Atest Gaz Sigma SmArt, User Manual

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1 Detected substances
Detectors equipped with catalytic sensors are used for measuring and detecting the presence of gases and
flammable gases in the range of up to 100% LEL.
2 Principle of operation
The catalytic sensor (figure 1) consists of two components: an active and a passive one, heated to a high
temperature. They are both constructed of a very thin coiled platinum wire, however, the active element
(figure 2) is additionally coated with a catalyst (e. g. palladium, platinum). A combustion reaction occurs on
the active element. Heat is generated as a result, which causes an increase in the temperature of this
element and a resultant change in its resistance. Whereas combustion is not possible on the passive
element, therefore, its properties do not change under the influence of a combustible substance. This
allows the passive element to compensate for the impact of ambient temperature. The same resistance
change of both elements occurs when the ambient temperature changes. The passive and active elements
are integrated in the Wheatstone bridge circuit, which ensures conversion of the change of resistance to
voltage.
Figure 1: Sample view of catalytic sensor
Figure 2: Active element construction
Atest-Gaz A. M. Pachole sp. j.
ul. Spokojna 3, 44-109 Gliwice, Poland
VAT No.: PL 9691433231
tel.: +48 32 238 87 94
fax: +48 32 234 92 71
e-mail: contact@atestgaz.pl
p. 2/5 Appendix: PU-Z-054-ENG R02
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Active element
Passive element
Output
Steel mesh
Side view Top view
1 mm
Platinum wire
Surface coted
with a catalyst