RU2461886C1 - Adaptation of sampling instants of selecting circuits and storage optical smoke detector - Google Patents

Abstract

FIELD: fire protection.

SUBSTANCE: device is described (100) for the detection of smoke, which contains (a) source (120) for the radiation for emitting light illumination (120a), which has a temporal sequence of radiation pulses, (b) detector (130) of radiation for receiving the measured radiation (130a), which, after at least partial light scattering (120a) of light falls on the detector (130) of radiation, (c) amplifying circuit (140) to enhance the output signal of the detector (130) of radiation, (d) an analog-digital converter (156) with the scheme (152) of sampling and keeping to convert the analog output signal of the amplifying circuit (140) to a digital value (156a), and (e) a control device (150) which is connected to the source (120) of radiation and the scheme (152) of sampling and keeping. The control device (150) is adapted to control the source (120) of radiation and the scheme (152) of sampling and keeping so that the temporary position of the sampling instant of the scheme (152) of sampling and keeping with respect to the radiation impulse depends on the time duration of the radiation impulse. It also describes a method for the calibration of the smoke detector (100) described.

EFFECT: unit is economical in production, and consumes little current.

9 cl, 6 dwg

Description

The present invention relates to the technical field of smoke alarms. The present invention relates in particular to signal processing in a smoke detection device based on measurements of scattered electromagnetic radiation. The present invention also relates to a method for calibrating a smoke detection device based on measurements of scattered electromagnetic radiation.

Optical or photoelectric smoke detectors typically operate according to a known light scattering measurement method. It uses the fact that clean air practically does not reflect light. However, if there are smoke particles in the measuring chamber, the backlight emanating from the light source is at least partially reflected in the smoke particles. Part of this scattered light then falls on the optical detector, which does not directly get the light from the backlight. In the absence of smoke particles in the measuring chamber, the backlight will not reach the optical detector.

The optical detector of an optical smoke detector is typically a photodiode that provides only a very small measurable signal. Therefore, an electro-optical amplification circuit is included behind the photodiode, which converts the current provided by the photodiode into a voltage, and this voltage amplifies it so that the signal can be further processed by the subsequent system. The subsequent system contains, for example, an analog-to-digital converter and a microcontroller for further data processing.

Amplifier circuits of photodiodes in optical smoke detectors use a variety of operational amplifiers, which are also integrated into components on specialized integrated circuits (ASICs) and / or microcontrollers. They disadvantageously determine the material costs and current consumption for the amplification circuit and, therefore, for the entire optical smoke detector.

The basis of the invention is related to the device the task of creating a smoke detector based on the principle of scattered radiation, which can be manufactured in an economical manner and also has a small current consumption. The basis of the invention is related to the method, the task of creating a calibration method for a smoke detector based on the principle of scattered radiation.

This problem is solved by means of sets of features of the independent claims. Preferred embodiments of the proposed invention are described in the dependent claims.

According to a first aspect of the invention, there is described a device for detecting smoke based on measurements of scattered electromagnetic radiation. The described device for detecting smoke contains (a) a radiation source for emitting backlight radiation that has a temporal sequence of radiation pulses, (b) a radiation detector for receiving the measured radiation, which after at least partial scattering of the backlight radiation enters the radiation detector, (c) an amplifier circuit for amplifying an output signal of a radiation detector; (d) an analog-to-digital converter with a sampling and storage circuit for converting an analog output signal to an amplifier circuit to a digital value, and (e) a control device which is associated with the radiation source and the sample and hold circuit. According to the invention, the control device controls the radiation source and the sampling and storage circuit in such a way that the temporal position of the sampling time of the sampling and storage circuit with respect to the radiation pulse depends on the duration of the radiation pulse.

The smoke detector described is based on the knowledge that the time shift of the analog output signal of the amplification circuit with respect to the radiation pulse of the radiation source, which occurs due to the variation in the duration of the radiation pulse of the backlight, can be compensated by appropriate temporal control of the sampling and storage circuit. In this way, it can be guaranteed that the analog output signal of the amplifier circuit is digitized at a point in time to which the output signal level has not yet reached its maximum, or to which the output signal level has already decreased again. By digitizing the output signal at a point in time at which it is at least approximately at its maximum level, a significant contribution can be made, on the one hand, to reliable and, on the other hand, smoke detection, which is characterized by a low probability of false alarms.

