Television analyzer of aerosol particles images

. In the paper an aerosol image analyzer is described, which allows to obtain in three projections the main geometric and optical parameters of the aerosol particles. It is necessary for the calibration of simple optical-electronic sensors. We describe a recognition algorithm that allows real-time obtaining of data on the shape, size, and color of studying aerosols.


Introduction
Simple optical aerosol particles detector requires calibration for each types of dust or aerosol suspension. The calibration is depending on size and shape of aerosol particles.
Among various methods for determining the size and shape of suspended particles, television methods are the most informative [1,2]. Usually, one image of each particle is recorded, corresponding to its projection on a plane perpendicular to the optical axis of the light beam.
Significantly increase the information content of measurements using this method allows obtaining two or more (for more complex shapes) particle images. It leads to increasing cost and complexity of particles measurement system [3].
In this paper we propose a method of obtaining 3 projections of aerosol particles images on co-perpendicular planes simultaneously.

The analyzer description
The functional diagram of proposed analyzer is shown in the Figure 1 [4]. Dynamic injection of aerosols into the area of control is carried out by a pumping cell with a channel width of 1.5 mm and a vacuum pump. The flow speed is selected by PC program so that no more than 1 particle (50 particles per second) gets into each frame of the video signal. Control of flow speed realised by dust particle photoelectric counter (PEC), the NI PCI-6024 I/O card and personal computer (PC) which are inserted into the analyzer functional diagram. The control program conducts amplitude and frequency analysis of the input signal from the PEC for preliminary detection of the particle sizes. The control signal generated by the program comes from the PC and the NI PCI-6024 I/O board for controlling the flow speed (vacuum pump) and focusing the video analyzer camera lens.

Results
The images of dust particles are shown in Figure 4. We have to note that low measurement level by size is determinate by CCD and optic system resolution. It is proximally 1 micrometer in any dimensions. And the measuring chamber volume (aerosol concentration) is 10 5 cm 3 . Measured aerosol particles may have different shapes [5]: 1. Isometric particles. They have almost same dimensions for three axes. It can be spheres, regular polyhedral or near that. This type is most studied.
2. Plates -the particles that have long size in two axes and one short dimension. It can be petals, flakes, scales, discs etc.
3. Fibers -the particles that have long size in one axes and short in other two. It can be knits, prisms, needles, mineral fibers etc.
Applied methods of digital image processing are depended on particle shapes. The special algorithm of digital image processing is developed. The first stage of the algorithm is to classify shape of particle: isometric, plate or fiber. On the second stage every classified particle is groped by size more or less than 30 um. For each group the next operations are performing: The control program and processing algorithms was performed in LabVeiw [6]. The obtained data about size, shape and quantity of particles (about 60 parameters of particle) are stored in Excel table. These data are used for modeling and design optical-electric sensors for particular type of aerosol and dust particles. Modeling algorithms are based on Mie solution to Maxwell's equations (Mie scattering) and its variations for different shapes particles.