would heat effect A/F readout?

Re: Re: would heat effect A/F readout?

Boost Junkie said:

EGTs won't change the readings from a true wideband O2. They can influence the output of narrow-band O2 sensors, though.

Steve

Click to expand...

BZZZT! Respectfully - I believe this may be wrong. There has been some traffic on the DIY-WB list recently about temp and it's effects on WB O2s. It apprently depends on which O2 you're running. The Bosch sensor is indeed influenced by heat and must be temp compensated in order to get a "true" reading. The NTK sensor on the other hand isn't effected by heat, however it IS apparently effected by backpressure I can repost the explanation on this if it would help, I get the impression this guy has spent more than a little time delving into this stuff with the various affordable O2s. He'd like to get a lab comparison sometime on the DIY setup but lacks the equipment right now...

BTW - the guy who designed those kits is now selling them assembled in varius stages (smack). Depnding upon how my assembly worked out I may be purchasing one as the prices really are darned decent for what they're offering IMO. The FJO is pretty competitive as well with the Motec sensors being pretty darned out of sight.

Boost Junkie said:

With my car pulling on a Dynojet the FJO wideband mounted just after the turbo outlet gives the same readings as a the shop's Horiba wideband stuck in the tip of the tail pipe. The temps at those two points would be several hundred degrees C different. Maybe it's their home-brew controllers that aren't doing the job.

Steve -- FJO dealer

Click to expand...

Does the shop use an NTK or a Bosch sensor? As I said above only one of them is effected by temprature, the other is effected by pressure. The home brew DIY boxes, supplied with enough input voltage, are apparently doing just fine against more expensive WB solutions when compared with one another. Below is the list E-mail that answered these questions - it would seem his testing is much like your's with regards to accuracy...


> > i was just wondering , although this is a WB o2 sensor, is the unit temperature compensated ?? As the temp can change the afr results read by most sensor quite a bit...

I have been meaning to put up technical details of how the NTK
sensor works, and that would include how the AFR varies with temperature.
As it turns out, the NTK sensor's technology (or do I mean the physics of the device) makes it less sensitive to temperature variations than say the switching technology Bosch LSM-11. But having said that, the DIY-WB sensor's heater circuit is a little more sophisticated than most LSM-11 setups, so temperature compensation is not really an issue with the DIY-WB.

Now, a little known fact: The NTK sensor (or I should say the physics) is much more sensitive to exhaust back pressure than to temperature variations of the sensor element. This does become an issue with turbo applications where at full boost (where back pressure is highest) an uncompensated meter will indicate a leaner mixture than is actually the case (it also works the other
way too, a lean mixture will read less lean than it really is). The only way to compensate accurately for this is to measure backpressure directly with another sensor and factor that into the Ip vs AFR map.

> Also has anyone compared the kit to a good commercial one such as the motec one , which uses the same sensor from what i gather ?

I have only seen anecdotal references to accuracy, and I'd be happy for someone with an exhaust gas analysis setup to do back-to-back tests with some of the commercial units. Those who have done simple tests have not seen any measurable differences between the DIY-WB and an Horiba and a DynoJet meter.

But, to do measurements properly requires equipment that I don't have, and certainly most tuning shops won't be able to give any more an indication of accuracy than what I've said above.

While I'm on the issue of temperature compensation, it is possible, with more complex circuit/software to measure the sensor element's actual temperature and to compensate accordingly (eg. see Bernd Felsche's DDL project)
http://members.iinet.net.au/~metapro/bernie/tech/EFI/DDL/DDL.html

And, I hear that Julian Edgar (of AutoSpeed fame) has abandoned plans to release a design that uses a Bosch LSM-11 with temperature compensation circuitry/software because the DIY-WB appears to be a much simpler/more accurate design. Julian actually rang me a left a message to this effect while I was on holidays - so it will be interesting what we see from AutoSpeed AFR measurement projects in the future ;-).

And to add grist to the rumor mill, I am playing with DIY-WB version II which I hope will have backpressure compensation as well as RPM and other logging channels - but no promises - the present design will always be very good value for money. I also have a real production Bosch LSU sensor that is/will be available
in Australia, hopefully at a comparable price to the NTK sensor (say AU$300 or less).

Enough rumors - lots of work to do ... And, BTW, I now offer the DIY-WB as a built and tested PCB:

http://www.techedge.com.au/vehicle/wbo2/wbo2.htm


Does that help? This is one of the guys doing the design work and research on these sensors. Quoted without his permission but I don't think he'll mind.

here is something interesting
" An Oxygen sensor is a chemical generator. It is constantly making
a comparison between the Oxygen inside the exhaust manifold and air
outside the engine. If this comparison shows little or no
Oxygen in the exhaust manifold, a voltage is generated. The
output of the sensor is usually between 0 and 1.1 volts. All
spark combustion engines need the proper air fuel ratio to
operate correctly. For gasoline this is 14.7 parts of air to one
part of fuel. When the engine has more fuel than needed, all
available Oxygen is consumed in the cylinder and gasses leaving
through the exhaust contain almost no Oxygen. This sends out a
voltage greater than 0.45 volts. If the engine is running lean,
all fuel is burned, and the extra Oxygen leaves the cylinder and
flows into the exhaust. In this case, the sensor voltage goes
lower than 0.45 volts. Usually the output range seen seen is
0.2 to 0.7 volts.

The sensor does not begin to generate it's full output until it
reaches about 600 degrees F. Prior to this time the sensor is
not conductive. It is as if the circuit between the sensor and
computer is not complete. The mid point is about 0.45 volts.
This is neither rich nor lean. A fully warm O2 sensor *will not
spend any time at 0.45 volts*. In many cars, the computer sends
out a bias voltage of 0.45 through the O2 sensor wire. If the
sensor is not warm, or if the circuit is not complete, the computer
picks up a steady 0.45 volts. Since the computer knows this is
an "illegal" value, it judges the sensor to not be ready. It
remains in open loop operation, and uses all sensors except the
O2 to determine fuel delivery. Any time an engine is operated
in open loop, it runs somewhat rich and makes more exhaust
emissions. This translates into lost power, poor fuel economy
and air pollution."