DE102016208358B3 - Fire detector, in particular thermal detector, with a photodiode for detecting ambient light, in order to accelerate depending on the issue of a possible fire alarm - Google Patents

Abstract

The invention relates to a fire detector (1), in particular a thermal detector, with a fire sensor (5), with a control unit (4) and with a photodiode (6) for detecting ambient light in a spectrally limited range from 400 nm to 1150 nm. The control unit is set up to analyze a sensor signal (BS) received from the fire sensor for at least one characteristic fire parameter, to evaluate it and to output a fire alarm (AL) in the event of a detected fire. In addition, the control unit is set up to analyze a photo signal (PD) received from the photodiode for the presence of flicker frequencies characteristic of open fire and, depending on this, to accelerate the signal path of the fire analysis. This allows faster alerting in case of fire.

Description

The invention relates to a fire detector, in particular a thermal detector, thermal fire detectors or heat detectors. Such a detector has at least one temperature sensor as the exclusive fire sensor. Such a temperature sensor can, for. B. be a temperature-dependent resistor (thermistor), such as. As a so-called NTC or PTC, or a non-contact temperature sensor with a thermopile or a microbolometer. Furthermore, the thermal detector comprises a control unit, preferably a microcontroller. The control unit is configured to analyze a temperature signal received from the at least one temperature sensor for at least one characteristic fire parameter, to evaluate it and to output a fire alarm in the event of a detected fire.

A characteristic fire characteristic is z. B. exceeding a minimum temperature in the (immediate) environment of the thermal detector, such. From at least 60 ° C, 65 °, 70 ° C or 75 ° C. Alternatively or additionally, an inadmissibly high temperature increase may be a characteristic fire parameter, such. At least 5 ° C per minute or at least 10 ° C per minute.

From the prior art flame detectors are still known, such as. B. from the DE 10 2011 083 455 A1 or from the EP 2 251 846 A1 , Such flame detectors are specially designed to detect open fire as well as issue an alarm in less than a second. They usually comprise two or more pyrosensors as radiation sensors. Such sensors are tuned for the detection of characteristic flicker frequencies of open fire, that is of flames and blazing embers, in the infrared range and optionally in the visible and ultraviolet range. The flicker frequencies are typically in a range of 2 Hz to 20 Hz.

The infrared pyrosensors are typically sensitive to infrared radiation in the wavelength range of 4.0 to 4.8 μm. This specific radiation is produced by the combustion of carbon and hydrocarbons. Another pyrosensor is sensitive to characteristic emissions of metal fires in the UV range. For outdoor use, flame detectors can also have a radiation sensor that is sensitive to infrared radiation in the wavelength range 5.1 to 6.0 μm. This radiation is primarily to interference, such. For example, infrared radiation from hot bodies or sunlight. On the basis of all sensor signals then a particularly reliable evaluation is possible, d. H. whether it is open fire or not.

From the EP 2 688 274 A1 For example, a smart phone with a fire detector application is known which has suitable program steps for analyzing video image data captured by an internal camera with regard to at least one information characteristic of fire and, if present, issuing an alarm via an output unit. This smartphone is also adapted to analyze the received video signal for the presence of flicker frequencies characteristic of open fire, and to switch from a first low frame rate to a second high frame rate for a significant deviation in two consecutive video frames.

On this basis, it is an object of the present invention to provide a thermal detector that alerts faster and more reliable with little technical overhead.

The object is achieved with the objects of the main claim. Advantageous embodiments of the present invention are indicated in the dependent claims.

According to the invention, the thermal detector comprises a photodiode for detecting ambient light in a spectrally limited range from 400 nm to 1150 nm, i. H. Ambient light in the optically visible region as well as in the adjacent near UV and infrared range. The control unit is also configured to analyze a photo signal received by the photodiode for the presence of flicker frequencies characteristic of open fire. It is further adapted to speed up the issue of a possible fire alarm by increasing a sampling rate for the detection of the temperature signal, by decreasing a filter time of a filter filter evaluation filter for fire analysis, and / or by lowering an alarm threshold.