It should be noted that the duration of one or more radiation pulses that are emitted by the radiation source can be adapted, for example, as part of the calibration of the described smoke detection device. With such a calibration, the optical and / or electronic signal paths inside the smoke detector are usually compared. In this case, a certain dispersion body is introduced into the measuring chamber of the smoke detector, and the digitized output signal of the analog-to-digital converter is determined.

The optical and / or electronic signal path includes, for example, controlling the radiation source by means of a control device, the efficiency of the radiation source, the optical scattering conditions inside the measuring chamber, the efficiency of the radiation detector, amplification of the amplification circuit and signal conversion in an analog-to-digital converter. If, when setting up a special smoke detector, the digital output signal of the analog-to-digital converter, for example, due to the relatively weak light signal of the radiation source, would be less than provided, then in accordance with the invention this could be compensated by lengthening the duration of the radiation pulse. If, for example, due to a special strong light source of radiation, the output signal of the analog-to-digital converter would be larger than provided, then this could be compensated by shortening the duration of the radiation pulse.

In addition, it should be noted that the temporary position of the sampling time of the sampling and storage scheme, of course, can adapt with respect to the control pulse for the radiation source. The control pulses for the radiation source, in particular, are correlated in time with the actual radiation pulses. This has the advantage that complete synchronization can be made between the control pulse and the sampling time in the control device of the smoke detector.

The control device can determine the sampling time, depending on the pulse width of the corresponding radiation pulse by means of a function stored in the control device, or by means of a table stored in the control device.

The radiation source can be controlled by the control device without feedback or feedback. In the case of feedback, the control device could also be called a control device that controls the radiation source and / or the mode of operation of the sampling and storage circuit. The term "management" in this application can mean both open-loop control and closed-loop control.

In the framework of this application, the concept of "radiation" is used for each type of electromagnetic radiation. In this case, electromagnetic radiation can have a discrete or continuous spectrum with any wavelengths. The radiation may be visible, infrared or ultraviolet light. X-ray or microwave radiation can also be used for scattering measurements in the framework of the claimed invention.

According to an example embodiment of the invention, the amplification circuit is a circuit made of discrete components. The discrete components are, in particular, bipolar passive components, such as resistors and capacitors, and active components, such as simple transistors. This means that no integrated components such as operational amplifiers or specialized (application-oriented) integrated circuits (ASICs) are used for the described amplifier circuit.

The rejection of the use of integrated circuits has the advantage that the described amplification circuit and, thus, the entire smoke detector can be manufactured in a particularly economical manner. Due to the adaptation of the sampling times described above to the duration of the radiation pulse or to the duration of the control pulse for the radiation source, it is possible to at least substantially compensate for undesirable artifacts, which, in comparison with the operational amplifier-based amplification circuit, can occur in a discrete amplification circuit in more a strong degree.

Along with lower costs, the use of a discrete amplification circuit provides the ability to reduce the current consumption of the entire smoke detector. This, in particular, has an advantage in battery powered smoke detectors.

According to another exemplary embodiment of the invention, the smoke detection device further comprises a temperature sensor, which is connected to the control device. Moreover, the control device is configured to control the radiation source and the sampling and storage circuit in such a way that the temporary position of the sampling time of the sampling and storage circuit with respect to the radiation pulse further depends on the temperature detected by the temperature sensor. This has the advantage that, for example, due to a deliberately forced temporal shift of the sampling moments by the control device, it can be guaranteed that also after changing the temperature, the analog output signal of the amplifier circuit is always at least approximately carried out when the output signal is relatively high level. Temperature artifacts can thus be advantageously eliminated or at least substantially reduced.

According to another embodiment of the invention, the temperature sensor is a temperature sensor integrated in the control device. This has the advantage that it is not necessary to introduce a separate temperature sensor into the smoke detector and to wire it accordingly. Since modern microprocessors are already equipped with a temperature sensor, the use of a temperature sensor integrated in the control device is also preferable from an economic point of view.

According to another embodiment of the invention, the analog-to-digital converter and the control device are implemented by means of a common integral component. A common integral component can be, for example, a simple microprocessor, which is more economical than a separate control device and a separate analog-to-digital converter.

According to another embodiment of the invention, the amplifier circuit comprises an integrator.

