Honda UEGO Sensor...

[Darrell Norquay]

Bryan Zublin wrote about Frank Parkers comments:

> > Sensor calibration is shown as 1 point cal in atmosphere.

> Frank,
> I don't quite understand this statement.  Do you mean that the sensor is 
> calibrated with it "measuring" open atmospheric conditions?  If so, wouldn't 

This is exactly what he means.  The sensor is calibrated to 21% oxygen with
it just exposed to air.  This is the simplest means of calibration, and it
is indicative of maximum "leaness" ie with no combustion at all.  Remember
that the device is really an OXYGEN sensor, it actually does not measure
air-fuel ratio directly, but only infers it from the remaining oxygen left 
in the spent exhaust after combustion.  The sensor has a reference port which
is exposed to air, and a measuring port, which is exposed to exhaust gases.
The electrochemical cell in between then puts out a signal relative to the 
DIFFERENCE in oxygen content between plain air and exhaust.  

This method of calibration only gives you a single point, ie you only have
a calibration factor for the lean end.  I'm not sure, but it seems to me 
that if you dunked the sensor in pure nitrogen or some other gas that 
contained no oxygen at all, you could also calibrate the high (rich) end.
This would be a reference calibration only, really you would have no idea
what the sensor was doing in between, but you could assume a straight line
for approximation.  You'd have to get factory cal curves or run your own
set of characteristic curves to fill in the blanks and do some linearizing.

I worked with a cell much like this a few years back, it was made by GTE
Labs but patents were held by a Chinese scientist.  It sounds similar in
operation, in that you pumped the cell with a constant current and measured
the resulting voltage drop across the cell to determine relative oxygen
content.  The cell I worked with was actually optimized to detect methane
in air, but they also made one for AFR applications that could measure out
to AFR's of 28 or more.  It was used by Waukeshau in the Lean Burn Combustion
System for large stationary engines running natural gas or digester gas from
biochemical processes.

I'd like to get in on this project, it sounds interesting.  I'm an analog
designer by trade, and I think I still have schematics for the unit I built
before.  I also have some papers on the principles involved, but I'm not 
sure they would be applicable to this particular unit without more details
on exactly how it works.

regards
dn

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 Darrell A. Norquay              Internet: dn at dlogtech.cuc.ab.ca     
 Datalog Technology Inc.         Voice: (403) 243-2220
 Calgary, Alberta, Canada        Fax:   (403) 243-2872            
 
       "Absolutum Obsoletum" - If it works, it's obsolete    
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