An Electrostatic Sensor for Nanometer-Sized Aerosol Particles Detection
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In this study, an electrostatic sensor was developed for detecting the number concentration of nanometer-sized aerosol particles. It consists of a size selective inlet, a corona charger, an ion trap, a Faraday cup, an electrometer, a signal conditioning and processing system, and an I/O control and human-computer interface. In the present sensor, aerosol flow is regulated and controlled by means of mass flow meters and controllers with a vacuum pump. An aerosol sample first passes through the size selective inlet to remove particles outside the measurement size range based on their aerodynamic diameter, and then pass through the unipolar corona charger that sets a charge on the particles and enter the ion trap to remove the free ions. After the ion trap, the charged particles then enter the Faraday cup electrometer for measuring ultra low current about 10-12 A induced by charged particles collected on the filter in Faraday cup corresponding to the number concentration of particles. Finally, signal current is then recorded and processed by a data acquisition system. A detailed description of the operating principle of the system as well as main components was presented. The performance of the prototype electrometer circuit used in this work was also evaluated and compared with a commercial electrometer, Keithley model 6517A, and good agreement was found from the comparison.
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