GB2611857A - Method for monitoring an optical measuring device and optical measuring device - Google Patents

Abstract

An optical measuring device including a first optical transmitter Tx1 for emitting an optical measurement signal into a measurement volume 20, and a first optical receiver Rx1 for detecting an optical signal influenced by particles in the measurement volume 20. The optical measuring device further includes a second optical transmitter Tx2 and a second optical receiver Rx2, where respective direct optical signals (S1-S3,fig.2) are detected between the first transmitter Tx1 and second receiver Rx2 via first direct optical path 42, second transmitter Tx2 and second receiver Rx2 via second direct optical path 44, and the second transmitter Tx2 and first receiver Rx1 via third direct optical path 46. The optical signals are received by a control unit 60. The optical signals (S1-S3,fig.2) may be used to calculate (240,fig.2) at least one test value (P,fig.2), which is then evaluated (250,fig.2) to assess the functionality of the optical measuring device. The calculation of a test value may be repeated so multiple consecutive test values may be obtained. The difference between test values may be compared, and if the difference exceeds a threshold value, the functionality of the measuring device may be defined as erroneous. The device may be a smoke detector.

Description

Description Title

Method for monitoring an optical measuring device and optical measuring device The present invention relates to a method for monitoring an optical measuring device comprising a first optical transmitter for emitting an optical measuring signal into a measurement volume and a first optical receiver for detecting an optical signal influenced by particles in the measurement volume, and such an optical measuring device, as well as a computing unit and a computer program for carrying out the method.

Background of the Invention

Many smoke detectors rely on the detection of optical signals. In smoke detectors according to the scattered light principle, light from a light source is radiated such that it cannot be directly detected by a detector. However, the light source and the detector are arranged so that their radiating and receiving directions intersect in a scattering volume. If there are particles scattering in this scattering volume, e.g., smoke particles, the scattered light can be detected and measured.

An optical labyrinth is usually applied around the scattering volume, which shields and absorbs external light and allows only smoke particles to pass into the scattering volume if possible. The housing of the smoke detector is also designed so that only little or ideally no light can be reflected from the light source to the detector.

The sensitivity of such a measurement according to the scattered light principle may change due to different influences. For example, aging, cold soldering joints, or dust deposits may lead to changes in sensitivity and thus to malfunction. In particular, reflections due to dirt and scattering in the optical labyrinth change greatly over time. Therefore, meaningful monitoring of the functionality of the smoke detector cannot be carried out directly over the components used to monitor the scattered light volume.

DE 10 2017 217 280 Al describes a smoke detector according to the scattered light principle, in which sensitivity is monitored by an additional direct transmission path between the light source and receiver, which can be interrupted by an optical switch. From the change of the signal reception when the switch position is changed, the sensitivity of the particle measurement can then be estimated. Alternatively, a separate measurement path with a second light emitter-receiver pair is proposed, wherein the light of the second light source is detected directly by the second receiver. Assuming that the measurement path for particle measurement is influenced similarly by impairments such as dirt as this second measurement path, the two measurement paths can then be compared and the measurement result of the particle measurement can thus be evaluated.

Disclosure of the invention

According to the present invention, a method for monitoring an optical measuring device as well as a computing unit and a computer program for carrying it out are proposed with the features of the independent claims. In addition, an optical measuring device is proposed that enables monitoring of its functionality. Advantageous embodiments are the object of the subclaims as well as the following description.

A method is proposed in which an optical measuring device according to the scattered light principle is monitored, in particular a smoke detector according to the scattered light principle. The measuring device comprises at least one first optical transmitter for emitting an optical measurement signal into a measurement volume and at least one first optical receiver for detecting an optical scattering signal influenced by the particles in the measurement volume. Here, the entire optical signal from the measurement volume is referred to as the scattering signal, which is produced by scattering particles, but also by reflections or refractions in the measurement volume. To check the sensitivity of the scattered light measurement, a first optical control signal starting from the first optical transmitter to be tested, i.e., a light source, is detected by a second optical receiver of the measuring device; a second optical control signal, starting from a second optical transmitter, is also detected by the second optical receiver; and a third optical control signal, starting from the second optical transmitter, is detected by the first optical receiver to be tested. Then, at least one test value is calculated from the detected first, second and third optical control signals, which is then evaluated to assess the functionality of the optical measuring device.

