US3521263A - Ionization fire alarm and improved method of detecting smoke and combustion aerosols - Google Patents

Ionization fire alarm and improved method of detecting smoke and combustion aerosols Download PDF

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Publication number
US3521263A
US3521263A US617226A US3521263DA US3521263A US 3521263 A US3521263 A US 3521263A US 617226 A US617226 A US 617226A US 3521263D A US3521263D A US 3521263DA US 3521263 A US3521263 A US 3521263A
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ionization
chamber
fire alarm
voltage
aerosols
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US617226A
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Thomas Lampart
Andreas Scheidweiler
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Cerberus AG
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Cerberus AG
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    • 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
    • G08B17/113—Constructional details

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  • the present invention pertains to an improved ionization fire alarm possessing increased sensitivity to smoke and combustion particles or aerosols and is of the type comprising at least one ionization chamber-also referred to as measuring chamber-which is essentially freely accessible for the ambient or surrounding air.
  • the inventive ionization fire alarm also includes one or more radioactive sources for producing ions, and an electric circuit for producing an alarm.
  • the present invention also pertains to an improved method of detecting smoke and combustion aerosols by means of an apparatus structure of the aforementioned type.
  • the voltage across the measuring chamber that is, across the ionization chamber which is accessible to the outside air, amounts to about 100 volts. Since the spacing between the electrodes generally only amounts to several centimeters, in certain zones or regions of the ionization chamber electric field strengths appear which amount to several hundred volts per centimeter. This is especially so if there is employed a cylinder as the geo- 3,521,263 Patented July 21, 1970 metric form for the ionization chamber. The following considerations will now clearly demonstrate the influences of the electric field strength upon the smoke sensitivity of such type of ionization fire alarm.
  • dn/dt represents the change with time of the ion concentration n and 6 is a proportionality factor.
  • the ion residence time is dependent in simple manner upon the electric field strength or intensity E. Further, it is namely true that wherein dr represents the length of the volume increment in the direction of the field and b represents the ion mobility. It will thus be evident that the individual volume increments, depending upon the magnitude of the prevailing field intensity, provide different contributions to the measuring effect, with the exception of the special case of a constant field in the total measuring chamber which, however, as a practical matter can only be realized with great difficulty.
  • Equation 1 As a simple example take the case of the cylindrical ionization chamber in which the field strength increases with 1/r towards the inner electrode. In this respect, by integration of Equation 1 above it follows that the number of deposition processes in the volume increment approximately increases by the second power with the spacing from the chamber axis.
  • FIG. 1 Field strength or intensity E is plotted along the ordinate as well as also the number of deposition processes A in the volume unit. Along the abscissa there is plotted the spacing r from the inner electrode 2.
  • the broken line curve A k'r shows the course of the deposition process.
  • the symbols a and k are proportionality factors.
  • the major portion of the depositions take place in the neighborhood of the chamber housing 1, whereas the zone or region about the inner electrode 2 practically contributes nothing to the measuring effect.
  • the geometry of the chamber owing to constructive measures generally markedly deviates from the ideal cylindrical form, so that still further regions of higher field strength exist.
  • FIG. 2 shows the physical structure of a measuring chamber of a known ionization fire alarm. It incorporates a cylindrical housing 1 defining the outer electrode and provided with numerous apertures or openings 1a. The smoke or combustion gases, as a practical matter, have almost unhindered access to the cylindrical housing 1. Further, this ionization chamber is composed of an inner electrode 2 which extends from beneath into the measuring compartment, as shown. The radioactive preparations 3 and 4 are disposed at the floor of the housing 1 in the region of the inner electrode 2. At suitable non-illustrated direct-current voltage source is electrically coupled to the chamber housing 1 and the inner electrode 2 in a manner that for instance the negative pole of the source is connected to chamber housing 1 and the positive pole to the inner electrode 2.
