[Diy_efi] WB free air calibration

Thu May 30 03:04:14 GMT 2002

On Wed, 29 May 2002 14:43:23 -0700, "rob files" <rncfiles at hotmail.com>
wrote:

>Ok, understood it is not lab grade (what tolerances qualifies as "lab =
grade"=20
>anyway).

The term "not lab grade" is a Plecanism, a euphemism for "sloppy and
uncalibrated" (no commercial AFR sensing vendor has every used any terms
like 'lab grade'). Bruce and Co. just made that up to excuse the mess
they're promoting as a WBO2 device. [Won't even operate properly on
+Batt voltages, sheesh; any real AFR meter will operate all the way down
to cranking voltage, so you can be SURE you have the sensor heated
before you blow smoke and vapor all over it].

IOW, the AFR readings you get with it won't be actual AFR numbers, but
rather something that imitates actual AFRs, in that the numbers go down
(hopefully) as you get richer, and go up as you go leaner (again
hopefully). Oh, and just because you think stoich is right, that doesn't
mean anything lean or rich of stoich is even close, because stoich is
*automatically* correct because of the way these sensors work, even when
the "non-lab grade" thingee is way off and completely uncalibrated. Let
me put it this way: because of the way the sensor itself works, even if
the electronics on either lean or rich side were off by 5 or even 50
AFR!, stoich would still be correctly read. Nothing ELSE would of course
be even close, but yeah, you can get stoich right. Woopee.

See below to understand just exactly how far you could be off with one
of these so-called "non-lab grade" things.

>On my base fuel map, the cold idle was showing 2v, which is about 12:1. =
=20
>Neato.  Full blown fuel tuning will begin shortly!

Yeah, it's neato if you can trust the 12:1 to be anywhere near 12:1.=20

See, when Bruce says, "it's not lab-grade" whenever someone asks about
errors/accuracy, that's supposed to mean, "forget the errors, we don't
need no stinking AFRs, we just need ballpark indicators". Not much
better than 10 leds hooked to a NB O2 sensor, really.

Look, IF the circuit were designed and/or working correctly, the Cal R
built into the connector *alone* SHOULD bring the free-air calibration
point within about 10mv everytime. Ours does. Yours is off by 90mv
apparently, others maybe more. Now let me explain what this means with
your particular circuit. At free-air O2 concentrations, being off by
0.090V when the range of your circuit from stoich to free-air covers
only 1.5V is a pretty big error. Add that to the 5% sloppiness in the
Cal R factory calibration to begin with, and you could be off as much as
10-15%. You don't think this is too bad, especially for a "non-lab
grade" device? Hmm? Well, ask yourself what 10-15% of 12AFR is.

Hell's bells, even WITHOUT the use of the Cal R, the factory slop from
sensor to sensor is around 15% at most. That figure is from published
NTK data, not just our own testing/calibration of over 100 sensors now,
which also confirms it. The fact that your circuit can only get to
within 10-15% of true AFR is pretty abysmal. It's also potentially
dangerously misleading.

See, even tho you may buy into the notion of "it's not lab grade, so
ignore the errors", you're STILL thinking in terms of real AFRs when you
say "2v, which is about 12:1. Neato."  That's the shell-game going on
with this expression of "it's not lab grade". You might as well just
come out and say, "it doesn't read out in AFR", but some other
completely uncalibrated and 'unrepeatable from device to device' NUMBER.
It could be actually 13AFR, and you think you're getting 12AFR and are
all tickled with the 'results'. Yeah, right. Specially in your situation
of running with some decent boost.

OK, there might be a place for that, a slightly better mixture indicator
than a NB O2 connected to 10 leds, but don't compare it to an actual
"AFR meter". I can guarantee you with both sets of my dentures, NO
commercial AFR meter is anywhere near as sloppy as this "non-lab grade"
thing you're using.

So the next time your 'dweeb-WBO2' reads you off a 12 AFR, just
remember, that might mean an actual AFR of 11, or it might be 13AFR. You
just won't know. The only thing you can be sure of is that when it reads
stoich, it's likely to actually be at stoich. If you're tuning right
around stoich, sure it's a fine 'instrument'.

You have a buddy with exactly the same engine, and you both have
'dweeb-WBO2's, you do some runs and say, 'yeah, at WOT, my AFRs are nice
& comfy at 12.5AFR', while your buddy's results are always way off from
that, using the same fueling. Can you compare readings? Nope, they're
NOT actual AFR numbers, but 'non-lab grade' aka
unrepeatable/uncalibrated NUMBERS. Just numbers, not AFRs.

Hey, but you saved a couple $100 bucks by not buying an FJO or whatever,
right? So, what's the problem; you got what you payed for. Junk.

Could you get lucky and win the 'non-lab grade' lotto and your
particular circuit and sensor Cal R combo, you actually read AFRs that
are close to actual AFRs?  Yes, indeed you could. I've heard some claim
they did. You could also win the lotto. Good luck.

Gar Willis
Principal Engineer (actual engineer, with 30+yrs exp. & MSEE from UC)
EGOR Techno
3491 Edison Way
Menlo Park, CA 94025
650-216-9874
garwillis at msn.com (email & PayPal transfers)
www.egortech.com (website best viewed with IE)

>>From: "Bruce" <nacelp at bright.net>
>>Reply-To: Diy_efi at diy-efi.org
>>To: <Diy_efi at diy-efi.org>
>>Subject: Re: [Diy_efi] WB free air calibration
>>Date: Wed, 29 May 1996 13:30:24 -0400
>>
>>
>>
>>It's not a lab grade devise.
>>get it on the car, and use it <G>.
>>Unless, your just extremely lucky, you'll immediately see where your =
off in
>>the calibration.
>>Bruce
>>
>>
>>----- Original Message -----
>>From: "rob files" <rncfiles at hotmail.com>
>>To: <diy_efi at diy-efi.org>
>>Sent: Wednesday, May 29, 2002 12:57 PM
>>Subject: [Diy_efi] WB free air calibration
>>
>>
>> > Hi all,
>> >
>> > After replacing some blown out parts, I got my diy-WB sensor working=
=20
>>last
>> > night.  Thanks to all the REAL contributors to the project.
>> >
>> > My free air reading is something like 3.91V.  I was wondering, does =
this
>> > mean all of my readings will be offset by 0.09 volts?  I was =
thinking
>>about
>> > adding a trim pot to the calibration resistor and adjusting Vout to =
be=20
>>the
>> > 4.0V free air value.  Any reason why this would be a bad idea?
>> >
>> > thank again,
>> > Rob
>> >
>> > _________________________________________________________________
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