Photo ionization detectors (PIOs) measure volatile organic compounds (VOCs) and other gases in minute concentrations.
The PIO is an efficient and relatively inexpensive detector that may produce instantaneous readings and can be operated continuously. PIOs may be used for monitoring the Lower Flammable Limit (LFL ) of atmospheres including the presence of low levels of contaminants.
However, the detection of particular products requires specific calibration. Other atmosphere tests, including for sufficient oxygen levels, should be carried out before confirming a space as being safe to enter.
How it works:
A PID uses an ultraviolet (UV) light source to break down VOCs in the air into positive and negative ions. The PID then detects or measures the charge of the ionized gas, with the charge being a function of the concentration of VOCs in the air. Note that the gas ions recombine to reform the original gas or vapor, so PIDs do not burn or otherwise permanently change the sample gas.