WB O2 and EGT compensation

[David Harris]

Since Kevin brought up WB O2 GP's. I thought I'd
mention that there is a GP for a complete unit made by
FJO (a company in Canada). I was going to join that
until I found out you guys had been working on a DIY
version.

One thing I was curious about was the EGT temperature
compensation. The reading on UEGO's has a temperature
dependent variable. I forget which way it goes but I
believe the UEGO reads richer than reality when EGT's
increase. This is why many WB O2 meters include an EGT
probe to get accurate readings.

I had asked FJO about how they obtained such good
accuracy without an EGT probe. Here is their response:

"While it is true that the UEGO sensors are somewhat
exhaust gas temperature dependent, this effect can
be minimized by several techniques, some of which use
the characteristics of the sensor itself. In fact,
using an EGT probe to compensate would prove to be
a less effective solution as the probe would not
accurately reflect the UEGO sensing element
temperature. In our wideband controller we have
employed techniques to reduce the effect of
temperature-induced error to less than 0.05 AFR with
an overall accuracy of better than 0.1 AFR.
Unfortunately, I can't go into detail on exactly how
this is achieved as this is proprietary information."

Since the current DIY solution is analog only, I
assume that we will have the same temperature induced
error. I'm guessing that FJO characterized the sensor
against a "real" WB O2 setup or came up with a
compensation curve vs temperature.

So what do you guys think they did? What about their
claims of accuracy? Do they sound feasible?

Dave
91 GVR4's #619 & #849


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