  • the shaded or cross-hatched region 7 represents that zone or region of the measuring chamber in which no essential amount of deposition takes place owing to the higher field strength.
  • the dashed or broken lines 8 depict the course of the electric field lines. As can beseen, the negative ions on their way to the inner electrode 2 must pass through the region 7 of higher field intensity or strength.
  • the flow of the positive ions is represented by reference numeral 6.
  • FIG. 3 depicts a different embodiment of measuring chamber of a known ionization fire alarm in which likewise a larger portion of the transfer or transport of charges takes place in the region of higher field strength.
  • the radioactive source 3 is applied to the inner electrode 2. Also in this case deposition essentially takes place only outside of the cross-hatched region 7.
  • reference numeral 1 represents the outer electrode.
  • the flow of the negative and positive ions is represented by reference numerals 4 and 5 respectively.
  • both electrodes 1 and 2 are coupled with a non-illustrated suitable directcurrent voltage source.
  • the present invention is generally characterized by the fact that there is present an electric field strength of less than 5 volts per centimeter in those regions of the measuring chamber in which the greater portion of the ionization current fiows.
  • the teachings of the present invention have surprisingly found that it is possible to provide increased sensitivity to smoke and combustion aerosols for an ionization fire alarm if there is provided an electric field strength within the ionization chamber of less than 5 volts per centimeter in the region of the ionization chamber in which the greater portion of the ionic current flows.
  • the ionization fire alarm of the present invention has still further significant advantages:
  • Another, significant object of the present invention is to provide an improved ionization fire alarm which possesses increased sensitivity to smoke and combustion aerosols, thereby positively protecting the area monitored by the fire alarm, and also overcoming the drawbacks of the prior art systems mentioned heretofore.
  • a further important object of the present invention concerns itself with an improved method of, and ionization fire alarm for, positively and reliably detecting smoke and combustion aerosols with extreme sensitivity and wherein the physical structure of the fire alarm system and its mode of operation is such that there is minimized the danger of dust deposition at the electrodes which could adversely affect the integrity of the system.
  • a further noteworthy object of this invention relates to an improved ionization fire alarm which operates at such a relatively low operating voltage that the fire alarm system is much easier to install than was heretofore possible, and further, owing to this expedient it is additionally possible to transistorize the electric circuitry.
  • FIG. 1 illustrates an ionization chamber having an inner electrode and an outer electrode and depicts the respective curves representing the field intensity and the deposition process undertaken by the combustion aerosols and the gas ions;
  • FIG. 2 schematically illustrates a prior art ionization chamber and is used to provide a better understanding of the principles of the invention
  • FIG. 3 schematically depicts a further prior art ionization chamber, also being used for purposes of explaining and clarifying the principles of the present invention
  • FIG. 4 schematically depicts the physical structure of a first embodiment of ionization chamber according to the teachings of the present invention
  • FIG. 5 depicts the physical structure of a second embodiment of ionization chamber according to the present invention.
  • FIG. 6 is a circuit diagram depicting the cooperation of the ionization chambers of the embodiments of FIGS. 4 and 5 with the electric circuitry;
  • FIG. 7 is a variant form of ionization fire alarm system employing two series connected ionization chambers.
  • ionization chamber 20 also referred to as measuring chamber, depicted in FIG. 4 it will be seen that such comprises a perforated or apertured cylindrical housing 1 providing the outer electrode as well as an inner electrode 2 arranged within the outer electrode 1. Further, a source of radioactive material 3 is applied to the inner electrode 2, as shown.
  • the arrows 9 represent the ionized chamber region brought about by the sphere of influence of the radiation. The direction of the radioactive rays is essentially parallel to the direction of the field lines 8.
  • the sphere of influence of the radioactive material 3 can be also selected such that ions are produced almost in the entire measuring or ionization chamber 20.
