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1 Detected substances
Detectors equipped with electrochemical sensors are used for measuring and detecting the presence of
specific substances in gaseous atmospheres in concentrations generally above single "ppm," but in some
cases (e.g. oxygen, hydrogen), the concentration may be tens or hundreds of thousands "ppm".
These gases have characteristic measurement ranges. Most of the detected substances are primarily volatile
inorganic compounds. Some organic compounds, such as ethylene, ethylene oxide, may also be detected.
Table 1 presents an example list of substances detected by electrochemical sensors.
2 Principle of operation
Electrochemical sensors are micro fuel cells. Figure 1 shows a simplified structure of an electrochemical
sensor.
The sensor inlet (1) is protected with anti-condensation membrane (6) which serves also as a protection
against dust. The simplest electrochemical sensor consists of two electrodes: sensing (2) and counter (3),
separated by a thin layer of electrolyte (4). Depending on the detected gas, the reduction or oxidation
reaction occurs on the first electrode, which is balanced by a counter electrode by water oxidation or
oxygen reduction respectively. In order to improve the performance of the sensor, a third electrode – the
reference electrode – is used (5). It has a constant potential that is not dependent on the concentration of
the measured gas. Owing to electrode reactions, electrons are generated, whose orderly flow – electric
current, is proportional to the concentration of the detected gas.
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p. 2/5 Appendix: PU-Z-032-ENG R02
•
Table 1: Substances detected by the electrochemical sensors
Name of the substance IUPAC name Molecular formula CAS
Oxygen Oxygen O2 7782-44-7
Ozon Trioxygen O3 10028-15-6
Hydrogen Hydrgen H2 1333-74-0
Ammonia Azane NH3 7664-41-7
Arsine Arsenic trihydride, Arsane AsH3 7784-42-1
Carbon monoxide Carbon monoxide CO 630-08-0
Chlorine Chlorine Cl2 7782-50-5
Chlorine dioxide Chlorine dioxide ClO2 10049-04-4
Ethylene oxide, epoxyethane Oxirane C2H4O 75-21-8
Formaldehyde Methanal HCHO 50-00-0
Hydrazine, diamine, diazane Hydrazine N2H4 302-01-2
Hydrogen chloride Hydrogen chloride HCl 7647-01-0
Hydrogen cyanide, Prussic acid Formonitrile, Hydridonitridocarbon HCN 74-90-8
Hydrogen sulfide, Sulfane Hydrogen sulfide H2S 7783-06-4
Nitric oxide Oxidonitrogen NO 10102-43-9
Nitrogen dioxide Nitrogen dioxide NO2 10102-44-0
Phosgene Carbonyl dichloride COCl2 75-44-5
Silane Silane SiH4 7803-62-5
Sulphur dioxide Sulphur dioxide SO2 7446-09-5
Ethylene Ethene C2H4 74-85-1
Tetrahydrotiofene (THT) Thiolane C4H8S 110-01-0