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Electrochemical Sensors
Published in John Vetelino, Aravind Reghu, Introduction to Sensors, 2017
The final gas interaction with a semiconductor surface, which will be discussed, relates to surface ion exchange. The previous interactions that have been discussed relate to surface states, adsorption (physisorption, chemisorption, and ionosorption), and reduction-oxidation reactions. The surface ion exchange relates to the replacement of atoms at the semiconductor oxide surface, which will most likely affect metal oxide electrical properties. The surface ion exchange interaction is not often seen in metal oxide gas sensors. It has been suggested [48] that the hydrogen sulfide sensor that uses tungsten trioxide as the metal oxide film operates on this basis. In particular, it has been postulated that the lattice oxygen is replaced with sulfur to form a tungsten disulfide (WS2) layer. This could result in higher conductivity since WS2is conductive. However, contributions due to hydrogen and water vapor also play a role in the interaction and should be considered. Also, the question of reversibility in responses would be difficult to explain for anion exchange interaction.
Entry Program Requirements
Published in John F. Rekus, Complete Confined Spaces Handbook, 2018
An instrument equipped with a carbon monoxide detector would be a good choice if measurements were routinely made around carbon monoxide-producing process equipment like ovens, furnaces, and boilers, or around street manholes where there is the danger of vehicle exhaust. Similarly, an instrument equipped with a hydrogen sulfide sensor would be an appropriate choice if measurements were made frequently around sanitary sewers, storm water drains, wastewater process equipment or other areas likely to contain hydrogen sulfide.
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Published in Neil McManus, Safety and Health in Confined Spaces, 2018
Neil McManus, Robert E. Henderson
Some operating environments render electrochemical sensors of this design impossible to use. For instance, a nonconsuming electrochemical hydrogen sulfide sensor would not normally be usable for monitoring for H2S in a natural gas pipeline containing no oxygen. Once all of the oxygen available in the electrolyte was consumed, the sensor would then fail to respond to hydrogen sulfide. When re-exposed to an oxygen-containing atmosphere, the sensor would regain its ability to detect H2S.
Field application of cost-effective sensors for the monitoring of NH3, H2S, and TVOC in environmental treatment facilities and the estimation of odor intensity
Published in Journal of the Air & Waste Management Association, 2023
HungSoo Joo, Sang-Woo Han, Chun-Sang Lee, Hyun-Seop Jang, Sung-Tae Kim, Jin-Seok Han
Table 3 shows the results of the fundamental performance tests using a chamber. The linearity of the three sensors was considerably high, ranging from 0.985 to 0.999; the hydrogen sulfide sensor showed the highest linearity. Lower detection limits were observed at 22.3 ppb for hydrogen sulfide, 18.6 ppb for ammonia and 26.7 ppb for the TVOC sensor. The lower detection limit for ammonia was better than that in previous reports (Han et al. 2012), while the lower detection limit of the TVOC sensor was slightly worse than that in the report by Choi (Choi et al. 2014). All three sensors showed high values for accuracy and repeatability. The hydrogen sulfide sensor showed the highest accuracy and the TVOC sensor showed the highest repeatability. The response time for the ammonia sensor was 9 to 12 minutes according to concentration levels; the hydrogen sulfide and TVOC sensors showed less than 2 minutes. Gong et al. reported that tested odor sensors showed good linearity with >0.97 of R2 in the conditions less than 500 ppb (H2S, NH3 and VOC) and they suggested standard performance criteria, i.e., less than 5% of repeatability, 20% of linearity and 10% of accuracy, respectively (Gong et al., 2015). Another previous study presented that the H2S sensor showed less than 1.7% of repeatability, 2.7% of accuracy and 400 seconds of response time, respectively (Zeng et al., 2016). Eventually, we decided that all three sensors were suitable for field application.