Re: O2 Sensors...MORE....

[Igor Kessel <e6941tb@ix.netcom.com>]

waves@epix.net wrote:
> 
> A comment was made that it is not wise to use nothing other than a DMM to
> seek voltage at the O2 sensor. This is not entirely true. non digital
> multi-meters will not fry or otherwise impair standard O2 sensors, according
> the instructor I had when I went to school at Bosch. As a matter of fact,
> they are actually preffered over DMM as you can see the swing in voltages
> much better.

They do, for a second or two, then the car stumbles and the reading drops to 0. The 
analogue metres have inherently less input impedance than the digital ones, 
therefore they shunt the Oxs brain, at least on my car. Unable to track the Duty 
Cycle fluctuations with the jumping digits of the digital multimetre, I built my own 
colour LED meter. It has a very high input impedance (the input cascade is based on 
LM2904 for all the EE typs here on the list. An LM358 works well also) and a very 
intuitive analogue LED display.
 
> After all, the typical O2 sensor is putting out simple analog signals.

Well, the O2 sensor is a passive device (it's essentially a variable resistor), and 
therefore does not produce any signals. It does, however, change it's conductance, 
and, therefore, alters the current flowing through it from the brain to the ground.

>One must also be careful not to
> smear anti-sieze compound around the openings of the sensor itself.

Yes, that is_very_important!

-- 
Igor Kessel
'89 200TQ - 18psi (TAP)
'98 A4TQ - on order
Philadelphia, PA
USA