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4. If the calibration model gases change composition while flowing from the tanks to
the sensor.
5. If the NOx sensor is subsequently used in an unheated sample line.
6. If the NOx sensor subsequently measures exhaust gases after these gases have passed
through a water separator.
IMPORTANT NOTE : ECM has found it very difficult to accurately calibrate the NTK
NOx sensor using model gases. Calibrate in an engine and in comparison to a NOx CLA if
possible.
The NOxCAN 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.
Calibration of NGK NOx Sensor and the Delta Tables (NOxCANg Only)
The NOxCANg kit (not the NOxCAN kit) uses the NGK Insulators (NGK) NOx sensor.
This sensor has a 20mm thread. The following applies to the calibration of the NOxCANg
kit only. For the NOxCAN kit, refer to the previous section.
There are two parts of the NOx sensor: the O2 (Lambda, AFR, FAR, PHI) measuring part
and the NOx measuring part. The O2 (Lambda, AFR, FAR, PHI) measuring part should be
calibrated in a similar manner as it is for the Lambda sensor (i.e. using “O2 Span”). It is
important to realize that when in the exhaust of a running engine, the NOx sensor is seeing
water vapor. Therefore it will report “wet” %O2 and ppm NOx numbers. Classical gas
analysis equipment (ex. NOx Chemiluminescent Analyzer (CLA)) typically have the water
removed from the gases before they reach the analyzer. Thus classical gas analysis
equipment will report “dry” numbers. When comparing “wet” to “dry” numbers make sure
to compensate for the removed water.
The NOxCANg kit requires that the user select whether he is using the NOx sensor in the
exhaust of an engine or in model gases (bubbled NOx + O2 + N2). This is selected by the
“Select NOx Curve” task. This selection modifies the calculated NOx. Additionally there
are four O2 compensation parameters (two gammas, and two betas) that affect the calculated
NOx. One set of gamma, beta is used for the engine NOx calculation and the other for the
model gas NOx calculation. These numbers are factory-set to nominal values, stored in the
sensor’s memory chip, and should not be changed without contacting ECM. Unlike the
NOxCAN kit, use of a heated NOx sensor mount (the BTU200) is not necessary with the
NOxCANg kit.
The calibration of the NOx measuring portion of the NGK NOx sensor can be performed
either in the exhaust of an engine or using model gases. Model gases are mixtures of NOx,
O2, and N2 that have been bubbled through water before reaching the sensor.
When calibrating the NGK NOx sensor using engine 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 “Engine” in the task “Select NOx Curve”.