Photo Ionization Detectors (PID)
A Photo-Ionization Detector measures VOCs and other toxic gases in low concentrations from ppb (parts per billion) up to 10,000 ppm (parts per million or 1% by volume). A PID is a very sensitive broad-spectrum monitor, like a low-level LEL monitor. All elements and chemicals can be ionized, but they differ in the amount of energy they require. The energy required to displace an electron and "ionize" a compound is a called its Ionization Potential (IP), measured in electron volts (eV). If the IP of the sample gas is less than the eV output of the lamp, then the sample gas will be ionized.