8-C-4
Chapter 8: Gas Analyzer Calibration
42/24-10 EN Rev. 9
Caldos25 and Caldos27: Substitute Gas Calibration
Example
Substitute gas calibration in the Caldos25 and Caldos27 is described using the
example of CO
2
Measurement in Flue Gas.
CO
2
Measurement in
Flue Gas
The composition of the various combustion products in the sample gas is known
in the case of CO
2
measurements of flue gas from single-component firings. The
flue gas out of the cooler primarily contains CO
2
, O
2
, N
2
and Ar. CO
2
cannot be
measured in mixed-firing flue gases.
Test Gases
The following table shows test gases for the calibration of the 0-20 Vol.-% CO
2
measurement range:
Fuel
Test Gas Composition in Vol.-% for
Zero
Middle
Concentration
Span
CO
2
O
2
N
2
Ar
CO
2
O
2
N
2
Ar
Gas Air
10
0
3 86 1
20 – 79 1
Oil Air 10
0
8 81 1
20 – 79 1
Coal
Air
10 10 79 1
20 – 79 1
Calibration with
Substitute Gases
Since the test gases in this table are not available everywhere, the analyzer
module can be factory-set for calibration with a substitute gas.
In this case an additional measurement range is calibrated for 0–20 Vol.-% CO
2
in
N
2
(N
2
and CO
2
/N
2
mixtures are available practically everywhere).
Component 1
CO
2
in Flue Gas
Meas. Range 1
0-10 Vol.-%
Meas. Range 2
0-20 Vol.-%
Measurement Ranges
Component 2
CO
2
in N
2
(Substitute Gas)
Meas. Range 1
0-20 Vol.-%
Calibration Method
Substitute Gas Calibration
Zero Component
Component 1 Meas. Range 1 or
Component 2 Meas. Range 1
Calibration Parameters
Span Component
Component 2 Meas. Range 1
Calibration
•
Calibrate zero with air (component 1) or N
2
(component 2).
•
Calibrate span with test gas 18 Vol.-% CO
2
in N
2
.
Other Measurement
Tasks
For other measurement tasks select the test gases and measurement ranges in a
similar manner according to the sample gas composition.
