The sensor consists of two cavities, one carrying electrodes with a potential difference of about 550 volts which initiates a gas discharge when helium is present in the chamber. The discharge gas passes into a second chamber that acts as the ionization chamber and any ions formed are collected by two plate-electrodes having a potential difference of about 160 v.
Courtesy of GOW-MAC Instruments
Figure 34. The Discharge Ionization Detector
