EP2423895B1 - Light scattering smoke alarm with means of suppressing an acoustic warning if battery voltage is low - Google Patents

Description

The invention relates to a fire detector having a working according to the optical scattered light principle detection unit and an electronic evaluation unit. It also includes an audible and / or visual detector for outputting an alarm in the event of a fire. Furthermore, the fire detector comprises an energy storage device, in particular a battery, for self-sufficient electrical supply of the fire detector and a voltage measuring unit for measuring a voltage applied to the energy storage battery voltage. It has warning means for emitting an acoustic warning in the event that the battery voltage falls below a first voltage limit. Furthermore, the fire detector comprises a sensitive to ambient light sensor and means for suppressing the output of the acoustic warning, if the ambient light falls below a predetermined brightness limit. Such automatic fire detectors can detect fires or their formation based on physical properties of the fire and trigger an alarm. Thus, the risk of the spread of a fire can be significantly reduced.

The considered fire detectors are typically designed as point detectors and especially designed for stand-alone operation. For the electrical supply of the fire detector, these have in particular a replaceable battery. It is also known that the fire alarms emit an acoustic warning signal when the battery voltage falls below a predetermined lower voltage value, such as 7.5 V when using a 9V blocks. The user of such a fire detector is thereby prompted to replace the soon-to-be-empty battery. Typically, the acoustic request is made by a momentary beeping of less than 1 second at certain intervals. The latter can be shorter be, the more the battery voltage falls below the lower voltage value, such as in 60- to 1-minute intervals.

From the product data sheet of the company Hager is a smoke detector of the type TG500A with a shielded against ambient light optical measuring chamber known. It is set up to emit an acoustic signal to change the battery, which is suppressed in the dark to prevent a disturbance of the night's sleep.

The documents EP1515290 and US4300133 also have relevant prior art.

By contrast, the fire detector according to the invention has an open scattered-light detection unit with a detection space outside the fire detector. The sensitive to ambient light sensor is also an optical receiver of the scattered light detection unit. As a result, both a scattered light from the smoke particles to be detected and the ambient brightness can advantageously be detected with a single component.

The ambient light sensitive sensor is e.g. a photosensitive resistor, a phototransistor or a photodiode, in particular a PIN photodiode. The brightness value limit may be e.g. be determined by means of a potentiometer. It typically corresponds to a brightness value threshold corresponding to darkened rooms or illuminance value of less than 10 lx, preferably less than 5 lx. The detection signal output from the sensor is preferably filtered by a low-pass filter, such as a low pass filter. with a time constant of several seconds, e.g. of 5, 10 or 30 seconds to filter out any interference signals present in the detection signal.

According to one embodiment, the acoustic warning can be output by the acoustic detector provided for outputting the acoustic alarm.

Alternatively or additionally, an optical warning is provided by the optical device provided for outputting the optical alarm Detector can be output. The output is preferably carried out by means of one or more LEDs, such as stroboscopic.

According to another embodiment, the fire detector has a sensor for detecting the presence or absence of persons in the vicinity of the fire detector. The suppression means are additionally arranged to suppress the output, in particular, of the audible warning in the case of detected absence of persons. As a result, the warning or the note to replace the soon-to-be-empty battery occurs only when a person is in the vicinity of the fire alarm. This reduces the power consumption advantageous.

The sensor for detecting the presence or absence of persons is preferably a motion detector known per se. Such a motion detector can work according to the Doppler radar principle. It may alternatively comprise an ultrasonic motion detector or body heat, i. be an infrared sensitive PIR motion detector. Furthermore, such a sensor may be arranged such that a binary detection of persons, that is, that a person is present or not, e.g. in a range of up to 5 m around the fire detector. For this purpose, the sensor can also have a potentiometer for setting the sensitivity for the detection of persons or moving objects. Preferably, such a sensor is only electrically supplied with electricity when the detected battery voltage falls below the first voltage limit, as e.g. via a controllable by the evaluation unit switching element.

Alternatively or additionally, the fire detector has means for detecting fluctuations in a detection signal output by the optical receiver of the scattered light detection unit. The suppressing means are additionally arranged to suppress the warning if no, in particular no appreciable, fluctuations are detectable in the detection signal. The special advantage with this Embodiment is that no separate sensor for detecting the presence or absence of persons, in particular no motion detector, is required.

