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Alphasense PID

A high-end PID from Alphasense to measure VOCs.

Image Credit: Alphasense

Under Construction

More details on working principles, usage, considerations, and resources are coming soon.

Working principle

PID technology appears to be the primary sensor element of choice for VOCs measurements and is often used for measurement of summary concentration [2, 47].

The sensor contains a ionization lamp. As compounds enter the detector they are bombarded by high-energy UV photons and are ionized when they absorb the UV light, resulting in ejection of electrons and the formation of positively charged ions. The ions produce an electric current, which is the signal output of the detector. The greater the concentration of the component, the more ions are produced, and the greater the current. The current is amplified and displayed on an ammeter or digital concentration display.

Substances with ionisation potential below the sensor's lamp specification will be measured as a whole, with very little specificity in the readings 123.

Limitations

When testing PID sensors in laboratory conditions, good performance has been achieved, however this has not been later on comparable to field results 3. Careful treatment of the readings, including electromagnetic noise, compensation for relative humidity changes, and power supply voltage stability, are a must for PID sensors 34.

References

  1. Chojer, H., P.T.B.S. Branco, F.G. Martins, M.C.M. Alvim-Ferraz, and S.I.V. Sousa. “Development of Low-Cost Indoor Air Quality Monitoring Devices: Recent Advancements.” Science of The Total Environment 727 (July 2020): 138385. https://doi.org/10.1016/j.scitotenv.2020.138385. ↩

  2. Zheng, Hailin, Vinayak Krishnan, Shalika Walker, Marcel Loomans, and Wim Zeiler. “Laboratory Evaluation of Low-Cost Air Quality Monitors and Single Sensors for Monitoring Typical Indoor Emission Events in Dutch Daycare Centers.” Environment International 166 (August 2022): 107372. https://doi.org/10.1016/j.envint.2022.107372. ↩

  3. Xu, Wei, Yunfei Cai, Song Gao, Shuang Hou, Yong Yang, Yusen Duan, Qingyan Fu, Fei Chen, and Jie Wu. “New Understanding of Miniaturized VOCs Monitoring Device: PID-Type Sensors Performance Evaluations in Ambient Air.” Sensors and Actuators B: Chemical 330 (March 2021): 129285. https://doi.org/10.1016/j.snb.2020.129285. ↩↩↩

  4. Lewis, Alastair C., James D. Lee, Peter M. Edwards, Marvin D. Shaw, Mat J. Evans, Sarah J. Moller, Katie R. Smith, et al. “Evaluating the Performance of Low Cost Chemical Sensors for Air Pollution Research.” Faraday Discussions 189 (2016): 85–103. https://doi.org/10.1039/C5FD00201J. ↩