[Diy_efi] WB free air calibration

[bcroe at juno.com]

Just thought I would add a few corrections to the "facts".

On Wed, 29 May 2002 22:56:19 -0700 Garfield Willis 

> We have two 'dweeb-WB' circuits here we use for demos for 
> those customers that have heard of it

> neither works properly until you get up to ALT output voltages, 
> so they both expose the sensor to late warmup, and from
> sensor to sensor, they each may take from 30secs to a 
> couple minutes to NEVER, for the sensor's heater to warm 
> up properly, once the ALT is turning. Depends on the sensor. 

The heater may be nearly completely warmed up in a minute 
before the engine is started.  The LED may not come on at this 
time, but it will very shortly after the engine is started.  If warmup 
is 2 minutes to NEVER, it means the WB unit was not properly 
set up for that sensor per instructions (add 15 ohm resistors).


> I have it on good authority that the dweed-O2 Cal R circuitry 
> was 'reverse-engineered' based on measuring just TWO 
> sensors.  Yuh, good plan. I could quote the person involved, 
> who didn't know he was communicating with us at the time, 
> but I wouldn't want to embarrass him. :)  I even have drawings 
> and explanatory notes; we do our intel homework.

The Rcal circuit wasn't "reverse engineered" at all.  It was 
derived from the equations in a technical paper on the 
sensor.  As a sanity check, results from some sensors 
(quite a few more than 2) were compared, with favorable 
results.


> 'Dweeb-O2' requires 14+V to operate, and will NOT operate  
> on even a fully charged +Batt w/o the ALT running, so it won't 
> even begin to warm up the sensor until the exhaust is 
> already flowing. 

Wrong, see above.  If you must check A/F while cranking the
engine, you will need a stationary supply for 14 V, but that is 
not hard since the engine is going nowhere.

All the talk about % error A/F is not very relevant.  A/F is a 
non linear function runing here from 10 to infinity, and % 
error just doesn't apply well to non linear functions.

What is relevant is the amount of fuel you add to the air, 
which IS a linear function and the reciprical of A/F.  Our 
good luck is the error in detecting stoich is essentially 
zero, so errors are in distance from that point.  What if 
from S you increase fuel by 10%, and the DIY WB makes 
a 10% error measuring THAT INCREASE?  It measures 
109% or 111%, your fuel measurement is off by under 
1%.  An inconsequential amount because 10% of 10%
is only 1%.

Bruce Roe

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