US3295121A - Electric alarm system, preferably for fire alarms - Google Patents

Electric alarm system, preferably for fire alarms Download PDF

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Publication number
US3295121A
US3295121A US24769462A US3295121A US 3295121 A US3295121 A US 3295121A US 24769462 A US24769462 A US 24769462A US 3295121 A US3295121 A US 3295121A
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chambers
radiating member
ionizing
voltage
connected
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Meyer Svend Scheel
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DANSKE SECURITAS AS
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DANSKE SECURITAS AS
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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 automatic alarm devices for analysing flowing fluid materials by the use of optical means
    • G08B17/11Actuation by presence of smoke or gases automatic alarm devices for analysing flowing fluid materials by the use of optical means using an ionisation chamber for detecting smoke or gas
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01NINVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N15/00Investigating characteristics of particles; Investigating permeability, pore-volume, or surface-area of porous materials
    • G01N15/06Investigating concentration of particle suspensions
    • G01N15/0656Investigating concentration of particle suspensions using electric, e.g. electrostatic methods or magnetic methods
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01NINVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00Investigating or analysing materials by the use of electric, electro-chemical, or magnetic means
    • G01N27/62Investigating or analysing materials by the use of electric, electro-chemical, or magnetic means by investigating the ionisation of gases; by investigating electric discharges, e.g. emission of cathode
    • G01N27/64Investigating or analysing materials by the use of electric, electro-chemical, or magnetic means by investigating the ionisation of gases; by investigating electric discharges, e.g. emission of cathode using wave or particle radiation to ionise a gas, e.g. in an ionisation chamber
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01TMEASUREMENT OF NUCLEAR OR X-RADIATION
    • G01T7/00Details of radiation-measuring instruments
    • G01T7/12Provision for actuation of an alarm
    • G01T7/125Alarm- or controlling circuits using ionisation chambers, proportional counters or Geiger-Mueller tubes, also functioning as UV detectors

Description

Dec. 27, 1966 s. s. MEYER 3,295,121

ELECTRIC ALARM SYSTEM, PREFERABLY FOR FIRE ALARMS Filed Dec. 27, 1962 ALARM DfV/CE United States Patent Ofiice Patented Dec. 27, 1966 3,295,121 ELECTRIC ALARM SYSTEM, PREFERABLY FOR FIRE ALARMS Svend Scheel Meyer, Copenhagen Herlev, Denmark, assignor to Danske Securitas A/S, Copenhagen V., Denmark, a Danish corporation Filed Dec. 27, 1962, Ser. No. 247,694

Claims priority, application Denmark, Dec. 30, 1961,

5,263/61 3 Ciaims. (U. 340-237) The invention relates to an electric alarm system, preferably for fire alarms, and of the kind consisting of two metallic ionizing chambers connected in series and each provided with a radioactive radiating member, one of the said chambers being closed to the ambient atmosphere whereas the other chamber is open and communicates with both the first chamber and the room to be watched, the walls of the two chambers being each connected to its separate pole of a source of voltage, and a voltage sensitive indicating member being connected to electrodes in the two chambers.

Electric alarm systems of the aforesaid kind are known and they are based on the phenomenon that the electric current which from the voltage source may be forced through the ionizing chambers depends on whether the ions transmitting current are formed in pure gases or in gases that are mixed with smoke or liquid particles. In the last mentioned case a part of the ions produced are deposited on the particles of the smoke or liquid, the said particles being of greater mass and moving at a substantially lower velocity than the gas ions. An amount of gas to which are added particles of smoke or liquid will thus convey a smaller amount of electric current than would the corresponding amount of pure gases. If smoke or liquid particles enter into the open ionizing chamber of such a system, the electric resistance in the said chamber will be increased whereby the potential relationship between the two series-connected ionizing chambers is altered which will cause the voltage sensitive indicating member to react.

Practice has disclosed that it is very difi'icult to ensure such a balance of the current conditions in the two seriesconnected ionizing chambers that the installation becomes sufficiently reliable in operation, in particular if a radioactive radiating member is used in each of the two ionizing chambers. It is furthermore diflicult to obtain so good and substantially symmetrical insulating conditions in the two chambers that the conditions of ionization, even without particles of smoke or liquid, are sufficiently uniform.

