o2 and EGT questions

[Ed Lansinger]

David Cooley wrote:

[in re O2 sensor voltage = f(A/F)]
>This is how they work.. At stoich, they are around .45-.5 volts.. lean, they
>drop , rich they increase towards 1 volt.

To clarify, at stoich, the voltage may be anywhere between 200 and 600mV
at high (900C) temperatures, 200 and 800mV at lower (500C) temperatures.
The width of this window can be important.  Still, you can do well if you
simply pick the midpoint of this range (400-500mV) as the transition point
and control off that.  As David points out, output voltage increases as
the mixture gets rich and decreases as it gets lean.

>>3. What thermocouple materials are used for EGT probes? (Copper/Constantan
>>just don't sound right)
>>
>They don't use a thermocouple..
[snip - David gives a good description of the physics of an O2 sensor here,
not an EGT probe]

There's iron/constantan (900C), NiCr/constantan (900C), NiCr/Ni (1200C),
etc., up through tungsten/tantalum (3000C) (I'm reading from the Bosch
Automotive Handbook).  We've got thermocouples all over our cars,
including for EGT.

You could use the resistive heating element in a heated O2 sensor to
measure EGT.  It would be slow to react, but it could work.

Omega Engineering has a wide selection of thermocouple probes, not to
mention a wide selection of engineering test & measurement catalogs.

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Ed Lansinger
General Motors Powertrain
Powertrain Control Center
Premium V Software & Calibration Group
Milford Proving Ground, Milford, MI
elansi01 at mpg.gmpt.gmeds.com  8-341-3049  (810) 684-3049
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