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Similarly, sometimes users would like Lambda (AFR, FAR, PHI) readings to match other
instruments such as gas-bench analyzer calculated values (ex. via Spindt or Brettschneider)
or company “heritage” Lambda measurement techniques. The Delta Lambda Table (found
in the task “Open Delta Tables”) allows to user to add a number (a “delta”) to “LAMR”
calculated by the LambdaCAN and NOxCAN(g) modules giving the “LAM” parameter:
LAM = LAMR + Delta Lambda Table value
(interpolated from table)
AFR, FAR, and PHI are calculated from “LAM”. A Delta Lambda Table can be created,
edited, and saved as a text file (.txt) on your PC. The file must be downloaded into the
LambdaCAN or NOxCAN(g) module where it is used. File LA42.TXT (for LSU4.2 sensor)
or file LA49.TXT (for LSU4.9 sensor) can be downloaded to make LambdaCAN and
NOxCAN(g) modules match default ETAS LA4 data (see Appendix C). Unlike the sensor
calibration information (i.e. zero, span) which is stored in a memory chip in the sensor’s
connector, the Delta Lambda Table is stored in the module.
Calibration of NTK NOx Sensor and the Delta Tables (NOxCAN Only)
The NOxCAN kit (not the NOxCANg kit) uses the NGK Spark Plugs (NTK) NOx sensor.
This sensor has an 18mm thread. The following applies to the calibration of the NOxCAN
kit only. For the NOxCANg kit, refer to the next 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 calibration of the NOx measuring portion of the NTK NOx sensor is more complex than
the O2 part. First some characteristics of the NTK NOx sensor must be understood:
The NTK NOx sensor was designed to be used in a hot exhaust pipe. If it is mounted in a
cold sample tube, the NOx measurement response will be very slow (i.e. hundreds of
seconds). Also, the zero and gain of the NOx measurement is sensitive to changes in the
exhaust pipe’s temperature. To reduce this sensitivity, ECM offers a heated NOx sensor
mount (the BTU200). With or without the BTU200, for best accuracy the NOx sensor
should be calibrated in a mounting pipe and pipe temperature similar to that it will be used
at.
The gases the NOx sensor is measuring must contain water. Since the combustion of
hydrocarbon fuels produces 5 to 15% water (depending on fuel type and Lambda), this is not
a problem unless the sensor is placed after a water separator. Also, for best accuracy, the
NOx sensor should be calibrated in gases with approximately the same amount of water
vapor as is in the exhaust it will be measuring.