MODIFICATION OF THE TSI-3025 CONDENSATION PARTICLE COUNTER FOR PULSE-HEIGHT ANALYSIS

Ultrafine particle sizes may be measured over a limited range with an ultrafine condensation particle counter (UCPC) by analyzing photodetec tor pulse heights. The pulse height analysis (PHA) technique has been employed successfully in our laboratory with a prototype UCPC. However , attempts to incorporate PHA into a commercial UCPC (the TSI model 30 25) met with initial lack of success, yielding anomalous and irreprodu cible pulse height spectra. Operating parameters and subsystems of the commercial UCPC, including condenser/saturator temperatures, aerosol flows, optical system (light source and detector), and post-photodetec tor electronics, were examined for contributions to the observed pulse height spectra. The optical system, specifically the light source and scattering geometry, was found to be the cause of the anomalous pulse height performance. Replacing the existing 90 degrees scattering, las er light-photodiode detection system with a forward-scattering, white halogen light source and photodiode from an older condensation particl e counter (the TSI 3020) resulted in satisfactory pulse height respons e from the instrument, allowing pulse height analysis with the commerc ially available UCPC.