Definition

A Photoionization Detector (PID) is a gas detection instrument used to measure the concentration of volatile organic compounds (VOCs) and other gases that can be ionized by ultraviolet (UV) light. In a PID, high-energy photons, typically in the vacuum ultraviolet (VUV) range, ionize gas molecules entering the detector by causing them to release electrons and form positively charged ions. The resulting ions generate an electrical current, which is measured and converted into a concentration reading.