[Wbo2] Using the Bosch WB sensor with L1H1 circuit board

[bcroe at juno.com]

22 Nov 2005  "James Holland" <J_Holland at btopenworld.com> writes:

> Fair, comment, one point that puzzles ,e is the need to calibrate 
> each individual sensor. Is it the sensor that needs to be calibrated 
> or the meter? 

Its easy to build a meter that is far more accurate than a 
particular sensor.  Multi digit displays may look cool, but 
they are meaningless if the input is way off.  

> If it is the sensor then what is the purpose of the calibration 
> resistor?

The sensor is inherently very accurate at Lambda/Stichiometric.  
But the signal output at other levels varys greatly from sensor 
to sensor.  A calibration resistor is added to make it reasonably 
accurate at some distance from S.  The resistor is not laser 
trimed to a very precise value, it is just one of a couple dozen 
values picked out of a bin, "nearest one".  Even if it WAS perfect, 
variations in the shape of the output transfer curve would make 
the reading perfect ONLY at 2 points.  

But a sensor may be capable of repoducing the SAME curve 
very accurately, over and over.  So if you measure EVERY POINT 
for that sensor, you can get much more accuracy until it wears 
out.   This is an expensive process, and virtually worthless to 
an engine tuner.  It might be worth while in some other uses.  

> when an OEM WBO2 sensor is replaced is the ECU recalibrated?

How would it be recalibrated?  The ECU accepts the accuracy the 
calibration resistor provides, which is good enough.  Bruce Roe

> Cheers
> James