02 Sensors

[David A. Cooley]

At 07:45 PM 6/6/99 +1000, you wrote:
>I was told a while ago that AFR meters have a limited lifespan due 
>to the conditions they operate in
>If this is the case why dont 02 sensors have to be replaced every
>250 hrs (or whatever the lifespan of the meters is)
>Are the 02 sensors just another way of measuring the AFR or not?

The sensors used in O2 AFR meters are much different than those used in
your car...  The ones used in a car are basically a "switch".  They put out
a known value at 14.7:1 A/F and change extremely rapidly on either side...
The ECM looks at the sensor and makes the car toggle from rich to lean and
back many times a second to keep an "average" A/F ratio of 14.7:1.  What
the ECM looks at is O2 cross counts... IE how many times in a certain time
period the O2 sensor goes from one voltage extreme, across the stoich
voltage (typically 450mV) to the other extreme.  an AFR meter (not the one
you build for $20.00 for your car) uses a linear O2 sensor that has a
voltage or current output that is varying in a linear fashion with the A/F
ratio.  they only last a short period of time, and are really expensive.
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           David Cooley N5XMT           Internet: N5XMT at bellsouth.net
     Packet: N5XMT at KQ4LO.#INT.NC.USA.NA   T.A.P.R. Member #7068
   Sponges grow in the ocean... Wonder how deep it would be if they didn't?!
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