阅读说明：本技术 用于求得测量气体的测量参数的测量装置 (Measuring device for determining a measurement parameter of a measurement gas ) 是由 H·莱因格鲁伯 W·辛德勒 K-C·哈姆斯 T·赖尼施 于 2018-12-28 设计创作，主要内容包括：本发明涉及一种用于借助于光声的方法求得测量气体(2)的测量参数的测量装置(1)。测量装置(1)具有用于测量气体(2)的流动通道(3),流动通道具有至少一个输入管路(4)、光声的测量单元(5)和输出管路(6)。测量装置(1)具有至少一个与测量单元(5)的有效频率(18)相匹配的声音滤波元件(8),声音滤波元件包括至少一个布置在流动通道(3)上的空腔谐振器(7)。(The invention relates to a measuring device (1) for determining a measurement parameter of a measurement gas (2) by means of a photoacoustic method. The measuring device (1) has a flow channel (3) for measuring a gas (2), which has at least one supply line (4), a photoacoustic measuring unit (5) and an output line (6). The measuring device (1) has at least one acoustic filter element (8) which is adapted to the effective frequency (18) of the measuring unit (5) and which comprises at least one cavity resonator (7) arranged on the flow channel (3).)

1. A measuring device (1) for determining a measurement parameter of a measurement gas (2) by means of a photoacoustic method, wherein the measuring device (1) has a flow channel (3) for the measurement gas (2), which flow channel comprises at least one inlet line (4), a photoacoustic measurement unit (5) and an outlet line (6), characterized in that the measuring device (1) has at least one acoustic filter element (8) which is adapted to an effective frequency (18) of the measurement unit (5) and which comprises at least one cavity resonator (7) arranged on the flow channel (3).

2. A measuring device (1) as claimed in claim 1, characterized in that the axis of the cavity resonator (7) is oriented perpendicularly to the axis of the flow channel (3).

3. The measuring device (1) according to claim 1 or 2, characterized in that at least one cavity resonator (7) is configured as a double-sided cavity resonator (7) having a first neck section (9) and a second neck section (10), wherein preferably the first neck section (9) is arranged opposite the second neck section (10).

4. A measuring device (1) as claimed in any one of claims 1 to 3, characterized in that the acoustic filter element has a plurality of cavity resonators (7) which open successively into the flow channel (3).

5. Measuring device (1) according to one of the claims 1 to 4, characterized in that at least one sound filter element (8) is designed for negative sound pressure amplification in a first frequency range, which comprises a fundamental frequency of the effective frequency (18).

6. Measuring device (1) according to one of the claims 1 to 5, characterized in that at least one sound filter element (8) is designed for negative sound pressure amplification in at least one second frequency range, which comprises a fundamental frequency of a multiple of the effective frequency (18).

7. A measuring device (1) as claimed in any one of claims 1 to 6, characterized in that at least one cavity resonator (7) is constructed cylindrically.

8. A measuring device (1) as claimed in claim 7, characterized in that at least two cavity resonators (7) are constructed cylindrically and have different lengths and/or different diameters.

9. A measuring device (1) as claimed in claim 7 or 8, characterized in that the length of at least one cavity resonator (7) is adjustable.

10. The measuring device (1) according to one of the claims 1 to 9, characterized in that the measuring unit (5) is arranged in a pressure-tight housing (11) to which a negative pressure and/or vacuum can be applied.

11. A method for suppressing noise interferences in a measuring device (1) for determining a measurement parameter of a measurement gas (2) by means of a photoacoustic method, wherein the measurement gas (2) is conducted through a flow channel (3) which extends over at least one inlet line (4), a photoacoustic measurement unit (5) and an outlet line (6), characterized in that at least one acoustic filter element (8) is arranged in the flow channel (3) and is set for negative acoustic pressure amplification in a first frequency range which comprises a fundamental frequency of an effective frequency (18).

12. Method according to claim 11, characterized in that at least one acoustic filter element (8) is arranged in the flow channel (3), which acoustic filter element is adapted for negative sound pressure amplification in at least one second frequency range, which second frequency range comprises a fundamental frequency which is a multiple of the effective frequency (18).

13. A method according to claim 11 or 12, characterized in that the adjustment of the filter (8) of the at least one sound comprises structurally determining and/or adjusting at least one or more of the following characteristics of the cavity resonator (7): shape, position, length, diameter, length of the cylindrical cavity resonator (7), diameter of the cylindrical cavity resonator.