The use of an integrator has the advantage that the output of the radiation detector can be amplified in a simple manner. In this case, the integrator can be considered as one and preferably as the first stage of a multi-stage amplification circuit.

The integrator may preferably be implemented using a known RC circuit. Moreover, in a known manner, the output signal of the radiation detector is integrated by means of charge storage on the capacitor. Of course, in this case, both the capacitance of the capacitor and the value of the ohmic resistance can be matched with the corresponding conditions with respect to the required time constant.

According to another exemplary embodiment of the invention, the sampling and storage circuit is a tracking and storage circuit.

In contrast to the sampling and storage scheme, which is used in most analog-to-digital converters, in the case of a tracking and storage circuit, the entire circuit of the analog-to-digital converter remains connected for a long period of time. This is true, for example, for the entire or at least a long period of time in which the analog output signal of the amplifier circuit increases.

The tracking and storing circuit can, for example, be connected immediately after the beginning of the increase in the output signal of the amplifying circuit and, when the maximum signal is reached, is again turned off or disconnected. In this way, not only the maximum signal, but also a longer increase in the output signal of the amplifier circuit is used to determine the level of the output signal.

The tracking and storage circuit may contain a capacitor, which is charged in a known manner by the output signal of the amplifying circuit. In this case, the charge accumulated on the capacitor is a direct measure for the level of the output signal of the amplification circuit and, therefore, also the density of the smoke particles that are in the measuring chamber.

It should be noted that the load of the analog-to-digital converter circuit, which, compared to the tracking and storage circuit, is connected longer, can already be taken into account when setting the operating point of the amplifying circuit.

The use of a tracking and storage circuit compared with the use of a conventional sampling and storage circuit with a single sampling and storage capacitor has the advantage that no so-called sampling and storage peaks occur that arise due to the short-term connection of the capacitor of the sampling circuit and storage.

According to another aspect of the invention, a method for calibrating a smoke detection device based on the measurement of scattered electromagnetic radiation is described. The method can be carried out, in particular, in a smoke detector of the above type. The described calibration method includes (a) setting the pulse width of the radiation source to emit backlight radiation, which has a temporal sequence of radiation pulses, which after at least partial scattering of the backlight radiation are accepted as the measured radiation by the radiation detector, and (b) setting the sampling times of the circuit sampling and storing an analog-to-digital converter, which converts the analog output signal of the amplifier circuit connected to the radiation detector to digitally e measured value, in relation to the beginning and / or end of the pulse duration of the radiation source. According to the invention, the temporary position of the sampling times of the sampling and storage circuit with respect to the radiation pulse depends on the time duration of the radiation pulse.

Also, the described calibration method is based on the knowledge that the time shift of the analog output signal of the amplification circuit, which arises due to the variation of the pulse duration of the backlight radiation, can be compensated by appropriate temporal control of the sampling and storage circuit. Thereby, it can be guaranteed that the digitization of the output signal occurs at a point in time at which it is at least approximately at its maximum level.

According to an exemplary embodiment of the invention, the set pulse duration depends on the reference measured value for the digital measured value, the reference measured value being determined by measuring the scattered radiation in a specific scattering medium.

Through the described reference measurement, the entire optical and electronic signal paths within the smoke detector can be determined. Deviations from the tolerances of the respective components of the smoke detector, such as a radiation source control unit, a radiation source, a measuring chamber, a radiation detector, an amplification circuit and an analog-to-digital converter (including a sampling and storage circuit), can thus be compensated by appropriate adaptation of the pulse duration radiation source. So, for example, with a weak radiation source, with a relatively ineffective radiation detector and / or with a relatively weak amplifier, the duration of the radiation pulse increases, in spite of this, to obtain a reliable radiation signal.

It should be noted that the forms of the invention have been described in relation to various objects of the invention. In particular, some forms of the invention are described by the claims related to the device, and other forms of the invention are described by the claims related to the method. However, the specialist, based on the study of the materials of this application, should be absolutely clear that, unless explicitly stated otherwise, in addition to the combination of features that relate to one type of object of the invention, any combination of features that relate to different types of objects of the invention is also possible .

Other advantages and features of the proposed invention result from the following as an example of the following description of the currently preferred forms of execution. The individual drawings of this application should be considered only as schematic, but not as presented in true scale.

