Zeroing and testing units developed for Gerdien atmospheric ion detectors

Abstract

Low current measurements in atmospheric ion detection using a Gerdien condenser are subjected to numerous sources of error. Zeroing and testing units described in this article, connected as modules to this type of detector, enable some of these errors to be found and eliminated. The zeroing unit provides digital compensation of the zero drift with a digital sample and hold circuit of 12-bit resolution. It overcomes difficulties related to zero drift and techniques used in the zero conductivity determination when the accelerating potential or airflow rate are zero. The testing unit is a current reference of nominally 10-12 A intended for testing and correcting the system on current leakage and other measuring deviations due to changes in atmospheric parameters. This unit is an independent battery-powered module, which provides a charge of 10-12 C per cycle (frequency of order 1 Hz) to the collecting electrode. The control of Gerdien devices is substantially simplified using the zeroing and testing units realized here. Both units are used during "zero conductivity" regime only. © 2005 American Institute of Physics.