14. Method according to any of claims 11 to 13, characterized in that the underpressure and/or vacuum is generated in a housing (11) to which underpressure and/or vacuum can be applied, in which housing the measuring unit (5) is arranged.

Technical Field

The invention relates to a measuring device for determining a measurement variable of a measurement gas by means of a photoacoustic method, wherein the measuring device has a flow channel for measuring the gas, the flow channel having at least one supply line, a photoacoustic measurement unit and an output line.

The invention further relates to a method for suppressing noise interferences in a measuring device for determining a measurement variable of a measurement gas by means of a photoacoustic method, wherein the measurement gas is conducted through a flow channel which extends over at least one inlet line, a photoacoustic measurement unit and an outlet line.

Background

For measurement methods in many fields of gas and particle measurement technology, photoacoustic spectroscopy (PAS) technology is used very successfully. In this case, the measurement gas (aerosol) to be examined is excited by means of an intensity-modulated laser to undergo density or pressure oscillations in an acoustically resonant measurement cell. The sound signal is received by a microphone and converted into an electrical signal.

Corresponding systems are used, for example, to determine the mass concentration [ mg/m ] of soot particles in the exhaust gas of a combustion gas³]。

The sound spectrum received by the microphone also includes undesired interference frequencies from different sources, for example flow noise of the inflowing measurement gas, engine noise or likewise different environmental noises and vibrations (structure borne sound). Here, sound mainly has the following paths:

-through the input/output line to the measuring unit as airborne or structural sound transmitted by the wall of the line;

the environment through the measuring unit, likewise as airborne sound or structure sound, for example, transmitted through the fastening device of the measuring unit.

In order to suppress interference, for example, structural sound at the measuring cell fastening can be suppressed by using damping elements, for example rubber dampers, the device housing can be provided with double walls in order to insulate the airborne sound from the environment, and potential sources of interference within the device (pumps, ventilators, etc.) can be correspondingly supported (for example by rubber dampers) or mounted in an external housing. Furthermore, the frequencies of the microphone and the subsequent amplifier may be selected, for example, corresponding to the effective frequencies. The interference factors can also be influenced in a targeted manner by suitable material selection.

Despite the variety of measures that have been taken, there is a need to further improve interference suppression. In particular, disturbances in the airborne acoustic path through the input and output lines into the PAS measurement unit are a significant problem. The greater the exhaust flow rate is selected (which helps improve power), the greater the flow noise.

Disclosure of Invention

The object of the invention is to effectively suppress interference noise even at high flow velocities and to improve the measurement accuracy and reliability of the measuring device.

This and other objects are achieved according to the invention by a measuring device of the type mentioned at the outset in that the measuring device has at least one acoustic filter element which is adapted to the effective frequency of the measuring unit and which comprises at least one cavity resonator arranged on the flow channel.

Here, preferably, the inside of the cavity resonator is connected with the inside of the flow channel. The sound filtering element effectively eliminates interference frequencies in the range of effective frequencies. As the cavity resonator, a cavity resonator which is opened toward the flow passage on one side is preferable. The desired properties of the acoustic filter can be influenced by the shape, size and, if necessary, arrangement of the individual cavity resonators relative to one another.

In connection with the disclosure of the present invention, the frequency that is evaluated for the purpose of determining the measurement characteristic is referred to as the "effective frequency". Generally, this is the resonance frequency of the measuring unit, and generally, the effective frequency coincides with the excitation frequency of the laser of the measuring unit. If necessary, the measuring units can also be operated at different effective frequencies. For example, in a measuring device for determining the mass concentration of soot particles in the exhaust gas of an internal combustion engine, an effective frequency in the range of approximately 1000 to 12000Hz is considered advantageous, wherein, however, other frequency ranges can also be used as appropriate depending on the respective application.

In an advantageous manner, the axis of the cavity resonator is oriented perpendicularly to the axis of the flow channel. This allows a simple construction of the cavity resonator, the acoustic properties of which can be determined well.

In an advantageous manner, the at least one cavity resonator is configured as a double-sided cavity resonator having a first and a second neck section, wherein preferably the first neck section is arranged opposite the second neck section. Thus, in the sound pressure curve, the peak of the negative sound pressure amplification becomes wide.

