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Setting up egrCAN (Calibration)
Ceramic sensors (i.e. O2 (Lambda) and NOx sensors) operate on a diffusion mechanism.
Gases diffuse through a passage into the sensor where oxidation, oxygen liberating, and
oxygen pumping occurs. The diffusion passage is like a filter and like a filter it can get
clogged. In fact, it is impossible for the passage not to get clogged when the sensor is being
used. This clogging of the diffusion passage is the main mechanism by which a sensor
“ages” resulting in a calibration shift.
The sensors shipped with LambdaCAN and NOxCAN(g) modules have been calibrated (i.e.
zeroed and spanned) before leaving the factory. It is recommended that they be calibrated
periodically during use. How often can only be determined by your experimentation.
Alternatively, the sensors can be sent to ECM for recalibration.
Calibration information (both factory calibration and user calibration) for the O2 and NOx
sensors is stored in a memory chip in the sensor’s connector. Therefore, the sensor does not
have to be used with the module it was calibrated with. Once calibrated, the sensor can be
sent to another site to be used. After use, the sensor can be returned to the calibration center
for recalibration thus compensating for any sensor aging. Centralization of calibration in this
way improves measurement consistency and extends useful sensor life.
Calibration of the O2 (Lambda) Sensor and the Delta Tables
The “Span O2” task is used to calibrate the O2 sensor. This task calibrates both the %O2
and Lambda (AFR, FAR, PHI) measurements from the sensor. To perform an O2 span:
1.
The sensor should on for at least 20 minutes. Most of the time, you only need to wait
2 minutes but some sensors, due to condensed material on them or other reasons, take
longer to stabilize.
2.
Put the sensor and the pressure sensor in ambient, stationary air.
3.
Calculate the %O2 in the air. The %O2 in air with no humidity is 20.945. This
percentage decreases with increasing humidity. To calculate the %O2 in non-zero
humidity air, use the “Calculate %O2 in Air” tool in the Configuration Software.
20.7 is a common number.
4.
Make sure O2 is a TPDO parameter.
5.
Select the Task “Span O2”. Enter the displayed (as the TPDO) O2 and the actual
%O2 (as calculated in 3 above), then click on “Span”.
Special Note Re. Calibration of “Intake” O2 Sensor
Sometimes after calibration of the “Intake” O2 sensor in air, the sensor will read a higher
(i.e. 0.2 to 0.8 higher) %O2 when installed in the intake of a running engine with zero EGR.
This is due to a thermal effect of the O2 sensor.
To compensate for this effect, perform the following in-situ SPAN of the intake O2 sensor:
Mount the intake O2 and pressure sensors to the intake manifold, bring the engine to
operating temperature with zero EGR, shut off the fuel, motor the engine for 5 seconds (to
fill the intake manifold with air), stop the engine, and perform the “Span O2” task.