Recently, condensation particle counters have been applied in the rapidly changing number concentration measurements. In ad-dition to cut-off size, a dynamic characteristic as time constant becomes important. It shows a time scale of the fastest possible changes in concentration to be measured by the instrument. In this study, the time constant of the condensation particle counter TSI 3010 was determined to be 0.83, 0.56, and 0.40 s at 1,2, and 3 1pm sampling flow rates. In increasing the flow rate, the time constant of the instrument decreases. Changes in cut-off sizes due to changes in the sampling flow rate at various temperature differences were studied. The experiments showed that the CPC TSI 3010 has almost the same cut-off size at the default (1 lpm sampling flow rate and 17 deg difference between the temperatures of the condenser and sat-urator chambers) settings as at a 3 1pm sampling flow rate and 23 deg difference. The CPC TSI 3010 response to the step and sinusoidal changes in number concentration are analyzed. The increasing sinusoidal oscillation frequency attenuates the CPC output. At 1/2 Hz frequency the CPC TSI 3025 is able to register almost the full amplitude of oscillations, while the CPC TSI 3010 attenuates around half of the amplitude.
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