In a further advantageous embodiment, the acoustic filter element has a plurality of cavity resonators which open into the flow channel one after the other. Thereby, in the sound pressure curve, a plurality of negative peaks can be achieved at different frequencies. The exact position of the peak in the frequency curve depends substantially on the length of the resonator neck. The effect of the defined form of the cavity resonator or the defined arrangement of the cavity resonators on the sound pressure curve can be determined by corresponding conventional tests. Thus, it is feasible for a person skilled in the art, given the teachings of the present disclosure, to provide a sound filtering element suitable for a given measuring device.

In an advantageous manner, the at least one sound filter element is designed for negative sound pressure amplification in a first frequency range of the fundamental frequency, which includes the effective frequency. This purposefully reduces the interference noise in the frequency field in which the respective measuring cell is operated.

In a further advantageous embodiment, the at least one sound filter element is designed for negative sound pressure amplification in at least one second frequency range of the fundamental frequency, which comprises multiples of the effective frequency. Thus, by combining a plurality of cavity resonators, one or more frequency ranges can be effectively attenuated and suppressed.

In a preferred embodiment, at least one of the cavity resonators is designed in the form of a cylinder. The cylindrical cavity resonator is simple to manufacture and also simple to clean. In addition to designing the sound filtering element with relatively simple computational and simulation models, high accuracy can be achieved.

In an advantageous manner, at least two cavity resonators are of cylindrical design and have different lengths and/or different diameters. By using a plurality of cavity resonators with slightly varying lengths, for example, wider, but not very deep depressions or negative peaks can be achieved in the sound pressure curve.

A further advantageous embodiment provides that the length of at least one cavity resonator can be adjusted. The properties of the sound filter element can thus be adapted, for example, to changing environmental conditions (for example changing pressure, another temperature or another measured gas). For example, the length adjustment can be realized in a simple manner by means of a corresponding threaded connection.

In a further advantageous embodiment, the measuring unit is arranged in a gas-tight housing. Here, "gas-tight" means that the housing is essentially pressure-tight and can be subjected to a negative pressure and/or vacuum. For this purpose, a vacuum pump can be provided on the measuring device, with which the housing can be evacuated. This reduces the airborne sound acting on the measuring unit and reduces the interference noise transmitted on this path. According to the technical definition, a pressure level below normal pressure is called negative pressure and a pressure level below 300hPa is called rough vacuum.

In a further aspect, according to the invention, a method of the type mentioned at the outset is proposed for achieving this object, in which at least one acoustic filter element is arranged in the flow channel, which acoustic filter element is adapted for negative sound pressure amplification in a first frequency range of a fundamental frequency, which fundamental frequency comprises an effective frequency.

In an advantageous manner, at least one acoustic filter element is arranged in the flow channel, said acoustic filter element being adapted for negative sound pressure amplification in at least one second frequency range comprising a fundamental frequency that is a multiple of the effective frequency.

In a further advantageous embodiment, the adjustment of the filter of the at least one sound comprises structurally determining and/or adjusting at least one or more of the following characteristics of the cavity resonator: shape, position, length, diameter, length of the cylindrical cavity resonator, diameter of the cylindrical cavity resonator. Thereby, by using cavity resonators having known properties, such as helmholtz resonators or the like, the sound filter element can be manufactured purposefully. Furthermore, this allows a structurally and computationally simple implementation of the sound filter elements used in the method.

In accordance with a further preferred embodiment of the method according to the invention, it is provided that the negative pressure and/or vacuum is generated in a housing, in which the measuring unit is arranged, to which the negative pressure and/or vacuum can be applied.

