Oxygen sensors

[Dale Ulan]

> I built such a circuit with two TLC25L2C op-amps.  I switches a 100K load
> across the sensor to take the 'heat' measurement.  The output of the thing is
> an the analog voltage from the sensor, buffered by the op-amp, and a digital
> clock at about 100 Hz that indicates whether the output is straight or loaded.
> The micro then compares the output between load and unloaded.  If the loaded
> voltage is within some fraction of the unloaded voltage, you can assume
> the sensor is hot enough to use.

How I saw it done in the controller in the 1991 GMC pickup truck
is the O2 chip has an internal voltage divider that places the output
of the O2 sensor at 0.450 volts until it warms up. Once its internal
resistance drops below a certain point, the size of the O2 amplitude
indicates primarily temperature.

The O2 amplitude is used in several tables to operate a PID controller.
Airflow is also used in a few tables. I was surprised, but the D term
appears to be used... and I've never seen it referenced in any papers
I've read.

Similar principle, but simpler hardware and software.

-Dale