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3.
“Span O2” the sensor in a manner similar to the Lambda sensor.
4.
“Zero NOx” the sensor in a running engine and in comparison to a CLA. The NOx
level doesn’t have to be exactly zero for the zero process. For example, if it is 12
ppm, the Configuration Software will allow this. Since water is in the gases that the
NOx sensor is seeing, it is best to use a “wet” NOx number from the CLA. If you do
not do this, you are putting an error into the measurement since %H2O, and hence the
difference between a “wet” and “dry” measurement, changes with stoichiometry.
5.
“Span NOx” the sensor in a running engine and in comparison to a CLA. Span at the
upper range of NOx to be measured. Again, it is best to use a “wet” NOx number
from the CLA.
When calibrating the NGK NOx sensor using model gases, the recommended procedure is:
1.
Hold the powered NOx sensor and pressure sensor in air for 20 minutes. Pressure
information is required if the calibration is to be pressure compensated.
2.
Select “Model Gas” in the task “Select NOx Curve”.
3.
“Span O2” the sensor in a manner similar to the Lambda sensor.
4.
“Zero NOx” the sensor in ambient, stationary air (i.e. same condition as “Span O2”).
IMPORTANT NOTE
: Do not zero in pure N2 or N2 that has been bubbled through
water! This will damage the sensor.
5.
Mount the sensor in a vessel and pass bubbled model gases of the composition NO +
O2 (approximately 20%) + N2 (balance) past the sensor. The ppm NO should be
close to the ppm that will be measured in use
. IMPORTANT NOTE
: Do not span in
a mixture that contains less than 1% O2! Use approximately 20% O2 for best
calibration.
6.
Correct the span NOx ppm content of the gas for water vapor using the formula:
NOx (corrected) = NOx (in tank) x ((%O2 in air)/20.945)
where: “%O2 in air” is determined using the “Calculate %O2 in Air” tool with
Rh=100%, the pressure in the bubbler, and the water temperature in the
bubbler.
IMPORTANT NOTE
: We have found that the best calibration is performed based
on measured NOx data from a NOx CLA sampling from the vessel holding the NOx
sensor (i.e. not using the above formula). We believe that this is because of reactions
that occur in the lines from the tanks to the sensor.
7.
“Span NOx” when the displayed NOx is stable.
8.
Select “Engine” in the task “Select NOx Curve” before using the NOx sensor in an
engine.
The NOxCANg module supports the Delta O2 Table and Delta Lambda Table features as
described in the lambda sensor calibration section. There is no Delta NOx Table feature.