Das Projekt "Grundlagenuntersuchungen zur Messung von Fein- und Feinstpartikeln in Emissionen und bei der Partikelabscheidung" wird vom Umweltbundesamt gefördert und von Universität Kaiserslautern, Fachbereich Maschinenbau und Verfahrenstechnik, Lehrstuhl für Mechanische Verfahrenstechnik und Strömungsmechanik durchgeführt. Das Vorhaben hat zum Ziel, ein Messverfahren fuer die Groessenanalyse partikelfoermiger Emissionen zu entwickeln. Die Partikelkollektive in Emissionen enthalten sowohl submikrone als auch groebere Partikeln, typischerweise ist ein Groessenbereich zwischen 10 nm und 25 Micrometer relevant. Prinzipiell koennen Groessenanalysen von Aerosolpartikeln in diesem Bereich mit optischen Partikelzaehlern und mit der Beweglichkeitsanalyse durchgefuehrt werden, wobei aber keines dieser Analysenverfahren allein in der Lage ist, den gesamten Groessenbereich zu erfassen. Aus diesem Grund ist es zwingend notwendig, die Messergebnisse mehrerer Analysegeraete in geeigneter Weise zu kombinieren, um die gewuenschte Information ueber die Groessenverteilung des gesamten Ensembles zu erhalten. Abgeleitet aus dem heutigen Kenntnisstand bieten sich als Analysegeraete fuer die Teilbereiche an: Ein differentieller elektrischer Mobilitaetsanalysator, ein Laser-Aerosolspektrometer und ein optischer Partikelzaehler (Weisslichtgeraet). Diese Geraete sind zu einer Einheit zusammenzuschalten.
Das Projekt "Signalverarbeitung fuer optische Partikelzaehler" wird vom Umweltbundesamt gefördert und von Universität Duisburg, Fachbereich 9 Elektrotechnik, Fachgebiet Prozess- und Aerosolmesstechnik durchgeführt. Optical particle counters (OPC) allow the determination of the particle number concentration and the size distribution. Instruments of different design are commercially available. One of the most important application areas of OPCs is clean technology. The development in clean technology is characterized by a drastic reduction in the allowed number concentration and the critical particle size which determines the lower size detection limit. With decreasing number concentration and decreasing lower detection limit the problem of false signals becomes more and more important. In the past a lot of effort has been put in redesigning the sensor of OPCs resulting in improved instrument behavior. Less effort has been put in improving the signal processing leading to a better SNR. Depending on the trigger level at a low SNR the particles might not be detected or the noise might cause false counts. The detection limit as well as the number of false pulses can be lowered by increasing the SNR. A higher amplification of the signal, thought as a possible solution, reduces the band width of the amplifier, which limits the flow rate. An additional effect caused by higher amplification may be that the noise level increases. If a flow false count rate is very important, the trigger level for detection has to be increased causing the instrument to become less sensitive. In this case the smallest detectable particle size increases. In this project a solution is worked out for optimizing the SNR for given OPCs. With the help of signal theory a correlation receiver was developed, which supplies a maximum SNR at the output. This receiver was realized in digital technology. It permits the on-line filtration of the particle signals for any commercial OPC. The results show a clear improvement in the SNR, which however, depends on the individual OPC. For a clean room monitor a gain of g gleich 2.06 gleich 6.28 dB was achieved, which means a reduction of the lower detection limit from 500 nm to a theoretical 421 nm with a constant false count rate. But the experiments have shown that it is possible to measure even 380 nm latex particles with security. With an unchanged lower detection limit false countings can be excluded with a security of more than plus minus 6 minus. On the whole it has been shown that in the field of optical particle measurement technology it is still absolutely possible to achieve considerable improvements and more research in the future is needed.
Das Projekt "Untersuchung des Rauschverhaltens von optischen Partikelzaehlern" wird vom Umweltbundesamt gefördert und von Universität Duisburg, Fachbereich 9 Elektrotechnik, Fachgebiet Prozess- und Aerosolmesstechnik durchgeführt. In many production systems and in research the measurement of particles gains more and more importance. With increasing technological advances smaller particles will gain importance. The areas which require reduced particle concentration are for example the semiconductor industry, the food production and the medicine technique. For particle measurements optical particle counters are often used. To fulfil the requirements these particle counters have to be improved. Goals are obtaining an enhancement of the accuracy of size analysis, a higher security of counting and a reduction of the detection limit with regards to the particle diameter. These demands can be met with the improvement of the signal processing. The signal processing of optical particle counters must detect the particle signal in the composite signal. The composite signal consits of the noise and the particle signal. The limit of the particle detection is set by the particle concentration and by the noise. The noise in the signal affects the signal processing in different ways. The amplitudes of the particle signals are stochastically falsified and it results in a wider particle frequency distribution. If the amplitude of the noise is greater than the threshold then the noise is counted as a particle. This effect occurs near the lower detection limit regarding to the particle diameter. To improve the signal detection a digital signal processing has to be developed which uses the features of the composite signal to minimise the signal to noise ratio. The essential condition for this development is to characterise the composite signal. The magnitudes are described with their moments of the distribution. The noise consists of - the noise of the electronics - the scattering light from molecules and - the scattered light from surfaces. The noise of the electronics has mostly thermal sources. The scattering light of molecules interacts with the molecules in the measuring cell. The number of molecules are function of the temperature, the gas species and the pressure. The scattered light from surfaces is produces from the lighttrap and the optics. The characteristics in the distributions of the noise and the particle signals, which are the same in all optical particle counters, have to be investigated. To detect the characteristics of the noise in optical particle counters the parameters temperature, gas species, pressure and the surface must be varied. With the investigation of the noise behaviour a digital signal processing system which improves the optical particle counter can be developed.