By using a second optical transmitter and a second optical receiver, as well as by measuring a plurality of control signals on all optical paths between the two transmitter-receiver pairs, there is thus enough information about the involved transmitters and receivers to assess their functionality. In particular, the functionality of the first transmitter and the first receiver involved in the scattered light measurement can also be monitored. In addition, the functionality of the control elements is also monitored, since any malfunction of a transmitter or receiver will trigger a change in at least one of the control measurements made.

In particular, the test value may be determined by S3

P -

wherein P is the test value, wherein S/ is the signal strength of the first optical control signal, wherein S2 is the signal strength of the second optical control signal, and wherein 33 is the signal strength of the third optical control signal. This results from considerations of the transmission factors of the optical signal paths between the transmitters and receivers, so that a statement about the functionality of the optical measurement paths can be provided by a simple quotient of the detected signals from the three control measurements. The signal strength may be determined, for example, as the current or voltage level of a constant signal or as the average or maximum amplitude of a modulated signal.

Preferably, detecting the first, second and third optical control signals and calculating a test value is repeated several times so that a plurality of consecutive test values is obtained. This test can be carried out at predetermined intervals. In this way, one obtains a time curve of the test values and can thus evaluate a time change in the signal qualities and the functionality.

The evaluation of the test value can take place in a variety of ways. For example, a difference between two test values may be determined, and if the difference exceeds a threshold value, the functionality of the measuring device may be defined as erroneous. Additionally or alternatively, a deviation of the test value from a predetermined reference value or a reference value determined in previous steps may be determined and, if the deviation exceeds a predetermined threshold value, the functionality of the measuring device may be defined as erroneous. Likewise, a proximity function or estimation function could also be formed from the plurality of test values, the properties of which, for example, a slope, are then evaluated. S2

The method may further include performing at least one scattered light measurement in the measurement volume by detecting the optical scattering signal from the measurement volume at the first optical receiver and correcting the result of the measurement based on the at least one test value. For example, the result may be corrected by adding a correction value or by multiplying with a correction factor. Since the test value can make a statement about the sensitivity and functionality of the components involved in the scattered light measurement, a scattering signal that is as correct as possible and thus correct detection of particles in the measurement volume can be ensured.

In addition, an optical measuring device according to the scattered light principle is proposed, in particular a smoke detector, wherein the measuring device comprises at least one first optical transmitter for emitting an optical measurement signal into a measurement volume, and at least one first optical receiver for detecting a scattered optical signal influenced by particles in the measurement volume. Moreover, the measuring device comprises a second optical transmitter and a second optical receiver, wherein the second optical receiver is adapted to detect optical control signals from the first optical transmitter and from the second optical transmitter, respectively, on a direct optical path and to transmit the detected control signals to a control unit, and wherein the first optical receiver is adapted to detect optical control signals of the second optical transmitter on a direct optical path and to transmit the detected control signals to a control unit. In principle, such optical measuring devices can also be used for other particle measurements according to the scattered light principle.

A computational unit according to the invention, e.g., a control equipment of an optical measuring device, is configured, in particular in terms of program technology, to perform a method according to the invention.

The implementation of a method according to the invention in the form of a computer program or computer program product with program code for carrying out all method steps is also advantageous, since this causes particularly low costs, in particular if an executing control equipment is still used for further tasks and is therefore already present. Suitable data carriers for providing the computer program are in particular magnetic, optical and electrical memories, such as hard drives, flash memories, EEPROMs, DVDs, etc. A download of a program via computer networks (internet, intranet, etc.) is also possible.

Further advantages and embodiments of the invention result from the description and the attached drawing.

The invention is shown schematically by way of exemplary embodiments in the drawing and will be described below with reference to the drawing.

Brief Description of the Drawings

Figure 1 schematically shows a construction of optical transmitters and receivers in a smoke detector according to one embodiment of the invention; and Figure 2 shows a flow chart for an exemplary process flow according to one embodiment of the invention.

