Heatable smoke alarm

Abstract

A smoke alarm has a housing with a heating device for heating walls of the housing to a temperature above the dew point. The heating device has at least one heating light emitting diode (LED). The heating LED has an opening angle for the emission of light, which opening angle leads to an irradiated area of the housing.

Claims

1. A smoke alarm being a scattered radiation fire alarm, comprising: a housing having walls; a heating device having at least one heating light emitting diode (LED) heating said walls of said housing to a temperature above a dew point by emitted light, light emitted from the at least one heating LED not being used to detect smoke; at least one radiation source; at least one detector for detecting at least one of scattered radiation or radiation generated by said at least one heating LED; and the smoke alarm configured to switch off said heating device for a duration within which said at least one radiation source emits a light pulse for detecting the scattered radiation, wherein said heating device and said radiation source do not emit light simultaneously.

2. The smoke alarm according to claim 1, wherein said heating device containing said at least one heating LED has a power of 0.2 W.

3. The smoke alarm according to claim 1, wherein said at least one heating LED is a white LED, a blue LED or an infrared LED.

4. The smoke alarm according to claim 1, wherein an efficiency of said heating device is at least 25%.

5. The smoke alarm according to claim 1, wherein said heating device is mounted on a housing top side facing a housing interior and is suitable for emitting radiation in a direction of a housing underside opposite said housing top side.

6. The smoke alarm according to claim 5, wherein an opening angle of said heating device is chosen such that at least 90% of said housing underside is illuminated by said heating device.

7. The smoke alarm according to claim 1, wherein said radiation source is one of at least two first radiation sources having a first wavelength; further comprising a second radiation source having a second wavelength, which is greater than the first wavelength; wherein said detector is a sensor which is sensitive to the first and second wavelengths; wherein said first radiation sources have first optical axes; said second radiation source has a third optical axis; said detector has a second optical axis, and said first radiation sources, said second radiation source and said detector are disposed such that their optical axes are directed at a common center; and wherein said first radiation sources, said second radiation source and said detector are disposed such that they lie on corner points of a base face of an imaginary pyramid, and are furthermore aligned such that a center forms a vertex of the imaginary pyramid.

8. The smoke alarm according to claim 7, wherein said heating device is disposed a same plane as said first radiation sources and said second radiation source.

9. The smoke alarm according to claim 8, wherein said first radiation sources, said second radiation source and said detector are disposed on an imaginary circle and said heating device is disposed at a center of the imaginary circle.

10. The smoke alarm according to claim 1, wherein said housing has perforations formed therein and formed on at least one side face of said housing.

11. The smoke alarm according to claim 1, further comprising a control device for controlling said heating device.

12. The smoke alarm according to claim 1, further comprising: a temperature sensor for measuring a temperature within the smoke alarm; and a temperature regulating device outputting a control signal for driving said heating device.

13. The smoke alarm according to claim 1, further comprising: a moisture sensor for measuring moisture within the smoke alarm; and a moisture regulating device for outputting a control signal for driving said heating device.

14. The smoke alarm according to claim 1, wherein an efficiency of said heating device is at least 35%.

15. A smoke alarm being a scattered radiation fire alarm, comprising: a housing having walls; a heating device having at least one heating light emitting diode (LED) heating said walls of said housing to a temperature above a dew point by emitted light, light emitted from the at least one heating LED not being used to detect smoke; at least one radiation source; at least one detector for detecting at least one of scattered radiation or radiation generated by said at least one heating LED; a first optical axis of the radiation source and a second optical axis of the at least one detector being situated within a luminous cone of said at least one heating LED; and the smoke alarm configured to switch off said heating device for a duration within which said at least one radiation source emits a light pulse for detecting the scattered radiation, wherein said heating device and said radiation source do not emit light simultaneously.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

(1) FIG. 1 is a schematic illustration of a three-channel scattered radiation fire alarm containing an LED as a heating device according to the invention; and

(2) FIG. 2 is a diagrammatic, cross-sectional depiction of a scattered radiation fire alarm.

