RE: quattro-digest V4 #1441

[Henry Harper <hah@srv.net>]

>
> Date: Thu, 4 Dec 1997 17:12:18 +0100
> From: Aleksander Mierzwa <alex@matrix.com.pl>
> Subject: Testing oxygen sensor
>
> Hi List!
>
> I've heard that one shouldn't attempt to measure the voltage of the
> oxygen sensor, since even the small resistance of the voltmeter can
> seriously change the sensor's output. Is that true?
>

Well,  the ideal voltmeter has *infinite* resistance so as not to pass any 
current and thereby (not) change the voltage it's trying to measure. That darn 
Ohm's law again. Or was it KCL?

The lambda computer essentially uses a voltmeter to see what the oxygen sensor 
is doing, only it does not share this information with you, right? As long as 
you have a nice normal >1MOhm input impedance voltmeter in parallel and not a 
_really_ crappy one I don't see a problem.

Still haven't got around to making the LM3914 meter to check for O2 sensor 
laziness.

Henry Harper
http://www.srv.net
1991 200 quattro, 80k, really accessible O2 sensor, gotta love that
1988 GTI 16v, 173k, at least 73k on present O2 sensor which is under the car on 
top of the cat