This time I want to show, how to measure the oxygen content in the exhaust system by first converting the pump current to a voltage signal and then make a lookup table with the oxygen percent vs. voltage signal on the Bosch wideband sensor LSU 4.9.
I know that, the subject has been discussed before by Fat Freddy and that he had some trouble regarding to the accuracy of his test and the same experiences did I, with respect to noise on the signal.
I needed a new approach to tackle this problem to get rid of the noise I was seeing.
The answer to this problem was to use my new precision multimeter current adapter which is called "µCurrent GOLD" http://www.eevblog.com/projects/ucurrent/
.This adapter converts very small current into a milli volt output signal. The only drawback by using the method of measurement is, that you has to break into the circuit, but besides this are there no other drawbacks.
The next step in this process was to make a lookup table based on the technical documentation from Bosch over the wideband oxygen sensor LSU 4.9.This image shows the original lookup table from Bosch´s datasheet with very few data points.
With these 5 data points have I chosen expand lookup table scaling a lot more exactly to 1601 new data points which is done by some software where it is possible find the correct non-linear curve. The new lookup table have a range from 0 to 21,245178 percent oxygen with an interval at 0,012096 (O2%).
To make this comment short, it´s not a easy task to convert a oxygen percent into a lambda value and then convert this to a milliamp value for then finally to convert this to a voltage value - are you confused - me too !!!.
As mentioned before has this lookup table has range from 0 % oxygen to 21,24, so it is only possible to measure excess oxygen content in the exhaust system as there were no calculation formula which describes the oxygen content below 0 % according to the Bosch datasheet.
The image below show the car during dynamically a road test where the engine are being accelerated to around 3500 - 4000 RPM. The peaks in this scope capture are when the gear changes happens - starting with 4 gear and ends with 6 gear.