By "fluctuations" is meant temporal changes in the detection signal in the frequency range of a few hertz, in particular in the range of 1 to 10 Hz. Such fluctuations are caused by partial temporary brightness variations, e.g. Persons living in the vicinity of the fire detector, such. in a range of up to 5 m around the fire detector, pass by. Detected fluctuations are therefore an indication that something is "happening" in the surrounding area of the fire detector. The likelihood of these fluctuations being experienced by a person, e.g. being attempted by a resident can be considered comparatively high. These fluctuations can be detected by means of a filter, e.g. by means of a low-pass filter. The filter frequency is preferably in the range of 1 to 10 Hz. The filtered value can then be compared with a predefinable fluctuation limit value. If the filtered value then exceeds this fluctuation limit value, the warning is output at least for a predeterminable time, e.g. 3 seconds, and / or until again no fluctuations in the detection signal can be detected.

The warning means may also be arranged to (cancel) the suppression of the output of the warning if the battery voltage detected by the voltage measuring unit falls below a second voltage limit which is lower than the first voltage limit value. This can e.g. be determined so that a power supply of the fire alarm is still possible for at least 7 days.

According to a further embodiment, the warning can be output in the form of periodic, short-term warning pulses. Finally, at least part of the voltage measuring unit, the warning means and / or the blocking means are realized by the electronic evaluation unit. The latter can be an analog and / or digital electronic circuit having, for example, A / D converters, amplifiers, comparators, operational amplifiers, logic gates, etc. Preferably, the evaluation unit is a processor-based processing unit, in particular a microcontroller, which is usually present "anyway" to the entire control of the fire alarm. The suppression means and warning means of the fire detector are preferably simulated by program steps executed by the microcontroller, possibly also using electronically stored values, eg for the voltage limit values and / or for the brightness limit value.

FIG 1

ein Beispiel eines erfindungsgemässen Brandmelders,

FIG 2

eine vorteilhafte Ausführungsform.

The invention and advantageous embodiments of the present invention will be explained using the example of the following figures. Showing:

FIG. 1

an example of a fire detector according to the invention,

FIG. 2

an advantageous embodiment.

FIG. 1 shows an exemplary fire detector 1 according to the invention. In the left part of the FIG. 1 is an open scattered light detection unit 2 with a lying outside the fire detector 1 detection space DR shown. Reference numeral 7 designates a light-emitting diode as a light source for irradiating the smoke particles to be detected in the detection space DR, and a reference numeral 8 designates a photodiode as an optical receiver for receiving the light scattered by the smoke particles. Typically, the LED 7 is periodically, such as every 30 seconds, and each only briefly, such as for 100 ms, driven. With DS the output from the optical receiver 8 detection signal is designated, which for further signal processing in the middle part of the FIG. 1 shown electronic evaluation unit 3 is supplied. The term "μC" symbolizes a microcontroller as a preferred embodiment of the evaluation unit 3. The latter is connected via corresponding connecting lines for electrical supply and for receiving the detection signal DS to the detection unit 2. The detection signal DS may be, for example, an analog voltage signal which correlates with the intensity of the light scattered on the smoke particles in the detection space DR.

Reference numeral 4 denotes an energy store, typically a battery for the electrical supply of the fire detector 1 and its electronic or electrical components. The battery 4 may be, for example, E-block with a nominal voltage of 9 V. The battery voltage U _Bat applied there is detected metrologically by the evaluation unit 3, such as by an A / D converter as a voltage measuring unit, and compared with a digital value corresponding to a first voltage limit U _Low , such as a voltage value of 7.5 volts when using a 9V battery. Alternatively, the applied battery voltage U _Bat can be supplied to a comparator or operational amplifier, which then compares this with a reference voltage for a first voltage limit U _Low .

Furthermore, the electronic evaluation unit 3 has not further shown warning means for outputting an acoustic warning AW in the event that the battery voltage U _Bat falls below the first voltage limit U _Low . For output, in the present example, an electroacoustic transducer is provided as an acoustic detector 5, which is controlled via an electrical AC voltage signal as a first drive signal AS1. Typically, the acoustic warning AW and an acoustic alarm message AA in the detected fire are output via the same acoustic detector 5. A second output control signal AS2 additionally activates an optical detector 6, such as an LED, for optical alarm signaling OA and optical warning OW.

According to the invention, the fire detector 1 has a sensor sensitive to ambient light, which is at the same time the optical receiver 8, that is to say the photodiode 8 of the scattered light detection unit 2. At the same time includes the fire detector 1 means not shown further for suppressing the output of acoustic warning AW if the ambient light falls below a predefinable brightness limit HG. In the simplest case, the microcontroller 3 evaluates the detection signal DS already detected by means of the A / D converter to determine whether the brightness limit value HG has been undershot or not. The latter can be stored as a digital value in the microcontroller 3. In the example of the present FIG. 1 the detection signal DS is averaged by means of a realized in software low-pass filter 10 with a filter frequency of, for example, 0.1 s, before this is then compared with the brightness limit HG. In the case of detected darkness then omits the output of the acoustic warning AW for changing the battery 4. Alternatively, the low-pass filter can be realized in analog circuit technology.