The essence of the invention thus lies in the use of a low-cost photodiode as a "mini-flame detector", the qualitative significance is sufficient to accelerate the signal path of fire analysis at detected Flackerfrequenzen as an indication of the presence of a fire, and this with the aim of faster to issue a fire alarm.

By increasing the sampling rate for the detection of the temperature signal, a temperature increase can be detected more quickly and a fire alarm can be output earlier.

The evaluation filter, the input side, the detected, preferably digitized temperature signal is supplied. It is preferably a digital filter, which is realized as a software program and is executed by the microcontroller as a control unit. The digital filter is preferably a low-pass filter or a so-called drag filter. In this case, a certain averaging of the detected sensor signal values takes place, so that a fire alarm is not output directly when a fire is detected. Rather, it waits to see if this event is not sporadic, but several times in succession, in order to avoid the output of a false alarm. By reducing the filter time or the filter time constant, the weighting filter responds less slowly. Since the probability of an occurring fire event in detecting the Flackerfrequenzen is assumed to be high or higher than usual, a fire alarm can be spent faster in favor of safety.

By lowering the alarm threshold, the thermal detector is switched to more sensitive and less robust so that the alarm threshold is reached faster. The fire alarm is therefore faster.

The signal path of the fire analysis begins with the metrological detection of the temperature signal output by the temperature sensor, then with the subsequent analysis and evaluation of the temperature signal and with the comparison with a predetermined alarm threshold, and ends with the output of a possible fire alarm.

By accelerating the signal path of the fire analysis is advantageously a faster output of a fire alarm possible, since in this case can be assumed with a higher probability of a fire. This is the case when the characteristic Flackerfrequenzen for a minimum time, such. B. of 2, 5 or 10 seconds. However, this does not mean that an alarm will be issued after this minimum time. For this purpose, the quality of the photodiode signal is to be regarded as too moderate compared to the sensor signals of the specifically spectrally limited pyrosensors in conjunction with a complex, powerful signal processing. Rather, a faster processing of the temperature signal, which is omitted because of the otherwise associated loss of false alarm security. In other words, the fire sensor responds more sensitively and faster upon detection of characteristic flicker frequencies, but this is advantageously taken into account because of the high probability of occurrence of a subsequent temperature rise due to a fire. If there then remains an "expected" increase in temperature, then no fire alarm takes place.

Preferably, the higher the level of the detected flicker frequencies, the faster the signal path is. The acceleration can z. B. depending on the Flackerfrequenzpegel proportional or progressive. It can alternatively or additionally take place only after exceeding a minimum detection level.

The photodiode is preferably a silicon photodiode and in particular a silicon PIN photodiode. It can be preceded by a daylight blocking filter which allows only light in a range from 700 nm to 1150 nm, in particular from 730 nm to 1100 nm, to pass. As a result, optical disturbances such as the flickering of fluorescent tubes or incident sunlight can be advantageously reduced. Such a photodiode, such as. B. OSRAM (type BPW 34 FAS), is compared to a pyrosensor particularly inexpensive available. The additional expense for the integration of such a photodiode in a thermal detector is thus very low in terms of circuitry and cost.

According to a particular embodiment, the temperature sensor is a non-contact temperature sensor, which comprises a heat radiation sensor sensitive to thermal radiation in the infrared range. The latter is for example a thermopile or a microbolometer. In particular, the heat radiation sensor is not imaging. In other words, it has a single pixel. Furthermore, the thermal detector comprises a detector housing with a detector hood, wherein the heat radiation sensor is then arranged in the detector housing and is optically aligned on the inside of the detector hood for the mathematical derivation of the ambient temperature. The detector hood is so thermally conductive in the region of the inside to an opposite region of the outside of the detector hood formed that adjusts itself to the inside housing temperature of the ambient temperature at the opposite region of the detector hood, in particular within a few seconds, such. For example 5 seconds. The temperature sensor installed in the detector housing makes the thermal detector less susceptible to contamination. In addition, no circuitry and assembly consuming installation of the thermistor in the housing is required.