Embodiments of the Invention Figure 1 schematically shows the construction of an optical measuring device according to the scattered light principle, in particular of a scattered light smoke detector according to a possible embodiment. A first optical transmitter Tx1, i.e., a light source, which outputs a light signal, and a first optical receiver Rx1 are provided.

To the extent that optical transmitters and optical receivers are mentioned in the present application, this means suitable light sources and optical detector modules of any type.

For example, an optical transmitter Tx1, Tx2 may be a directional or non-directional light-emitting element that emits light at one or more wavelengths. Here, electromagnetic radiation from the entire optical spectrum is understood as light, which includes visible wavelengths as well as non-visible spectral regions such as ultraviolet or infrared light. For this purpose, for example, LEDs, laser diodes or other light sources can be used. The light emitted from the optical transmitter can subsequently be guided by further optical components, for example by focusing or beam-reflecting lenses, apertures, spectral filters for filtering certain wavelengths, beam dividers or the like.

For example, as an optical receiver Rx1, Rx2, photodiodes or phototransistors can be used to convert light into electric voltage or current signals, which can then be evaluated.

Suitable components that are capable of converting light signals into measurable signals are known to the person skilled in the art. It will be appreciated that the optical receiver associated with a transmitter must be selected so that it can detect the expected light signal, i.e., it must cover a suitable wavelength range and have sufficient detection sensitivity to be able to detect the desired level of scattered light. Here too, lenses, filters or other optical components can be used to appropriately detect the light signal from the measurement volume. Additionally, downstream electronic components may be provided, such as an amplifier or electronic filter, to process the output signal of the optical receiver.

The first optical receiver Rxl is arranged relative to the first optical transmitter Txl in such a way that a direct reception of the light signal emitted by the first transmitter is not possible, so that no direct optical path is present between the first optical transmitter and the first optical receiver. Shields, such as apertures and light-absorbing walls, can be arranged in the smoke detector (not shown) in a suitable way so that they form an optical labyrinth.

However, the first optical transmitter Txl is intended to radiate at least a portion of its light into a measurement volume 20, and the first optical receiver Rxl is intended to be capable of detecting scattered or reflected light from the measurement volume 20 or at least from a portion of the measurement volume. Ambient air collects in this measurement volume 20, for example in a measurement chamber that is opened in one or more directions outwardly, thus allowing airflow with particles. As long as the measurement volume 20 is free of optically effective particles, no corresponding substantial scattering or reflection effects occur, so that no corresponding light signal fraction is detected by the first receiver Rxl, but only a fraction that occurs by reflections of the optical labyrinth. However, once particles such as smoke particles are present in the measurement volume, a portion of the light emitted from the first transmitter into the measurement volume is scattered, broken, and/or reflected in different directions.

At least a portion of the light thus deflected is thus also radiated in the direction 32 of the first optical receiver Rxl out of the measurement volume so that a scattered light signal can be detected by this first receiver Rxl. The receiver can preferably be designed and arranged relative to the measurement volume such that scattered light from as large a portion of the measurement volume as possible can be detected. The strength of the scattered light signal will depend on the scattering particle type, particle size, particle density in volume, wavelengths of the emitted light, geometric arrangement of the optical elements and other factors. Nevertheless, such a signal change that is above, for example, a certain noise threshold may indicate the presence of a relevant number of smoke particles. Here, the entire light signal is referred to as the scattered light signal, which comes from the measurement volume, even if portions thereof are also caused by refraction or diffuse reflections, depending on the particle type.

Preferably, suitable measures are taken to prevent dirt, such as dust particles, from penetrating into the measurement volume, which could alter the scattered light signal as far as possible. Optionally, various passive or active elements may be utilized to assist in the continuous introduction and passage of ambient air into this measurement volume, such as a particular arrangement of ventilation channels or even fans. This can ensure that the measurement in the measurement volume within the smoke detector allows a meaningful evaluation of existing particles in the ambient air. Alternatively, designs in which the measurement volume itself lies outside the smoke detector are also possible, as long as the light signals to be detected can be separated from the ambient light.

