US3872449A - Fire detector and method employing assymetrical integrator - Google Patents

Fire detector and method employing assymetrical integrator Download PDF

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Publication number
US3872449A
US3872449A US449287A US44928774A US3872449A US 3872449 A US3872449 A US 3872449A US 449287 A US449287 A US 449287A US 44928774 A US44928774 A US 44928774A US 3872449 A US3872449 A US 3872449A
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signal
capacitor
fire
time constant
resistor
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US449287A
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English (en)
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Andreas Scheidweiler
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Cerberus AG
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Cerberus AG
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    • GPHYSICS
    • G08SIGNALLING
    • G08BSIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
    • G08B17/00Fire alarms; Alarms responsive to explosion
    • G08B17/10Actuation by presence of smoke or gases, e.g. automatic alarm devices for analysing flowing fluid materials by the use of optical means
    • G08B17/11Actuation 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

  • the integrator mcludes a diode in the integration circuit, so that it will discharge an integrating capacitor rapidly, upon drop 5 340/228 1 g i i g in signal level exceeding the first threshold.
  • an alarm R 420 is given. Providing for rapid discharge of the integrated signal prevents false alarms resulting from re- [56] References Cited petitive short pulses exceeding a first threshold level which, however, do not persist.
  • the present invention relates to sensing, and indicating presence of a fire, and more particularly to indicate presence of a fire reliably, while rejecting spurious responses, which might lead to false alarms. Specifically, the present invention relates to a method to reliably detect a fire, and to a system to carry out the method, in which electrical signals are processed.
  • Fire alarm systems in which an alarm signal is generated as soon as a characteristic of a fire exceeds a certain threshold value are known.
  • Various types of fire sensors respond, specifically, to certain characteristics of fires. Difficulties arise when such fire sensors are used in rooms, or spaces in which the specific characteristic of the fire may occur for a short period of time, intermittently, or in pulses, without a fire actually being present.
  • One such sensor uses smoke as the sensing characteristic. In offices, garages, automotive repair shops, and the like, smoke may arise, intermittently, without a fire actually being present. Fire sensors installed in such locations may provide false alarms. It has been tried to avoid the undesirable influence of such pulsed smoke on the sensors by introducing a time delay, either mechanically, or electrically.
  • a mechanical time delay can be introduced by partly masking, or interfering with the accessibility of a measuring chamber of the fire sensor to free ingress of air, for example by means of covers, shrouds, or the like. Time delays can also be introduced electrically by electrically delaying a signal derived from the sensor. Delaying the response of the sensor has the result that the threshold value of the response circuit connected to the sensor will be reached only after a predetermined time corresponding to the delay time.
  • the method includes a plurality of steps: I.
  • the electrical signal from the sensing element is processed to determine if it exceeds a first threshold level. If it does, an output signal is generated, independent of the input signal, so long as the input signal exceeds the threshold value.
  • the output signal which exceeds the first threshold is applied to an integrator which is non-symmetrical, that is, has two time constants, one long or slow time constant if the signal is increasing, and a short or rapid time constant if the signal is decreasing; thus, the charge time constant of the integrator will be substantially greater, or longer, than the discharge time constant.
  • the output signal from the integrator is applied to a second threshold detector which provides the alarm signal when its threshold level is exceeded.
  • the system includes an integrator which has a diode in its integrating circuit so poled that it is blocked upon a rising signal applied thereto, so that the time constant of the integrator will be determined by circuit parameters without consideration of the diode and, for decreasing input signals, the diode becomes conductive to provide a low resistance, short time constant discharge path for the integrating capacitor of the integrator.
  • FIG. 1 is a highly schematic diagram of a fire alarm system in accordance with the present invention.
  • FIG. 2 is a series of graphs illustrating the operation of the circuit of FIG. I, and the method, in accordance with the present invention.
  • the fire alarm sensor selected for the example is an ionization-type fire sensor.
  • an ionization chamber 1 acting as the fire sensor, is connected in series with a reference chamber 2.
  • the ionization chamber 1 can be referred to as the sensing chamber, and is accessible to outside, ambient atmosphere.
  • Chambers I, 2 are series connected between energized conductors 3, 4.
  • the junction 5 between the chambers l, 2 will have a voltage arise thereat which changes continuously as the smoke or aerosol concentration in the sensing chamber 1 changes. This voltage is applied to a threshold detector 6.
  • the threshold detector 6 will have an output only if the input thereto, from junction 5. exceeds a certain threshold value.
  • threshold detector 6 The output from threshold detector 6 is applied to an integrator l. which includes a resistor 7, having a resistance value r.
