8-C-2  Chapter 8: Gas Analyzer Calibration  42/24-10 EN Rev. 9 
Caldos27: Notes for Calibrating 
 
Sample Components  The Caldos27 analyzer module has at least one sample component with one 
measurement range and, for measurement ranges ≥ Class 1, the standard gas 
substitute gas component.  
 
Associated Gas 
Influence 
The Caldos27 analyzer module measurement technique is based on the differing 
thermal conductivity of various gases. 
 
Since this technique is non-selective, the concentration of a sample component 
can be accurately measured only in a binary or quasi-binary gas mixture. 
 
If other associated gas components are present in the sample gas their effect on 
factory calibration must be considered. 
 
Test Gases  Zero Calibration:  Test gas or sample-component-free process gas or substitute 
gas 
 
Span Calibration:  Test gas or process gas having a known sample gas concen-
tration or substitute gas 
 
Test Gas for 
Corrected Sample 
Components 
During calibration cross-sensitivity and/or carrier gas corrections by other meas-
urement components are switched off. Therefore, a corrected measurement com-
ponent should be calibrated only using a test gas consisting of the measurement 
component and an inert gas like N
2
. 
 
Calibration with 
Substitute Gases 
If test gases are not available for calibration, the Caldos27 analyzer module can 
be factory-set for calibration with substitute gases (see the “Calibration Methods” 
section, page 8-A-10). 
 
Substitute gas calibration of the Caldos27 analyzer module is described using the 
example of “CO
2
 Measurement in Flue Gas”, on page 8-C-4. 
 
Single-Point 
Calibration with 
Standard Gas 
Single-point calibration of the Caldos27 analyzer module with standard gas is 
described on page 8-C-3. 
 
Sequence of 
Calibration 
Zero point calibration must always precede end point calibration. 
 
Wait Until End of 
Warm-Up Phase 
The Caldos27 analyzer module should only be calibrated after the warm-up 
phase, i.e. approx. 30 minutes after connecting the power supply. 
 
The time required for the warm-up phase depends on the measurement range.