1 shows an optical scattering principle a smoke detector according to an embodiment of the invention,

Figure 2 shows in a schematic representation the entire optical and electronic signal path inside the optical smoke detector shown in figure 1,

Fig. 3A is an exciting circuit for a light source of the optical smoke detector shown in Fig. 1,

FIG. 3B is a sampling and storage circuit that is integrated in a control device of the optical smoke detector shown in FIG. 1,

FIG. 4 shows, for the optical smoke detector shown in FIG. 1, a time mode comparison between controlling a light source and an output signal of an amplification circuit.

It should be noted here that in the drawings, the reference positions of the same or corresponding components differ from each other only by the first digit.

In addition, it should be noted that the following forms of execution represent only a limited selection of possible embodiments of the invention. In particular, it is possible to combine the features of the individual forms of execution with each other in a suitable manner, so that for a person skilled in the art using the embodiments presented here, many different forms of execution should be considered as clearly disclosed.

The following description relates to a smoke detector that detects the presence of smoke through the occurrence of light scattering on smoke particles. The light may be infrared, visible or ultraviolet light. As stated above, any type of electromagnetic radiation with any wavelength can be used instead of light to detect smoke.

1 shows an optical scattering principle smoke detector 100. The smoke detector comprises a measuring chamber 110 into which, for example, smoke penetrates during a fire. The measuring chamber is designated as a scattering volume 110. In the measuring chamber 110 there is a light source 120 configured as a photodiode, to which control pulses are supplied via the control line 170a and which, accordingly, is prompted to emit backlight pulsed light 120a. In addition, in the edge region of the measuring chamber 110, there is also a light detector 130 configured as a photodiode, which receives the measured light 130a, which, after at least partially scattering the backlight 120a on the smoke particles, enters the light detector 130. The optical barrier 111 prevents the backlight light 120a from directly reaching the light detector 130.

An amplifier circuit 140 is connected to the output of the light detector 130, which converts the photocurrent that occurs when light is incident on the light detector 130 into a voltage signal that can be further processed by the control device 150. According to an exemplary embodiment presented here, the amplifier circuit 140, as will be described in more detail below with reference to FIG. 3B, is made only of individual discrete electronic components. Components of operational amplifiers or specialized integrated circuits (ASICs) in amplifier circuit 140 are not included for cost reasons.

As can be seen from FIG. 1, a sampling and storage circuit 152 and an analog-to-digital converter 156 are also integrated in the control device 150. Both of these components are used to convert the analog output signal of the amplifier circuit 140 to a digital measured value 156a, which can be further processed by a method not shown and, for example, if a certain limit value is exceeded, initiate a fire alarm message.

According to an exemplary embodiment presented here, the retrieval and storage circuit functions as a tracking and storage circuit 152. As already noted above in the description of the invention, in the case of a tracking and storing circuit, the entire circuit of the analog-to-digital converter remains connected for a longer period of time. According to the exemplary embodiment presented here, the tracking and storing circuit is connected immediately after the beginning of the increase in the output signal of the amplifier circuit 140 and is turned off again when the signal maximum reaches the output signal of the amplifier circuit 140. In this way, not only the signal maximum, but also a long section of the increase in the output signal of the amplifier circuit to determine the level of the output signal.

The control device 150 further comprises a drive circuit 170 for a light source 120, which is connected via a control line 170a to a control device 150 or to a drive circuit 170. The drive circuit 170 will now be explained in more detail with reference to FIG. 3A.

As can also be seen from FIG. 1, the control device 150 also includes an internal temperature measuring diode 158, with which the temperature of the control device 150 and, if necessary, also the temperature of the entire smoke detector 100 can be determined. Alternatively or in combination, the temperature can also be detected using an external temperature sensor sensing element 168. The external sensing element 168 of the temperature measuring sensor may be, for example, a thermistor or a so-called negative temperature coefficient of resistance (NTC) thermistor.

To ensure the smooth operation of the smoke detector 100, a calibration is performed before commissioning. At the same time, a certain scattering body, not shown in FIG. 1, is placed in the measuring chamber 110, and the digitized output signal 156a of the analog-to-digital converter 156 is determined, which is compared with a predetermined reference value. Through the use of a given scattering body, the entire optical and electronic signal path inside the smoke detector is automatically detected.