According to a possible embodiment of the invention, a second optical transmitter Tx2 (control transmitter) and a second optical receiver Rx2 (control receiver) are now additionally used as control elements for the scattered light measurement. These second optical transmitters and receivers are not used for the scattered light measurement itself. In so doing, these two elements are arranged so that the second receiver Rx2 can directly receive light from both the first transmitter Txl on an optical path 42 and the second transmitter Tx2 on an optical path 44. Moreover, the second transmitter Tx2 is arranged such that the first receiver Rxl, which detects the scattered light from the measurement volume 20 for the particle measurement, can receive light of the second optical transmitter Tx2 on a direct optical path 46.

In so doing, the strength of the scattered signal and that of the control signals may be determined so as to be approximately proportional to the intensity of the respective transmitted light if all other conditions remain constant.

The free space between transmitter and receiver for determining the control signal is preferably designed so that its aging influences can only insignificantly affect the light transmission.

The additional transmitters and receivers and the further optical paths are preferably arranged outside the measurement volume so that influence on these further optical paths by dirt or particles in the measurement volume can be avoided.

In addition the directions of the optical paths from one of the optical transmitters to one of the optical receivers, respectively, are also preferably similar to one another so as to minimize influences by age-related changes on the directional dependencies of the transmitter and receiver. Accordingly, preferably, the spectral ranges of the irradiation powers of both transmitters Txl, Tx2 should be similar.

All transmitters and receivers may be connected to a control unit 60 that controls the optical signals of the light sources and further processes the detected signals of the receivers. This control unit may be part of the smoke detector or the measuring device, but it may also be separate from the measuring device and connected to the transmitters and receivers by suitable communication means.

With this combination of two optical transmitters Txl, Tx2 and two optical receivers Rxl, Rx2, further measurements are now carried out in addition to the scattered light measurement for smoke detection in the measurement volume. Based on these further measurements, it is then possible to make statements about the sensitivity or functionality of the safety-relevant scattered light measurement.

For this purpose, the transmission factors of the various elements are considered. In this case, G(x) is the transmission factor of the element x, i.e., a respective optical transmitter or receiver. This transmission factor is defined for a transmitter as the irradiation power that travels from the spatial area of the optical transmitter to the environment completely (and is not, for example, absorbed by any dust layer present on the optical transmitter) divided by the drive signal value of the optical transmitter. The digital control signal value is independent of aging processes of the system.

For a receiver, the transmission factor is defined as the output measurement value divided by the irradiation power that travels from the environment to the spatial area of the optical receiver. This irradiation power also includes, for example, the portion that is absorbed by any age-related dust layer on the optical receiver and is thus no longer detected. Aging processes have already been included in the measurement value measured by the receiver; this value is therefore not to be changed further by aging processes.

The change in the sensitivity of an optical transmission path then essentially depends on the change of the product from the transmission factor of the transmitter and the transmission factor of the receiver of that transmission path.

In the case of direct transmission of light, as between the second optical transmitter Tx2 and the second optical receiver Rx2, between the second optical transmitter Tx2 and the first optical receiver Rx1 and between the first optical transmitter Tx1 and the second optical receiver Rx2, the measurement result substantially corresponds to the product of the transmission factors of transmitter and receiver multiplied by an unknown factor k, which assumes that this factor is largely constant over time.

Functional monitoring of the scattered light measurement is described below using exemplary method steps as shown in Figure 2.

A scattered light measurement in the measurement volume is regularly or nearly continuously carried out in step 200 by emitting light or an optical signal from the first optical transmitter into the measurement volume and detecting the scattered light signal from the measurement volume by the first optical receiver. In this case, a signal So is electrically measured, for example as a current or voltage level, which corresponds to a light signal. The signal strength may be determined, for example, as the level of a constant signal or as the average or maximum amplitude of a non-constant signal. The measured signal may also already be electronically amplified. The signal is then checked for exceeding a threshold value at regular intervals in step 280. As long as there are no particles in the measurement volume, the signal So will ideally be zero or nearly zero. In contrast, an existing signal indicates scattered light and thus scattered particles. Thus, once the threshold value is exceeded, in step 290 an alarm signal, such as an audible and/or visual signal, may be issued, which is indicative of the possible smoke generation.

According to a possible embodiment of the invention, several control measurements are then performed at regular intervals.