According to a further embodiment and independently of the invention made, the control unit is set up to monitor the photosignal output by the photodiode for a minimum brightness value and to set down an alarm threshold for the output of a possible fire alarm in order to accelerate the thermal signal path , Because of the more sensitive attitude of the thermal detector is then in the dark, such. B. at night, advantageously a faster alerting possible. This is possible because at lower brightness, such. B. with Lux values of less than 1 lux, with fewer disturbances from the detector environment is expected as the day. Such disorders are z. B. Temperature fluctuations due to opening and closing of doors and windows with concomitant drafts and the switching on and off of heat sources such as heating and stove.

According to one embodiment, the thermal detector is wired or wirelessly connected to a parent central. The control unit is set up to output the undershooting and undershooting of the minimum brightness level as a day / night identifier to the control center. This can be superordinate controlled by the center z. As the down of blinds or reducing the heating power in the building be prompted.

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

1 an exemplary thermal detector with a temperature sensor and with an ambient light photodiode for detecting open fire according to the invention in a sectional view,

2 the example according to 1 in a plan view along in 1 registered line of sight,

3 a first embodiment of the fire detector according to the invention with a non-contact temperature sensor having a thermopile sensitive to thermal radiation in the infrared range as a heat radiation sensor,

4 a second embodiment of the fire detector according to the invention with a common light guide for detecting the ambient light by means of the photodiode and as an indicator in the sense of a ready-to-operate display,

5 a spectral characteristic of a silicon photodiode with and without an upstream daylight filter,

6 an example of a photo signal received by a photodiode with characteristic flicker frequencies for open fire,

7 that to the photosignal according to 6 associated frequency spectrum,

8th a functional block diagram of a detector control unit with an adjustable time constant weighting filter to accelerate the fire analysis thermal signal path according to the invention;

9 a second functional block diagram of a detector control unit with a temperature sensor with thermopile according to the invention, and

10 a third functional block diagram of a detector control unit in addition to alternately driving an indicator LED and for detecting the ambient light by means of the indicator LED LED, switched in an operating mode as a photodiode according to the invention.

1 shows an exemplary thermal detector 1 with a temperature sensor 5 and with a photodiode 6 for detecting ambient light for the detection of open fire according to the invention in a sectional view.

In the present example, the detector indicates 1 a housing 2 on, which is made up of a basic body 21 and a detector hood 22 composed. With the main body 21 then can the detector 1 preferably releasably attached to a mounted on a ceiling detector base. Both housing parts 21 . 22 are usually made of a light-tight plastic housing. In the detector hood 22 a central opening is provided in which a thermistor 5 as a temperature sensor protected against possible mechanical effects is attached. Due to the central arrangement is a direction independent detection of the ambient temperature UT in the immediate vicinity of the detector 1 possible (see also 2 ). In the interior IR of the detector 1 is also a circuit carrier 3 recorded on the next to a microcontroller 4 as a control unit, the photodiode 6 is arranged. Opposite to the photodiode 6 is a recess AN in the detector hood 22 present, through which the photodiode 6 in the environment around the detector 1 "Can see through". With FOV, the associated optical detection range is the photodiode 6 designated. Open fire in this detection area FOV, symbolized by a flame symbol, can then pass through the photodiode 6 be captured optically. In the present example, the recess is AN in the detector hood 22 provided with a transparent cover AB to protect against contamination. The cover AB is preferably made of a translucent plastic. It may also already be provided with or have a daylight filter. In the case of a detected fire, a fire alarm AL and a day / night identifier T / N, symbolized by an arrow, can be output.

2 shows the example according to 1 in a plan view along in 1 registered viewing direction. Z is the geometric central axis of the detector 1 designated.

