02 Sensors

[Gar Willis]

On Sun, 06 Jun 1999 13:28:06 -0400, "David A. Cooley"
<n5xmt at bellsouth.net> wrote:

>an AFR meter (not the one
>you build for $20.00 for your car) uses a linear O2 sensor that has a
>voltage or current output that is varying in a linear fashion with the A/F
>ratio.  they only last a short period of time, and are really expensive.

I'm afraid this is largely a marketing "factoid". It's true that ALL O2
sensors degrade via contaminants over time, and this limits their range,
which is true of both the switch-type and the wide-band O2 types.

But there's also a current marketing/disinformation myth that one of the
well-known US mfgs. of high end AFR meters has been promoting, which is
that the stock Honda/NTK sensors are "not suitable for measuring rich
AFR, and will only last a short time in this environment", all the while
that SAME frigging company has been buying their sensors from a Honda
dealer whose Parts Dept. mgr. is a buddy of mine! HAH, howja like DEM
apples!? [Remember, if you're NOT Horiba, who owns the exclusive rights
to build AFR meters with sensors bought directly from NTK, then you as a
mfg. will HAVE to be getting your 'NTK' sensors from the "grey" or
"parts distribution" market, namely a Honda dealership]. I think the
current disinfo campaign relys on the notion that since the Honda VTEC
systems are relying/using the Honda/NTK sensor in a lean-burn engine
regime, and NOT an enriched/performance one (of course), that they feel
they can get away with foisting this myth on the unsuspected & gullible
public, as if Honda's use of them on the lean-burn side PROVED (or even
spoke to the issue) that they were therefore unsuitable on the rich
side. Certainly NO NTK or Honda papers have EVER suggested such
bullshit. But it's also pretty disgusting that the company is promoting
this outright lie outta one side of their mouth, whilst buying their
bloody sensors from Honda. Exact same part no. and everything, as we use
with EGOR. They CAN'T even buy them in bulk directly from Honda, cuz
Honda won't sell parts that way. My buddy say's they've approached him
on that tact, as well as hoping for some steep discounting since they
buy around 100/mo., but Honda isn't willing to deal their parts that
way, and the best these guys get is the SAME trade level of discounting
as WE do!! Heh. Fact is, the company is lucky they can BUY that many
from a Honda Parts Dept. without raising objections from Honda. Since
Honda isn't interested in making their repair/replacement parts a
commodity item, their main issue is keeping the parts required for their
service operations, in stock.

Lastly, the current pump type sensors now used in almost ALL wide-band
AFR meters (except some that are Bosch LSM-11 based), have an inherent
hedge against contaminants, because they can be recalibrated to adjust
for the diminished O2 pumping/sensing capacity of these sensors over
time/contamination. What happens is that beyond a certain point, the
current pump circuitry (or of course the sensor), whose quiescent value
is programmed during the calibration, simply runs outta steam. This is
an issue of robustness of the sensor interface circuit design, in
addition to longevity of the sensor. B)

Finally, there is NO O2 sensor at present whose output "varies in a
linear fashion with the A/F ratio". I know that David may have said that
as a simplification for discussion's sake, but it bears observation that
even the UEGO sensors are highly non-linear, just in a different way
that makes them able to be used over a wide RANGE of measurement, and to
be self-calibrating in free-air.

Gar