o2 and EGT questions

David Cooley cooldave at nando.net
Thu May 11 21:53:52 GMT 1995

>1. Do O2 sensors have a 'cusp' output where Vo decreases  as mixture
>goes from lean to stoich, and then increases as mixture becomes rich? Or
does it
>have a generally positive (or negative) slope, with a characteristic
>voltage at stoich?
>                           /
>                 ^        /
>                 |       /
>                 Vo   - -    Slope
>                     /
>                    / 
>                   /

This is how they work.. At stoich, they are around .45-.5 volts.. lean, they
drop , rich they increase towards 1 volt.

>2. Who are vendors/where can info on O2 sensors be found?
Not sure where to find info... Maybe bosch, as they seem to make a whole line
including for the american cars.

>3. What thermocouple materials are used for EGT probes? (Copper/Constantan
>just don't sound right)
They don't use a thermocouple.. It is a ceramic with a thin metallic coating
inside and out for the electrodes.  Once it is hot (approx. 600 deg. F)
It becomes a battery.. The voltage is dependant on the difference in O2
levels between the 2 electrodes... Outside air is exposed to the outside of
the ceramic, and the inside is in the exhaust stream.  A large difference
(rich) makes a large voltage (approx 1 volt) and a small difference (lean)
makes a small voltage.  They are also High impedance devices.. Hooking any
meter to it while it is hot, if it has less than 10 meg ohms resistance,
will ruin the sensor.

David Cooley                                            (919) 319-2734 Office
cooldave at nando.net                                      (919) 319-2896 FAX
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