Accelerated durability test of a condensation particle counter with high particle loading

We investigated changes in particle detection performance of a condensation particle counter (CPC) for automobile exhausts (model 3790, TSI Inc.) during an accelerated durability test with high particle loading. The CPC was exposed to carbon particles for over 100 h with a mode diameter of 80 nm at a number concentration of 106 cm−3, i.e., 100 times more than the maximum of the designed concentration range of the CPC specified by the manufacturer. This was equivalent to exposure at the designed maximum concentration (i.e., 104 cm−3) for five years. The detection efficiencies of the CPC evaluated regularly at 23, 41, and 55 nm during the test remained unchanged, which indicated that the particle loading was less than the level at which the performance of the CPC would be degraded by contamination of the interior of the CPC. Based on this observation, it was concluded that the changes in the detection performance of our customers׳ CPCs, which we observed occasionally during annual maintenance and recalibration, were due to causes other than particle loading within the designed concentration range. The unchanged detection efficiencies in our test of exposure equivalent to five years suggest that yearly calibration should be sufficient for maintaining the measurement accuracy of a CPC if it is operated under normal conditions.