DETAILED DESCRIPTION OF THE INVENTION

(3) Referring now to the figures of the drawings in detail and first, particularly to FIG. 1 thereof, there is shown a smoke alarm 1 containing two first radiation sources S1, a second radiation source S2 and a detector D. In this example, the first radiation sources S1 and also the second radiation source S2 and the detector D are arranged on a circle. The first radiation source S1 has a first optical axis 7, the second radiation source S2 has a third optical axis 9, and the detector D has a second optical axis 8. The optical axes 7, 8, 9 meet at the center of the circle. The optical axes 7, 9 form the center of the cone of the incident radiation 2 and the optical axis 8 forms the center of the cone of the scattered radiation 3 to be detectable.

(4) The scattering volume includes the point of intersection of the optical axes 7, 8, 9 and is the intersection volume of the cone of the incident radiation 2 and the detectable scattered radiation 3. A heating device H is furthermore arranged at the center of the circle. In this case, the heating device H lies on a different plane from the scattering volume 4. This ensures that the heating device H does not restrict the function of the smoke alarm 1.

(5) The heating device H contains a heating LED suitable for emitting light and for emitting power loss in the form of heat. The heating LED has an opening angle for the emission of light, which opening angle leads to an irradiated area of the housing, the heating area 5. Expediently, in this embodiment, the two first radiation sources S1, the second radiation source S2 and the detector D and also the heating device H are arranged in one plane, in particular on a common circuit board. The arrangement of all the optical components S1, S2, D, H on a circuit board has the advantage that the circuit board can be populated during production in the same work step and can then be inserted as a whole into the housing of the smoke alarm.

(6) FIG. 2 shows a smoke alarm 1 containing a radiation source S and a detector D. The radiation source S and the smoke alarm 1 are arranged at an outer boundary of the housing top side O such that the first optical axis 7 of the radiation source S and the second optical axis 8 of the detector D meet at a point at the housing underside U opposite the housing top side O. A scattering volume 4 (not illustrated here) encompasses the point of intersection of the optical axes 7 and 8. The heating device H is likewise arranged at a housing top side O. Expediently, the radiation source S, the detector D and the heating device H are arranged on a circuit board. The heating LED is suitable for emitting radiation in a cone-shaped fashion within an opening angle, such that at least one part of the housing underside U is illuminated by the heating radiation. The area of intersection of a radiation cone of the heating LED and the housing underside U is identified as heating area 5. The point of intersection of the optical axes 7 and 8 lies in the heating area 5.

(7) The side faces 10 of the housing have perforations 6. The perforations 6 serve for gas exchange with the surroundings. Smoke-containing gas can pass into the smoke alarm 1, such that smoke particles can be situated in the scattering volume 4. The perforations 6 are configured as a light trap.

(8) For regulating the heating device H, sensors (not illustrated) for temperature and/or moisture and a temperature and/or moisture regulating device can additionally be present, which serve to switch on the heating device H as soon as temperature and/or air humidity afford(s) the possibility of dew formation in the smoke alarm 1.

(9) Furthermore, a control device can be present, which switches off the heating device H for a short time duration. While the heating device H is switched off, a light pulse is emitted by the first radiation sources S1 and/or the second radiation source S2, which light pulse can be scattered at smoke particles in the scattering volume 4. The detectable scattered radiation 3 is detected by the detector D. As soon as the measurement process has ended, the heating device H can be switched on again. This duration of the measurement process is in the milliseconds range, in particular 0.5 to 10 ms. The alternately pulsed operation of heating device and radiation sources prevents corruption of the measurement.

(10) Furthermore, the detector D can also be used to monitor the function of the heating device H. For this purpose, further scattered radiation generated by light emitted by the heating device H is detected by the detector D. As a result, it is possible to monitor the functioning of the heating device H.

(11) The following is a summary list of reference numerals and the corresponding structure used in the above description of the invention: 1 Smoke alarm 2 Incident radiation 3 Detectable scattered radiation 4 Scattering volume 5 Heating area 6 Perforation 7 First optical axis 8 Second optical axis 9 Third optical axis 10 Side face D Detector H Heating device Housing top side S Radiation source S1 First radiation source S2 Second radiation source U Housing underside