Drawings

The invention is explained in detail below with reference to fig. 1 to 10, which show exemplary, schematic and non-limiting embodiments of the invention. Wherein:

figure 1 shows a schematic view of a measuring device according to the invention,

figure 2 shows a frequency spectrum of an example of a sound signal recorded in a measuring unit,

figure 3 shows an exemplary diagram of an acoustic filter element with a single cavity resonator,

figure 4 shows a graphical representation of the sound pressure curve determined for the sound filter element of figure 3,

figure 5 shows an example diagram of an acoustic filter element with three successively arranged one-sided cavity resonators of the same length,

figure 6 shows a graphical representation of the sound pressure curve determined for the sound filter element of figure 5,

figure 7 shows an example diagram of an acoustic filter element with three successively arranged double-sided cavity resonators of the same length,

figure 8 shows a graphical representation of the sound pressure curve determined for the sound filter element of figure 7,

figure 9 shows an example diagram of an acoustic filter element with three successively arranged single-sided cavity resonators of different lengths,

figure 10 shows a graphical representation of the sound pressure curve determined for the sound filter element of figure 9,

fig. 11 shows an exemplary diagram of an acoustic filter element with three double-sided cavity resonators of different lengths arranged one after the other, an

Fig. 12 shows a graphical representation of the sound pressure curve determined for the sound filter element of fig. 11.

Detailed Description

The main elements of the measuring device 1 are schematically shown in fig. 1. The essential components of the measuring device 1 are arranged in a protected manner in a housing 11, wherein the measuring gas 2 is fed to the measuring device 1 in a measuring gas inlet 12 and the measuring gas 2 leaves the measuring device 1 again in a measuring gas outlet 13 after the measurement. The path of the measurement gas 2 in the interior of the measurement device 1 is defined by a flow channel 3, which extends from a measurement gas inlet 12 to a measurement gas outlet. The flow channel 3 guides the measurement gas 2 through a photoacoustic measuring cell 5, in which the measurement gas is excited in a known manner by means of pulsed or modulated laser radiation.

Thereby, the flow channel 3 can be divided into three sections: an inlet line 4 from the measurement gas inlet 12 to the measurement cell 5, a flow path 14 which leads through the measurement cell and is delimited by the measurement cell and an outlet line 6 which extends from the measurement cell 5 to the measurement gas outlet 13.

In order to reduce the transmission of structural sound from the housing 11 to the measuring unit 5, the measuring unit 5 is mounted on a damping element 15 (e.g. a rubber cushion).

The damping element 15 damps vibrations acting on the housing 11 from the outside and ambient noise. In order to also reduce the airborne sound acting on the measuring cell 5, a vacuum pump 16 can be used to generate a negative pressure or vacuum in the interior of the housing 11. The higher the quality of the vacuum, the more effectively airborne sound can be suppressed.

Alternatively or additionally, additional acoustic elements, for example a helmholtz resonator 17 (if appropriate also a plurality), can also be arranged in the interior, with which a reduction in the noise level in a defined frequency range can be achieved. The helmholtz resonator 17 is preferably tuned in such a way that interference frequencies in and near the effective frequency of the photoacoustic measurement unit 5 are absorbed.

In order to reduce the sound transmission through the line elements of the flow channel 3 in the structure sound path, the flow channel can have at least partially a flexible tube (for example made of a material) Silicone, etc.). In this way, the frequency range of the sound used and heard can be excluded as much as possible (<10kHz) on the structure acoustic path.

Disturbances which merely reach the measuring unit 5 on the airborne sound path via the inlet line 4 and the outlet line 6 can hardly be effectively overcome by the measures described above and are therefore a great problem. This interference is usually a broadband interference which also partially contains the useful frequency(s) and thus contributes to the measurement value noise. As a source of these disturbances, flow noise is dominant, except for the engine noise itself (transmitted through the exhaust and exhaust systems). Flow noise is generated at all edges, cross-sectional variations, flow obstructions, etc., i.e., mainly on components such as valves, distributors (spliters), baffles or filters. The higher the exhaust flow rate, the higher the flow noise. However, in order to increase the dynamics of the measurement, it is desirable to increase the exhaust gas flow rate, which also increases the flow velocity in the flow channel 3.

In particular in mobile measuring devices, the transmission of disturbing sound through hoses is problematic due to the compact design and the low weight. This noise is particularly pronounced when large flows (for example above 6l/min) pass through the measuring chamber 5.

