44
2 Environmental Conditions in the Mine
Platinum
catalyst
Ceramic
coating
Active
pellistor
with
catalyst
Common
Inactive
pellistor
Platinum
alloy wire
Deactifier
Fig. 2.5 Scheme of a catalytic sensor used in gas measurement. Modified from Equipco Services
2.3.4 Infrared Sensors
Infrared sensors sensors are based on the principle that gas molecules are excited by
infrared radiation of a certain wavelength, generating vibrations that absorb energy
from it. A typical infrared photometer consists of two infrared rays. One of these
passes through a container in which the gas to be analysed is located, and the
other through a container which does not contain the gas, and is used as a reference (Fig. 2.6) (MSA 2007). Concentration can be deduced based on the difference
in the absorbed radiation between the two tubes (Kumar et al. 2013).
In
S
frared
ource
R
Gas inl
Reference
Sample
let
Purge valve
Detec ctor
Fig. 2.6 Scheme of an infrared (IR) sensor