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1 Detected substances
Detectors equipped with photoionization sensors are used for measuring and detecting the present gas
substances, whose energy of ionization is lower then 10.6 eV. They are mostly volatile organic compounds
(VOC).
Examples of VOCs that can be detected by a PID sensor equipped with a 10.6 eV lamp:
Aliphatic hydrocarbons – e. g. pentane, octane, hexane,
Aromatic hydrocarbons – e. g. toluene, xylene, benzene,
alcohols – e.g. ethanol, propanol,
aldehydes, ketones, esters,
amines, sulphides,
others, including: aviation fuels, petrol, and some inorganic compounds.
PID sensors can also be equipped in e. g.: a 11.7 eV lamp, which, besides the substances enumerated above,
is able to detect such substances as: methanol, acetylene or formaldehyde. This lamp has a very short life
span (approx. 1 week).
2 Principle of operation
The principle of operation of the PID sensor is based on the phenomenon of photo-ionization. In the PID
sensor, the gas passes through the UV beam generated by the lamp energized by the current source. UV
radiation leaves the lamp through the window. The emission of electrons occurs as a result of a collision of
a photon having a higher energy than the ionization energy of the volatile compound. The voltage between
the electrodes causes a stream of positive ions and negative ions that will flow in opposite directions. At
that point, a current with intensity proportional to the gas concentration will appear in the circuit.
A properly amplified signal will provide information about the gas concentration.
Figure 1: Schematic diagram of the photoionization sensor
Atest-Gaz A. M. Pachole sp. j.
ul. Spokojna 3, 44-109 Gliwice, Poland
VAT No.: PL 9691433231
tel.: +48 32 238 87 94
fax: +48 32 234 92 71
e-mail: contact@atestgaz.pl
p. 2/4 Appendix: PU-Z-034-ENG R02
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M+ e-
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U
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UV lamp
Current source
Window
Cations and electrons
Amplifier
Electrodes
Potential
difference