PN 9000-133-VE, Rev U
Detectors
Component
Function
Combustibles Detector
The Combustibles Detector is a dual element device. The
elements differ only in that one is coated with a catalyst. The
catalyst causes oxidation to occur at a lower-than-normal tem-
perature. The temperature of the catalyzed element changes as
the combustible mixture burns. The temperature change causes
the resistance of the catalyzed element to change. The resistance
change is interpreted by the microprocessor and the corre-
sponding combustibles reading is displayed.
The catalytic combustibles detector will detect combustible gas
present in a sample. The sample must, however, contain enough
oxygen to fully burn the combustible present. The combus-
tibles detector responds to all unburned combustibles gases.
This includes gases such as CO and H
2
. You should attempt to
match your calibration gas with a mixture of CO and H
2
that
most closely matches the combustibles mix in your process. We
recommend using an even mixture of CO and H
2
as the combus-
tibles component within your span gas.
Examples:
• Flue gas containing 1000 PPM CO, 1000 PPM H
2
and 1 % O
2
with an H
2
O, CO
2
, and N
2
balance will be sensed to contain
2000 PPM combustibles by the catalytic detector (provided
the combustibles calibration gas consists of equal parts CO
and H
2
.
• Flue gas containing 1000 PPM CO, 1000 PPM H
2
and 500 PPM
O
2
with a H
2
O, CO
2
, and N
2
balance will be sensed to contain
only 1000 PPM combustibles by the catalytic detector, since
there is less than stoichiometric oxygen present. In this case,
the combustibles detector output will be set to full scale.
• If there is little or no other combustible component in the flue
gas, the combustibles analyzer can be calibrated on a mixture
of CO and air to give a CO measurement.
Methane Detector
The Methane Detector is a dual element device. The elements
differ only in that one is coated with a catalyst. The catalyst
causes oxidation to occur at a lower-than-normal temperature.
The temperature of the catalyzed element changes as the mix-
ture burns. The temperature change causes the resistance of the
catalyzed element to change. The resistance change is inter-
preted by the microprocessor and the corresponding reading is
displayed.
• The AMETEK catalytic methane detector will detect methane
gases present in a sample. The sample must, however, contain
enough oxygen to fully burn the methane present.
• The methane span gas should be 2 % CH
4
with 8–10 % oxygen
present in the mixture.
Overview
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