Prosense PQ Series Installation And User Manual page 7

1. Very high gas concentrations
The measuring method of PQ series detector based on heat produced by reaction on the
oxidation of a flammable gas when pellistor sensor used. There is not enough oxygen in the
sensor to perform oxidation process correctly in case of high gas concentrations. Hence the
measuring signal decreases at high gas concentrations and even can lead to measuring signal
within the measuring range again. In case of high flammable gas concentration, do not reset
latching alarms without having ensured a safe condition in the environment via performing
necessary checks.
2. Minimum oxygen concentration
The measuring principle of heat of reaction needs a minimum oxygen concentration of 15 %
by volume; otherwise the measuring values will be too low because of oxygen deficiency.
3. Long-term gassing with methane at very low temperatures
If the Prosense PQ series flammable gas detectors with pelistör sensor are operated applying
with methane at very low temperatures, the measuring signal at long term exposition may
decrease after alarm activation and may lead to misinterpretation.
If a gas alarm occurs, necessary actions need to be taken immediately. The decrease of the
measuring signal should not mean that the gas concentration has been decreased. We
recommend to keep alarms on the associated controllers and not to reset these alarms
without performing measurement with an independent gas detector to make sure conditions
are safe.
PRS-UM-PQ-EN-Rev.05-18.06.2020 7