Testing low-cost PID and electrochemical sensors

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Initial testing of our SINTSENSE analytical systems with PID, SO2, NOX, OX, H2S, and CO sensors have indicated some drift when testing them in ambient air. Especially the electrochemical sensors have been prone to inversion, and some of the sensors show opposite polarities.

There is enough examples of published data from sensors of this type without calibration and validation of drift, cross-sensitivity etc., so a proper calibration needs to be done. I have access to a very elegant gas and liquid mixing system that should make it possible to evaporate a solution of benzene, and air mixtures of SO2, CO etc. Air because these sensors require oxygen to function.

In the mean time I thought it would be a good idea to test the sensors on the exhaust from my beloved BMW vehicles. So I gave it a go. From the figure it can be seen that for both vehicles the PID sensor saturates at about 35 ppm. No worries: I have on for the working range of 50 ppb to 6000 ppm to try next.



The CO sensor behaved oddly for both tests, peaking at 700 ppb before the signal inverted. Expected CO concentration is in the range of 5000 ppm for these fine BMW combustion engines. The inversion is the result of the auxiliary electrode voltage being increased. This could be the result of the oxygen concentration in the gas being abruptly changed from 20 to approximately 0.5 % vol. Humidity and temperature changes could also potentially change the sensor response.

More testing in the lab needed. The PID response at least appears to be sound.


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