How does a PID sensor work?

PID is the abbreviation of Photo Ionization Detector. PID sensor is a common gas sensor, which is widely used in environmental monitoring, industrial production and other fields. This article will introduce How does a pid sensor work?

Industrial PID TVOC Sensor FS4PIDTVOC (7)
Industrial PID TVOC Sensor FS4PID/TVOC

How does a PID sensor work?

A PID uses an ultraviolet (UV) light source to “break” organic matter into positive and negative ions (ionization) that can be detected by a detector. The molecular fragments and electrons that are formed are positively and negatively charged, generating an electric current between two electrodes. The detector amplifies the current and displays the “PPM” concentration. After being detected, the ions recombine to become the original gas and vapor.

PID is a non-destructive detector, it does not “burn” or permanently alter the gas to be measured so that the gas detected by the PID can still be collected for further measurement.

Ionisation potential

All elements and compounds can be ionized, but the energy required to replace an electron in an element, i.e. to ionize a compound, is called the ‘ionization potential’ (IP) and is measured in electron volts (eV). The energy emitted by a UV lamp is also measured in eV.

If the IP of the gas to be tested is lower than the output energy of the lamp, then the gas can be ionized.

Benzene has an IP of 9.24 eV and can be “seen” by a standard PID (with 10.6 eV). Methylene chloride has an IP of 11.32 eV and can only be “seen” by a PID with 11.7 eV. Carbon monoxide, with an IP of 14.01 eV, cannot be ionized by a PID. The IP values for each substance can be found in various chemistry manuals.

Industrial PID TVOC Sensor FS4PIDTVOC (5)
Industrial PID TVOC Sensor FS4PID/TVOC
Industrial Grade PID Benzene Sensor FS4PIDC6H6 (4)
Industrial Grade PID Benzene Sensor FS4PID/C6H6

What substances can PID actually measure?

A large number of what can be detected by PID are organic compounds containing carbon. This includes:

– Aromatics: Series of compounds containing the benzene ring, e.g. benzene, toluene, naphthalene, etc.

– Ketones and Aldehydes: Compounds containing a C=O bond. Examples include acetone, methyl ethyl ketone (MEK), acetaldehyde, etc.

– Ammonia and amines: N-containing hydrocarbons. Examples include diamine, etc.

– Halogenated hydrocarbons: e.g. trichloroethylene (TCE), perchloroethylene (PERC), etc:

– Sulphides:

– Unsaturated hydrocarbons: e.g. butadiene, isobutylene, etc.

– Alcohols: e.g. isopropyl alcohol (IPA), ethane, etc.

– Saturated hydrocarbons: In addition to organics, PID can also measure some inorganic gases that do not contain carbon:

– Ammonia

– Semiconductor gases: arsenic, phosphine, etc., and

– Hydrogen sulfide

– Nitric oxide

– Bromine and iodine, etc.

Which substances cannot be measured by PID?

Radioactivity, air (N2, O2, CO2, H2O), common poisonous gases (CO, HCN, SO2), natural gas (methane, ethane, etc.), acid gases (HCl, HF, HNO3), Freon gas, ozone, non-volatile gases, etc.