Overview EQMS-200 VOCs online monitoring system adopts PID (photoionization detector ) for gas detection. The target gas is irradiated I bombarded by ultraviolet light produced by the ion lamp, and is ionized after absorbing enough uv energy. The concentration of the target gas can be detected by detecting the tiny current generated after the ionization of the gas. http://www.zetian-group.com/products/eqms-200-vocs-online-monitoring-system/