What is pid on a gas monitor?
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PID is a sensor technology in a gas monitor, Photo Ionization Detector (PID), which uses the high energy of ultraviolet photons to ionize gaseous substances, and then measures the weak electric current generated by the ionization of the substances to calculate the total amount of ionized gas in the air.
Working Principle
Photo-ionization (PID) sensor, the principle is simple, is the use of a high-voltage alternating electric field, so that some inert gases ionized to produce ultraviolet light, ultraviolet light energy than the visible light to higher, it will ionize the gas into a positively charged ions and negatively charged ions, and then we use the electronic method to detect the number of these ions, so as to determine the concentration of the gas being measured.
PID is capable of detecting compounds, especially volatile organic compounds (VOCs), at the parts per billion (ppb) to parts per million (ppm) concentration levels. It complements non-dispersive infrared, electrochemical, and catalytic combustion gas sensors, and is one of the more technically advanced and expensive gas detectors.
How is a PID sensor constructed?
Its structure consists of a UV light source, a pair of high-frequency electric field generators, a pair of electron-collecting electrodes, and a set of weak current-to-voltage circuits. The UV light ionizes the gas, which releases electrons, which are collected by the electron collection electrodes, and then turned into a voltage signal that can be recognized by an analog-to-digital converter by the weak current-to-voltage circuit.
Not all gases can be ionized, but most VOCs are easily ionized, and that's because the ionization energy is relatively low.
PID is mainly used for volatile organic compounds detection
(1)Aromatic: series of compounds containing benzene ring, such as: benzene, toluene, ethylbenzene, xylene, etc;
(2) Ketones and aldehydes: compounds containing C=O bonds. For example: acetone, butanone (MEK), formaldehyde, acetaldehyde, etc;
(3) Amines and amino compounds: N-containing hydrocarbons. For example: diethylamine, etc;
(4) Halogenated hydrocarbons: e.g. trichloroethylene (TCE), perchloroethylene (PCE), etc;
(5) Sulfur-containing organics: methyl mercaptan, sulfides, etc;
(6) Unsaturated hydrocarbons: butadiene, isobutene, etc;
(7) Saturated hydrocarbons: butane, octane, etc;
(8) Alcohols: isopropyl alcohol (IPA), ethanol, etc.
Selectivity and sensitivity:
PID can detect VOCs at the PPM level very accurately and sensitively, but cannot be used to qualitatively differentiate between different compounds. When using PID, special attention should be paid to the calibration factors (CF, also called response factors), which represent the sensitivity of measuring a specific VOC gas with PID, and it is used in that after calibrating PID with one gas, the concentration of another gas can be directly obtained through CF, thus reducing the trouble of preparing many kinds of standard gases.
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