Digital pulse analyzer for simultaneous measurement of pulse height, pulse width, and interval time on an optical particle counter

Abstract

This study examined the development of a digital pulse analyzer (DPA) used for obtaining the pulse height distribution (PHD), pulse width distribution (PWD), and interval time distribution (ITD) simultaneously by processing output signals from an optical particle counter (OPC). The characterization was performed by testing the response of the DPA as a function of its input frequency and pulse height using dummy signals from a signal generator (model DG1022, Rigol Technologies Inc., People's Republic of China) and actual OPC signals (Model KC-03, Rion Co. Ltd, Japan). Polystyrene latex particles of various sizes yielded by a scanning mobility particle sizer were used during the calibration of the DPA. It was found that the geometric mean of the PHDs was in accordance with Mie theory and could be used for converting pulse height into data which represents the size of particles. Furthermore, by using the PWD and ITD, we could estimate the viewing volume and dead time of the OPC. The DPA could successfully discriminate particles from baseline noise or voltage spikes by applying a novel algorithm to detect pulses based on the pulse area (integral of the voltage–time curve). The results showed that the ranges of particle diameter, viewing volume, and dead time measured by the OPC-DPA system were 0.2–1 µm, (0.78 ± 0.09) mm3, and (45.9 ± 12.6) µs, respectively. The new algorithm can be applied to pulse height analyzers in general, in the measurement of aerosol particles or scintillator-based particle detectors.