Can Humidity Interference Affect PID Results?

by Emily Lane 23 April 2018 Humidity
Can Humidity Interference Affect PID Results?


A common frequently asked question is “can humidity interference affect my PID detector results?”  Like many sensors and measurement instrumentation, traditional PIDs can indeed be affected by the environmental conditions i.e. dust, dirt and in particular, humidity.  The major producers of oil & gas are located in the Gulf States and in or close to the Gulf of Mexico, which are of course areas of high temperature and high humidity. 

Humidity can disrupt PID measurements in two ways leading to false low or conversely high readings. 

The cause of low readings is because water vapour absorbs the photons released by ionisation within the sensor as can be seen in the simplified cross sections of a PID sensor (figure 1).





Figure 1: Cross section of a PID sensor with and without water vapour present


The effect worsens with increasing humidity as shown by figure 2.


Figure 2

Figure 2: Effect of water vapour absorption

Contamination can also build up between the electrodes, represented by the dotted lines in figure1, effectively short circuiting them.  This leads to a high, ‘false positive’ reading with no VOC present at humidity greater than 90% RH.  The dramatic effect can be seen in figure 3.

Figure 3

Figure 3: Effect of contamination


 Find out more, download our FREE Buyers Guide to 'Humidity interference in VOC measurements'


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