable resistor 6 connected in series across the supply.
  • the field-effect transistor operates as. an amplifier element and as threshold device, the voltage at which the transistor response to an input Signal being adjustable by means of the variable resistor 6.
  • the drain electrode of the field-effect transistor 4 is connected to the negative terminal 11 of the direct-current source by means of a resistor 7, and to the base of a further transistor 8, the emitter of which is connected to negative terminal 11 and the collector of which is returned by way of a resistor 3, connected in series with ionization chamber 1, to the positive terminal 12 of the DC. source.
  • an indicating apparatus at a central station shown to the right of terminals 11, 12, consists of a meter 9 connected in series with a DC. source 10 between the terminals.
  • transistor 8 is cut off.
  • the ionization chamber 1 responds to the presence of combustion aerosols, its resistance increases so that the voltage between the source and grid or gate electrodes of the field-effect transistor 4 rises to the turn-on value.
  • resistor 7 There then appears across resistor 7 a voltage drop which causes transistor 8 to become conductive. Consequently, there then appears across resistor 3 a voltage applied by way of the voltage divider formed by the series combination of ionization chamber 1 and resistor 2 to the gate electrode of fieldeffect transistor 4, such that transistor 4 is made still more conductive. Accordingly, positive feedback is provided.
  • a further substantial advantage results from the switching-off of the voltage across the ionization chamber when the alarm device has responded to an alarm condition. It is generally known that, as a result of the electrical charging of combustion aerosols in the ionization chamber, a separation of the aerosols at the electrodes of the ionization chamber takes place to a greater or lesser extent depending upon the magnitude of the electric field strength set up within the chamber. Such separation deleteriously affects the functional reliability of the fire alarm. However, if the voltage applied across the ionization chamber is removed when the alarm responds, then, since there is substantially no electric field within the chamber, there can be no further separation of aerosols. The fire alarm of the instant invention is therefore suitable for continuous use without making provision for extensive cleaning operations.
  • Ionization chamber 1 has been considered merely as a resistance. In practice, however, it also has a selfcapacitance which, in FIG. 2, is shown as a capacitor 13. This fact has a positive effect upon the reliability of the feedback system, since the resulting time-constant substantially reduces the probability of the appearance of a false alarm as a result of the effect of external interference in the form of short voltage peaks or impulses.
  • the ionization chamber has an internal resistance of the order of 10 ohms and an internal capacity of some 10 pf., so that a time-constant of approximately 1 second is produced.
  • the field-effect transistor also possesses a small self-capacitance, so that without additional circuit components the fire-alarm device of FIG. 2 has considerable protection against spurious signals.
  • field-effect transistor 4 and transistor 8 do not pass current in the quiescent or rest condition of the apparatus. Therefore, the rest current and thus the power consumption of the alarm in the normal operational condition is kept small, which is a very important consideration in equipment with several hundred alarm devices per group.
  • This arrangement also provides the additional advantage that the transistors commence to conduct if the ambient temperature rises considerably, so that the fire-alarm also operates as a maximum-temperature alarm.
  • the invention can, however, obviously also be operated with both transistors conductive in the rest condition, or with one transistor conductive and one cut off.
  • the fieldetfect transistor 4 and the transistor 8 require only a small amount of power in comparison with the known controlled rectifier arrangements of FIG. 1. This is particularly important if the alarm is coupled with a device which, for test purposes, applies an alarm-simulating condition to all alarms in a group of alarms simultaneously and supervises the simultaneous response of all the alarms. In this case, because of technical installation consider.- ations and because of the necessity of providing the appropriate amount of power, the alarm current of each individual alarm device in a group must be kept as small as possible.