These drawbacks are eliminated in a system according to the invention thereby that the ionizing chambers are connected by a joint diaphragm of electrically insulating material in which a slender radiating member is so disposed as to project into both ionizing chambers, the electrodes consisting of a metal grid surrounding the radiating member along at least a part of its length.

As a result, a variation in the strength of the active radiation from the radiating member will act upon both chambers in the same proportion, whereby the system will be reliable in operation.

In one embodiment of the system according to the invention the radiating member consists of a glass tube filled with a radioactive gas such as krypton, which will ensure a uniform distribution of the active radiation throughout the length of the radiating member.

In another embodiment of the system according to the invention the radiating member is disposed in such manner that it is displaceable in its longitudinal direction, as a result of which corrections to compensate for a geometrical or material difierence between the two ionizing chambers may be made by displacement of the radiating member.

In a third embodiment of the system according to the invention the metal grid is connected to a tap of a capacitive voltage-dependent voltage divider the extreme ends of which are connected each to their separarte ionizing chamber and which constitute one branch of a bridge arrangement that is fed with current, partly from the direct current source, partly from an alternating current source which constitutes the other branch of the bridge arrangement, the indicating member being inserted between the said tap and a point'of the alternating current voltage source, which point is balanced in relation to the said extreme ends.

As a result, the internal resistances of the ionizing chambers will normally determine the direct voltage across each of the two voltage-dependent capacitors of the voltage divider, whereas a variation in the internal resistance of the open ionizing chamber will produce a variation in the direct voltage of the capacitor connected in parallel with this chamber, which will involve a substantial non-balance in the normally balanced bridge arrangement, whereby the system becomes very sensitive to particles of smoke or liquid entering the open ionizing chamber.

In a preferred embodiment of the system the indicating member may consist of an amplifier in the output circuit of which there is inserted a signal relay or a similar alarm device.

The invention will now be further described with reference to the drawing, in which FIGURE 1 shows an embodiment of an electric alarm system according to the invention, and

FIGURE 2 a modification of same.

In the drawing, 1 and 2 are ionizing chambers having a joint diaphragm 3 of electrically insulating material in which there is provided a slender radiating member 4 in such manner that it projects into both of the chambers 1 and 2. The one ionizing chamber 1 is closed to the ambient atmosphere, whereas the other chamber 2 is open both to the first chamber and the atmosphere, the wall of the chamber being, for example, provided with perforations 5 through which the chamber communicates with rooms to be watched for any occurring particles of smoke or liquid. The walls of the two chambers are at points 6 and 7 connected by terminals 8 and 9 each to their separate pole 10 and 11 of a voltage source 12, for example a storage battery, which is constantly impressing the ionizing chamber with a positive voltage of about 200 volts, whereas the other pole 11 of the battery and and consequently the terminal 9 may be earthed. The radiating member may according to the invention be a glass tube filled with a radioactive gas as krypton. The radiating member 4 is surrounded at least along a part of its length by a metal grid 13 which is connected to a voltage sensitive indicating member which in the em bodiment according to the invention that is shown in FIGURE 1 consists of a cold-cathode tube 14, the cathode 15 of which is connected to the negative pole 11 of the battery 12, its anode 16 being connected to the positive pole 10 of the battery, whereas the control grid 17 of the tube is connected to the metal grid 13 across a terminal 18. During normal operation of the system the gas in the two chambers will be ionized by the radiating member 4- and the ions produced will charge the metal grid 13 and thereby control the grid 17 to such potential that the cold-cathode tube 14 is non-conductive. A signal relay 19 inserted in series with the anode 16 of the tube receives no current in this condition and is therefore not in its attracted position. The radiating member 4 is according to the invention disposed in such manner that it is displaceable in its longitudinal direction and it is adjusted in such manner that a slight decrease in the conditions of ionization in the open chamber 2 will cause such an increase in the grid voltage of the tube that the tube becomes conductive, whereby the signal relay 19 receives current and alarms. If particles of smoke occur in the room to be watched, the particles will enter the open ionizing chamber 2, and these particles will absorb a number of the ions in the said chamber, and since the smoke particles are of relatively great mass, the charged particles of smoke will move at lower velocity than the free ions so that the ionizing current in the open chamber is reduced, whereby the voltage of the control grid 17 is increased and the tube 14 bursts into glow, after which the signal relay 19 attracts and alarms. For example, a visible signal such as a lamp mounted near the ionizing chambers may be connected to the contacts of the relay 19 so as to indicate which of a plurality of systems has reacted to any particles of smoke or liquid or egg. has reacted owing to a fault.

