Page: 26
EnergyTech 401
CODEL
Operating and Maintenance Manual
Monitoring Solutions
It is not necessary to calculate K because we know that when the constant K is
correct :
Y is 0 when the CO level is 0.
If there is any drift in the measurement it can only be due to a change in some
optical or electronic gain and can always be corrected by setting Y to zero when
the CO level is zero.
In practice, however, it is not always possible to produce a zero CO level, but if
we consider the calibration curve, we can see that :
if
Y = 0 when CO = 0
then
Y = a when CO = b
We can also see from Figure 6 that at high CO levels, the parameter Y becomes
completely insensitive to variable CO levels in the duct, such that:
Y = a when the CO > b
By making Y = a when CO > b, Y = 0 when CO = 0 and all these errors are
eliminated.
A gas cell containing pure carbon monoxide can be introduced into the IR beam
at the source. This cell represents a value of 10,000ppm.metres and provides a
reference point for the calibration of the instrument. Any further CO in the duct
will have negligible effect on the reference point because the calibration curve is
flat at these high concentrations of CO. Well-designed cross-duct analysers
introduce this gas cell regularly - every few seconds - to continuously check and
(if necessary) modify their zero position.
Summary of Contents for Energy Tech 401
Page 71: ...Section 5 Normal Operation Issue A Revision 1 Date 24 07 19 Ref 100606 Page 71 ...
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