In a first measurement in step 210, an optical control signal is transmitted from the first transmitter (scattered light emitter) and received directly by the second receiver (control receiver). The measurement result Si via the optical path 42 is thus S, = k, * G(Tx,) * G(Rx2) (1) wherein ki is a substantially constant factor, G(Tx/) is the transmission factor of the first transmitter and G(Rx2) is the transmission factor of the second receiver.

In a second measurement in step 220, an optical control signal is transmitted from the second transmitter and received directly by the second receiver. The measurement result 52 via the optical path 44 results in S2 = 1c2 * G(Tx2) * G(Rx2) (2) wherein k2 is a substantially constant factor, G(Tx2) is the transmission factor of the second transmitter and G(Rx2) is the transmission factor of the second receiver.

Finally, in a third measurement in step 230, an optical control signal is transmitted from the second transmitter and directly received by the first receiver via the optical path 46 so that a third measurement result is obtained 53 = k3 G(Tx2) * G(RX1) (3) wherein ks is a substantially constant factor, G(Tx2) is the transmission factor of the second transmitter, and G(Rxi) is the transmission factor of the first receiver.

In so doing, these three control measurements 210, 220, 230 need not take place in this order, but may also be performed in a different order. In addition, it is possible to perform the second measurement 220 between the second transmitter and the second receiver and the third measurement 230 between the second transmitter and the first receiver at the same time, as in both cases the same transmitter is used. In this case, the first and second receivers as well as the subsequent signal processing must be able to receive and measure signals at both receivers simultaneously. Optionally, in such a construction, the first measurement 210 between the first transmitter and the second receiver could then also take place simultaneously with the scattered light measurement 200 between the first transmitter and the first receiver. However, each measurement could also be performed individually.

The measurement signal between the first receiver and the first transmitter via the measurement volume, i.e., the indirect scattered light signal along the optical paths 30 and 32 in Figure 1, results in So = ko * G(Tx3) * G(Rxi) wherein ko depends on the transmission path with particles in the optical labyrinth or scatter volume, G(Tx-0 is the transmission factor of the second transmitter, and G(Rxi) is the transmission factor of the first receiver.

However, ideally, this signal is equal to zero as long as no scattering particles are present in the measurement volume and will deliver even a small signal with a low particle count. If now the sensitivity or accuracy of the measured signal via the measurement volume is to be determined, i.e., a possible change of the transmission factors of the first transmitter, G(Txl) and of the first receiver, G(Rx1) is to be determined, this cannot take place directly from the variable signal So. Instead, the values for the transmission factors of the first transmitter G(Tx./) and the first receiver G(Rx/) are indirectly estimated from the three measurements of the control signals 5/, 52 and 53 described above.

The following results are from equations (1) and (3): G(Tri) -kJ. * G(Rx2) and G (Rxi) -k3 * G(Tx2) Thus, for the product of the transmission factors in the scattered light path, i.e., of the first transmitter and the first receiver, as a measure of the sensitivity of the scattered light measurement, it is obtained: G(Txj.) * G(Rxi) = k1 * k3 G(Rx2) * G(Tx2) and by means of equation (2) it follows that 1C2 51 * 53 G(Txi) * G(Rxi) = ki * k3 S2 Thus, one can only determine a test value P from the three measured control signals 51, 52 and S3 in step 240, which provides an indirect statement about the first transmitter and the first receiver and thus via the transmission path through the measurement volume: -Si S3

P Si 53 (4) (5) (6) (7) (8) (8)

Therefore, for example, one can now evaluate the progression of this test value P over several runs of control measurements. To this end, the three control measurements 210, 220, 230 for the signals Si, S2 and 53 are to be repeated once or more times, for example at predetermined intervals. The measurement intervals may be fixed or variably adjustable. In this respect, the measurements for Si, S2 and S3 can be directly consecutive or carried out simultaneously, as already described above. Thus, one obtains a series of at least two consecutive values for the test value P. To assess the functionality of the smoke detector, both the three measurements Si to S3 individually and the test value P obtained from equation (9) can be considered. In addition, further combinations of measurements may be utilized to monitor certain functions.

