Onetest-502 series sampler adopts coaxial cylindrical electrode design, which has the advantages of stable sampling air flow, uniform ion distribution measurement and strong anti-interference ability. It can accurately measure the positive and negative ions of small particle size existing in nature, and the high concentration of negative ions produced by the negative ion generator and its products, and show the level of air quality; At the same time, an external multi-parameter module can be selected to measure PM2.5, PM10, temperature, humidity, formaldehyde, VOC, carbon dioxide and other air quality parameters, so as to measure air quality more comprehensively. The instrument is equipped with a large-capacity rechargeable battery and a DC12V power adapter, which can be used for the measurement of outdoor time.