It will be appreciated by those skilled in the art that both the cold-cathode tube 14 and the signal relay 19 'may be substituted by other devices responsive to voltage and current, such as transistors, without falling outside the scope of the invention.

In the embodiment of the invention disclosed in FIG- URE 2, the metal grid 13 is connected across the terminal 18 to a tap 20 of a voltage divider which consists of two voltage dependent capacitors 21 and 22 the outer terminals 23 and 24 of which are connected to the closed ionizing chamber 1 across the terminal 8 and to the open ionizing chamber 2, respectively, across the terminal 9. The ionizing currents in the two chambers will in that case act as leak resistances between the terminals 8, 18 and 9, 18, which is indicated in FIGURE 2 by dotted resistances 25 and 26. It will be appreciated that such parts of the system as in FIGURE 1 are located to the right of the terminals 8, 9 and 18 are omitted in the system shown in FIGURE 2. The voltage divider 21, 22 constitutes one branch of a bridge arrangement which is fed with current from a source of alternating current through a transformer 27 which constitutes the other branch of the bridge arrangement, and in this embodiment of the system the indicating member consists of an alternating current amplifier 28 inserted between the tap 20 on the voltage divider 21, 22 and a point 29 located on the secondary winding of the transformer 27 and balanced in relation to the extreme points 8 and 9 of the voltage divider. A source of direct current, such as a battery 12, has its positive pole connected through a high-ohmic resistance 30 to the one outer terminal 8 of the voltage divider, whereas the negative battery pole which may be earthed is in connection with the other outer terminal 9 of the voltage divider. The secondary winding of the transformer 27 is shielded against direct current by means of capacitors 31 and 32. When the system is in operation the source of radiation 4 is adjusted in such manner that the ionization current in the two ionizing chambers 1 and 2 produces leak resistances 25 and 26 of equal magnitude, and in that case the bridge arrangement is in balance since the two capacitors 21 and 22 of the voltage divider are impressed with uniform potentials. If particles of smoke enter the open ionizing chamber 2, the ionizing current in the said chamber will be reduced, whereby the voltage across the one capacitor 22 of the voltage dividerincreases and the voltage across the other capacitor 21 of the voltage divider decreases as a result of which the capacitance of the first-mentioned capacitor is reduced and the capacitance of the last-mentioned capacitor is increased so that the bridge arrangement gets unbalanced and an unbalanced potential occurs across the input terminals of the amplifier 28. As a consequence, a signal relay 19 inserted in the output circuit of the amplifier 28 across a rectifier 33 receives current and gives alarm to indicate that smoke has entered the open ionizing chamber 2.

It will be appreciated that the voltage divider 21, 22 can be built up of several voltage-dependent capacitors if two individual capacitors cannot stand up to the full direct voltage supplied. It will also be appreciated that the direct voltage can be connected to the capacitors 21, 22 through balanced voltage-reducing voltage dividers to ensure that the said capacitors obtain maximum voltage sensitivity.

What I claim and desire to secure by Letters Patent 1. An area monitoring electric alarm system preferably for fire alarms comprising, two metallic ionizing chambers connected together at a common wall, the chambers having registered apertures in the common wall for intercommunication between the interiors of the chambers, one of the chambers having closed walls to the area to be monitored, the other chamber having Walls open to the area to be monitored, the chambers being connected across terminals of a voltage source, an elongated radioactive radiating member disposed within both chambers through the registered apertures the radiating member being displaceable in its longitudinal direction relative to the chambers, a plurality of interconnecting electrodes in both of the chambers, a voltage sensitive indicating member electrically connected to the electrodes, the electrodes being in the form of a metal grid surrounding the radiating member along at least a part of the length of the radiating member, and said common wall mutually separating and electrically insulating the ionizing chambers and the radiating member.

2. An electric alarm system according to claim 1 wherein the elongated radioactive radiating member is a protracted glass tube filled with a radioactive gas radiating beta-particles.

3. An electric alarm system according to claim 1 wherein the metal grid is connected to a tap of a capacitive voltage-dependent voltage divider, one extreme end of which is interconnected to the open ionizing chamber and another extreme end of which is interconnected to the closed ionizing chamber, said voltage divider constituting one branch of a bridge circuit that is fed with electrical energy from a direct voltage source and partly from an alternating voltage source, said alternating voltage source being connected to the extreme ends of the voltage divider through a transformer constituting a second branch of the bridge circuit and having a center terminal between said extreme ends, an amplifier having its input terminals connected to said tap and said center terminal and its output connected to a signal relay for an alarm device.