The change of the test value over time can then be evaluated in step 250, e.g., by comparing the slope of a proximity function over the obtained test values with a threshold value. If the slope is above this threshold, the slope is considered sudden. Alternatively, the difference between consecutive values could also be directly considered and also compared with a threshold to detect a sudden change down or up.

Alternatively or additionally, it is also possible to define a reference value for the test value from previous measurements or as a preset and to evaluate deviations from this reference value in the test step 250. In all of these cases, the time course may additionally be taken into account; for example, if a short sudden change in the test value is detected, but all subsequent measurements again correspond to the reference result, this temporary change may be assessed differently than a change in the test value that remains at this level after a sudden increase or decrease, or is strengthened over the course of the following measurements. The latter can be evaluated as an indication of a permanent malfunction, such as a faulty soldering joint or dirt of the transmitter-receiver pair that performs the particle measurement in the measurement volume.

A strong change in a single measurement result Si, S2 or S3 may indicate interference with the transmitter or receiver involved. Optionally, this result can then also be controlled by the remaining measurements. For example, if only the first control signal Si suddenly changes sharply, this may be caused by changes of any type in the signal path 42 between the first transmitter and the second receiver, such as malfunctions of the transmitter or receiver or dirt on the transmitter or receiver.

If again the measurement result Sz hardly changes, it can be concluded that the strength of the transmit power of the transmitter Tx1 has possibly changed accordingly. This result can also be combined with the evaluation of the test value P. For example, if deviations are found in the evaluation of the test value or the individual control measurements that indicate a malfunction, an optical or audible signal may be delivered in response in step 260. Additionally or alternatively, information about the evaluation or the suspected malfunction may be transmitted to another device, such as a central controller or a computer. In addition, the evaluation can be saved in order to be able to track a time course of possible malfunctions.

Additionally or alternatively, it is possible to use the time variation of the test value to adjust and correct an evaluation 280 of the scattered light measurement 200, for example, by a variable correction factor by which the measured scattered light signal is multiplied.

Slow changes in signal quality can thus also be included in order to obtain the most correct scattered light measurement.

As the first receiver is required for at least the third control measurement 230, the scattered light measurement 200 is temporarily interrupted for this purpose according to a possible embodiment. For example, to ensure sufficient monitoring of the measurement volume, a ratio between the number of scattered light measurements and the number of additional control measurements 210, 220, 230 may be established. The scattered light measurement may be performed at intervals or continuously, wherein a short interruption of the scattered light measurement 200 may then be provided for the third measurement 230, and after the measurement the scattered light measurement is resumed from the measurement volume. For example, it could be determined that near continuous monitoring of the measurement volume by the scattered light measurement takes place between the first and the second transmitters and that these are interrupted once per minute for short control measurements.

However, generally it would also be possible to use light of different wavelengths or codings for the first and the second transmitters, for example, if both receivers are designed to also receive these two wavelengths or codings. If the receivers are then able to distinguish signals between these two wavelengths or codings, all measurements could also be taken simultaneously.

In an alternative embodiment, for example, the described control method may also be operated in a system in which two transmitters are used for particle measurement but which operate at different wavelengths to achieve different sensitivities to different particle sizes. In this case, only one receiver Rx1 can still be used for the particle measurement. The sensitivities of the required receivers Rx1 for particle measurement and Rx2 for control measurement then extend across both wavelength ranges used.

In a further alternative embodiment the described control method may also be operated, for example, in a system in which two receivers are used for particle measurement, but which, however, operate at different wavelengths, for example, by corresponding optical pre-filtering to achieve different sensitivities to different particle sizes. In this case, only one transmitter Tx1 can still be used for the particle measurement. The optical bandwidth of the Tx1 transmitters required for particle measurement and Tx2 for control measurement then extends over both wavelength ranges used.

For all measurements, uniform or modulated light signals may optionally be used. It is also possible for one or both optical transmitters to constantly send a signal, but for performing the control measurements, the receivers may only temporarily receive signals or evaluate only temporarily received signals. All measured signals, as well as intermediate values calculated therefrom, and the test value can be temporarily stored or permanently stored. It is optionally also possible to transmit stored values via a wired or wireless connection to another device, for example for permanent storage or for reading out during a functional control of the smoke detector by an external device. In other embodiments, the measured signals could also be transmitted to another device, such as a central controller, where the test values are then calculated and the evaluation of the control measurements is performed.

