Return of the diy_EGOmeter (YES, it's finally ALIVE!!)

[David Chambers]

garfield at pilgrimhouse.com wrote:
> 
> On Wed, 08 Apr 1998 17:00:31 -0700, garfield at pilgrimhouse.com wrote:
> 
> >it's a comin,
> >honest engine. Give me another week before you tar and feather me for
> >dragging my virus-infested butt. Whimper. Man how can such tiny lil
> >critters make you feel like sucha pieceOyou-know-what.
> 
> Man, that was almost a week ago, and I'm way worse than I was then. What
> a sissy! I'm tellin yous man, these virii vermin are kickin me
> buttocks!! My doctor wants to hospitalize me if I develop even a hint of
> a secondary lung infection; I'm right on the doorstep of viral
> pnuemonia! Whimper is right! Crapola, what a BORE.
> 
> BUT, do I have good news for YOUS GUYS!!! I got in some quality time
> today testing our diy_EGOmeter, and I just got finished sending off a
> missive to Frank with the nitty gritty details, but suffice it to say,
> it looks like we have a *weiner*. The free-air O2 ion pumping current my
> circuit settles at (the so-called free-air calibration point) is only 5%
> off from what Frank gets with his NTK sensor and interface box!!!! This
> is stunning confirmation that we are go-for-launch, and that the Honda
> OEM sensors are indeed essentially the same as the NTK sensors. I
> measured 6.3 mA @0.445V, and he (Frank) gets 6.0 mA @ 0.428V. Before you
> think them stoich voltages are somewhat different, lemme tell ya that we
> discovered there's a real black-hole steep Ip null right at stoich, just
> like that cliff-edge part of the conventional Lambda curve. The voltage
> of the measurement cell, VsCell, goes along niceNlinearly heading for
> stoich, as you crank up the O2 cell current, IpCell, but just as you get
> to 0.450V, all hell breaks loose, and even a tiny lil tweak of IpCell,
> and you're on the other side of stoich by 200-400mV. So what I'm saying
> is that Frank's instrument's feedback loop locks stoich up at 0.428V,
> and mine at 0.445V (hey, mine's more precise than NTK's, hee hee;
> alright, it's also a tad twitchy at the moment), but for all intents and
> purposes, it's smack on the same point in the curve of IpCell vrs.
> VsCell. Hence, the free-air calibration currents diff. by only 5%.  You
> couldn't ask for a better reassurance that the Honda OEM sensor and the
> NTK "special salsa" version are essentially the same, except for their
> method/values of embedding CAL resistances. The most important thing is
> that since the sensors perform basically identical, we can just plan on
> calibrating the boxes each of us build with this "free-air
> self-calibration" procedure, and care not a wit about what the internal
> CAL Rs are set at, for their various original usage. "We don't need no
> stinking CAL Rs", is the bottom line. Besides, as I mentioned to Frank,
> use of the CAL Rs also can't compensate for sensor aging nor
> deterioration due to lead/dirt contamination, like a self-calibration in
> free-air can, so it's better we don't mess with them Rs anyway, eh?
> 
> Actually, I have a theory about what the CAL Rs in the Honda sensors
> actually are, and will test me hypothesis when I get a couple more, but
> the main thing is we aren't dependent on even knowing what they mean,
> since the sensors can be self-calibrated in free-air. In fact, this is
> THE method of choice for the Horiba boxes, since they don't ship their
> sensors with ANY embedded CAL R in the cable. They ASSUME you're going
> to self-calibrate it yourself.
> 
> I mentioned to Frank that I have a couple tweaks still needed to the
> circuit, one to detune the hyperactive feedback; I didn't count on the
> Ip vrs Vs relationship being so sensitive near stoich (hence it twitches
> on it's way to settling, instead of gracefully landing via a smooth
> approach, when you first turn it on), and I need to replace one of the
> parts in the "warm-up" circuit with one I've got on order; the current
> part doesn't like anything but 12V supply (some times it switches,
> sometimes it lounges), and I want the whole thing to function on 5V. But
> the bottom line is, at this point, looks like we get our O2 meters
> finally! As soon as I get the last tweaks done and everything checked
> out completely, I'll post the schematic & parts list up in my group's
> aviation DropBox, which I'll post the URL for when the stuff's ready.
> Give me another week or so to recover and clean up things, and we can
> all go about building a clone of ole diy_hUEGO. [Too bad they don't make
> the O2 sensor tips in the shape of a cone; that would be so fitting].
> 
> Cheers,
> Garfield
This sounds great. Do you need anything done in the way of a user
interface to the output of this?. Ie a processor circuit some LED
displays and software to run same.
Dave