SMOKE ALARM ACCORDING TO THE SCATTERED LIGHT PRINCIPLE HAVING A TWO-COLOR LIGHT-EMITTING DIODE WITH DIFFERENT SIZES OF LED CHIPS

• US 20150228171A1
• Filed: 02/13/2015
• Published: 08/13/2015
• Est. Priority Date: 02/13/2014
• Status: Active Grant

• Current Assignee: Siemens Schweiz AG (Siemens AG)
• Original Assignee: Siemens Schweiz AG (Siemens AG)
• Inventors: AEBERSOLD, HANS
• Granted Patent: US 9,569,946 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G08B 17/107 for detecting light-scattering due to smoke
• CPC Class Codes: G08B 17/113 Constructional details
• CPC Class Codes: H01L 2224/48091 Arched
• CPC Class Codes: H01L 2224/48247 connecting the wire to a bond pad of the item
• CPC Class Codes: H01L 2924/00014 the subject-matter covered by the group, the symbol of which is combined with the symbol of this group, being disclosed without further technical details

Abstract

An optical smoke alarm contains a detector unit that works according to the scattered light principle with a light-emitting diode to irradiate particles to be detected and a photo sensor which is spectrally sensitive thereto to detect the light scattered by the particles. The light-emitting diode contains a first LED chip being a surface-emitting radiator for emitting a first light bundle with light in a first wavelength range of from 350 nm to 500 nm. It contains a second LED chip being a surface-emitting radiator for emitting a second light bundle with light in a second wavelength range of from 665 nm to 1000 nm. The two LED chips are arranged next to each other. A ratio of the optically active surface of the first LED chip to the optically active surface of the second LED chip is within a range of from 2 to 20.

Claims

1. An optical smoke alarm, comprising:

a detector unit working according to a scattered light principle;

a light-emitting diode for irradiating particles to be detected and disposed in said detector unit, said light-emitting diode having a first LED chip being a surface-emitting radiator for emitting a first light bundle with light in a first wavelength range of from 350 nm to 500 nm, said light-emitting diode having a second LED chip being a surface-emitting radiator for emitting a second light bundle with light in a second wavelength range of from 665 nm to 1000 nm, said first and second LED chips disposed next to each other, a ratio of an optically active surface of said first LED chip to an optically active surface of said second LED chip being within a range of from 2 to 20; and

a spectrally sensitive photosensor to detect light scattered by the particles, said spectrally sensitive photosensor disposed in said detector unit.

2. The optical smoke alarm according to claim 1, wherein the ratio of said optically active surface of said first LED chip to said optically active surface of said second LED chip is within a range of from 2.5 to 6.5.

3. The optical smoke alarm according to claim 1, wherein said first LED chip is embodied to emit light with a wavelength of 460 nm±

40 nm or 390 nm±

40 nm, and said second LED chip to emit light with a wavelength of 940 nm±

40 nm or 860 nm±

40 nm.

4. The optical smoke alarm according to claim 1, wherein said light-emitting diode has an axis of symmetry and a respective main direction of radiation of said first and second LED chips is parallel toward the axis of symmetry.

5. The optical smoke alarm according to claim 1, wherein said light-emitting diode has an axis of symmetry, said first and second LED chips each have a main direction of radiation and at least one of the main directions of radiation is inclined toward the axis of symmetry.

6. The optical smoke alarm according to claim 1, further comprising a diaphragm mechanism having a diaphragm aperture formed therein and is disposed in said detector unit between said light-emitting diode and said photosensor, said diaphragm mechanism is disposed and aligned such that the first and second light bundles emitted by said first and second LED chips pass substantially completely through said diaphragm aperture.

7. The optical smoke alarm according to claim 1, further comprising a diaphragm mechanism having a diaphragm aperture formed therein and disposed in said detector unit between said light-emitting diode and said photosensor, said diaphragm mechanism is disposed and aligned such that less than 75% of the first light bundle emitted by said first LED chip and less than 75% of the second light bundle emitted by said second LED chip pass through said diaphragm aperture.

8. The optical smoke alarm according to claim 1, further comprising a diaphragm mechanism having a diaphragm aperture formed therein and disposed in said detector unit between said light-emitting diode and said photosensor, said diaphragm mechanism is disposed and aligned such that one of the first and second light bundles emitted by one of said first and second LED chips passes substantially completely through said diaphragm aperture, while less than 75% of the light bundle emitted by the other one of said first and second LED chips passes through said diaphragm aperture.

9. The optical smoke alarm according to claim 6, wherein said light-emitting diode has an axis of symmetry and said light-emitting diode is disposed rotated about the axis of symmetry such that the light emitted by said second LED chip is directed more toward said photosensor than the light emitted by said first LED chip.

10. The optical smoke alarm according to claim 9, wherein:

said light-emitting diode has a housing made of a transparent plastic;

said housing forms an optical lens along a region after a light outlet from said first and second LED chips; and

/or

an optical lens unit is disposed between said light-emitting diode and said diaphragm aperture.

11. The optical smoke alarm according to claim 10, wherein:

said light-emitting diode has a transverse axis extending perpendicular toward the axis of symmetry and through said first and second LED chips disposed next to each other, a light plane extending through the axis of symmetry and the transverse axis is defined;

said optical lens or said optical lens unit optically defines a focus point lying on the axis of symmetry, wherein, with the focus point as a vertex, an angle of radiation is defined that extends starting from the axis of symmetry within the light plane, wherein a first dimming angle value and a second dimming angle value is determined for the angle of radiation by two opposing inside edges of said diaphragm mechanism bounding said diaphragm aperture; and

said diaphragm mechanism is aligned and dimensioned such that the first and second dimming angle values are of different sizes.

12. The optical smoke alarm according to claim 11, wherein said diaphragm mechanism is aligned and dimensioned such that the first and second dimming angle values differ in size from each other by a factor of two to six.

13. The optical smoke alarm according to claim 1, further comprising an electronic control unit connected to said light-emitting diode and to said photosensor, said electronic control unit is configured to output a warning and/or an alarm when a minimum concentration value of smoke can be detected.

14. The optical smoke alarm according to claim 13, wherein said electronic control unit is configured to control said first LED chip with a specified nominal current and said electronic control unit is configured to control said second LED chip with a reduction factor that can be defined in comparison with the specified nominal current.

15. The optical smoke alarm according to claim 14, wherein the reduction factor is defined by a different spectral sensitivity of said photosensor for scattered light to be detected in the first and second wavelength ranges.

16. The optical smoke alarm according to claim 1, wherein said photosensor is a silicon PIN photodiode.

17. The optical smoke alarm according to claim 13, wherein said first and second LED chips can be controlled by said electronic control unit with alternate pulsing or simultaneous pulsing.