[Diy_efi] Re: [Efi332] Fw: wide-band O2 sensor comparison

Garfield Willis garwillis at msn.com
Tue Aug 13 14:50:24 GMT 2002


e-mailed & posted.

On Mon, 12 Aug 2002 09:29:40 -0700, Andrew Brownsword <asword at telus.net>
wrote:

>FYI, I'm only on the DIY list and I'm receiving these messages.

Yes, I'm on the DIY moderator's "private shit list", so he vetts
everything I post, and decides if it goes thru. I guess he demurred on
squelching this one; quite out of character for him.

>If the sensors are individually consistent in how they are "off", then =
it
>should be possible to use a commercial meter to do the calibration once.=
  It
>might not even be necessary to do that if you can use an engine with a
>properly working HEGO closed loop -- the flip-flopping across stoich =
ought
>to be visible on the DIY-WB, giving a reference point for interpreting =
the
>device's output.  Is this not the case?

Nope. Yes, you could use a commercial meter to calibrate or check ANY
other AFR meter, IF you had a way of correcting the calibration. Unless
you wanted to write down the 'corrections' curve and use it as a 'double
lookup table' (first the reading to AFR, then the correction to actual
AFR). That's the first IF. Then, since each sensor is different from the
next by about 15% (NTK's statement, not just mine, but the test data
over a large lot confirms it), you would also need to do this
recalibration for each and every individual sensor, AND whenever you
replaced/swapped sensors. Believe me, it's alot easier to just get the
circuit designed properly. Then you don't need TWO AFR meters to get one
decent one. :)

Your second question is also a resolute NOPE. The errors we're dealing
with both from a circuitry and a calibration standpoint, INCREASE as you
get away from stoich. You can see this even in the data BruceP recently
posted also. These sensors are *automatically* dead-nuts accurate right
at stoich, because it's the only place where the oxygen pump is asleep;
so it's just like a NB sensor, and just like a NB, physically a
necessity that stoich is found correctly, if nothing else. But aging, or
a flawed control circuit, or a flawed calibration circuit or technique,
and the errors GROW as you move away from stoich in either the rich or
lean direction, because that's where the oxygen pump part of this unique
sensor design comes into play. The errors are proportional to how far
you are from stoich, because the oxygen pumping magnitude & servo
control response are proportional to how far you are away from stoich.
Consequently, a place where the oxygen pump and the associated circuitry
to control it, are NOT operating (stoich), cannot be used as a
"reference" point. It's like the old adage of a stopped clock being
right at least twice a day. No useable reference there.

HTH,
Gar


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