  • FIG. 3 shows a combination of an alarm device in accordance with the invention together with a device for the periodic supervision of the operational effectiveness of the alarm device.
  • a plurality of alarm devices can be provided although only one is shown for purposes of explanation.
  • the collector of transistor 8 in each alarm device is connected by means of an individual diode 14 with a common lead 15 which, at the central location, is connected with the negative pole of voltage source 10 by means of the parallel combination of two circuits, one circuit comprising a switch 17 in series with a resistor 18, and the other circuit comprising a resistor 16 in series with a current-indicating meter 19.
  • An actual alarm given by an alarm device results in current flowing in the meter 9 connected in supply lead 11.
  • the current flowing in case of an actual alarm can be given a desired value, preferably about twice the rest current.
  • the re-setting of an actuated alarm device is effected by interrupting the supply lead 11 by means of an interrupter 20.
  • FIG.'4 shows a modification of the circuit arrangement described in FIG. 2.
  • the emitter-collector path of a further transistor 21 the base of which is connected through a resistor 22 with the collector of transistor 8 and through a resistor 23 with supply lead 12.
  • transistor 21 also becomes conductive and thus practically short-circuits variable resistor 6.
  • the voltage applied between the gate and source electrodes of field-effect transistor 4 is thus additionally increased and brought practically to the full supply voltage.
  • the minimum supply voltage or maintaining voltage necessary to maintain an alarm condition which has arisen in an alarm device is thus given only by the threshold voltage of the field-effect transistor.
  • the arrangement of FIG. 4 is particularly suitable when the supply voltage applied to the alarm device cannot be assumed to be constant, i.e., when the supply leads have a relatively high resistance represented as a resistor 24, or when the source of supply voltage itself is not of sufficiently low impedance.
  • FIGS. 2-4 have been described merely in relation of combustion smoke detectors, in which the combustion sensitive element consists of an ionization chamber, it is obviously also possible for similar circuit arrangements to be constructed using optical, thermal or other sensitive elements to provide the alarm condition.
  • the sensitive element 1 would consist of a photocell which, by means of the field-effect transistor and the associated electronic circuitry, controls a light source. In this case, feedback is effected optically, light from the light source being allowed to fall upon the photocell. Similar arrangements would be provided for other sensitive elements.
  • a fire alarm device comprising: combustion detector means for providing an electric signal in response to a phenomenon accompanying combustion; amplifying means responsive to said electric signal for amplifying said electric signal; and feedback circuit means connecting said amplifying means to said combustion detector means, said feedback circuit means including said combustion detector means, said feedback circuit means including means for producing a change in voltage across said combustion detector means upon response of said amplifying means to maintain said response of said amplifying means.
  • a fire alarm device as defined in claim 3 further comprising biasing means for said first and second transistors for biasing said first and second transistors into a non-conducting rest condition, said first and second transistors conducting current upon the presence of said electric signal from said combustion detector means.
  • a fire alarm device as defined in claim 3 wherein said first output electrodes of said first transistor includes an emitter electrode, and variable resistor means connecting said emitter electrode to said power supply.
  • a fire alarm device as defined in claim 3, further including variable resistor means for coupling said first output terminals of said first transistor across said power supply; a third transistor having an emitter-collector path shunting said variable resistor and having a base electrode coupled with said second output electrodes of said second transistor, whereby said third transistor substantially shortcircuits said variable resistor when said first and second transistors respond to said electric signal from said combustion detector means.