According to the invention, the control unit 4 now set up, one from the photodiode 6 to analyze the received photosignal for the presence of flicker frequencies characteristic of open fire and, depending thereon, to accelerate the signal path of the fire analysis. It is also set up to monitor the photosignal to an undershooting and undershooting of a minimum brightness level and output as a day / night identifier T / N, symbolized by a sun and moon symbol, such. B. to a parent headquarters.

3 shows a first embodiment of the fire detector according to the invention 1 with a non-contact temperature sensor 5 comprising a thermal radiation sensitive to heat radiation W in the infrared range 50 as a heat radiation sensor.

Unlike the previous embodiment, the thermopile 50 in the detector housing 2 on the circuit carrier 3 arranged and for detecting the ambient temperature UT visually on the inside IS of the detector hood 22 aligned. The optically detected surface on the inside IS of the detector hood 22 is in the 3 designated as the measuring surface M. In particular, the thermopile 50 again centrally in the detector housing 2 arranged to provide a possible direction independent detection of the ambient temperature UT in the immediate vicinity of the detector 1 to enable. Here is the detector hood 22 in the central area 23 the inside of the IS such Wärmeleittechnisch to an opposite region of the outside of the detector hood 22 designed such that the adjusting on the inside of IS housing temperature T of the ambient temperature UT at the opposite region of the detector hood 22 follows. In the simplest case, the wall thickness in the central area 23 be reduced, such. B. to half a millimeter. Alternatively, this central area 23 thermally opposite the remaining surrounding detector hood 22 be isolated. In most cases, there will be no change in the wall thickness of the detector hood 22 to be required.

The current ambient temperature UT or the following housing temperature T is from the heat radiation sensor 50 recorded thermal radiation value according to the pyrometric measurement principle derived mathematically. In this case, the emissivity for the heat radiation W of the measuring surface M is included in the calculation. This value can be determined metrologically and is typically in the range of 0.75 to 0.9. In this case, the blacker the measuring surface, the greater the emissivity. An emissivity of 1.0 corresponds to the theoretically maximum achievable value for a black emitter.

The arithmetic determination can be made by a Thermopile 50 integrated microcontroller are executed, the output side outputs the currently determined temperature value and thus represents a non-contact temperature sensor. Alternatively, the thermopile 50 only output a current heat radiation value, which then passes through the microcontroller 4 the fire detector 1 is detected and further processed for arithmetic determination of the current temperature value. This is preferably in the microcontroller 4 the associated emissivity stored.

4 shows a second embodiment of the fire detector according to the invention 1 with a common light guide 7 for ambient light detection by means of the photodiode 6 and as an indicator in the sense of an operational readiness indication.

For this purpose, an indicator light emitting diode LED is adjacent to the photodiode 6 on the circuit carrier 6 arranged. The light guide 7 is such that it has a first end of both the indicator LED LED and the photodiode 6 opposite. The second end of the light guide 7 preferably protrudes through a central recess in the detector hood 22 , As a result, ambient light is through the light guide 7 through the photodiode 6 detectable. Irrespective of this, light from the indicator LED is passed through the light guide in the opposite direction 7 through at the second end of the light guide 7 decoupled. The indicator LED LED is typically cyclically for emitting an optically visible pulse, such. B. every 30 seconds, ready for operation of the fire alarm 1 driven. In particular, the second end of the light guide 7 formed as an optical lens L. As a result, ambient light can be detected from a larger optical detection range FOV. In addition, the operational indicator of the fire alarm is 1 recognizable in a larger solid angle range. The light guide 7 is preferably in one piece and made of a transparent plastic.

The photodiode shown 6 is preferably a silicon photodiode and in particular a silicon PIN photodiode.

