Claims
- 1. An ionization smoke detector comprising
- first and second electrodes spaced to define therebetween a smoke detecting chamber, a collector electrode in said smoke detecting chamber between said first and second electrodes,
- an ion source positioned for emitting radiation into said smoke detecting chamber for causing ionization of a gas therein,
- a power supply connected to said first and second electrodes to establish ion current flow through said smoke detecting chamber,
- comparator circuitry connected to said collector electrode, said collector electrode being adapted to apply a predetermined voltage to said comparator circuitry during clean air conditions,
- a first voltage divider network connected to said power supply and to said comparator circuitry, said first voltage divider network generating a reference voltage for application to said comparator circuitry, said reference voltage having a predetermined offset value from said clean air voltage applied to said comparator circuitry by said collector electrode, said comparator circuitry being adapted to generate an alarm signal when the voltage applied to said comparator circuitry by said collector electrode is equal to or less than said reference voltage,
- a test electrode disposed in said smoke detecting chamber between said first and second electrodes,
- a second voltage divider network connected to said power supply circuit and to said test electrode, and
- switch means connected to said second voltage divider network, said switch means having open and closed conditions and being connected to said second voltage divider network such that, when said switch means is in open condition, the voltage applied to said test electrode is the same as the voltage applied to said first electrode by said power supply, and when said switch means is in closed condition a test voltage is applied to said test electrode, said test voltage on said test electrode being effective to reduce the voltage on said collector electrode to a value equal to or less than the said reference voltage to cause said comparator circuit to generate an alarm signal.
- 2. The ionization detector of claim 1 wherein the test voltage applied to said test electrode when said switch is closed is less than the voltage on said first electrode and greater than the clean air voltage of said collector electrode.
- 3. The ionization detector of claim 1 wherein said second voltage divider network includes two series-connected resistors, said switch means is connected in series with said two resistors, and said test voltage is generated at the junction of said two resistors.
- 4. The ionization detector of claim 3 wherein said switch comprises a transistor with the collector-emitter path being connected in series with said two resistors, and means for applying a voltage to the base of the transistor to cause current flow in said collector-emitter path to cause said test voltage to appear on said test electrode.
- 5. The ionization detector of claim 3 wherein said switch comprises an optically coupled isolator comprising a photo-responsive device connected in series with the second resistor between the test electrode and ground, and a light source positioned to illuminate the photo-responsive device when energized, and means for energizing the photo-responsive device.
- 6. An ionization smoke detector comprising
- a housing, inner and outer electrodes spaced in said housing to define therebetween a smoke detecting chamber, a collector electrode in said smoke detecting chamber between said inner and outer electrodes,
- an ion source positioned in said housing for emitting radiation into said smoke detecting chamber for causing ionization of a gas therein,
- a power supply connected to said inner and outer electrodes to establish ion current flow through said smoke detecting chamber,
- comparator circuitry connected to said collector electrode, said collector electrode being adapted to apply a predetermined voltage to said comparator circuitry during clean air conditions,
- a first voltage divider network connected to said power supply and to said comparator circuitry, said first voltage divider network generating a reference voltage for application to said comparator circuitry, said reference voltage having a predetermined offset value from said clean air voltage applied to said comparator circuitry by said collector electrode, said comparator circuitry being adapted to generate an alarm signal when the voltage applied to said comparator circuitry by said collector electrode is equal to or less than said reference voltage,
- a test electrode disposed in said smoke detecting chamber between said outer and collector electrodes, said outer, test and collector electrodes being substantially parallel to one another,
- a second voltage divider network connected to said power supply circuit and to said test electrode, and
- switch means connected to said second voltage divider network, said switch means having open and closed conditions and being connected to said second voltage divider network such that, when said switch means is in open condition, the voltage applied to said test electrode is the same as the voltage applied to said outer electrode by said power supply, and when said switch means is in closed condition a test voltage is applied to said test electrode, said test voltage on said test electrode being effective to reduce the voltage on said collector electrode to a value equal to or less than the said reference voltage to cause said comparator circuit to generate an alarm signal.
- 7. The ionization detector of claim 6 wherein said switch is a magnetically operated switch that is operated by applying a magnet to the exterior of the detector housing.
- 8. The ionization detector of claim 7 wherein the test voltage applied to said test electrode when said switch is closed is less than the voltage on said first electrode and greater than the clean air voltage of said collector electrode.
- 9. The ionization detector of claim 6 wherein said second voltage divider network includes two series connected resistors, said switch means is connected in series with said two resistors, and said test voltage is generated at the junction of said two resistors.
- 10. The ionization detector of claim 9 wherein said switch comprises a transistor with the collector-emitter path being connected in series with said two resistors, and means for applying a voltage to the base of the transistor to cause current flow in said collector-emitter path to cause said test voltage to appear on said test electrode.
- 11. The ionization detector of claim 9 wherein said switch comprises an optically coupled isolator comprising a photo-responsive device connected in series with the second resistor between the test electrode and ground, and a light source positioned to illuminate the photo-responsive device when energized, and means for energizing the photo-responsive device.
- 12. The ionization detector of claim 9 wherein the test voltage applied to said test electrode when said switch is closed is less than the voltage on said first electrode and greater than the clean air voltage of said collector electrode.
Parent Case Info
This is a continuation of application Ser. No. 224,387, filed Jan. 12, 1981, now abandoned.
US Referenced Citations (7)
Continuations (1)
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Number |
Date |
Country |
Parent |
224387 |
Jan 1981 |
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