  • the voltage across resistor 7 is applied to capacitor 8 over a resistor 9, which has a resistance R.
  • the capacitor 8 is charged with a time constant of RC, in which C is the capacitance of capacitor 8.
  • threshold detector 10 When the voltage across capacitor 8 reaches the alarm threshold of a second threshold detector 10, threshold detector 10 will generate an alarm signal.
  • the time required after the first threshold detector 6 provided an output signal exceeding its first threshold value until the second threshold detector provides an alarm is determined by the time constant of the R/C circuit determined by resistor 9 and capacitor 8. This is the alarm delay time.
  • a diode 1 1 is connected in parallel to resistor 9.
  • the diode 11 is so poled that the voltage across capacitor 8 can discharge through the diode. As soon as the voltage from the first threshold detector 6 drops, and specifically when the signal from the sensor drops below the threshold level of the first threshold detector 6, ca-
  • pacitor 8 can discharge through diode 11. This discharge will occur with the time constant rC, in which the time constant of the discharge circuit is governed by the resistance value of resistor 7 and the capacitance of capacitor 8. Resistor 7 is selected to be substantially less than resistor 9. The capacitor discharge will, then, occur much more rapidly when the signal from the sensor 1 disappears than the charge build-up on the capacitor 8 when the first threshold level is exceeded.
  • Curve S is indicative of separate smoke pulses which, for example, may arise in an office upon presence of heavy smokers. Similar pulses may arise in an automobile garage. Clearly, no fire is present, and the pulses, essentially, are disturbance pulses. in case of a fire, there would be a continuous increase in smoke concentration.
  • a simple first alarm sensor without time delay, would provide an alarm when the first pulse exceeds the alarm threshold, indicated at A and as shown at curve S.
  • a known fire sensor with time delay would have different characteristics; in accordance with curve V, the voltage at the input to the threshold detector would, first, increase slowly; after termination of the pulse S, the voltage would drop slowly, with the same time constant. As can be seen by consideration of curve V, several sequential smoke pulses would, eventually, cause the level of the signal to rise until, finally, the alarm threshold is exceeded, providing a false alarm, as indicated at A
  • a fire sensor in accordance with the present invention under conditions of smoke pulses, would provide signals as shown in curve B. Upon sensing of the first smoke pulse, the input voltage to the second threshold detector would follow curve B, and rise.
  • the charge time that is, the RC time constant may be in the order of from between to 60 seconds
  • the discharge time constant, rC may be in the order of from 0.1 to 5 seconds, the two respective time constants having a relationship of l to l0, at least.
  • the first sensors may be responsive to other parameters than smoke, for
  • combustion gases or other indieia of fire, and suitable sensors of known types may be used.
  • suitable sensors of known types may be used.
  • Various changes and modifications may be made within the scope of the inventive concept.
  • Method to indicate occurrence of a fire having means generating a signal indicative of fire comprising detecting a first threshold level of said fire indication signal, and providing a first signal representative of the fire indication signals having exceeded said first threshold level;
  • Fire alarm system carrying out the method of claim 1 having fire sensing means (1, 2) providing an output signal indicative of a fire
  • first threshold detector (6) having the fire indicating signal applied thereto and providing a first signal representative of the fire indicating signals having exceeded the first threshold of said first threshold detector;
  • a non-symmetrical integrator integrating the first threshold signal with the first integrating time constant (RC) and a drop of the first signal with a second integrating time constant (rC) which is small with respect to said first time constant;
  • a second threshold detector (10) sensing when the integrated signal has reached a second threshold level, and providing an alarm output.
  • the fire sensing means comprises an ionization chamber (1), in which the ion current changes upon presence of smoke or first aerosols.
  • the integrator (l) comprises a capacitor (8) and a resistor (9) con nected to charge the capacitor (8), the signal indicative of fire being connected through the resistor (9) to charge the capacitor.
  • first resistor (9) and poled to block signals from the first threshold detector (6) charging the capacitor (8) so that said signals flow through the first resistor, but pass discharge current from the capacitor and permit discharge of the capacitor through the second resistor (7), the resistance value of said second resistor (7) being small with respect to the resistance value of said first resistor (9);
  • the second threshold detector (10) being connected across the capacitor (8) and providing an alarm signal when the charge across the capacitor (8) reaches the second threshold level.
  • the integrator comprises a first timing circuit (8, 9) having a time constant in the order of lO-60 seconds, a second timing circuit (7, 8) having a time constant in the order of 0.1-5 seconds, and a diode (11) connected and poled in the integrator to render the timing circuit with the shorter time constant effective upondecrease of the signal applied to the integrator, to provide for nonsymmetrical integration of signals exceeding the first threshold level, in increasing, and decreasing direction of said signals.