In this connection, it should also be taken into account that the sound properties of the flow channel (not only in the supply line 4, but also in the measuring unit 5 and in the discharge line 6) cannot be varied at will, since here too possible negative effects have to be taken into account. In order to be able to take into account, for example, the ventilation time (rise time/fall time) of the internal combustion engine in the measurement results, a shape of the flow channel 3 that is as slender as possible is preferred, for example, which shape is as constant as possible, mainly in the region of the feed line 4 and/or the discharge line 6, and in particular is free of a buffer volume or widening of the flow channel 3. In other words, the flow channel 3 has a constant cross section in the region of the feed line 4 and/or the discharge line 6 and no buffer volume. In this case, a "region" is to be understood in particular to mean a section which corresponds to a multiple of the cross section of the flow channel 3. This is, for example, a section of the flow channel 3 which is at least three times the cross section at the measurement gas inlet 12, on the inlet line 4, and a section of the flow channel 3 which is at least three times the cross section at the measurement gas outlet 13, on the outlet line 6. In particular, impermissible changes in the cross section in the feed line 4 (and possibly also in the discharge line 6) must be avoided. In particular, a cross-sectional change is considered "impermissible" if it changes the time profile of the volume flow in the region of the measuring cell 5 so strongly in relation to the profile originally present at the measuring gas inlet 12 that the permissible measurement tolerance is exceeded or possibly exceeded at a specific time.

In order to minimize the influence of the flow on the airborne sound path through the flow channel 3 to the measuring unit 5, an acoustic filter element 8 is provided in the feed line 4, which is designed for negative sound pressure amplification in at least one frequency range that is matched to the effective frequency. The acoustic filter element 8 comprises at least one, preferably a plurality of, cavity resonators 7 arranged on the flow channel 3, of which preferred embodiments are exemplarily described below. Embodiments of one or more cavity resonators are selected such that the cavity resonators as a whole constitute a notch or band-stop filter for sound. The properties of the acoustic filter element defined by the cavity resonator/resonators 7 can be matched by variations in the shape and size of the cavity resonator 7, in particular its length l and diameter d.

Alternatively or additionally, the second sound filter element 8' may be arranged in the flow channel 3 in the region of the outlet line 6. The second sound filter element 8' may be identical to the first sound filter element 8 in terms of its dimensions and characteristics, however, the two may also be designed differently, when this is advantageous due to different dimensions or pipe diameters.

The desired characteristics of the sound filter element 8 (and of the second sound filter element 8') are described next in connection with fig. 2. Fig. 2 shows the frequency spectrum of the sound signal recorded by the measuring unit 5. The measuring cell 5 is excited by an effective frequency 18, wherein the signal strength at the effective frequency 18 is evaluated for determining a measurement variable of the measurement gas 2. The frequency spectrum can be substantially divided into three band ranges, a low range I up to frequencies of 3900Hz, a band range II in the middle of frequencies between 3900Hz and 5100Hz, and a high band range III of frequencies above 5100 Hz. The middle band range II includes an effective frequency 18, which in this example is about 4100 Hz.

In order to reduce the disturbing influence of noise in the middle band range II, a band-stop filter is used as the sound filter element 8, which attenuates the frequencies in the middle band range II, as can be seen clearly in the course of the frequency line.

As sound filter elements 8, 8', a comparatively simple arrangement of cylindrical cavity resonators 7 is preferably used, the cavity resonators 7 opening into the flow channel 3 transversely to the flow direction.

The applicant of the present invention studied the effect of such a cylindrical cavity resonator 7 on the sound pressure level with respect to frequency. The aim is to adapt the acoustic filter element 8 in such a way that the noise level is reduced in the region of the effective frequency 18 in the relevant measurement range and is as low as possible for large and small throughflows. In this connection, a 3D simulation is carried out with the simulation software COMSOL to better understand the basic properties of such a sound filter element 8 and to develop a method for designing such a sound filter element 8.

The simulation results are shown in fig. 3 to 12, together with the used sound filter element and the sound pressure distribution calculated therefrom.

Series simulations are performed based on a plurality of models each defining a particular geometry of the component. Only cylindrical cavity resonators are used, respectively. The calculation of the sound pressure curve and other sound parameters is performed over a frequency range of 20Hz to 16000Hz, and the sound pressure level is plotted in logarithmic relation to the sound pressure.

The first sound filter element 8 studied is shown in fig. 3, and the corresponding sound pressure curve is shown in fig. 4. The diameter of the flow channel 3 is constantly 4 mm. The cylindrical cavity resonator 7 protruding from the flow channel perpendicularly to the flow channel 3 has a diameter of 5mm and a length of 21mm (measured from the axis of the flow channel 3). By this configuration, a sound filtering element with two groove-shaped negative peaks of sound pressure amplification is achieved, wherein the peaks are at about 4100Hz and at 12900 Hz.

