A new particle sensor based on true RMS value measurement

Direct-reading instruments which can provide real-time PM2.5 measurements are widely used because they are cheap and easy to use. However, these direct-reading instruments suffer from zero drift problems and have to be calibrated before use. Direct-reading instruments based on average value measurement can't give a correct assessment of PM2.5 mass concentrations when particles' diameter changes greatly. In this paper, a new particle sensor based on true RMS value measurement is designed. Three photodiodes are installed in the sensor at different scattering angles. The advantages of true RMS value measurement method are demonstrated from theory consideration. Field experiments have shown that: (1)PM2.5 mass concentrations based on true RMS value measurement are better than based on average value measurement, (2)PM2.5 mass concentrations got from different scattering angles are highly correlated, (3)this new particle sensor can achieve reasonable accuracy for running more than 120 hours.