Das Projekt "Entwicklung eines On-line Partikeldetektors" wird vom Umweltbundesamt gefördert und von Universität Duisburg, Fachbereich 9 Elektrotechnik, Fachgebiet Prozess- und Aerosolmesstechnik durchgeführt. In semiconductor technology clean process gases must be provided to manufacture large scale integrated chips. To prevent micro contamination of wafers, the process gases must be controlled by on-line detection of suspended particles. In this project the on-line particle detection is realized by means of optical method. Due to the low particle concentration, the entire cross section of the gas pipe has to be controlled. Thus it is necessary to install an illuminating plane of over 32 mm2 perpendicularly to gas flow. In clean gases paricles down to 0,1 my m must be detected. In this size range molecule noise leads to False-Count-Rate. To reduce the F.C.R. an additional illuminating plane is arranged parallel to the original one, and the F.C.R. is decreased via anew Pipeline-Cross-Correlation-Function, which is developed in this project. Using this P.C.C.F. method the influence of molecule noise on particle detection can be strongly reduced, and detection becomes possible without any dead time. To create the illuminatingplanes non-imaging optical elements are used, where beam bend is caused by reflection and diffraction exclusively. Applying computer simulation, the optical characteristics of those non-imaging optics are investigated, and it is shown that the scattered light intensity is nearly independent on local position of detected particles in the plane. The application of the non-imaging optics leads to high precision combined with low manufacturing costs. The results of optical simulation show that the pre-condition to detected particles with non-condition to detected particles with non-imaging optics in clean process gases in fulfilled, i.e. the entire gas flow is controlled, and the low detection limit is expanded down to 0,1 micron and local dependence of detector is smaller than 4 percent within measuring volume 6,4 mm x 6,4 mm. The algorithm of P.C.C.F. is based on classical cross-correlation. The difference between them is that output result from P.C.C.F. is a function of real time, t, but not a function of delaying time, t, which corresponds to the time difference between the two signals. Therefore, it is possible to set P.C.C.F. in on-line measurement. To examine the efficiency of P.C.C.F., a particle signal mixed with two acquired noise are simulated on computer. The results of simulation show that, in output process of P.C.C.F., the noise is reduced and the level of particle signal becomes higher. The signal-noise reatio is improved from one to four.
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.