Fig. 5 shows the second sound filter element 8 studied, and fig. 6 shows the sound pressure curve determined accordingly. The diameter of the flow channel 3 is constant 4 mm. The sound filter element 8 of fig. 5 has three identical cylindrical cavity resonators 7 arranged one on each side on the flow channel 3 and having a length of 21mm each. The distance between two cavity resonators 7 arranged side by side is 10.5mm and the diameter is 4mm each. The sound pressure curve of this configuration has two negative peaks, which are arranged substantially at the same positions as in the first filter of fig. 3, however it can be seen that the two peaks are wider and the damping effect is clearly more strongly pronounced.

Fig. 7 shows the third sound filter element under consideration, and fig. 8 shows the correspondingly determined sound pressure curve. The diameter of the flow channel 3 is constant 4 mm. The acoustic filter element 8 of fig. 7 has three identical cylindrical cavity resonators 7 arranged on the flow channel 3. The cavity resonator extends on both sides of the flow channel 3, wherein a shorter second neck or neck section 10 is opposite to the longer first neck or neck section 9. The first necks 9 are 21mm long and the second necks 10 are 10.5mm long, respectively. The distance between two cavity resonators 7 arranged side by side is 10.5mm and the diameter is 4mm each. Compared to the sound pressure curve of the investigated second sound filter element 8 shown in fig. 6, the sound pressure curve of this configuration has an additional negative peak, which lies between the two (surviving) preceding peaks, at about 9200 Hz. The peak in the middle is configured to be significantly wider than the peaks on both sides.

Fig. 9 shows the fourth sound filter element 8 under consideration, and fig. 10 shows the sound pressure curve determined accordingly. The diameter of the flow channel 3 is constant 4 mm. The sound filter element 8 of fig. 9 has three cylindrical cavity resonators 7 arranged one on each side on the flow channel 3, each with a slightly different length of 23mm, 21mm and 19 mm. The distance between two cavity resonators 7 arranged side by side is 10.5mm and the diameter is 4mm each. The sound pressure curve of this configuration has two distinct negative bandwidths extending between about 4000Hz to about 5000Hz and between about 11900Hz to about 15000 Hz.

Fig. 11 shows the fifth sound filter element 8 under consideration, and fig. 12 shows the correspondingly determined sound pressure curve. With respect to the filter element shown in fig. 9, on the one hand the distance between the cavity resonators 7 is increased to 21mm in each case, and each cavity resonator 7 is supplemented by an opposite second neck or neck section 10. The lengths of the second necks 10 are 10.5mm, respectively. Other parameters remain unchanged. This configuration also achieves two clearly negative bandwidths, which are located essentially at the same locations as in the above example in fig. 10. Additionally, one of the very distinct peaks is at about 9200 Hz.

In addition to the 3D simulation set forth above, the calculations are repeated from a highly simplified two-dimensional model and the results compared to each other. It has been shown that the results of 3D simulation and 2D calculation are essentially equivalent in quality, except for the scaling factor.

This shows a significant advantage of the acoustic filter element 8 according to the invention based on a simple cylindrical cavity resonator 7, since the filter characteristics can be designed in a first step from a simple 2D model. The found optimal configuration can then be checked on the basis of more complex modeling (for example in a simulation on the basis of a 3D model) or likewise tested in an actual implementation. (for example, the measurement results of such a practical implementation are shown in FIG. 2 and have been explained in connection with the description of the figures).

In order for those skilled in the art to practice the invention in practice, the inventors have concluded from simulations and calculations that:

the exact position of the peak depends substantially on the length of the resonator neck.

The depth (or height) of the peak depends on the number of resonators.

By using more resonator necks with slightly variable length, a wider, but not very deep, recess is achieved.

By varying the radius and diameter, and varying the distance between the necks, additional slight movements can be achieved, however, these parameters play a minor role.

List of reference numerals

1 measuring device

2 measuring gas

3 flow channel

4 input pipeline

5 measuring cell

6 output pipeline

7 cavity resonator

8 Sound Filter element

9 first neck section

10 second neck section

11 casing

12 measurement gas inlet

13 measuring gas outlet

14 flow path

15 damping element

16 vacuum pump

17 Helmholtz resonator

18 effective frequency