References Cited by the Examiner UNITED STATES PATENTS 3/1960 Great Britain.

NEIL C. READ, Primary Examiner. D. K. MEYER, Assistant Examiner.

Claims (1)

1. AN AREA MONITORING ELECTRIC ALARM SYSTEM PREFERABLY FOR FIRE ALARMS COMPRISING, TWO METALLIC IONIZING CHAMBERS CONNECTED TOGETHER AT A COMMON WALL, THE CHAMBERS HAVING REGISTERED APERTURES IN THE COMMON WALL FOR INTERCOMMUNICATION BETWEEN THE INTERIORS OF THE CHAMBERS, ONE OF THE CHAMBERS HAVING CLOSED WALLS TO THE AREA TO BE MONITORED, THE OTHER CHAMBER HAVING WALLS OPEN TO THE AREA TO BE MONITORED, THE CHAMBERS BEING CONNECTED ACROSS TERMINALS OF A VOLTAGVE SOURCE, AN ELONGATED RADIOACTIVE RADIATING MEMBER DISPOSED WITHIN BOTH CHAMBERS THROUGH THE REGISTERED APERTURES THE RADIATING MEMBER BEING DISPLACEABLE IN ITS LONGITUDINAL DIRECTION RELATIVE TO THE CHAMBERS, A PLURALITY OF INTERCONNECTING ELECTRODES IN BOTH OF THE CHAMBERS, A VOLTAGE SENSITIVE INDICATING MEMBER ELECTRICALLY CONNECTED TO THE ELECTRODES, THE ELECTRODES BEING IN THE FORM OF A METAL GRID SURROUNDING THE RADIATING MEMBER ALONG AT LEAST A PART OF THE LENGTH OF THE RADIATING MEMBER, AND SAID COMMON WALL MUTUALLY SEPARATING AND ELECTRICALLY INSULATNG THE IONIZING CHAMBERS AND THE RADIATING MEMBER.
US24769462 1961-12-30 1962-12-27 Electric alarm system, preferably for fire alarms Expired - Lifetime US3295121A (en)

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DK526361A DK101900C (en) 1961-12-30 1961-12-30 Electrical alarm system, preferably for fire alarm.

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AT (2) AT250834B (en)
CH (1) CH397472A (en)
DK (1) DK101900C (en)
GB (1) GB1020771A (en)
SE (1) SE309180B (en)

Cited By (21)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3514603A (en) * 1966-12-22 1970-05-26 Johnson Service Co Ionization chamber detection apparatus having a low voltage source means
US3676678A (en) * 1969-04-25 1972-07-11 Nittan Co Ltd Single chamber ionization smoke detector
US3728703A (en) * 1970-10-12 1973-04-17 Edward Co Inc Fire detector stabilizer circuit
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
US4012729A (en) * 1975-06-19 1977-03-15 Statitrol Corporation Multi-element ionization chamber
US4023152A (en) * 1973-10-01 1977-05-10 Matsushita Electric Works, Ltd. Ionization type smoke sensing device
US4222046A (en) * 1978-07-31 1980-09-09 Honeywell Inc. Abnormal condition responsive means with periodic high sensitivity
US4245174A (en) * 1978-04-24 1981-01-13 Isotec Industries Limited Dual ionization chamber
US4280052A (en) * 1978-11-09 1981-07-21 Solomon Elias E Multiple chamber ionization detector
US4364031A (en) * 1979-12-14 1982-12-14 Cerberus Ag Ionization smoke detector with increased operational reliability
US20130154657A1 (en) * 2011-12-14 2013-06-20 Microchip Technology Incorporated Method and Apparatus for Detecting Smoke in an ION Chamber
US20130154670A1 (en) * 2011-12-14 2013-06-20 Microchip Technology Incorporated Method and Apparatus for Detecting Smoke in an ION Chamber
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
US9071264B2 (en) 2011-10-06 2015-06-30 Microchip Technology Incorporated Microcontroller with sequencer driven analog-to-digital converter
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
US9437093B2 (en) 2011-10-06 2016-09-06 Microchip Technology Incorporated Differential current measurements to determine ION current in the presence of leakage current
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