Figure 2 shows a schematic representation of the entire optical and electronic signal path inside the optical smoke detector 100, which is now denoted by 200. This signal path includes, in particular, controlling the light source 220 through the control device 250, the efficiency of the light source 220, optical scattering conditions inside the measuring chamber 210, the efficiency of the light detector 230, amplification of the amplification circuit 240 and signal conversion in an analog-to-digital converter inside the control device 250.

If during setup it is established that the digitized output signal of the analog-to-digital converter, for example, due to the relatively weak light source 220, is less than provided, then this is compensated by correspondingly extending the pulse duration of the light source. If, for example, due to a particularly strong light source 220, the output of the analog-to-digital converter is greater than provided, this can be compensated by shortening the duration of the light pulse.

This means that, in contrast to the known optical smoke detectors, in the smoke detector 100 described herein, tuning is not done by adapting the gain of the amplifier circuit 240, but by adapting the pulse width of the backlight pulse emitted by the light source 220.

In order to keep the duration of the light source 220 on within the predetermined limits, the light source 220 can be obtained by a preliminary selection from various, with respect to their light intensity, light sources of different efficiencies with specific light powers.

FIG. 3A shows an exciting circuit 370 for a light source 120 of the optical smoke detector 100 of FIG. 1. The light source is now indicated at 320.

The drive circuit 370 includes a transistor 372, the collector of which is supplied through a light source 320, which, when current flows appropriately, emits a backlight 320a, connected to the supply voltage Vcc. The base of the transistor 372 through the ohmic resistance 374 is connected to the input control signal Uin. The collector of transistor 372 through an ohmic resistor 374 is connected to ground GND.

At an appropriate level of the input control signal Uin, the transistor 372 switches, and current flows through a light source 320 made in the form of an LED. The corresponding current through the LED 320 depends, in a known manner, on the supply voltage Vcc and the resistance 376.

FIG. 3B shows an amplifier circuit 340 containing discrete components only, as used in accordance with an exemplary embodiment shown here for the amplifier circuit 140 of the optical smoke detector 100 of FIG. 1. The discrete amplifier circuit 340 comprises an impedance R1, by which the current through the photodiode 330 is converted into a primary voltage signal. Capacitor C1 serves to smooth the voltage signal. The capacitor C2 represents, along with the resistance R4, a time current integrator 342, which can be considered as a first amplification stage. Parts of the amplifier circuit 340 on transistors T1, T2 and T3 can be considered as a second amplification stage, with T2 and T3 representing a controlled current source.

As seen from FIG. 3B, the entire amplifier circuit 340 is powered by a supply voltage Vcc. Reference numeral 352 denotes the sampling and storage circuit located at the output of amplifier circuit 340, which, together with an analog-to-digital converter 356 connected to it, provides reliable conversion of the analog output signal of amplifier circuit 340 to a digital measured signal.

The presented amplifier circuit 340, as well as its output, are designed for very low current consumption from about 3 μA to 5 μA. On this basis, the amplifier circuit 340, as well as its output, is not able to quickly compensate for electrical changes in the load. Such load changes can, however, be caused by connecting a typical input and output cascade (with a low-impedance coupled capacitor) for the analog-to-digital converter 356. Thus, the measured analog output signal of the amplifier circuit 340 would for a short time be due to at least one peak to be highly inconsistent . Of course, it would be possible to perform the amplifier circuit 340 also low impedance, however, this would lead to increased current consumption of the amplifier circuit 340.

In order to circumvent this drawback and, despite this, with low current consumption, to avoid the mismatch of the analog output signal of the amplifier circuit 340, in accordance with the embodiment described here, the sampling and storage circuit operates as a tracking and storage circuit 352.

FIG. 3C shows a sampling and storage circuit 352 operating as a tracking and storage circuit integrated in the control device of the optical smoke detector 100 shown in FIG. 1.

The central element of the tracking and storing circuit 352 is a capacitor 353 that takes over the storing function for the analog values that are applied to the input IN of the tracking and storing circuit 352. Added to this is an electronic switch 355, which determines the sampling and storage phase. At the OUT output, the tracking and storing circuit 352 provides a signal provided for digitization by an analog-to-digital converter 356.

