DE102005053121A1 - Particle sensor e.g. photo-acoustic soot sensor, for use in exhaust gas system of e.g. passenger car, has laser diode emitting laser radiations, and acoustic sensor partially designed as piezoelectric unit that is arranged within chamber - Google Patents

Abstract

The sensor has a laser diode (1) for emitting laser radiations (2) on a test sample, where the radiations are focused using a lens system (3) such that a light beam and/or a cross-section of laser radiations is produced in an area of an acoustic sensor. The acoustic sensor is partially designed as a piezoelectric unit (4) that is arranged within a measuring chamber (5). The chamber has two windows through which the laser beam flows in and out, and a photo-detector and/or a photo-cell is arranged behind one of the windows in a radiation direction. An independent claim is also included for an application of a quartz tuning fork unit for detecting acoustic waves as an acoustic sensor of a particle sensor.

Description

The The invention relates to a particle sensor for detecting particles, especially soot, with a radiation source for emitting electromagnetic radiation on a test sample and with a sound sensor for detecting acoustic waves according to the preamble of claim 1.

It are various measuring techniques for the measurement of soot concentrations known for different Purposes are applied. Partially this will be fixed only Particles detected by other measurements, the total mass (volatile and solid particles), some measurement techniques are particularly sensitive to size Particles (optical processes), others on small particles, which outweigh the numbers, but hardly contribute to the mass. As a result, the measured values obtained are only very difficult to compare. On the other hand, the sampling conditions a very big influence on the relationship from solid to liquid and condensed material and can lead to strong measured value fluctuations.

From the DE 200 17 795 U1 In addition, a photoacoustic soot sensor is known, which is designed as a portable sensor for photoacoustic on-line determination and permanent monitoring of soot masses or concentrations, in particular for the determination of soot in the exhaust gas.

This photoacoustic sensor can selectively measure carbon as it is the Periodically heats carbon by absorbing periodic laser radiation what about the periodic expansion and the emission of a sound wave leads. This sound wave is amplified in an acoustic resonator chamber and over Microphone measured. The intensity of the signal indicates the carbon concentration.

adversely with this sensor is that this in a 19-inch casing is fitted and weighs about 20 kg. Another disadvantage is that the resonator chamber an exact tuning of the resonant frequency As well as the optimization of inlet and Rusströmöffnungen required to these Make no noise to produce.

Task and advantages of Invention:

task the invention it is in contrast, a Particle sensor for detecting particles, in particular soot, with a Radiation source for emitting electromagnetic radiation or of photon radiation, especially of visible or infrared Light, on a test sample and with a sound sensor for detection acoustic waves, to propose, which is particularly compact or small building can be realized.

These Task is, starting from a particle sensor the introductory mentioned type, by the characterizing features of the claim 1 solved. By in the subclaims mentioned measures are advantageous embodiments and further developments of the invention possible.

Accordingly a particle sensor according to the invention is characterized characterized in that the sound sensor is at least partially formed as a piezoelectric element is. With the aid of such a piezoelectric sound sensor the particle sensor can be made particularly compact and physically small become. This allows completely novel applications for the e.g. continuous measurement of particles such as soot or the like be realized in multi-phase systems with at least one gas phase. For example, a particle sensor according to the invention may be connected to an exhaust system a vehicle, in particular a car, trucks, commercial vehicles or the like, are arranged.

Preferably meets the acoustic wave of the particles or sample directly or directly on the sound sensor. Optionally, there are several sound sensors or piezoelectric elements provided.

In Advantageously, the sound sensor or the piezoelectric element as Transducer of the emitted from the particles acoustic wave in a favorable electrical, particularly easy to evaluate signal educated. As a result, in particular, the further processing or evaluation of the signals particularly easy to implement.

For example the sound sensor or the piezoelement has a disk shape, a ring shape, a recess or cavity or the like. in this connection the sound sensor can be advantageously arranged in such a way that the particles in the immediate vicinity of the sound sensor or in Interspace or in the interior or in the recess or the cavity of the ring Arrange.

