EGOR Output Signal Survey

Thu May 17 13:47:10 GMT 2001

> Date: Wed, 16 May 2001 04:12:24 -0500
> From: bcroe at juno.com
> Subject: EGOR Output Signal Survey
> 
> It appears all the design problems of a practical
> wideband OX sensor circuit have been solved.
> That leaves the question of just what to do with
> the output.  I am proposing some ideas here.
> Your feedback would be greatly appreciated 
> before things are finalized.
> 
> The first item is the Rcal resistor, the resistor 
> built into each wideband sensor at the factory
> to cancel differences between sensors.  A simple 
> circuit has been designed to use this feature, and
> I think it should be included in any group design.

Very much agreed. EGOR is pretty much pointless unless
it can deal with the variances in individual sensors.

> 
> Next is the output voltage.  A curve seen in some 
> equipment reads like
>     A/F             Volts
>     22:1           3.5
> 14.57:1         3.0     stoich
>   10.5:1          2.0
> 
> A circuit from the list runs about 0.5 V lower
> than above, but otherwise the same.  My ckt
> runs 0.2 V lower than above.  

Can I ask how you know that? Are you calibrating 
from a known source? Not trying to back you in a 
corner here, just curious.

This is one of my biggest questions about EGOR-
How do we *know* what the voltage to AFR curve is
without calibrating one or more against a standard?
True, you can use the known characteristics of the 
sensor, but with part variances and tolerance, you
could still be off a fair amount. (especially on a
0-1v range) 

>I propose we use 
> a design that can produce any of the above by
> changing a couple of resistors.  
> I have a reason for running mine at 2.8 V stoich 
> instead of 3 V.  The most accuracy is desired 
> around stoich, so my circuit is intended to be 
> dead on at that point.  Calibration and other 
> errors come into effect as you move away from 
> stoich.  To minimize errors, the stoich output V 
> is the same as my reference power supply, and 
> my reference power supply is 2.8 V.  The reason
> for that is to allow use of newer parts, eliminating
> a couple dozen other parts.

Personally, I'd like to see the following 3 ranges:

0-1v, inverted; rich = 1V  (for the guys doing WB
control of the stock ECM)

0-5v, normal, for the guys with dataloggers and for
general purpose use.

0-16v (0-12 acceptible), for use with stock ECMs 
datalogging via ALDL. 

The rationale for the last one is based on some wide
band testing I've done recently via the ALDL. Using
the 5V A/D inputs, you end up with .1 Lambda being
.2 volts or so. The noise floor in my particular ECM
seems to be higher than that, so I'd like to use the
0-16v Fuel Pressure A/D to get better resolution (and
lessen noise-induced errors)

As far as the max of the range (in terms of what you
use for voltage reference parts), it's not really that
critical, as long as you know what the voltage to AFR
curve is. I'm with you, use the cheapest, easiest to
obtain part you can that's close to the voltage range.

Maybe a better solution would be to design it 0-5v,
then stick an Op-Amp divider/multiplier on the output
to do the scaling. Or isn't that feasible with the
design?

> 
> My next item is a real time display, a readout.
> I propose a bar graph with a center LED to 
> indicate operation at stoich.  As operation 
> moves more rich, a column of green LEDs would
> light forming a bar growing away from stoich.
> For lean operation, a column of red LEDs would
> grow in the opposite direction.  The length of the
> bar would show how far you are from stoich, and
> the color indicates in which direction.
> 
>      RRRRRRRRRRSGGGGGGGGGG
> 
> If we have a readout, how should it be calibrated,
> and to what resolution?  I would suggest 10 
> divisions in either direction might be good for a
> dashboard gauge, but up to 20 each way might 
> be better for wide range tuning and operation.

For the dasboard gauge thing, I could see it, but 
you can get Westach to make you an actual gauge
(I have one) that will take the voltage input and
display it on a calibrated face. Much nicer (and
better damped) than peering at an LED display.

Personally, If you were to add any display, it'd be
nice to see a numeric one like the Horiba has. Nice
to, but not necessary.

Somewhat Editorial Sidebar: After using the gauge 
for tuning and using a datalogger/ECM datalogging,
there is just no substitute for actually seeing 
the relationship of AFR to RPM *after* the run is
done, rather than trying to read it on the fly. There
is just no way to do much useful tuning without that
datalogging capability. IMO.  <editorial off>

> 
> Allright, there is one more factor.  That almost 
> perfectly linear delta fuel to delta voltage
> relation, shifts as you pass stoich, to a slightly 
> different very linear relation.  I propose that the 
> gain (number of divisions per volt) BE SLIGHTLY 
> DIFFERENT on the 2 sides of stoich.  So now a 
> given increase in fuel will cause the SAME 
> number of divisions movement of the bar, from 
> one side of the display to the other.  Circuit wise 
> this function is almost free. 

Are you saying you want to "linearize" the AFR such
that a linear voltage is linear AFR? That'd be a 
*very* good idea, provided you can be sure you know
that your calibration is true.

I'm working on a way to do this in the ECM (via a 
table lookup -> out to ALDL AFR commanded), but it
requires a lot of table entries to get it accurate.
Anything to get the voltage more linear would be a
big help.

> 
> Something else we could add is a switch for
> free air calibration.  This would normally be 
> off scale, but it would reduce gain to put an
> indication at 22:1.

This would be very nice... like hold a button down,
and 2.8 V (the ref) = free air.

> There is a warmup time approaching a minute
> for the sensor.  

If you're lucky. :)  I've had to "Reboot" WB circuits
several times before it "takes" and sez it's warmed.
Could be a quirk of the circuit, though.

>I suggest the display be blanked
> (turned off) during warm up.   Besides giving an
> indication of operation, it allows the considerable
> LED current to be "stolen" from the sensor 
> heater circuit, saving power, heat, and heat sinks.
> The cost is one transistor. 

This would be fine. Would be nice to have some 
indication for the user, though, maybe a single
"warming" LED? 

> One more output that might be useful would 
> have a 1 volt output range, reading 0 to 1 volt as 
> we moved from 15:1 to 14:1 A/F.  The idea is to
> look like a conventional narrow band OX sensor.

Even more so... have stoich be .450, and let 'er
swing full range (AFR-wise), as I mentioned above.

The integrator/BLM rates could then be modded to have
the thing hit stoich based on EGOR... then maybe some
more code to do full-tilt wide-band control. (Much
work to do there)

Thanks for your work on this, Bruce and gang. The 
ECM world is a much better place to live. :)

Later,

Dig
turbodig at yahoo.com
'91 Syclone, with Wide-Band Option.

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