A Chemiluminescence detector (CLD) uses several chemical conversion techniques that take advantage of NO and NO2 chemical reactions that emit light as part of that process.

Chemiluminescence is different from fluorescence or phosphorescence in that the light produced stems from a chemical reaction rather than by the absorption of photons by the molecule.

Servomex CLD analyzers use a thermally-stabilized photodiode to detect and measure the intensity of the light that is produced by the reaction of nitric oxide (NO) with ozone (O3), yielding an excited state of NO2 (referred to as NO2*) plus oxygen (O2). Because this NO2* is in an energy state that it does not like to stay in, it quickly drops to the more stable ground state and, in the process, emits a chemiluminescent light.

As the photons emitted from the reaction fall upon the photodiode, a low DC current is generated, which is then immediately amplified to reduce noise adding to the signal. The intensity of the chemiluminescent light is directly proportional to the concentration of the NO molecules in the gas stream that were converted to NO2 by the reaction with up to a 100% conversion rate.

When run in the NOx mode, the analyzer first converts the NO2 in the gas stream to NO, then it is passed to the O3 reaction chamber, resulting in a total NOx value for the sample gas, allowing the analyzer to then internally calculate the speciated concentrations of NO, NO2 and total NOx using the same analyzer.

The rapid response of the SERVOPRO NOx CLD analyzer makes it well suited for Vehicle and Engine emissions certification testing, as well as Continuous Emissions Monitoring (CEMs), combustion efficiency, and process gas monitoring.

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