Oxygen sensors

[Nate]

On Thu, 3 Nov 1994, Andy Harrah wrote:

> When I first got interested in O2 sensors, I went down to the Patent Office
> to do some research.  Its about 10 miles from me.
> 
> I found an interesting GM patent (no. 4,130,095 Dec. 1978) that describes
> how they can tell of the sensors are hot enough to be given reliable data.
> The model of the O2 sensor is like a battery.  The terminal voltage is a
> function of the CO or oxygen content, and the internal resistance is a function
> of the temperature.  These things are really high impedance devices.  GM uses
> a clever approach that alternates between taking samples with a high impedance
> input, and one that loads down the sensor.

How about you wait till after you reset (thus ignition is just turned on) 
then wait till motor comes up to RPM over 300 RPM, then count the minutes 
that it is over 300 RPM, and figure it's pretty hot by then?

I know it's cheap, but it works for a home brew job. The home brewers 
would have a monitoring set up like a LCD or something anyway, because we 
hate idiot lights. Assuming this, one would be able to find a bad sensor 
problem.

I hate adding circuits into something that really don't need to be there. 
When I'm the one whos got to wire wrap it all together!

You would be watching the RPM's for other stuff anyway.

GM has it right, because this would also tell you when the sensor was 
going bad. If you didn't get a reading after a while, then you know it's 
bad. If you didn't sense this way, then you might think that the thing 
was idling, well maybe..... Now that I think about this, is there really 
a reason for this temp measurement? Would make it a bit more accurate on 
when it went into "full on" mode, but so what... The darn thing is 
probably wrong in mixture anyway no matter what they do, while it's 
warming up.

Besides, if they want to be so accurate, then why doesn't my car get 70 
MPG???