Alternatively, it is possible to dispense with such a photodiode produced especially for light detection. In this case, the light guide lies 7 with its first end only the indicator LED opposite. The light extraction of the LED light is again at the second end of the light guide 7 into the environment of the fire alarm 1 ,

According to the invention, the indicator LED is now provided for ambient light detection, since in principle any light emitting diode is also suitable for the detection of ambient light, albeit with significantly lower efficiency. In this case, the indicator light emitting diode LED is alternately switched to a light generation operation mode and a photodiode operation mode (refer to the explanations below in FIG 10 ).

In contrast to 1 and 3 points the fire alarm 1 by way of example two opposing temperature sensors 5 for detecting the ambient temperature UT on.

5 shows a spectral characteristic of a silicon PIN photodiode with and without upstream daylight filter. The maximum, normalized to 100% spectral sensitivity S _Rel is at a light wavelength λ of about 900 nm, ie in the near infrared range. The solid curve shows the spectral sensitivity S _{Rel of} a silicon PIN photodiode with upstream daylight filter. In this case, light having a wavelength λ of less than 730 nm is suppressed. By contrast, the dashed branch of the characteristic curve shows the spectral sensitivity S _{Rel of} the silicon PIN photodiode without a daylight filter.

6 shows an example of one of a photodiode 6 received photosignal PD with characteristic flicker frequencies for open fire measured in millivolts. It will be at the photodiode 6 generated photovoltage measured as a photosignal PD. The measurement took place over a period of 4 seconds and shows cyclic voltage spikes in the range of 20 to 30 mV, which correlate with the flickering of the flames of open fire.

7 shows this to the photosignal PD according to 6 associated frequency spectrum. A denotes the spectral amplitude, measured in dB and plotted against the frequency f in Hertz. Considering only the frequency range of at least 2 Hz, which is decisive for the flickering, one recognizes the reciprocal decrease of the amplitude for increasing frequencies above 2 Hz. The spectrum shown is typical and significant for open flickering fire.

8th shows a functional block diagram of a detector control unit 4 with a weighting filter 41 with adjustable filter time to accelerate the thermal signal path of the fire analysis according to the invention.

The shown function blocks 40 - 44 are preferably implemented as software, ie as program routines that are executed by a processor unit of a control unit designed as a microcontroller. The respective program routines are in a memory of the microcontroller 4 loaded or loadable. The memory is preferably a non-volatile electronic memory such. B. a flash memory. The microcontroller 4 In addition, it may have specific functional blocks that are already used as hardware functional units in the microcontroller 4 are integrated, such. B. analog / digital converter 51 . 52 , Signal processors, digital input / output units and bus interfaces.

In the present example, the microcontroller includes 4 two analog / digital converters as an example 51 . 52 to obtain a current temperature signal BS from the fire sensor 5 ie from an NTC, and a photosignal PD from a photodiode 6 to digitize. The digitized temperature signal then becomes a (digital) weighting filter 41 fed along the thermal path. The weighting filter 41 is preferably a digital low-pass filter, which performs a certain signal smoothing or averaging. However, this filtering causes a delayed filter response at the output of the weighting filter 41 analogous to a filter time constant for a low pass. The unspecified output signal of the weighting filter 41 subsequently becomes a comparator 44 fed, which compares this with an alarm threshold LEV, such. B. with a temperature value of 65 °. Exceeds the filter output this comparison value LEV, the output of a fire alarm AL, such as. B. to a parent fire panel.

