On 4 Feb 1998, Trevor Boicey wrote:
> It's VERY difficult to read with a digital multimeter.
ISN'T!
;-)
A digital multimeter is just what you need.
The readings are stable, and very easy to read.
BUT, you must ensure you have a good ground connection to the sensor body.
These are very sensitive signals, and just hooking up to any suitable
ground point on the car itself or even the exhaust manifold does not give
reliable readings. I'm pretty convinced that just about all reported
problems re. getting stable readings are caused by problems with
grounding.
Ensure that the ground connection of the multimeter is connected directly
to the sensor body. You also should twist the two wires connecting the
meter around themselves a few times - and you should have no problem
whatsoever.
Running a flexible coaxial cable with the shield connected to the sensor
body and the centre connector to the sensor lead is the best solution for
a permanent cable.
Connecting the grounding to the sensor body can for instance be done
using a stainless steel hose clip.
Please keep in mind that we are speaking of sensite signals with an
impedance in the Mega-ohm class. Running measurements on such signals over
ground connections that are subject to rusty connections in the exhaust
system, ground connections carrying 10s of amps of charging current, as
well as a myriad of noise sources is simply just a matter of asking for
trouble.
Why these sensors aren't produced with two wires, one for the signal and
one for the ground connection, is beyond me. It just goes to proove that
the average car design engineer knows pretty little about electronics.
> The actual
> range of the unit is very nonlinear
Somewhat unlinear, but very manageable. You'll find a graph at:
http://proffa.cc.tut.fi/~k124476/dataBySubject/Oxy.html
A standard 3 1/2 digit voltmeter in the 2 volt range have no problem
making sense of that.
> It's confusing, but instead of the unit outputting 0.5V at correct,
> it will oscillate from 0.2V to 0.8V when correct, spending roughly
> half the time at each.
No, it will not.
At least not with carburettors or old fashioned injection without
feedback.
And btw, 0.5V is not the *correct* reading. Please see:
http://www.kvaleberg.com/t_tune.html
Egil
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