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(Ta) temperature calculation if an INLET probe is not fitted.
CO/CO2 R : The CO/CO
2
ratio, is the ratio of measured CO divided by calculated CO
2
.
It gives an indication of the following :-
• How good a gas sample the instrument is reading.
• How clean the boiler is running.
For example : A new or clean domestic boiler will display a ratio of less
than 0.004, a unit in need of cleaning 0.004-0.008 and a unit in need of
major overhaul will show greater than 0.008.
This only shows a reading when a combustion test is being carried out. ‘- -’
is displayed while in clean ambient air.
P INDEX : The CO/CO
2
ratio expressed as a percentage %, called the ‘Poison (PI)
Index’ i.e. P INDEX % = 100 x CO/CO
2
. ‘- -’ is displayed while in
clean ambient air.
XAIR % : Excess air calculated from the measured oxygen and type of fuel
(λ) used. During a combustion test ‘O2 > 20%’ will be displayed while in
clean ambient air.
Prs : Flue draught pressure reading. Displayed when pressure sensor fitted. See
UNITS menu 5.2.3. for scales.
NO: Nitric Oxide reading in ppm or mg/m3. Displayed when Nitric Oxide sensor
fitted. Also displayed as NO (n) when referenced to oxygen. The display
will read ‘O2 > 20%’ if referenced values selected and instrument is in
clean ambient air.
NOx : Calculated total Nitric oxides displayed in ppm or mg/m3. Where NOx =
NO + P%NO, note P can be set from 0-9%, default = 5%. See SELECT
menu 5.2.2. Also displayed as NOx (n) referenced to oxygen. The display
will read ‘O2 > 20%’ if referenced values are selected and instrument is
sampling clean ambient air.
SO2 : Sulphur Dioxide reading in ppm or mg/m3. Displayed when Sulphur
Dioxide sensor fitted. Also displayed as SO2 (n) referenced to oxygen. The
display will read ‘O2 > 20%’ if referenced values selected and instrument is
in clean ambient air.
O2 ref % : Toxic gas measurements can be referenced to defined oxygen levels.
(O2r) See SELECT menu 5.2.2 for details.
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