If the switch 355 is closed, then the capacitor 353 is charged. In order for the capacitor 353 to be quickly charged, the capacitor 353 may have a small capacity. However, the capacitor 353 with low capacitance has the disadvantage that it also discharges quickly, and thus, the output voltage of the amplifier circuit 340 cannot be maintained for too long.

The switch 355 has a high blocking resistance in the off state, and the insulation of the capacitor 353 is very good. In this way, an undesired stand-alone discharge of the capacitor 353 can be counteracted.

The charge accumulated on the capacitor 353 is a direct measure of the output level of the amplifier circuit 340 and, therefore, also the density of the smoke particles that are in the measuring chamber 110.

In contrast to the sampling and storage scheme, in which the switch 355 is closed only for a relatively short time, and in which due to the short-circuiting of the switch 355, unwanted surges or short-term mismatches of the detected analog signal occur, in the case of the tracking and storing circuit 352 the entire analog-digital circuit converter 356 remains connected for an extended period of time. This is true, for example, for the entire or at least a long period of time in which the analog output signal of the amplifier circuit 340 increases.

The tracking and storing circuit 352 can, for example, be connected immediately after the start of the rise of the output signal of the amplification circuit 340 by closing the switch 355 and again disconnecting or disconnecting when the maximum signal is reached. Thus, in a preferred manner, not only the maximum of the signal, but also a longer increase in the output signal of the amplifying circuit 340 is used to charge the capacitor 353 and, thereby, to determine the level of the output signal. Unwanted peaks, which, as described above, usually occur in the sampling and storage scheme, do not appear in the tracking and storage circuit 352.

It should be noted that the load of the analog-to-digital converter 356, which, in comparison with the sampling and storage circuit, is longer connected in the described tracking and storage circuit 352, can already be taken into account when setting the operating point of the amplifying circuit 340.

FIG. 4 shows, for the optical smoke detector 100 shown in FIG. 1, a comparison of the timing between the control of the light source (above) and the output of the amplification circuit 140, 340 (bottom).

As already explained above, in accordance with the invention, the optical and electronic signal paths are set inside the smoke detector 100 by correspondingly matching the time duration of the control pulses. Since the backlight pulses at least approximately follow the course of the control pulses, thereby, by varying the time duration T, the duration of the backlight pulse also varies.

The lower diagram in FIG. 4 shows the characteristics of three different output signals that are obtained for different time durations T for a control pulse for a light source. In this case, the solid line 491 represents the output signal of the amplification circuit with a relatively long pulse duration T. The dashed line 492 represents the output signal of the amplification circuit with an average pulse duration T. Dotted line 493 represents the output signal of the amplification circuit with a relatively short pulse T.

As can be seen from figure 4, the maximum of the corresponding output signal with increasing length of the control pulse T moves back. This shift in accordance with the invention is compensated by the fact that the so-called memorization time at which the analog-to-digital conversion itself is carried out is correspondingly shifted backward with respect to time t0 at which the control pulse has its rising edge. This setting of the memorization time is carried out using the control device 150 shown in FIG.

As can also be seen from FIG. 4, according to the exemplary embodiment presented here, the smoke signal of the smoke detector is determined by generating a difference between the maximum of the output signal of the amplifier circuit at time t2 and the offset value of the output signal of the amplifier circuit at time t1. In this case, the time t1 is preferably selected so that the corresponding measurement of the bias value, which is also carried out by means of a tracking and storing circuit and by means of an analog-to-digital converter connected to it, is in no way distorted by the measurement of scattered light.

It should be noted that also the temperature of the entire smoke detector 100 and, in particular, the temperature of the amplifier circuit 140 and / or control device 150 can contribute to the maximum shift of the output signal of the amplifier circuit 340. By determining the corresponding temperature using the internal heat-sensitive diode 158 and / or Using an external temperature-sensitive sensor 168, this temperature effect can also be compensated for by appropriate adaptation of the memorization time and, thereby, contribute to reliable smoke projection.

