[Diy_efi] Bernd: UEGO sensor question

[Perry Harrington]

On Sat, Jul 13, 2002 at 12:10:02PM -0500, bcroe at juno.com wrote:
> The Vs output is like a battery, a very low current one.  If 
> it were a variable resistance, the pull up or pull down 
> resistor value would be critical (which it is not) like the 
> pullup on a water temp thermistor.  

Bernd explained it as a bias voltage, which makes some sense.  For
it to bias would require that it has the ability to draw current
from it and cause the voltage to fall, which would imply it's
a load, ala resistor.

> 
> The WB "pullup" resistor is more of a current source, 
> since the voltage at both ends is controlled.  It can be 
> used to detect when the "battery" is not yet operational, 
> by shifting the voltage out of normal range.

With this explanation it makes a bit more sense.  I've looked
over the schematic and don't see where this bias is 'turned off'.
Since the Vs output will always be 0-1.1v in operation, how
do you sense when it has warmed up (gone from 0v to 1.1v)?

Does the 2v just present an offset from the 0-1.1v, so the range
is 2-3.1v?  Da, and the middle is 2.5v, which is your stoich reference?

I'm not worrying about the cal resistor right now, as I assume that is
only used:

- In analog amplifier circuits to set the gain,
- In applications where calibration via free-air is unavailable (Honda).

Is my understanding that the Cal resistor is used as a scalar for the current
value.  In the DIY-WB circuit it seems that the 2.5v voltage would be non-linear
since it's using -4v as ground and +4v as Vdd, this would make the 2.5v really
-1.5v instead.  The whole output after the U4c is puzzling me.  The current paths
and voltages are not clear to me.  The bias from the Lm431 I don't understand.

> 
> Bruce Roe
> 

--Perry

-- 
Perry Harrington			Data Acquisition & Instrumentation, Inc	
perry at dainst dot com					 http://www.dainst.com/

Those who would give up essential liberty to purchase a little temporary safety
deserve neither liberty or safety. Nor, are they likely to end up with either.
                             -- Benjamin Franklin

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