  • transport of the charges essentially takes place in the chamber region or space which is subjected to a small field strength or intensity.
  • Those locations 7 of the measuring or ionization chamber 20 in which higher field strengths occur make only a very small contribution to the total current since such regions 7 are essentially located outside of the ionization zone.
  • FIG. 5 A variant embodiment of measuring or ionization chamber 20 is depicted in FIG. 5, where once again the same reference numerals have conveniently been employed to designate like or analogous components.
  • the radioactive sources 3, 4 emit their rays, not as with the previous embodiment in the direction of the electric field lines 8, but rather transverse to such field.
  • the 6 ionic current 5 essentially flows in the region of lower field strength.
  • FIG. 6 schematically depicts a simple embodiment of ionization fire alarm designed according to the teachings of the present invention.
  • the ionization or measuring chamber 10 which may be of the type previously considered with regard to FIGS. 4 and 5, is electrically coupled at its inner electrode 2 with the negative pole of the operating voltage U via a resistor 11 and at its chamber housing 1 with the positive pole of said operating voltage U
  • a radioactive source 3 similar to the arrangement of FIG. 4.
  • the voltage U across the measuring or ionization chamber 10 is, at the same time, the gate voltage for a suitable semi-conductor element such as the field-effect transistor 12 providing a sensing or indicating means which senses voltage changes across the electrodes 1, 2 of the ionization chamber 10.
  • This voltage U is chosen such that the field effect transistor 12 in its quiescent state blocks current flow, that is to say, at the working resistor 13 there is no voltage drop.
  • the voltage across the ionization chamber is advantageously of a magnitude smaller than 20 volts.
  • the gate-controlled rectifier 14 is therefore likewise blocked and the relay 15 is not energized.
  • the chamber voltage U increases and upon exceeding a predetermined threshold triggers ignition of the controlled rectifier 14, whereby the relay 15 triggers a suitable alarm.
  • Triggering of the alarm can be carried out in any appropriate manner, as for instance shown and described in the commonly assigned US. Pat. 3,233,100 of Thomas Lampart, one of the co-inventors herein, and entitled Determining Presence of Aerosols in Gases, and granted Feb. 1, 1966.
  • the field-effect transistor 12 operates both as a threshold device as well as also as an amplifier element.
  • FIG. 7 depicts a different embodiment of fire alarm system designed according to the teachings of the present invention, and wherein there are employed two symmetrical ionization chambers 10' and 16 which are connected in series.
  • the chamber 10 is the measuring chamber whereas the other chamber 16 serves as a reference or comparison chamber. Both of these chambers 10, 16 are constructed in a manner similar to that previously described herein.
  • the field effect transistor 12 functions as an impedance transformer which transforms the high-ohm intrenal chamber resistance of about 10 ohms into the range of several kiloohms.
  • the voltage U serves to regulate the alarm threshold.
  • the voltage at the gate of the field effect transistor 12 increases, and therefore, also at its cathode or emitter If this value exceeds the regulated threshold U then the controlled rectifier 14 ignites and the relay 15 is energized, for the reasons previously considered.
  • An ionization fire alarm having increased sensitivity to smoke and combustion aerosols, comprising: means for forming at least one ionization chamber which is essentially freely accessible for the ambient air, said ionization chamber providing a measuring chamber; at least one source of radioactive means for producing ions within said ionization chamber; electric circuit means electrically coupled with said ionization chamber for producing an alarm; means for generating an electric field strength within said ionization chamber of less than volts per centimeter in the region of said ionization chamber in which the greater portion of the ionization current flows.
  • a method of detecting the presence of smoke and combustion aerosols in a gaseous atmosphere resulting from combustion comprising the steps of:
  • step of ionizing at least a portion of said gaseous atmosphere further includes the steps of:
  • step of ionizing at least a portion of said gaseous atmosphere further includes the step of: providing a source of radiation which has a sphere of influence within said chamber such that ions are only produced throughout a relatively small portion of said chamber.
  • a method as defined in claim 12 wherein said step of providing an electric field within said chamber includes the step of applying a voltage across said chamber having a magnitude less than 20 volts.

