# US 2014/0197957 A1 · Evaluation of scattered-light signals in an optical hazard alarm and output both of a weighted smoke density signal and also of a weighted dust/steam density signal

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- Number: US 2014/0197957 A1
- Document ID: US20140197957A1
- Status: Published application
- Kind: A1
- Application number: 13/876,686
- Filed: 2012-09-25
- Published: 2014-07-17
- Earliest claimed: 2011-09-30
- Assignees: Siemens Aktiengesellschaft
- Applicants: Siemens Aktiengesellschaft
- Inventors: Martin Fischer
- Web page: https://patentgrep.com/patent/US20140197957A1

## CPC

- G08B 17/107: for detecting light-scattering due to smoke
- G08B: SIGNALLING SYSTEMS, e.g. PERSONAL CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS

## Abstract

A method evaluates two scattered-light signals in a hazard alarm operating in accordance with the scattered light principle. The particles to be detected are irradiated with light in a first wavelength range and with light in a second wavelength range. The light scattered by the particles is converted into a first and second non-normalized scattered light signal. The two scattered light signals are normalized in relation to one another such that their amplitude curve approximately coincides for larger particles such as dust and steam. The two normalized scattered light signals are transformed into a polar angle and a distance as polar coordinates of a polar coordinate system. Finally a respective smoke density signal and a respective dust/steam density signal is formed from a current distance value, wherein for this purpose the respective current distance values, depending on a current polar angle value, are weighted in opposition to one another.

## Claims

### Claim at position 1

1-11. (canceled)

### Claim 12

A method for evaluating two scattered light signals in a hazard alarm operating in accordance with a scattered light principle, the method comprising:
irradiating particles to be detected with a first light in a first wavelength range and with a second light in a second wavelength range;
converting light scattered by the particles into first and second non-normalized signals;
normalizing the first and second non-normalized signals to one another and producing two normalized scattered light signals having amplitude curves that approximately coincide for dust- and steam-sized particles;
transforming the two normalized scattered light signals into a polar angle and a polar distance as polar coordinates of a polar coordinate system;
forming a weighted smoke density signal and a weighted dust/steam density signal by weighting the polar distance depending on the polar angle, the polar distance being weighted oppositely in forming the weighted smoke density signal and the weighted dust/steam density signal; and
outputting the weighted smoke density signal and the weighted dust/steam density signal for further evaluation.

### Claim 13 (depends on 12)

The method as claimed in claim 12, wherein
the weighted smoke density signal is compared in a smoke comparison with a smoke signal threshold and a fire alarm stage is signaled based on the smoke comparison, and/or
the weighted dust/steam density signal is compared in a dust/steam comparison with a dust/steam signal threshold and a dust/steam warning stage is signaled based on the dust/steam comparison.

### Claim 14 (depends on 12)

The method as claimed in claim 12, wherein
if the polar angle is formed from as a quotient between first and second normalized scattered light signals, then:
the polar distance is weighted degressively during formation of the weighted smoke density signal for increasing polar angle values, and
the polar distance value is weighted progressively during formation of the weighted dust/steam density signal for increasing polar angle values, and
if the polar angle is formed from as a quotient between second and first normalized scattered light signals, then:
the polar distance is weighted progressively during formation of the weighted smoke density signal for increasing polar angle values, and
the polar distance is weighted degressively during formation of the weighted dust/steam signal for increasing polar angle values.

### Claim 15 (depends on 12)

The method as claimed in claim 12, wherein
the first light is infrared light and the first wavelength range is between 600 and 1000 nm, and
the second light is blue light and the second wavelength range is between 450 and 500 nm.

### Claim 16 (depends on 12)

The method as claimed in claim 12, wherein
the first light is infrared light and the first wavelength range is 940 nm±20 nm, and
the second light is blue light and the second wavelength range is 470 nm±20 nm.

### Claim 17 (depends on 12)

The method as claimed in claim 12, wherein the first and second non-normalized signals are normalized to amplitude curves that approximately coincide for particles having a particle size 0.5 and 1.1 μm.

### Claim 18

An optical hazard alarm operating in accordance with a scattered light principle, comprising:
a detection device comprising:
at least one light source to irradiate particles to be detected with a first light in a first wavelength range and with a second light in a second wavelength range; and
an optical receiver to convert light scattered by the particles into first and second non-normalized signals; and
an electronic evaluation unit comprising:
a normalization unit to normalize the first and second non-normalized signals to one another and produce two normalized scattered light signals having amplitude curves that approximately coincide for dust- and steam-sized particles;
a processor to transform the two normalized scattered light signals into a polar angle and a polar distance as polar coordinates of a polar coordinate system; and
a signal formation unit to form a weighted smoke density signal and a weighted dust/steam density signal by weighting the polar distance depending on the polar angle, the polar distance being weighted oppositely in forming the weighted smoke density signal and the weighted dust/steam density signal, the weighted smoke density signal and the weighted dust/steam density signal being output for further evaluation.

### Claim 19 (depends on 18)

An optical hazard alarm as claimed in claim 18, wherein
if the polar angle is formed from as a quotient between first and second normalized scattered light signals, then:
the polar distance is weighted degressively during formation of the weighted smoke density signal for increasing polar angle values, and
the polar distance value is weighted progressively during formation of the weighted dust/steam density signal for increasing polar angle values, and
if the polar angle is formed from as a quotient between second and first normalized scattered light signals, then:
the polar distance is weighted progressively during formation of the weighted smoke density signal for increasing polar angle values, and
the polar distance is weighted degressively during formation of the weighted dust/steam signal for increasing polar angle values.

### Claim 20 (depends on 18)

The optical hazard alarm as claimed in claim 18, wherein
the first light is infrared light and the first wavelength range is between 600 and 1000 nm, and
the second light is blue light and the second wavelength range is between 450 and 500 nm.

### Claim 21 (depends on 18)

The optical hazard alarm as claimed in claim 18, wherein
the first light is infrared light and the first wavelength range is 940 nm±20 nm, and
the second light is blue light and the second wavelength range is 470 nm±20 nm.

### Claim 22 (depends on 18)

The optical hazard alarm as claimed in claim 18, wherein the first and second non-normalized signals are normalized to amplitude curves that approximately coincide for particles having a particle size 0.5 and 1.1 μm.

### Claim 23 (depends on 18)

The optical hazard alarm as claimed in claim 18, wherein the electronic evaluation unit has:
a comparison unit to compare the weighted smoke density signal with a smoke signal threshold; and
a signaling unit to signal a smoke alarm stage based on the comparison.

### Claim 24 (depends on 18)

The optical hazard alarm as claimed in claim 18, wherein the electronic evaluation unit has:
a comparison unit to compare the weighted dust/steam density signal with a dust/steam signal threshold; and
a signaling unit to signal a dust/steam warning stage based on the comparison.