Optics: measuring and testing – For size of particles – By particle light scattering
Reexamination Certificate
2001-07-24
2002-12-17
Pham, Hoa Q. (Department: 2877)
Optics: measuring and testing
For size of particles
By particle light scattering
C356S338000, C356S340000, C356S343000
Reexamination Certificate
active
06496258
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
The present application is a National Stage Application of International Application No. PCT/EP00/00781, filed Feb. 1, 2000. Further, the present application claims priority under 35 U.S.C. §119 of German Patent Application No. 199 04 691.3-52 filed on Feb. 5, 1999.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an optoelectronic measuring device and a method for in-situ characterization of fluid-borne particles in the sub-micrometer size range.
2. Discussion of Background Information
A number of different methods are known and used for determining the particle quantities such as particle size and concentration. Optical methods and devices allow an in-situ determination of relevant quantities while conventional methods such as electron microscopy allow only an off-line and/or ex-situ characterization and usually require a partial suctioning of the gas flow. A known device (U.S. Pat. No. 5,815,264) allows, for instance, irradiation of the particles to be tested and imaging the elastic scattering on a two-dimensional optical detector. However, the geometrical, high-resolution imaging of the separate particles allows the determination of the particle sizes only as long as the particle size is within or above the range of the utilized radiation wave lengths. Furthermore, the process can only be used in a limited range of particle concentration because, on the one hand, the particles must be visually separable on the detector and, on the other hand, it must be ensured that at least one single particle is represented within the high enlargement to be realized and the accordingly small examination volume. Additional deficits result from the shallow focus of the optical imaging which can lead to different image scales for the various depths and, thus, to inaccuracies of the size determination.
Additionally, a device is known for determining the particle size which evaluates the emission of laser-induced plasma (U.S. Pat. No. 5,316,983). Here, the plasma emission is evaluated regarding its intensity, its spatial presence, and its time trajectory, as well as the amplitude of the sound waves induced thereby.
Another optical process that enables the determination of particle composition and particle size (European Patent EP 0 837 316 A2) by irradiating particles and subsequently evaluating the thermal radiation and the scattering inside of a laser resonator is based on the examination of the vaporizability, the determination of the particle temperature, and the ratio of elastic scattering and thermal radiation, and depends on the use of several different optical detector units and a geometrical arrangement that cannot be selected freely. Thus, resulting in a considerable constructive and technical expense which strongly limits the usability of the method and questions its economic value. An additional, principle disadvantage of an invasive method is caused in several particles being evaporated completely due to the laser impact and a subsequent physical and/or chemical analysis becoming impossible. The utilization of optical methods demands the optical accessibility of the test objects and thus relies on constructive modifications.
Several methods and devices are known for the determination of the aggregate size, for example, by means of combined measurements of scattering and extinction or the determination of elastic scattering at different angles (e.g., according to J. A. Pinson, D. L. Mitchell, R. J. Santoro, and T. A. Litzinger, SAE Technical Paper Series 932650, Society of Automotive Engineers, Warrendale, Pa., 1993), however, only one method exists for the primary particle size which enables the in-situ measuring of this quantity by evaluating the thermal particle radiation (German Patent DE 196 06 005). Common devices and methods for determining the particle concentration are usually based on the extenuation of light or the filtering and subsequent evaluation of the filter loading. Further, a method is known that allows the concentration measurement of carbon black by detecting Planck's heat radiation after laser excitement by means of a quick digital camera (Japanese Patent JP 08-094526A). However, the two-dimensional imaging method here is dependent on a perpendicular arrangement of the laser light sheet and the detector which causes a strong limitation of the usability within technical systems. No suitable in-situ methods have existed until now for the simultaneous determination of primary particle size and concentration.
The characterization of particles in the nano-scale within different technical and industrial systems are very important regarding the variety of objective configurations. For example, the industrial production of carbon black and other technical powders relies on suitable measurement methods for characterizing the product and allowing a specific processing control as well without affecting the process itself. The resulting requirements, such as a largely automated data entry and processing and the in-situ measuring of the quantities cannot be fulfilled by prior art without considerable constructive modifications of the test objects, in spite of its great technical importance.
SUMMARY OF THE INVENTION
The invention therefore provides a method and a measuring device which enables a simultaneous in-situ determination of primary particle size and mass concentration of various particles. The invention also provides a device for determining the mass concentration and/or the primary particle size which enable an easy application in different technical and industrial test objects even when an optical access is only possible from a single side.
According to the present invention, a sensor unit allows the simultaneous determination of the primary particle size and the mass concentration by evaluating the thermal radiation after a pulsed excitement. The thermal excitement can occur, e.g., by way of a high-energy laser pulse. Here, an advantageous embodiment uses short pulses with a pulse duration of about 10 ns and wave lengths in the visual range of the spectrum, such as the ones to be achieved with pulsed solid state lasers. The detection occurs, e.g., by a temporally high-resolution photo multiplier module after suitable spectral filtering, for instance, for suppressing disturbing radiation.
According to one aspect of the invention, sensor unit allows the excitement and detection by way of only one optical access which is particularly advantageous regarding optically dense media with strong absorbing characteristics and in test objects hard to access. A sufficiently strong signal can always be determined in the detection of backscattering in any optical density. Here, the spectral selection of the exciting radiation and the signal occurs by way of suitable dichroitic elements, such as mirrors with reflection and/or transmission ranges, dependent on wave lengths, outside of the test object or by way of a local separation of the rays, for instance, by a hole within a mirror reflecting entirely.
The invention also provides for a method that includes simultaneously determining the primary particle size and the mass concentration from the time signal trajectory following a thermal excitement requiring only one excitement impulse. Here, the simultaneous determination of the two quantities allows, in particular, the simultaneous evaluation of the primary particle number density as well.
Advantageous variants of the sensor unit and/or the method according to the invention are described herein. For example, the detection occurs advantageously by means of a sensor module which already integrates all essential optical and electronic components, such as imaging optics, spectral filtering, and voltage supply. This embodiment allows the adaptation of the sensor unit to the test object without any further adjustment expense in simultaneous utilization of fiberoptical components which has a deciding advantage with regard. to the practical use and the maintenance expense of the device. Additional components
Leipertz Alfred
Schraml Stephan
Will Stefan
Esytec Energie-und Systemtechnik GmbH
Greenblum & Bernstein P.L.C.
Pham Hoa Q.
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