In a particular embodiment of the invention is the sound sensor within a measuring volume or within a measuring space in which the test sample is located or through which the test sample or the Sample gas flows through. The measuring volume can be smaller than with the acoustic method Resonator fail.

Advantageously, the measurement sample is a multiphase mixture having at least one gas phase, in particular air and / or exhaust gas, for example, a Ver combustion engine or the like, formed. In addition, it may well be possible that a liquid phase is also present in the multiphase mixture or in the measurement sample.

advantageously, the particles are in particular carbon black and / or Carbon particles, for example volatiles and / or as a solid and / or are formed as condensate or the like.

Preferably the sound sensor and / or the piezoelectric element at least partially one U shape on. In a U-shape is particularly advantageous that the Particles to be examined between the two legs or forks or the like during the measuring phase can be arranged in a particularly advantageous manner can.

Furthermore At least one of the legs of the "U" or a forks are dimensioned so advantageous that this is particularly sensitive to the acoustic waves or this is e.g. in Can transform kinetic energy.

In An advantageous variant of the invention is the sound sensor and / or the piezoelectric element at least partially as a quartz element educated. It has been shown that a quartz element or a Piezo element made of quartz particularly advantageous the acoustic waves the particle of the test sample in kinetic energy or in electrical Convert energy or into an electrical signal or transform can.

Farther are appropriate quartz elements particularly inexpensive to produce. In some cases, piezoelectric quartz elements are already available in many different ways Shapes and / or sizes commercially available, so that a particularly economically favorable realization of the invention possible is.

advantageously, the sound sensor is designed as an already commercially available quartz tuning fork element, so that is a particularly favorable Implementation of the invention can be realized.

In a particular embodiment The invention relates to the sound sensor and / or the piezoelectric element at least partially formed as a resonator with a resonant frequency. The formation of the sound sensor or piezoelectric element as a resonator with a resonant frequency, in particular substantially the frequency corresponds to the acoustic wave of the emitted sample, allows an advantageous reinforcement or particularly sensitive transformations of the acoustic wave in a favorable electrical signal. This allows the particle sensor according to the invention is particularly sensitive or can e.g. also very low particle concentration or soot concentrations e.g. in the exhaust gas.

It For example, it has been shown that the already commercially available Quartz tuning Fork elements have a natural resonant frequency, which corresponds very well to the frequency of the acoustic wave Particle is adapted or the acoustic wave can at their natural resonance frequency be adjusted very well. This is an elegant way a Particularly simple implementation of the invention with very high accuracy and reproducibility possible. Corresponding quartz tuning Fork elements or quartz oscillators are already with very high quality made, which makes the measurement particularly accurate.

Advantageously, an adaptation of the radiation and / or wavelength of the radiation source to the particles and / or measurement sample is provided. For example, a wavelength of the radiation source is selected, which can be absorbed particularly well by the particles or the measurement sample. For example, the wavelength of the radiation source is selected between about 500 and 1000 nm, preferably about 800 nm. A wavelength of 680 or about 800 nm advantageously avoids cross-sensitivity through NO _x , eg in the exhaust gas or in atmospheric air. Accordingly, the particle or Rußmessung can be realized exactly.

In Advantageously, a modulated radiation is provided. For example is an adaptation of the modulation to the particle and / or measurement sample and / or the sound source and / or the piezoelectric element and / or the Resonator provided so that a particularly advantageous or accurate measurement the particle or its concentration realized in the measurement sample can be.

Preferably is a radiation source, a laser, in particular a laser diode, intended. It has been shown that just with laser light or with a laser diode on the one hand very accurate measurements with the photoacoustic Particle sensor can be realized. On the other hand is through the use of a laser diode a particularly compact design the particle sensor according to the invention realizable.

Furthermore is an advantageous modulation of the laser light when used a laser or a laser diode without great effort possible. Also this simplifies the implementation of the invention in an advantageous manner.