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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)
  • Other Investigation Or Analysis Of Materials By Electrical Means (AREA)
US617226A 1966-02-22 1967-02-20 Ionization fire alarm and improved method of detecting smoke and combustion aerosols Expired - Lifetime US3521263A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
CH254966A CH446131A (de) 1966-02-22 1966-02-22 Ionisationsfeuermelderanlage

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US3521263A true US3521263A (en) 1970-07-21

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US (1) US3521263A (xx)
AT (1) AT268101B (xx)
BE (1) BE694152A (xx)
CH (1) CH446131A (xx)
DE (1) DE1259227B (xx)
DK (1) DK126607C (xx)
FR (1) FR1511451A (xx)
GB (1) GB1109587A (xx)
NL (1) NL162493C (xx)
SE (1) SE328226B (xx)

Cited By (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3735138A (en) * 1971-10-27 1973-05-22 Honeywell Inc Ionization smoke detector
US3775616A (en) * 1970-06-08 1973-11-27 Nittan Co Ltd Ionization smoke detector
US3795904A (en) * 1970-05-16 1974-03-05 Preussag Ag Feuerschutz Fire alarm with ionization chamber
US3913082A (en) * 1973-02-02 1975-10-14 Jenson Robert S Ionization aerosol detector
US4038649A (en) * 1975-09-16 1977-07-26 Emhart Industries, Inc. Smoke detection alarm device
US4053776A (en) * 1976-05-25 1977-10-11 The United States Of America As Represented By Thesecretary Of The Interior Sub-micron particle detector
EP0030621A1 (de) * 1979-12-14 1981-06-24 Cerberus Ag Ionisationsrauchmelder mit erhöhter Betriebssicherheit
US4286160A (en) * 1977-01-27 1981-08-25 Ried Jr Louis Ionization particle detector
US4488044A (en) * 1981-11-20 1984-12-11 Pittway Corporation Ionization chamber for smoke detector and the like
US4755682A (en) * 1986-10-07 1988-07-05 The United States Of America As Represented By The United States Department Of Energy Ionization monitor with improved ultra-high megohm resistor
US4808977A (en) * 1987-08-20 1989-02-28 Hedrick Terry J Electromechanical evacuation exit indicating flag

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5189399A (en) * 1989-02-18 1993-02-23 Hartwig Beyersdorf Method of operating an ionization smoke alarm and ionization smoke alarm

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB398722A (en) * 1932-11-07 1933-09-21 Paul Malsallez Improvements in process and apparatus for detecting, controlling and analysing gases, mixtures of gases, smokes and dusts suspended in said gases
US2145866A (en) * 1929-08-14 1939-02-07 Gioacchino Failla Electrotechnique
GB1009271A (en) * 1963-03-04 1965-11-10 Associated Fire Alarms Ltd Improvements in or relating to smoke detector circuits
US3233100A (en) * 1962-01-10 1966-02-01 Cerberus Ag Determining presence of aerosols in gases

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2145866A (en) * 1929-08-14 1939-02-07 Gioacchino Failla Electrotechnique
GB398722A (en) * 1932-11-07 1933-09-21 Paul Malsallez Improvements in process and apparatus for detecting, controlling and analysing gases, mixtures of gases, smokes and dusts suspended in said gases
US3233100A (en) * 1962-01-10 1966-02-01 Cerberus Ag Determining presence of aerosols in gases
GB1009271A (en) * 1963-03-04 1965-11-10 Associated Fire Alarms Ltd Improvements in or relating to smoke detector circuits

Cited By (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3795904A (en) * 1970-05-16 1974-03-05 Preussag Ag Feuerschutz Fire alarm with ionization chamber
US3775616A (en) * 1970-06-08 1973-11-27 Nittan Co Ltd Ionization smoke detector
US3735138A (en) * 1971-10-27 1973-05-22 Honeywell Inc Ionization smoke detector
US3913082A (en) * 1973-02-02 1975-10-14 Jenson Robert S Ionization aerosol detector
US4038649A (en) * 1975-09-16 1977-07-26 Emhart Industries, Inc. Smoke detection alarm device
US4053776A (en) * 1976-05-25 1977-10-11 The United States Of America As Represented By Thesecretary Of The Interior Sub-micron particle detector
US4286160A (en) * 1977-01-27 1981-08-25 Ried Jr Louis Ionization particle detector
EP0030621A1 (de) * 1979-12-14 1981-06-24 Cerberus Ag Ionisationsrauchmelder mit erhöhter Betriebssicherheit
US4364031A (en) * 1979-12-14 1982-12-14 Cerberus Ag Ionization smoke detector with increased operational reliability
US4488044A (en) * 1981-11-20 1984-12-11 Pittway Corporation Ionization chamber for smoke detector and the like
US4755682A (en) * 1986-10-07 1988-07-05 The United States Of America As Represented By The United States Department Of Energy Ionization monitor with improved ultra-high megohm resistor
US4808977A (en) * 1987-08-20 1989-02-28 Hedrick Terry J Electromechanical evacuation exit indicating flag

Also Published As

Publication number Publication date
GB1109587A (en) 1968-04-10
NL6701753A (xx) 1967-08-23
DK126607C (da) 1977-06-20
CH446131A (de) 1967-10-31
NL162493B (nl) 1979-12-17
BE694152A (xx) 1967-07-31
SE328226B (xx) 1970-09-07
AT268101B (de) 1969-01-27
DK126607B (da) 1973-07-30
NL162493C (nl) 1980-05-16
DE1259227B (de) 1968-01-18
FR1511451A (fr) 1968-01-26

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