DIY-WB... It's alive...

[rr]

Just did some additional checking. The spec sheet for the LM9044
makes no mention of a bias voltage output to the O2 sensor. There
is mention of an open circuit detect that forces the output of the amp
to a 'home' position.

On the '747 ECM there are no additional resistors conected to the
ECM O2 input that would provide a bias voltage. On the test
bench with the O2 + signal open the ECM reports 459mV as the
sensor voltage.

With a Fluke 83 measuring this input to ground the ECM then reports
a 409mV O2 sensor voltage. The Fluke reports a 397 mV level
on the O2 + input (open). This is quite a change for a high input
impedence DVM.

If I get bored later (yea right!) I'll drag the argon in from the garage
and measure the output of a heated O2 sensor at stoich.

While researching the NTK WB sensor I noted that the sensors
reference voltage is 450mV. The UEGO control loop is required
to change the pumping current to maintain that voltage.

Then from the archives is an article by Paul Timmerman
(ptimmerm at mashtun.JPL.NASA.GOV) that goes into detail of
how an O2 sensor operates. A piece from the article:

    "The active mode described in this forum was an ion pump,
    maintaining a fixed potential VII of 0.45 volts.  When you
    are at stoich, the simple cell is calibrated to give 0.45 volts
    when you have one atmoshpere with 12% oxygen near sea
    level." (March, 1998)

So, I'll still say that it is the O2 sensor that generates the 450mV
signal.

BobR.


terryk wrote:

> If you disconnect the sensor, the pin reads 450mV, right? This means the
> bias is from the ECM.
>
> Correct me if I'm wrong.
>
> ----- Original Message -----
> From: "rr" <RRauscher at nni.com>
> To: <diy_efi at diy-efi.org>
> Sent: Monday, September 03, 2001 7:06 AM
> Subject: Re: DIY-WB... It's alive...
>
> >
> > The general consensus has been that the ECM applies the bias. I have
> > not found any evidence of this. Maybe some ECMs do. My belief is
> > that the sensor that generates this voltage.
> >
> > BobR.
> >
>
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