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Instruction Manual
IM-106-5500, Original Issue
August 2005
1-7
CCO 5500
Since the vpm measurement is already normalized for temperature and
pressure, the only further normalization required is for the dilution effects of
water vapor and oxygen. These are straightforward calculations as shown
below:
20.9% is taken as the level of free oxygen in dry air.
NOTE
If the measured O
2
% is a wet measurement the measured O
2
concentration
must be corrected to a dry measurement. This is performed automatically by
the software if the measured O
2
concentration is defined as a wet
measurement; where:
(O
2
% measured) DRY = (O
2
% measured) WET x 100
100 - H
2
O%
If no correction is required for oxygen then standard O
2
= O
2
measured.
If no correction is required for water vapor then H
2
O% = 0
After all these calculations have been performed the resulting measurement
is the effective mass concentration of the pollutant normalized to standard
conditions (in mg/Nm
3
).
Measured conditions -
Where measured values are required (e.g. to calculate rates of emissions)
they need to be recalculated for measured temperature and pressure as
shown below:
substituting,
the measured mass concentration of the gas is:
Principles of Cross-Duct Gas Analyzers
Cross-duct analyzers work on the basic principle that infrared (IR) energy is
absorbed by particular gases in a manner very specific to the gas.
Although cross-duct analysis will differ from gas to gas, the basic principles
are similar for all measured gases. This section examines the analysis of
carbon monoxide in detail.
mg/Nm
3
= mg/m
3
(STP) x 20.9 - 0%
2
standard x100
20.9 - (0%
2
measured) DRY = 100 - H
2
O%
mg/m
3
= N.vpm x 273 x measured pressure
T standard pressure
vpm = ppm x standard pressure
measured pressure
mg/m
3
= N.ppm x 273
T