A data processing system, consisting of a peak detector, an AD-converter and a minicomputer was developed, which enables the simultaneous counting of particles with different diameters. A computer program was written to handle the output of data in groups of 1, 2, ..., 1024 channels. The maximum number of particles that can be counted in a single channel (1024 mode) is 16777215. The resolving time of the system was determined from oscilloscope photographs of pulses generated by monodisperse PSL and DOP particles and amounts to about 15 μsec. The optical counter was calibrated for the size range 0.3-9 μm with monodisperse PSL and DOP aerosols. The response curve is non-singular in between 0.8 and 1.4 μm. The ratio between the standard deviation (σK) and the median (Kg) of the channel number distribution for monodisperse aerosols decreases continuously with increasing Kg from 0.7 (at 8) to 0.04 (at 922). Count losses due to coincidence and pulse processing were calculated. Completely ambiguous results have to be expected for concentrations higher than about 450 particle cm-3. © 1979.