The arrangement of the first transmitter and receiver and the second transmitter and receiver shown in the figure serves only to clarify the principle of operation. It is to be understood that the four required optical transmitting and receiving elements may also be geometrically differently arranged and aligned as long as the described transmitting and receiving conditions are met. In particular, elements such as apertures, imaging optics and an optical labyrinth, which have already been described above in general, are not shown here. The various elements may be arranged spatially outside of only one plane. Also, the beam directions of the light source and the detection direction of the receiver will typically not only cover one direction, but rather, for example, radiation in several directions for uniform illumination of the measurement volume and detection of light from a wide detection cone in the measurement volume.

It will be appreciated that the elements and embodiments shown and described above may also be combined with one another and/or supplemented by further components and elements. The measurement and evaluation method described can also be extended or changed with additional steps. The exact design of the measurement volume, an optical labyrinth or a housing of the smoke detector does not play a role for the methods described herein, as long as the required conditions between the optical transmitters and receivers are met.

Claims (11)

1. Claims 1 A method for monitoring an optical measuring device comprising a first optical transmitter for emitting an optical measurement signal into a measurement volume and a first optical receiver for detecting an optical signal influenced by particles in the measurement volume, wherein the method comprises: detecting (210) a first optical control signal (Si) from the first optical transmitter with a second optical receiver of the optical measuring device; detecting (220) a second optical control signal (52) from a second optical transmitter with the second optical receiver; detecting (230) a third optical control signal (S3) from the second optical transmitter with the first optical receiver; calculating (240) at least one test value from the detected first, second and third optical control signals; and evaluating (250) the at least one test value for assessing the functionality of the optical measuring device.
2. 2. The method according to claim 1, wherein the test value is determined by Si * S3 P = S2 wherein P is the test value, wherein 5/ is the signal strength of the first optical control signal, wherein 52 is the signal strength of the second optical control signal, wherein S3 is the signal strength of the third optical control signal.
3. 3. The method according to claim 1 or 2, wherein the detection (210, 220, 230) of the first, second and third optical control signals (Si, 52, Ss) and the calculation (240) of a test value (P) is repeated once or more, so that multiple consecutive test values are obtained.
4. 4. The method according to claim 3, wherein the evaluation (250) of the test value comprises: determining a difference between two test values and, if the difference exceeds a threshold value, defining the functionality of the measuring device as erroneous.
5. 5. The method according to claim 3 or 4, wherein the evaluation of the test value comprises: determining a deviation of the test value from a reference value and, if the deviation exceeds a predetermined threshold value, defining the functionality of the measuring device as erroneous.
6. 6. The method according to any of the preceding claims, further comprising: performing at least one scattered light measurement in the measurement volume by detecting the optical signal from the measurement volume at the first optical receiver and correcting the result of the measurement based on the at least one test value.
7. 7. A computing unit adapted to perform all method steps of the method according to any of the preceding claims.
8. 8. A computer program that causes a computing unit to perform all method steps of the method according to any one of claims 1 to 6 when performed on the computing unit.
9. 9. A machine-readable storage medium having a computer program stored thereon according to claim 8.
10. 10. An optical measuring device comprising a first optical transmitter (Tx1) for emitting an optical measuring signal into a measurement volume (20) and a first optical receiver (Rx1) for detecting an optical signal influenced by particles in the measurement volume (20), further comprising a second optical transmitter (Tx2) and a second optical receiver (Rx2), wherein the second optical receiver (Rx2) is configured to detect optical signals from the first optical transmitter (Tx1) and from the second optical transmitter (Tx2) respectively on a direct optical path (42, 44) and to transmit the detected signals to a control unit (60); and wherein the first optical receiver (Rx1) is configured to detect optical signals of the second optical transmitter (Tx2) on a direct optical path (46) and to transmit the detected signals to a control unit (60).
11. 11. The optical measuring device according to claim 10, further comprising a control unit adapted to perform the method according to any of claims 1 to 6.