Technical Manual Page 52 CODEL
OPS.080 Issue : C Rev. : Date : 16/7/08 Doc. i/d : 0080/6 Ref. : 080040
7. Calibration and Measurement Verification
7.1. Introduction
The following sections provide information on the analyser calibration at the time of supply (Factory Calibration),
methods by which measurement/calibration can be verified and, should it be necessary, facilities for calibration
adjustment.
7.2. Factory Calibration
4000 Series analysers use very tightly controlled infrared wavebands that are specific to each of the gases
measured. The scale-shape for each measurement (i.e. the relationship between concentration and output) is
therefore uniquely defined and the output, at any measurement level, is only dependent on gas concentration,
gas temperature and any system zero error.
Flue gas temperature is a continuous measured input. Any zero error detected during commissioning is
corrected as part of the commissioning procedure (Section 5. Commissioning) and any subsequent zero drift is
automatically detected, measured and corrected (Section 7.3.1. Automatic Zero Calibration).
Factory test procedures ensure that analyser calibration is traceable to national standards and, with the inherent
stability of scale-shape and automatic zero, only a significant fault (that would be detected by the analysers'
diagnostic routines) or incorrect installation/commissioning can cause a calibration error. The analyser is
equipped with means by which the factory calibration can be modified on site (Section 7.4. Re-calibration), but
great care should be taken to ensure that calibration adjustment is necessary before proceeding with this routine
as it will overwrite the factory calibration settings.
7.3. Verification
Even though 4000 Series analysers are designed to maintain their calibration stability almost indefinitely, it is
often necessary to verify measurement performance. This may be a routine check after an extended period of
operation, to confirm unusual measurements or as an audit requirement by some external authority.
4000 Series analysers have a range of verification options, designed to provide varying levels of independence
from both the analyser itself and CODEL standards. Which one is chosen depends on the resources available
and legislative demands. The different methods can be used in combination to minimise the amount of external
work required to maintain performance confidence.
7.3.1. Automatic Zero Calibration
This automatic procedure is carried out by the analyser itself and provides regular checking and, if necessary,
adjustment of the zero for each measurement. The automatic zero calibration procedure provides a regular
check on analyser performance without the need for operator intervention. The operation of this is covered in
the IEM for Windows
R
manual.
7.3.2. Manual Zero Verification
The zero of all measurement channels can be verified manually at any time after being powered-up for at least
four hours.
The purge air must be dry to the specified level (-20°C). Any water vapour in the measurement
path will show an offset not only on the water vapour measurement itself, but also on any other
measurements that the analyser automatically corrects for cross-sensitivity to water vapour.
Any calibration subsequently initiated to correct these apparent offsets will be incorrect.
If an analyser error is still suspected contact CODEL or the local service agent but, first consult Section 9. Fault
Finding to establish what information to provide.
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