According to the invention, the microcontroller 4 also set up by the photodiode 6 to analyze received photosignal PD for the presence of flicker frequencies characteristic of open fire and, depending thereon, to accelerate the fire analysis signal path. The spectral signal analysis can, for. B. by means of a digital Fourier transform or by means of a wavelet analysis. Technically, this is on the one hand by the function block flicker frequency detector 42 accomplished. In the case of detected flickering fire, this gives a flicker indicator F to a logic block 40 then the sample rate f the _{clock of} the A / D converter 51 for the digitization of the temperature signal BS increases and / or the filter time constant T _{filter is} lowered. The Flackerindikator F can z. B. be a binary value, such as. B. 0 or 1, or a digital value, such as. B. in the range of 0 to 9. The value 0 can be for the binary case z. B. the absence of Flackerfrequenzen and the value 1 corresponding to the presence represent. In the digital case, the value 0 z. B. represent the absence of Flackerfrequenzen. The values 1 to 9 can be z. For example, indicate the presence of flicker frequencies where high numbers indicate high flicker frequency levels and low numbers indicate flicker frequency levels. By increasing the sampling rate f _clock is the digitized temperature signal BS faster at the weighting filter 41 for further processing. On the other hand, the weighting filter speaks 41 by reducing the filter time constant T _filter faster, so that an actual increase in the temperature signal BS also leads to a faster fire alarm AL. The increase in the sampling rate f _clock and / or the reduction of the filter time constant T _filter can, for. B. for the digital case of Flackerindikators F depending on its value range.

Alternatively or additionally, the logic block 40 be programmed that the alarm threshold LEV is lowered, such. B. from 65 ° to 60 °. As a result, an acceleration of the thermal path and thus a quicker fire alarm AL takes place for the case of fire occurring with an increased probability due to the detected flicker frequency.

Alternatively or additionally, the logic block 40 be programmed so that the alarm threshold LEV is lowered in particular when a light / dark indicator H / D, the function block 43 of the microcontroller 4 is provided, falls below a minimum brightness value, such. B. a value of 1 lux. This exemplary value corresponds to a dark to very dim environment. In such an environment is to be expected with less thermal disturbances from the detector environment as during the day, such. B. with the temperature fluctuations described above. By assuming lesser disturbances from the detector environment, the alarm threshold LEV can be lowered. Due to the more sensitive setting, the thermal path is accelerated by the lowered alarm threshold LEV by the output signal of the weighting filter 41 is exceeded faster. The day / night detection is performed by a low-pass filtering of the photosignal PD with a time constant of less than 1 Hz, in particular less than 0.1 Hz.

9 shows a second functional block diagram of a detector control unit 4 with a temperature sensor 5 with thermopile 50 according to the invention.

In contrast to the previous embodiment, the current ambient temperature UT or the following housing temperature T with a temperature calculation block 54 of the microcontroller 4 determined. The latter is a digitized heat signal WS by means of an A / D converter 51 from a thermopile 50 supplied as an example of a heat radiation sensor. In the computational determination, the emissivity for the heat radiation W in the infrared region of the measurement surface M is included in the calculation.

10 shows a third functional block diagram of a detector control unit 4 in addition to alternately driving an indicator light emitting diode LED and for detecting the ambient light by means of the indicator light emitting diode LED, switched in an operating mode as a photodiode 5 according to the invention.

Compared to the previous one 8th controls the logic block 40 alternately a switching unit via a switching signal US 55 in such a way that in a first phase the indicator LED LED with a current signal IND from a pulse generating unit 45 can be controlled for short-term lighting, such. Every 30 seconds. In a second phase, the logic block controls 40 the switching unit 55 so that the low photo signal PD from the indicator LED LED an amplifier 60 is supplied. This in turn is followed by an A / D converter 52 for digitizing the photosignal PD. The amplifier 60 is preferably a transimpedance amplifier.

LIST OF REFERENCE NUMBERS

1

Fire detector, thermal detector, heat detector, point detector

2

Detector housing, plastic housing

3

Circuit carrier, printed circuit board

4

Control unit, microcontroller

5

Fire sensor, temperature sensor, thermistor, NTC, temperature sensor with thermopile, temperature sensor with microbolometer

