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NewsProfessional knowledge Advantages and disadvantages of PID detection gas concentration technology

Advantages and disadvantages of PID detection gas concentration technology

Update time:2021.06.22

1. What is PID?

PID is the English acronym for Photo Ionization Detection-that is, "Photo Ionization Detection".

The basic principle of PID is to use the ultraviolet (VUV) generated by the vacuum discharge phenomenon of inert gas to ionize the gas molecules to be measured, and to obtain the concentration of the gas to be measured by measuring the current intensity generated by the ionized gas.

2. What are the advantages of the photoionization (PID) detection method?

    (1) High precision, which can meet the quantitative detection of low-concentration benzene;

    (2) The anti-interference is strong, and the common gas (alkane) in the petrochemical industry is not easy to affect it;

    (3) With pump-suction air intake, quick response and quick recovery;

    (4) It is a non-destructive detector, it will not "burn" or permanently change the gas to be measured.

3. Principle of PID sensor

The PID sensor is composed of main parts such as ultraviolet light source and ion chamber. There are positive and negative electrodes in the ion chamber to form an electric field.

Excited by a high-energy ultraviolet light source, negative electrons and positive ions are generated. These ionized particles form a current between the electrodes, which are amplified and processed by the detector and then output.

A current signal is output, and a concentration of ppm level is finally detected.

4. What gases can PID detect?

Mainly various synthetic unsaturated hydrocarbons and macromolecules, long-chain organic compounds.

    (1) Organic compounds containing carbon:

         ① Halogenated hydrocarbons, thiohydrocarbons, unsaturated hydrocarbons (such as olefins), etc.

         ② Aromatics: benzene, toluene, xylene (including ortho, meta, and para xylene), naphthalene, etc.

         ③ Alcohols: methyl mercaptan, propenol, n-butanol, 2-butoxyethanol, etc.

         ④ Ketones and aldehydes: acetaldehyde, acetaldehyde, acetone, acrolein, etc.

         ⑤ Amines: dimethylamine, dimethylformamide, etc.

   (2) Some inorganic gases that do not contain carbon: ammonia, semiconductor gases (such as arsenic, selenium, bromine, iodine), etc.

5. What gases cannot be detected by PID?

    PID cannot detect most of the small molecules and compounds with saturated bonds that exist in nature.

   (1) Air (N2, O2, CO2, H2O)

   (2) Common poison gas (CO, HCN, SO2)

   (3) Natural gas (methane, ethane, propane, etc.), hydrogen

   (4) Acid gas (HCl, HF, HNO3)

   (5) Freon

   (6) Ozone

   (7) Radioactive substances, etc.

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