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
USRE30323E (en) * 1968-09-26 1980-07-01 Hochiki Kabushiki Kaisha Smoke detector adapted to a smoke sensing apparatus

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1991934A (en) * 1929-09-23 1935-02-19 Harry F Mccray Apparatus and process for utilizing emanations from radio-active material
US2646556A (en) * 1950-06-17 1953-07-21 C O Two Fire Equipment Co Supervised alarm system
US2702898A (en) * 1953-10-06 1955-02-22 Electro Watt Electrical And In Gas-responsive control apparatus
US2759174A (en) * 1952-08-26 1956-08-14 American District Telegraph Co Fire detector
GB831812A (en) * 1957-02-01 1960-03-30 Minerva Detector Company Ltd Improvements in or relating to fire detectors

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1991934A (en) * 1929-09-23 1935-02-19 Harry F Mccray Apparatus and process for utilizing emanations from radio-active material
US2646556A (en) * 1950-06-17 1953-07-21 C O Two Fire Equipment Co Supervised alarm system
US2759174A (en) * 1952-08-26 1956-08-14 American District Telegraph Co Fire detector
US2702898A (en) * 1953-10-06 1955-02-22 Electro Watt Electrical And In Gas-responsive control apparatus
GB831812A (en) * 1957-02-01 1960-03-30 Minerva Detector Company Ltd Improvements in or relating to fire detectors

Cited By (31)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3514603A (en) * 1966-12-22 1970-05-26 Johnson Service Co Ionization chamber detection apparatus having a low voltage source means
US3676678A (en) * 1969-04-25 1972-07-11 Nittan Co Ltd Single chamber ionization smoke detector
US3728703A (en) * 1970-10-12 1973-04-17 Edward Co Inc Fire detector stabilizer circuit
US4023152A (en) * 1973-10-01 1977-05-10 Matsushita Electric Works, Ltd. Ionization type smoke sensing device
US4012729A (en) * 1975-06-19 1977-03-15 Statitrol Corporation Multi-element ionization chamber
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
US4245174A (en) * 1978-04-24 1981-01-13 Isotec Industries Limited Dual ionization chamber
US4222046A (en) * 1978-07-31 1980-09-09 Honeywell Inc. Abnormal condition responsive means with periodic high sensitivity
US4280052A (en) * 1978-11-09 1981-07-21 Solomon Elias E Multiple chamber ionization detector
US4364031A (en) * 1979-12-14 1982-12-14 Cerberus Ag Ionization smoke detector with increased operational reliability
EP0030621B1 (en) * 1979-12-14 1985-01-16 Cerberus Ag Ionisation smoke signaller with particular operational reliability
US9805572B2 (en) 2011-10-06 2017-10-31 Microchip Technology Incorporated Differential current measurements to determine ion current in the presence of leakage current
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
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
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
CN104067324A (en) * 2011-12-14 2014-09-24 密克罗奇普技术公司 Method and apparatus for detecting smoke in an ion chamber
CN104094328A (en) * 2011-12-14 2014-10-08 密克罗奇普技术公司 Method and apparatus for detecting smoke in ion chamber
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
WO2013090327A1 (en) * 2011-12-14 2013-06-20 Microchip Technology Incorporated Method and apparatus for detecting smoke in an ion chamber
WO2013090322A1 (en) * 2011-12-14 2013-06-20 Microchip Technology Incorporated Method and apparatus for detecting smoke in an ion chamber
US20130154670A1 (en) * 2011-12-14 2013-06-20 Microchip Technology Incorporated Method and Apparatus for Detecting Smoke in an ION Chamber
US20130154657A1 (en) * 2011-12-14 2013-06-20 Microchip Technology Incorporated Method and Apparatus for Detecting Smoke in an ION Chamber
CN104094328B (en) * 2011-12-14 2016-11-09 密克罗奇普技术公司 For detecting the method and apparatus of the smog in ion chamber
CN104067324B (en) * 2011-12-14 2016-11-16 密克罗奇普技术公司 For detecting the method and apparatus of the smog in 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

Also Published As

Publication number Publication date
GB1020771A (en) 1966-02-23
SE309180B (en) 1969-03-10
AT248300B (en) 1966-07-25
CH397472A (en) 1965-08-15
AT250834B (en) 1966-11-25
DK101900C (en) 1965-06-08

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