List of Reference Items

100 smoke detector

110 Measuring chamber / scattering volume

111 barrier

120 Light source / light source / LED

120a backlight emission / backlight

130 Radiation detector / light detector / photodiode

130a Measured radiation / measured light

140 Amplifier circuit

150 control device

152 Sampling and storage scheme / tracking and storage scheme

156 Analog to Digital Converter

156a Measured value

158 Internal temperature measuring diode

168 External temperature sensor / NTC sensor

170 Excitation circuit

170a control line

200 smoke detector

210 Measuring chamber / scattering volume

220 Light source / light source / LED

230 radiation detector / light detector / photodiode

240 Amplifier circuit

250 control device

270a control line

320 Light source / light source / LED

320a backlight emission / backlight

330 radiation detector / light detector / photodiode

330a Measured radiation / measured light

340 Amplification circuit

342 Integrator

352 Sampling and storage scheme / tracking and storage scheme

353 storage capacitor

355 switch

356 Analog to Digital Converter

370 Excitation circuit

372 Transistor

374 Resistance

376 Resistance

Vcc Supply Voltage

GND Mass

R Resistance

T1-T6 transistor

C1-C6 Capacitor

R1-R10 Resistance

IN Input

OUT Output

Uin Control Input

491 The output signal of the amplifier circuit with a large pulse duration T

492 The output signal of the amplifier circuit with an average pulse duration T

493 Output signal of the amplification circuit with a short pulse duration T

T Time duration of the control pulse for the LED

Claims (9)

1. A device for detecting smoke based on measurements of scattered electromagnetic radiation, the device (100, 200) comprising
a radiation source (120, 220, 320) for emitting backlight radiation (120a, 320a), which has a temporal sequence of radiation pulses,
a radiation detector (130, 230, 330) for receiving the measured radiation (130a, 300a), which, after at least partial scattering of the backlight radiation (120a, 320a), falls on the radiation detector (130, 230, 330),
an amplifier circuit (140, 240, 340) for amplifying the output signal of the radiation detector (130, 230, 330),
an analog-to-digital converter (156, 356) with a sampling and storage circuit (152, 352) for converting the analog output signal of the amplifier circuit (140, 240, 340) to a digital value (156a) and
a control device (150, 250) that is connected to a radiation source (120, 220, 320) and a sampling and storage circuit (152, 352) and which is configured to control a radiation source (120, 220, 320) and a circuit (152, 352) sampling and storing in such a way that the temporal position of the sampling moment of the sampling and storing circuit (152, 352) with respect to the radiation pulse depends on the time duration of the radiation pulse. 2. The device according to claim 1, in which the amplification circuit (140, 240, 340) is a circuit made of discrete components. 3. The device according to claim 1 or 2, additionally containing
a temperature sensor (158, 168), which is connected to the control device (150), and the control device (150) is further configured to control the radiation source (120, 220, 320) and the sampling and storage circuit (152, 352) in this way that the temporary position of the sampling point of the sampling and storage circuit (152, 352) with respect to the radiation pulse additionally depends on the temperature detected by the temperature sensor (158, 168). 4. The device according to claim 1, in which the temperature sensor is a temperature sensor (158) integrated in the control device (150). 5. The device according to claim 1, in which the analog-to-digital Converter (156, 356) and the control device (150) are implemented by means of a common integral component. 6. The device according to claim 1, in which the amplifier circuit (140, 240, 340) contains an integrator (342). 7. The device according to claim 1, in which the sampling and storage circuit is a tracking and storing circuit (156, 356). 8. A method for calibrating a device (100) for smoke detection based on measurements of scattered electromagnetic radiation, in particular for calibrating a device (100) according to any one of claims 1 to 7, the method comprising
setting the pulse duration of the radiation source (120, 220, 320) for emitting radiation (120a, 320a) of the backlight, which has a temporal sequence of radiation pulses, which after at least partial scattering of the radiation (120a, 320a) of the backlight are accepted as the measured radiation (130a, 330a) a radiation detector (130, 230, 320), and
setting the sampling moments of the circuit (152, 352) for sampling and storing an analog-to-digital converter (156, 356), which converts the analog output signal of the amplifier circuit (140, 240, 340) connected to the radiation detector (120, 220, 320) to the digital measured value (156a), with respect to the beginning (t0) and / or the end of the pulse duration of the radiation source (120, 220, 320), and the temporary position of the sampling moments of the sampling and storage circuit (152, 352) with respect to the radiation pulse depends on the time radiation pulse duration. 9. The method according to claim 8, wherein the set pulse duration depends on the reference measured value for the digital measured value (156a), the reference measured value being determined by measuring the scattered radiation in a specific scattering medium.

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