[Diy_efi] wide band O2's

[WopOnTour]

Bruce
I'm wondering if the various sensors you had an opportunity to test included 
the ECM AFM1540 and if so, how it faired in comparison the LA-3. It too is 
compatible with ETAS INCA via the Bosch SMB interface. (I'm presuming CAN) 
All of ECMs range of product are capable of field calibration using ambient 
air.
WopOnTour
----- Original Message ----- 
From: "Bruce A Bowling" <bbowling at earthlink.net>
To: <diy_efi at diy-efi.org>
Sent: Wednesday, July 06, 2005 8:25 AM
Subject: Re: [Diy_efi] wide band O2's


> The WB02 subject is a very interesting one. I spent about 7 solid months 
> researching the subject and performing numerous test. There are so many 
> aspects to this whole subject, circuit configuration is just one of them.
>
> Build a gas flowbench and flow some calibration gas over the sensor, this 
> is a real eye-opener. I did not test a lot of meters (but several I did 
> test, I will not post the results because it was not a real detailed test, 
> people should do this themselves), but the one that was the most accurate 
> was the ETAS LA-3, maybe this is why it costs $4K. But there is no where 
> near $4K of parts in it, just a simple '332 processor but real good analog 
> circuitry for the pump, etc. And they use a switcher power supply for the 
> heater (high frequency w/ averaging), this yields a nice clean heater 
> supply voltage without PWM switching noise being injected in the 
> pump/nernst. Heater PWM noise getting into the pump/nerst servo is a real 
> problem, one has to be careful to sample on the same point of the PWM and 
> not during switching.
>
> Garfield Willis did some testing years ago on these, check the archives 
> for his name and see his comments. He held a lot of info to himself, but 
> everything he alluded to I was able to verify independently with my 
> testing, and someone else I corresponded with also came up with the same 
> results. In a nutshell: the sensor (each) needs gas calibration - they 
> tend to vary all over the place, enough that the cal resistor is not 
> enough (concluded from bench testing), the standard calibration curves 
> assume one gas mixture type (this is an issue with nitrous, alcohol, E85, 
> propane, etc), the heater control is absolutely critical (especially when 
> the battery voltage drops low enough not to provide enough voltage even at 
> 100% PWM, this is why both ETAS and the PWC use a switcher supply for the 
> heater), there are significant pump current offsets on both sides of 
> stoich (and they are different, and depend on the particular sensor). And 
> there are things like barometric partial pressure correction, exhaust 
> backpressure compensation, etc.
>
> It all depends on how accurate you want the meter, and under what 
> conditions. The only way to determine if a particular meter is accurate is 
> to measure it with a known gas source. And run the meter with varying 
> supply voltage (like from 8 volts to 16 volts, particularly the low end). 
> The PWC site gives detailed info on how to make a gas flowbench and all 
> other pertinent info (like baro correction and Brettschneider 
> gas-composition PC applications, etc) in order to perform a study of WB02 
> meters.
>
> - Bruce
>
>
> At 12:38 AM 7/6/2005, you wrote:
>>Adam
>>Here is an interesting article on  WBO2 calibration from the Bruce & Al at 
>>Megasquirt
>>http://www.msefi.com/msinfo/PWC/
>>Regards
>>WOT
>
>
>
>
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