Photo-ionization detector for volatile gas measurement and a method for self-cleaning the same

Abstract

A photo-ionization detector (PID) includes an ultraviolet (UV) lamp that transmits UV light into an ionization chamber to ionize volatile gases. An ion detector in the ionization chamber includes interdigital electrodes that collect resulting ions using an electrical field perpendicular to the UV light propagation. A pump in the PID circulates gases through the ionization chamber in a direction perpendicular to the electrical field and to the UV light propagation. The PID additionally provides a UV monitor having interdigital electrodes that release electrons when struck by the UV light. The size of a monitor current in the UV monitor indicates the intensity of the UV light. The UV monitor is in a UV monitor chamber that protects the UV monitor from exposure to the ionized gases and improves the accuracy of UV intensity measurements. The interdigital electrodes of the ion detector and the UV monitor can be manufactured by forming an electrode layer on a substrate and selectively patterning the electrode layer to produce interdigital electrodes. If the substrate is not transparent to UV light, the substrate can be removed or patterned to match the interdigital electrodes. To remove contamination in the PID, the pump is turned off while operation of the UV lamp continues. The UV light creates ozone that accumulates in the ionization chamber and removes contamination from the ionization chamber.