[Wbo2] Using the Bosch WB sensor with L1H1 circuit board

[Ron Vinsant]

James Holland wrote:

> I tried to post this yesterday but hit reply instead of reply all, I 
> apologise to Allen if it seemed like I was having a go at him but I 
> did want to raise a few points,  I don't want to get into the who did 
> what or when.
>
> I am interested in what tests were performed to verify accuracy. I am 
> curious as to the effects of variations in exhaust temperature and the 
> effect of backpressure too. The Bosch datasheet shows that these do 
> have an influence but never having made any backpressure measurements 
> (or EGT) I can't really equate those values to real world cases.
>
> These were my comments on environmental testing, I think some of the 
> points have been answered:
>
> I design electronics for military applications so I do appreciate 
> designing to meet temperature ranges and designing to meet 
> environmental requirements. Environmental testing is a good thing in 
> terms of design proving but very expensive and needs a clearly defined 
> set of requirements. What level of testing do you think should be 
> carried out? Proper selection of components will allow you to meet the 
> required temperature spec BUT what spec do you really need? If the 
> unit is going to be inside the vehicle then a commercial temperature 
> range is probably more than adequate, how many of us are going to be 
> out tuning our vehicles when its 40C below. None of the Mitsubishi 
> ECUs that I have seen have been conformally coated, they are clearly 
> designed to be used inside the vehicle where its dry and indeed they 
> are mounted up under the dashboard. Vibration testing is to some 
> extent irrelevant, if you sell something as a kit you can't control 
> the build quality.
> High specs and thorough testing costs money, there has to be a balance 
> between cost and performance. What I want is the cheapest possible 
> piece of kit that will do what I want it to do.
> This wasn't intended to be a long winded rant but I think there are 
> some good points here that everyone should consider when they are 
> building their WB kit, wherever they get their design from.
>
> Cheers
> James
>
>
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>
James,
Your comments are well taken; by me anyway. I have also wondered about 
calibration issues. I have been using a F.A.S.T. fuel injection system 
on a 5.7L small block Chevy with closed loop A/F ratio control. I have 
used a couple of A/F meters to see how my system was controlling the 
A/F. Spark plug color and exhaust pipe color told me that I should 
question my control system.
My quest for answers got me to this forum where I have found thought 
provoking conversations that have taught me a lot. Peters comments have 
been particularly helpful.
I have never been able to completely correlate one meter to another at 
low flow rates (idle). At high flow rates I get very good correlation. I 
am told this is due to partial gas pressure problems at the sensor tip 
(any sensor).
Now to my real point. The sensors themselves, as far as I have been able 
to determine, do not have a specified tolerence. If anyone can point me 
to either a Bosch or NTK datasheet that says otherwise, I would be greatful.
 I did see a graph faxed to me by a NTK engineer that showed "typical" 
voltage vs. A/F but no where was a max or min accuracy stated. He told 
me that he beleived that the sensors have a 5% tol when NTK 
manufacturing tests them in a specific production test set up but he 
could not tell me how this test was done (flow rate, gass pressure,angle 
of attack of the gas etc.).
I notice that at California Smog test stations a couple of canasters of 
"calibrated test gases" are used to set up the emmission measurment 
instruments. I was told by a local technition that A/F is derived from 
the gas content of the exhaust and not specifically measured by a sensor.
Can anyone comment on the issue of measurment accuracy, or even 
repeatability of the sensors themselves? We could discuss the merits of 
the rest of the instrument later.

Ron Vinsant