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Comparing to an ETAS LA4 Meter
Many ETAS meters with new sensors will not correctly show the %O2 when the sensor is
held in air. The actual %O2 in air depends on the humidity and will be almost always less
than 20.945%. Since the measurement of %O2 is the fundamental mechanism by which the
wideband sensor determines Lambda, the effect that this error has on meter accuracy is
obvious. This %O2 measurement error will have a negligible effect at Lambda=1 but the
effect on Lambda will increase the further Lambda gets from Lambda=1.
All lambda meters should read the correct %O2 when the sensor is held in air. Due to sensor
aging and changes in ambient pressure (due to weather and altitude changes), this may not be
the case. However, LambdaCAN and NOxCAN(g)’s “Span O2” feature allows to user to
restore the system’s accuracy.
The O2 span is performed by holding the sensor in air and entering the actual %O2 in air.
However, if you are comparing a LambdaCAN or NOxCAN(g) to an ETAS meter and you
want the LambdaCAN or NOxCAN(g) to match the ETAS meter, then you must span the
LambdaCAN or NOxCAN(g) to whatever the ETAS meter says the %O2 is in air – even if it
is wrong.
Therefore, if you want a LambdaCAN or NOxCAN(g) to match an ETAS meter, whether or
not the ETAS meter reads the correct %O2 in air, do the following:
1.
Make certain that the “LA42.TXT” (for the LSU4.2 sensor) or “LA49.TXT” (for the
LSU4.9 sensor) curve is downloaded to the LambdaCAN or NOxCAN(g) module as
the “Delta Lambda Table”. This is for the case of matching the “Default Curve” in
the ETAS meter. Other curves are available and the user can create his own curve.
2.
Turn on the ETAS meter and hold the sensor in air. Read the %O2 on the ETAS
meter. This value should be 20.945 or less since 20.945 is pure air with no humidity.
We have seen values of over 22%.
3.
O2 span the LambdaCAN or NOxCAN(g) to the %O2 given on the ETAS meter even
if it is wrong.
This procedure is to be used only if you want the LambdaCAN or NOxCAN(g) to match a
specific ETAS meter and sensor combination. Normally, the LambdaCAN and NOxCAN(g)
are spanned to the correct %O2 in air.