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3.5 Influence of vibrations, impacts
Vibrations and impacts affect the detector's operation, as they may cause:
damage to delicate parts of the sensor (e. g. detector element, compensation element),
shift of the sensor's zero.
It should be ensured that the detector is not exposed to shock and vibration in excess of the amplitude of
vibrations amounting to 0.15 mm of the frequencies of over 10 Hz. Under no circumstances should the
peak acceleration exceed the value of 19.6 m/s
2 .
3.6 Influence of physicochemical phenomena
In the case of chemical compounds with high flash point (approx. 50°C and above) it is necessary
to remember that in typical environmental conditions (ambient temperature below 40°C), it is
unlikely that they will be able to produce atmospheres close to 100% LEL. Particularly in the case
of ambient temperatures below 0°C it may occur that achieving measurable concentrations by the
catalytic sensor (of 10% LEL) is impossible. Another measurement method is required in this case.
High concentration
s of inserting gases (e. g. argon, helium) can change the thermal equilibrium of
the sensor, resulting in the apparent reading of the presence of a combustible substance.
4 Factors shortening the lifetime of the sensor
4.1 Poison and inhibitors
For every reaction with the presence of a catalyst that cause permanent (poisons) or temporary
deceleration (inhibitors) of this reaction, which results in reduced sensor sensitivity – in particular the lack
of reaction to a combustible substance.
For catalytic sensors, on the active element side, we distinguish the following poisons:
silicons (organosilicone compounds) – e. g. PDMS (polydimethylsiloxane), HDMS
(hexamethyldisiloxane), sealants, adhesives, raising agents, specific oils and lubricants, some
medical supplies,
organometallic compounds – e. g. Grignard compounds, lead tetrachloride (leaded petrol, certain
aviation fuels),
organophosphorus compounds – e. g. in herbicides, insecticides, phosphoric esters in fire-proof
hydraulic fluid,
and inhibitors:
sulfur compounds – e. g. hydrogen sulfide, mercaptans, carbon disulphide, sulfur dioxide,
halogen compounds – e. g. methyl chloride, some freons (among others R134a), vinyl chloride,
olefins – e. g. styrene, propylene, acrylonitrile.
Acetylene is a poison for the passive element of the catalytic sensor.
Atest-Gaz A. M. Pachole sp. j.
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VAT No.: PL 9691433231
tel.: +48 32 238 87 94
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e-mail: contact@atestgaz.pl
p. 4/4 Appendix: PU-Z-054-ENG R03
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