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  • 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)
  • Fire Alarms (AREA)
  • Other Investigation Or Analysis Of Materials By Electrical Means (AREA)
  • Alarm Systems (AREA)
US449287A 1973-03-30 1974-03-08 Fire detector and method employing assymetrical integrator Expired - Lifetime US3872449A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
CH462173A CH570016A5 (de) 1973-03-30 1973-03-30

Publications (1)

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US3872449A true US3872449A (en) 1975-03-18

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US449287A Expired - Lifetime US3872449A (en) 1973-03-30 1974-03-08 Fire detector and method employing assymetrical integrator

Country Status (17)

Country Link
US (1) US3872449A (de)
JP (1) JPS5619671B2 (de)
AT (1) AT340807B (de)
BE (1) BE812331A (de)
CA (1) CA1063260A (de)
CH (1) CH570016A5 (de)
DE (1) DE2408374B2 (de)
DK (1) DK137099B (de)
ES (1) ES425125A1 (de)
FI (1) FI55420C (de)
FR (1) FR2223766B1 (de)
GB (1) GB1430035A (de)
IT (1) IT1014554B (de)
NL (1) NL7403973A (de)
NO (1) NO136383C (de)
SE (1) SE389569B (de)
ZA (1) ZA741754B (de)

Cited By (13)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3999079A (en) * 1972-07-26 1976-12-21 Toichi Chikuma Fire detector
US4091363A (en) * 1977-01-03 1978-05-23 Pittway Corporation Self-contained fire detector with interconnection circuitry
US4123656A (en) * 1976-07-07 1978-10-31 Hochiki Corporation Storage type smoke detector
US4131888A (en) * 1976-08-18 1978-12-26 American District Telegraph Company Dual projected-beam smoke detector
US4222046A (en) * 1978-07-31 1980-09-09 Honeywell Inc. Abnormal condition responsive means with periodic high sensitivity
US4238677A (en) * 1977-04-08 1980-12-09 Societe Gamma-Electronic Smoke detector by ionization associated to a velocimetric measurement electronic circuit
US4250500A (en) * 1979-10-22 1981-02-10 Rca Corporation Smoke detector
US4364031A (en) * 1979-12-14 1982-12-14 Cerberus Ag Ionization smoke detector with increased operational reliability
US4539488A (en) * 1981-11-30 1985-09-03 Zenith Electronics Corporation Pulse wave to parabola wave converter
US4638304A (en) * 1983-12-13 1987-01-20 Nittan Co., Ltd. Environmental abnormality detecting apparatus
US5019805A (en) * 1989-02-03 1991-05-28 Flash-Alert Inc. Smoke detector with strobed visual alarm and remote alarm coupling
US6188318B1 (en) 1999-06-29 2001-02-13 Pittway Corp. Dual-technology intrusion detector with pet immunity
CN102455288A (zh) * 2010-10-15 2012-05-16 西门子公司 通过在线信号电平监控对传感器装置的光电信号路径进行校准

Families Citing this family (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CH576175A5 (de) * 1974-12-19 1976-05-31 Cerberus Ag
DE3127324A1 (de) * 1981-07-10 1983-01-27 Siemens AG, 1000 Berlin und 8000 München Verfahren und anordnung zur erhoehung der ansprechempfindlichkeit und der stoersicherheit in einer gefahren-, insbesondere brandmeldeanlage
DE102014019172B4 (de) 2014-12-17 2023-12-07 Elmos Semiconductor Se Vorrichtung und Verfahren zur Unterscheidung von festen Objekten, Kochdunst und Rauch mit einem kompensierenden optischen Messsystem
DE102014019773B4 (de) 2014-12-17 2023-12-07 Elmos Semiconductor Se Vorrichtung und Verfahren zur Unterscheidung von festen Objekten, Kochdunst und Rauch mittels des Displays eines Mobiltelefons