Landscapes

  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Business, Economics & Management (AREA)
  • Emergency Management (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Fire-Detection Mechanisms (AREA)
US693937A 1966-12-29 1967-12-27 Fire alarm with bistable characteristics Expired - Lifetime US3559196A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
CH1875166A CH468683A (de) 1966-12-29 1966-12-29 Feuermelder mit einer elektrischen Rückkopplungsanordnung

Publications (1)

Publication Number Publication Date
US3559196A true US3559196A (en) 1971-01-26

Family

ID=4435069

Family Applications (1)

Application Number Title Priority Date Filing Date
US693937A Expired - Lifetime US3559196A (en) 1966-12-29 1967-12-27 Fire alarm with bistable characteristics

Country Status (7)

Country Link
US (1) US3559196A (sv)
AT (1) AT278597B (sv)
BE (1) BE707959A (sv)
CH (1) CH468683A (sv)
DK (1) DK122548B (sv)
GB (1) GB1200120A (sv)
SE (1) SE330659B (sv)

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3792279A (en) * 1970-11-19 1974-02-12 Nittan Co Ltd Ionization smoke detector
US3866195A (en) * 1973-05-07 1975-02-11 Fire Alert Company Combustion product detector and method of calibrating
US3946374A (en) * 1970-08-13 1976-03-23 Sci Systems, Inc. Rate-of-change combustion and contamination detection device
US4109240A (en) * 1973-11-26 1978-08-22 Cerberus Ag. Ionization-type fire sensing system
US4213046A (en) * 1977-02-21 1980-07-15 Hartwig Beyersdorf Ionization fire-signal device
US20080252473A1 (en) * 2006-09-15 2008-10-16 Nano-Proprietary, Inc. Smoke Detector
US20150294556A1 (en) * 2014-04-14 2015-10-15 Stephen D. Ainsworth Alarm System Testing Device

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE2327497C3 (de) * 1973-05-30 1981-12-24 Benno 5430 Wettingen Aargau Perren Melder für Widerstandsänderungen mit nachgeschalteter Alarmeinrichtung
DE2546970C3 (de) * 1975-10-20 1981-09-10 Preussag Ag Feuerschutz, 2060 Bad Oldesloe Ionisations-Rauchmelder
DE2726186C3 (de) * 1977-06-10 1981-05-14 Pan Data Ab, Stockholm Elektrische Überwachungsvorrichtung

Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3946374A (en) * 1970-08-13 1976-03-23 Sci Systems, Inc. Rate-of-change combustion and contamination detection device
US3792279A (en) * 1970-11-19 1974-02-12 Nittan Co Ltd Ionization smoke detector
US3866195A (en) * 1973-05-07 1975-02-11 Fire Alert Company Combustion product detector and method of calibrating
US4109240A (en) * 1973-11-26 1978-08-22 Cerberus Ag. Ionization-type fire sensing system
US4213046A (en) * 1977-02-21 1980-07-15 Hartwig Beyersdorf Ionization fire-signal device
US20080252473A1 (en) * 2006-09-15 2008-10-16 Nano-Proprietary, Inc. Smoke Detector
US7821412B2 (en) 2006-09-15 2010-10-26 Applied Nanotech Holdings, Inc. Smoke detector
US20150294556A1 (en) * 2014-04-14 2015-10-15 Stephen D. Ainsworth Alarm System Testing Device
US9564045B2 (en) * 2014-04-14 2017-02-07 Stephen D. Ainsworth Alarm system testing device

Also Published As

Publication number Publication date
DK122548B (da) 1972-03-13
GB1200120A (en) 1970-07-29
AT278597B (de) 1970-02-10
CH468683A (de) 1969-02-15
BE707959A (sv) 1968-04-16
SE330659B (sv) 1970-11-23
DE1566687B1 (de) 1971-04-01

Similar Documents

Publication Publication Date Title
US3665461A (en) Apparatus for monitoring the conductors or lines of fire alarm installations
US3530450A (en) Fire alarm systems with monitoring device for fire alarms connected in groups to a central station
US4595914A (en) Self-testing combustion products detector
US4377808A (en) Infrared intrusion alarm system
US3559196A (en) Fire alarm with bistable characteristics
SE328225B (sv)
GB1347306A (en) Fire detector
US3909813A (en) Ionization-type fire sensor
US3676680A (en) Ionization fire alarm with insulation monitoring system
US3392379A (en) Static logic annunciator
US4455553A (en) Smoke detector of the ionization type
US3774186A (en) Smoke detector failure alarm
US4041479A (en) Output circuit of an ionization smoke sensor
US3676877A (en) Fire alarm system with fire zone locator using zener diode voltage monitoring
US2697824A (en) Test circuit for flame detector systems
US2871466A (en) Automatic fire alarm system
US2217797A (en) Fire alarm system
US4222046A (en) Abnormal condition responsive means with periodic high sensitivity
US3271756A (en) Method and apparatus for detecting a hazardous condition
US3678511A (en) Alarm circuit
US3015042A (en) Pulse responsive circuit with storage means
US3733596A (en) Alarm circuit
US3268881A (en) Detection device
US3795904A (en) Fire alarm with ionization chamber
US4218677A (en) Detecting loop digital interface circuitry