6

Photodiode, IR photodiode, silicon PIN photodiode

7

optical fiber

21

body

22

Detector cover, housing cover

23

central housing part

40

Function block, logic block

41

Function block, weighting filter

42

Function block, flicker frequency detector

43

Function block, day / night recognition block

44

Function block, comparator

45

Function block, pulse generation unit

50

thermopile

51, 52

A / D converter, analog / digital converter

54

Temperature calculation block

55

Switching unit, multiplexer

60

Amplifier, transimpedance amplifier

A

Amplitude, signal amplitude

FROM

Cover, transparent cover, window

AL

Fire alarm, alarm message, alarm information

AT

Recess, recess, opening

BS

Sensor signal, fire sensor signal, temperature signal

e

Receiver, receiving unit, photosensor

F

flicker indicator

f

frequency

FOV

Coverage area, field-of-view

f _bar

Sampling frequency, clock frequency

FZ

Filter time setting signal, setting signal

H / D

Chiaroscuro Indicator

L

Lens, optical lens

LEV

alarm threshold

LED

Indicator LED

N

Insect repellent, net

OF

Smoke inlet opening

PD

Photosignal, photodiode signal

S

Transmitter, transmitter unit, LED

SA

Scattered light arrangement

_Srel

relative spectral sensitivity

SZ

Stray light center, measuring volume

T

temperature value

TS

temperature signal

t

Time, timeline

T / N

Day / night identification

T _filter

Filter time, filter time constant

FZ

Adjustment signal, Filterzeiteinstellsignal

UT

ambient temperature

Z

Main axis, symmetry axis

λ

Light wavelength

Claims (7)

Thermal detector containing a temperature sensor ( 5 ) as an exclusive fire sensor and a control unit ( 4 ), wherein the control unit ( 4 ) is set up, one from the temperature sensor ( 5 ) to analyze and evaluate at least one characteristic fire parameter and output a fire alarm (AL) in the case of a detected fire, wherein - the thermal detector is a photodiode ( 6 ) for detecting ambient light in a spectrally limited range from 400 nm to 1150 nm, and - the control unit ( 4 ) is further adapted to receive a signal from the photodiode ( 6 ) to analyze the presence of flicker frequencies characteristic of open fire and, depending thereon, the output of a possible fire alarm (AL) by increasing a sampling rate for the detection of the temperature signal (BS), by decreasing a filter time (T _Filter ) of a weighting _filter ( 41 ) of the control unit ( 4 ) for fire analysis and / or by lowering an alarm threshold (LEV). Thermal detector according to claim 1, wherein the photodiode ( 6 ) is a silicon photodiode, in particular a silicon PIN photodiode. Thermal detector according to claim 1 or 2, wherein the photodiode ( 6 ) is preceded by a daylight blocking filter, which only light in a range of 700 nm to 1150 nm, in particular from 730 nm to 1100 nm, happen. Thermal detector according to one of the preceding claims, wherein the temperature sensor ( 5 ) is a thermistor arranged in or on the thermal detector, in particular an NTC. Thermal detector according to one of the preceding claims, wherein the temperature sensor ( 5 ) is a non-contact temperature sensor which comprises a heat radiation sensor sensitive to heat radiation (W) in the infrared range, in particular a thermopile or a microbolometer, wherein the thermal detector comprises a detector housing ( 2 ) with a detector hood ( 22 ), wherein the heat radiation sensor ( 6 ) in the detector housing ( 2 ) and for the mathematical derivation of the ambient temperature (UT) visually on the inside (IS) of the detector hood ( 22 ), and wherein the detector hood ( 22 ) in the region of the inner side (IS) in such a way thermally conductive to an opposite region of the outside of the detector hood ( 22 ) is formed, that the on the inside (IS) adjusting housing temperature (T) of the ambient temperature (UT) at the opposite area of the detector hood ( 22 ) follows. Thermal detector according to one of the preceding claims, wherein the control unit ( 4 ) is also adapted to that of the photodiode ( 6 ) is monitored for an undershooting of a minimum brightness value and is set up to lower an alarm threshold (LEV) for the output of a possible fire alarm (AL). Thermal detector according to claim 6, wherein the thermal detector is wired or wirelessly connected to a central control unit and wherein the control unit ( 4 ) is set up to output the undershooting and undershooting of the minimum brightness level as day / night identifier (T / N) to the central office.

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