In general, it is advantageous to form the measurement sample as an aerosol. This means in the sense of the invention, in particular a very fine distribution solid and / or volatile and / or liquid substances in at least one gas, eg a smoke and / or a mist. In the sense of the invention, an aerosol is a multiphase mixture such as, for example, exhaust gas from combustion processes, in particular from internal combustion engines or the like.

In Advantageously, a vehicle, in particular a car, has trucks or commercial vehicle, a ship or an aircraft, a particle sensor according to the invention on. Another field of application are workshop measuring instruments for emission tests (AU) and diagnosis.

One embodiment The invention is illustrated in the drawing and is based on the Figures in more detail below explained.

in the Individual shows:

1 a schematic structure of a particle sensor according to the invention and

2 three schematic representations of different arrangements or orientations of a sound sensor of the particle sensor according to the invention.

In 1 schematically the arrangement or the structure of a particle sensor according to the invention is shown schematically. A laser 1 or a laser diode 1 emits a laser radiation 2 by means of a lens system 3 is focused in an advantageous manner, so that in the region of a piezoelectric element 4 an advantageous light beam 2 or cross section of the laser radiation 2 is produced.

The piezo element 4 is inside a measuring chamber 5 arranged. The measuring chamber 5 has two windows 6 respectively. 7 on, through which the laser light 2 enters or exits. In the direction of radiation behind the window 7 is a photodetector 8th or a photocell 8th arranged that out of the measuring chamber 5 emerging, actual laser beam 2 detected. As a result, it is advantageously possible to control or adapt the particle measurement or the laser radiation actually emitted 2 can be realized according to the invention, this serves as a reference measurement.

The measurement of the particle concentration or particle mass or the like by means of the photoacoustic effect, wherein the laser radiation 2 is absorbed by the particles, in particular soot or carbon of an exhaust gas. The laser light 2 generated by the modulated or pulsed expression of the electromagnetic radiation according to periodic pressure fluctuations, directly as acoustic waves on the piezoelectric element 4 meet and at least partially stimulate this to swing.

Preferably, especially the pawls of the tuning fork or the legs of the U-shaped piezoelectric element 4 vibrated. Advantageously, the pawls of the fork or the legs of the "U" are dimensioned such that they have a resonant frequency which corresponds approximately to the frequency of the acoustic wave. As a result, an amplification of the acoustic wave or its amplitude emitted by the particles or the test sample is realized in an advantageous manner.

The piezo element 4 generates an electrical signal 9 with a frequency f, called a login amplifier 10 is supplied. In addition, the login amplifier is added 10 to eliminate interference effects, the reference frequency from the function generator 11 fed. This will cause a balance of the modulated laser light 2 and that of the piezoelectric element 4 generated electrical signal 9 realized. The expansion takes place at twice the frequency. In normal light with f = 50 Hz (eg incandescent lamp) each half-wave is used, ie the filament glows at 100 Hz, ie also the acoustic signal would have 100 Hz (2f). In the special case of the laser diode this is operated in a certain polarity, ie it is essentially turned on and off. One can not talk about an alternating voltage and half waves. Thus, the light frequency and the sound frequency are identical to the switch-on frequency.

Without further explanation, for example, exhaust gas or the like in the measuring chamber 5 flowed in and out of this again, so that, for example, a continuous or discontinuous flow through the measuring chamber 5 can be realized by the measuring sample or the measuring gas, in particular exhaust gas.

As a general rule can according to the invention a particularly accurate determination of the particles in a gas sample be determined. For example, the concentration or the Mass of the particles to be determined in the measurement sample.

Especially through the use of particularly small realizable piezo elements 4 such as by the use of so-called quartz tuning Fork elements, a particularly compact, small-scale and very accurate measurement or determination can be realized.

In 2 is shown schematically, such as the laser radiation 2 in relation to the piezo element 4 can be arranged. The variant according to 2a shows an oblique arrangement. This can also be varied so that the laser radiation 2 substantially perpendicular to the cross section of the piezoelectric element 4 is aligned.

