EGOR Output Signal Survey

[Bruce Plecan]

> 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.

Definetely

> 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.  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.

Simple is a GOOD thing.

> 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.

> What are meaningful divisions?

This is where we kinda get to too much of a good thing.  IMO, as long as the
results are repeatable, is the number one concern.  If there is enough
resolution to see that the changes are having the expected results we're in.
For me 10 is fine, but I can see where others would want the 20 flickering
lights.

  The A/F to
> voltage curve is pretty badly curved, but is
> that even what we want to display?  Here is
> how I see it.  Imagine we have this box of air
> and add a bit of fuel.  We get a voltage reading
> from our sensor when we burn the fuel.  Every
> time we add a larger amount of fuel (increase
> injector pulse width), Ip and our Vout shift a
> proportional amount.  A nice linear function of
> fuel increase to voltage.  So why is the A/F
> curve so UN straight?  BECAUSE the function
> described above IS NOT A/F, IT IS F/A.  So I
> propose a linear display of the voltage out is
> really what we need, to relate tuning to output.
> We can MARK it in A/F, but the markings will
> not be linearly spaced.

Mark a high end, and a low end reading and be done with it.  The MAGIC is
the tuning, not in the display.   Let me rephrase that, knowing where you
are, and beeing able to see that your going in the right direction is what
we need.  IMO, too often folks get lost in their tuning.

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

I'd agree with that, avoiding a too soon reading.

> 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.

YES, YES, YES.
Using the 0-1 will allow data logging with all the conventional scanners!!!.
C/L can be blocked, and then just info logged to see where things are.
THANKS
Bruce
>
> All these outputs could exist at the same time, or
> just put in parts for the ones you want.  I await
> your opinions on the subject.  Bruce Roe
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