Ease of Calibration & Maintenance

by Emily Lane 11 April 2018 Fire Investigation
Ease of Calibration & Maintenance



Conventional PIDs may use humidity suppression/compensation techniques but each of them has disadvantages:

  • Humidity sensor – these typically have a slower response than the PID sensor itself which causes a drifting compensation
  • Desiccant tube – these both slow the PID response and also reduce it by adsorption plus they need replacing from time to time which adds cost
  • Humidify the calibration gas – this only works at one level of humidity and is no longer accurate when the humidity changes

Importantly none of these solutions solves a false positive at high humidity



Figure 4:  Ion Science Ltd PID sensor design

Looking again at figure 4, the presence of the porous membrane should be noted.  It is made from a hydrophobic material which means that it rejects the ingress of water and mitigates the chance of low readings. 

To further deal with high humidity, the addition of a third, fence electrode (also shown in figure 4) overcomes the possibility of high readings since it behaves as a conductive break and stops the excess current flow caused by the presence of high humidity and contamination which would otherwise lead to a false positive.


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Ease of calibration & maintenance


Tags: Fire Investigation