Wide Ratio O2 meter

[garfield at pilgrimhouse.com]

Hey maties.

After some further converse with Frank, I think I can attempt to
"eXplain" how this latest generation of "ion pump" sensors work.

Brace yourself for a drink from a firehose. The way a std "Nernst Cell"
O2 sensor works is it's a "solid electrolyte" battery with exhaust gases
on one side and atmospheric on the other, and the voltage you are
reading from this "battery" is a measure of ratio of the "partial
pressures" of O2 across the cell membrane of this Nernst cell. That much
is considered old hat, the Nernst equation, and all that.

The problems with these older sensors was that they were "passive", in
that they were dependent not only on achieving an adequate temp, but
also exhaust gas flow, so both sides of the cell are supplied with
representative quiescent gas pressures. Hence, they were slow to heat,
slow to respond, etc.

Enter the next generation. Instead of relying on atmospheric oxygen to
supply one side of the Nernst battery, and expecting a certain
commensurate amount of exhaust gas & temp to get the cell "in range",
the sensor now supplies it's OWN oxygen for the reference side (used to
be atmospheric). It does so with a current-controlled oxygen ion pump.
And instead of measuring the resultant voltage from the Nernst cell
directly, from whatever the partial pressure ratio of exhaust O2 vrs.
atmospheric is, it does the following:

The oxygen ion pump is used/controlled to supply *just enough* oxygen
ions on the reference side that the Nernst cell exposed to the exhaust
gas ALWAYS reads 0.45V. This corresponds to the amount of oxygen needed
to achieve "stoich", if you will, at the Nernst cell membrane exposed to
the exhaust gas. Thus, the amount of current needed to drive the oxygen
ion pump to produce this "compensating" amount of oxygen is directly
related to the ABSENCE of O2 in the Nernst measurement cell. Since the
oxygen ion pump can both pump oxygen ions IN as well as OUT, it's able
to either feed (if the mixture is rich) or remove (if the mixture is
lean) oxygen from the Nernst measurement cell, in order to achieve
stoich at that cell membrane. Therefore, at stoichiometric exhaust O2,
the pump is neither supplying nor depleting ANY oxygen, the ion pump
current is zero, and you're "in the O-zone". Heh.

So instead of directly MEASURING the existing oxygen ion concentration
in the exhaust gas, you feed the Nernst cell membrane being exposed to
exhaust gas, WITH oxygen ions sufficient to achieve stoich in that
membrane (the sensor), measure the amount of oxygen it took by how much
current you fed to your oxygen ion pump, and voila, you know the exhaust
gas oxygen level, indirectly, by knowing how much oxygen it took to
raise-it-to/deplete-it-from stoich. Neat, huh?

Thas it, dudes. Not that complex after all, eh? We'll see if that guy
was right about it taking us 5 years to figure this out. Hee hee.
Somehow, I think not. We'll just take this as another "you can't
possibly do that" sorta challenge, eh what? I like them most of all.

Garfield

P.S. This also could explain why these sensors are capable of being
somewhat "self-calibrating" AND "lead-tolerant". The Nernst battery
voltage for stoich of 0.45v apparently doesn't change, but the log knees
on each side (lean or rich) of the curve DOES with
age/lead-contamination. Well, if we're not relying on these knees or
getting THEM calibrated, but simply hitting the stoich point, which
doesn't change, then all yous gots ta do is calibrate to atmospheric O2
levels, namely how much ion pumping does it take to deplete a
hot-but-no-exhaust-gas sensor to stoich. I'm guessing here no small
amount, but I'd guess this is what's cal'd into the Honda connectors,
and the car ECU's do NOT do auto-recalibration, but I'll bet the Lambda
meters sold commercially DO. Just a SWAG (scientific wild ass guess),
mindya.