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PID - VOC Gas Detectors

PID Detectors - Using Photo-ionization Detectors to Measure VOCs

Photoionization detectors use high-energy ultraviolet light from a lamp housed within the detector as a source of energy used to remove an electron from neutrally charged VOC molecules, producing a flow of electrical current proportional to the concentration of contaminant.

The amount of energy needed to remove an electron from the target molecule is called the ionisation potential (IP) for that substance. The larger the molecule, or the more double or triple bonds the molecule contains, the lower the IP. Thus, in general, the larger the molecule, the easier it is to detect! This is exactly the opposite of the performance characteristics of the catalytic hotbead type combustible sensor.

Photoionization detectors are easily able to provide readings at or below the OEL or TLV® for all of the VOCs listed in Table 1, including diesel. The best approach to VOC measurement is often a multi-sensor instrument equipped with both LEL and PID sensors
Multi-sensor Detectors with PIDs Catalytic hot-bead combustible sensors and photoionization detectors represent complementary,
not competing detection techniques. Catalytic hot-bead sensors are excellent for the measurement of methane, propane, and other common combustible gases that are not detectable by means of a PID. On the other hand, PIDs can detect large VOC and hydrocarbon molecules that are effectively undetectable by hot-bead sensors, even when they are operable in PPM measurement ranges. 

The best approach to VOC measurement in many cases is to use a multi-sensor instrument capable of measuring all the atmospheric hazards that may be potentially present. Having a single instrument equipped with multiple sensors means no condition is accidentally overlooked.

Please see a selection of PID detectors below as single gas models or multi gas models. 

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