FIG. 2 shows an advantageous embodiment of the inventive fire detector 1. Compared to the previous FIG. 1 The fire detector 1 also has means for detecting fluctuations in a detection signal DS output by the optical receiver 8 of the scattered light detection unit 2. The means may comprise a low-pass filter 11 with an exemplary filter frequency of 10 Hz. In contrast, higher-frequency signal components from 10 Hz are suppressed as potential interference signals in the detection signal DS. Furthermore, the means for suppressing the output of the acoustic warning AW are adapted to suppress the warning if no or no appreciable fluctuations are detectable. This is preferably done by comparing this filtered detection signal DS with a predefinable fluctuation limit value FG. By suitably setting the two limit values HG, FG, for example by means of a potentiometer, it is possible that at night the output of the warning for changing the battery is suppressed despite possibly existing fluctuations. Both limit values HG, FG can also be stored as corresponding digital values in the evaluation unit 3. U _{Low2 denotes} a second voltage _limit . If the battery voltage U _Bat also _{falls below} this voltage _value U _Low2 , the suppression of the output of the warning AW, OW is omitted.

LIST OF REFERENCE NUMBERS

1

Fire detectors, smoke detectors

2

detection unit

3

electronic evaluation unit, microcontroller

4

Energy storage, battery

5

acoustic detector, piezo speaker, beeper

6

optical detector, LED

7

LED, LED

8th

optical sensor, light-sensitive resistor, photodiode, phototransistor, PIN photodiode

10

Averaging filter, low pass filter

11

Fluctuation detection means, low-pass filter

AA

acoustic alarm

AS1

first drive signal

AS2

second drive signal

AW

acoustic warning

DR

detection space

DS

detection signal

FG

fluctuation limit

HG

brightness limit

OA

optical alarm

OW

visual warning

U _Bat

battery voltage

U _low

first voltage limit

U _Low2

second voltage limit

Claims (9)

1. Fire detector, which has

   - a detection unit (2) working on the optical scattered-light principle,

   - an electronic evaluation unit (3),

   - a detector (5, 6) for outputting an acoustic and/or optical alarm (AA, OA) when a fire is detected,

   - an energy store (4), in particular a battery, for the autarkic supply of electrical power to the fire detector,

   - a voltage measuring unit for measuring a battery voltage (U_Bat) present at the energy store (4),

   - warning means for outputting an acoustic warning (AW) if the battery voltage (U_Bat) falls below a first voltage threshold (U_Low),

   - a sensor (8) sensitive to ambient light as well as

   - means for suppressing the output of the acoustic warning (AW) if the ambient light falls below a predefinable brightness threshold (HG),

   characterised in that the detection unit (2) is an open scattered-light detection unit with a detection space (DR) situated outside the fire detector and that the sensor (8) sensitive to ambient light is at the same time an optical receiver of the scattered-light detection unit (2).
2. Fire detector according to claim 1, characterised in that the acoustic warning (AW) can be output by the acoustic detector (5) provided to output the acoustic alarm (AA).
3. Fire detector according to claim 1 or 2, characterised in that additionally an optical warning (OW) can be output by the optical detector (6) provided to output the optical alarm (OA).
4. Fire detector according to one of claims 1 to 3, characterised in that the fire detector has a sensor for determining the presence or absence of people in the vicinity of the fire detector and that the suppression means are additionally set up to suppress the output of the warning (AW, OW) if an absence of people is detected.
5. Fire detector according to one of claims 1 to 3, characterised in that the fire detector has means for detecting fluctuations in a detection signal (DS) output by the optical receiver (8) of the scattered-light detection unit (2) and that the means for suppressing are additionally set up to suppress the warning (AW, OW) if no fluctuations can be detected.
6. Fire detector according to one of the preceding claims, characterised in that the warning means are set up to cancel the suppression of the output of the warning (AW, OW) if the battery voltage (U_Bat) detected by means of the voltage measuring unit falls below a second voltage threshold (U_Low2) which is lower than the first voltage threshold (U_Low).
7. Fire detector according to one of the preceding claims, characterised in that the warning (AW, OW) can be output in the form of periodic short warning pulses.
8. Fire detector according to one of the preceding claims, characterised in that at least part of the voltage measuring unit, the warning means and/or the suppression means are implemented by the evaluation unit (3).
9. Fire detector according to claim 8, characterised in that the electronic evaluation unit (3) is a processor-aided processing unit, in particular a microcontroller.

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