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2735007A (en) * 1956-02-14 Time-base generator
US2811711A (en) * 1951-05-19 1957-10-29 Electronics Corp America Fire method and apparatus
US3531692A (en) * 1969-03-03 1970-09-29 Combustion Eng Activity detector having increased accuracy of response
US3582676A (en) * 1968-09-24 1971-06-01 Bendix Corp Pulse length normalizing and short pulse eliminating circuit

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS482587U (de) * 1971-05-25 1973-01-12

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2735007A (en) * 1956-02-14 Time-base generator
US2811711A (en) * 1951-05-19 1957-10-29 Electronics Corp America Fire method and apparatus
US3582676A (en) * 1968-09-24 1971-06-01 Bendix Corp Pulse length normalizing and short pulse eliminating circuit
US3531692A (en) * 1969-03-03 1970-09-29 Combustion Eng Activity detector having increased accuracy of response

Cited By (15)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3999079A (en) * 1972-07-26 1976-12-21 Toichi Chikuma Fire detector
US4123656A (en) * 1976-07-07 1978-10-31 Hochiki Corporation Storage type smoke detector
US4131888A (en) * 1976-08-18 1978-12-26 American District Telegraph Company Dual projected-beam smoke detector
US4091363A (en) * 1977-01-03 1978-05-23 Pittway Corporation Self-contained fire detector with interconnection circuitry
US4238677A (en) * 1977-04-08 1980-12-09 Societe Gamma-Electronic Smoke detector by ionization associated to a velocimetric measurement electronic circuit
US4222046A (en) * 1978-07-31 1980-09-09 Honeywell Inc. Abnormal condition responsive means with periodic high sensitivity
US4250500A (en) * 1979-10-22 1981-02-10 Rca Corporation Smoke detector
US4364031A (en) * 1979-12-14 1982-12-14 Cerberus Ag Ionization smoke detector with increased operational reliability
EP0030621B1 (de) * 1979-12-14 1985-01-16 Cerberus Ag Ionisationsrauchmelder mit erhöhter Betriebssicherheit
US4539488A (en) * 1981-11-30 1985-09-03 Zenith Electronics Corporation Pulse wave to parabola wave converter
US4638304A (en) * 1983-12-13 1987-01-20 Nittan Co., Ltd. Environmental abnormality detecting apparatus
US5019805A (en) * 1989-02-03 1991-05-28 Flash-Alert Inc. Smoke detector with strobed visual alarm and remote alarm coupling
US6188318B1 (en) 1999-06-29 2001-02-13 Pittway Corp. Dual-technology intrusion detector with pet immunity
CN102455288A (zh) * 2010-10-15 2012-05-16 西门子公司 通过在线信号电平监控对传感器装置的光电信号路径进行校准
CN102455288B (zh) * 2010-10-15 2014-10-15 西门子公司 通过在线信号电平监控对传感器装置的光电信号路径进行校准

Also Published As

Publication number Publication date
NL7403973A (de) 1974-10-02
GB1430035A (en) 1976-03-31
JPS49131099A (de) 1974-12-16
SE389569B (sv) 1976-11-08
FI55420B (fi) 1979-03-30
ZA741754B (en) 1975-01-29
ATA144074A (de) 1977-04-15
DK137099C (de) 1978-06-12
AT340807B (de) 1978-01-10
CH570016A5 (de) 1975-11-28
NO136383B (de) 1977-05-16
BE812331A (fr) 1974-07-01
FR2223766B1 (de) 1978-12-01
FI55420C (fi) 1979-07-10
NO741081L (no) 1974-10-01
DE2408374B2 (de) 1978-06-01
DK137099B (da) 1978-01-16
DE2408374A1 (de) 1974-10-17
CA1063260A (en) 1979-09-25
JPS5619671B2 (de) 1981-05-08
AU6689674A (en) 1975-09-25
IT1014554B (it) 1977-04-30
FR2223766A1 (de) 1974-10-25
ES425125A1 (es) 1976-06-16
NO136383C (no) 1977-08-31

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