The variant according to 2 B shows an arrangement wherein the laser radiation 2 along the legs of the U-shaped piezoelectric element or along the pawls of the tuning fork 4 impinges on the base of the "U" or on the connection area of the pawls of the fork. In principle, it is also conceivable to realize a fork with more than two pawls and to use according to the invention.

According to 2c becomes the piezo element 4 with acoustic resonators 12 provided, whereby the amplitude of the acoustic wave is advantageously amplified by resonance of the laser light. In this case, an adaptation to the quartz tuning fork element or the piezoelectric element can be advantageous 4 respectively. In general, a particularly sensitive measurement setup can be realized with such an arrangement.

In Advantageously, in a particle sensor according to the invention provided a temperature stabilization, whereby the quality or the quality the measurement can be further improved.

Advantageously, the electrical signal depends 9 or their amplitude from the content of the particles in the measurement sample or the measurement gas. The higher the amplitude, the higher the content of particles, eg soot or carbon in the exhaust gas.

In addition, the wavelength of the radiation 2 or the laser 1 adapted in an advantageous manner to the absorption by the particles or the carbon black or carbon. In addition, advantageously, the modulation frequency of the laser light 2 to the piezoelectric element 4 or the sound sensor 4 customized. For example, the laser 1 modulated at a certain frequency, substantially the resonance frequency of the piezoelectric element 4 or quartz tuning fork element 4 equivalent. The periodic absorption of the laser light 4 The presence of soot or carbon particles leads to their periodic expansion, which results in a sound wave that becomes more intense when more particles are present in the same volume of space.

The sound wave is in the piezo element 4 coupled and via login technology according to the modulation frequency of the laser 1 evaluated. The signal intensity is a measure of the carbon concentration in the volume element. About an additional measurement of the laser intensity with the photodetector 8th can be fluctuations of the laser 1 be compensated. The coupling of the signal can take place via different arrangement geometries, as for example in 2 is shown.

Claims (11)

Particle sensor for detecting particles, in particular soot, with a radiation source ( 1 ) for emitting electromagnetic radiation ( 2 ), in particular of visible or infrared light ( 2 ), on a test sample and with a sound sensor ( 4 ) for detecting acoustic waves, characterized in that the sound sensor ( 4 ) at least partially as a piezo element ( 4 ) is trained. Particle sensor according to claim 1, characterized in that the sound sensor ( 4 ) at least partially has a U-shape. Particle sensor according to one of the preceding claims, characterized in that the sound sensor ( 4 ) at least partially as a quartz element ( 4 ) is trained. Particle sensor according to one of the preceding claims, characterized in that the sound sensor ( 4 ) at least partially as a resonator ( 4 ) is formed with a resonant frequency. Particle sensor according to one of the preceding claims, characterized in that the resonant frequency of the resonator ( 4 ) substantially corresponds to the acoustic wave of the illuminated test sample. Particle sensor according to one of the preceding claims, characterized in that an adaptation of the wavelength of the radiation source ( 1 ) is provided to the particles and / or measurement sample. Particle sensor according to one of the preceding claims, characterized in that a modulated radiation ( 2 ) is provided. Particle sensor according to one of the preceding claims, characterized in that the radiation source ( 1 ) as a laser unit ( 1 ) for generating laser light ( 2 ) is trained. Particle sensor according to one of the preceding claims, characterized in that the radiation source ( 1 ) as a laser diode ( 1 ) is trained. Particle sensor according to one of the preceding claims, characterized in that the sound sensor ( 4 ) essentially as a quartz tuning fork element ( 4 ) is trained. Using a Quartz Tuning Fork Element ( 4 ) for detecting acoustic waves as a sound sensor ( 4 ) of a particle sensor for detection of particles, in particular soot, with a radiation source ( 1 ) for emitting radiation ( 2 ), in particular of visible or infrared light ( 2 ), on a test sample.