[sci.electronics] Oxygen Sensor Info Needed

robp@attctc.Dallas.TX.US (Robert Parnell) (08/31/89)

Recently I saw an ad for an oxygen sensor that is used to adjust the air/fuel 
mixture for an internal combustion engine.  It had a sensor that mounted in
the exhaust manifold, and a small box with an LED bar graph display that 
mounted in the driving compartment.  Mid scale on the display indicates proper
fuel/air ratio, above or below indicates too rich or too lean a mixture.  The
idea behind the device is that with a lean mixture more oxygen will remain in 
the exhaust gases than with a rich mixture.

The sensor that mounts in the exhaust system is a standard automotive part
used in electronic fuel injection systems, and it's my guess that the small
box is nothing more than an ohm or volt meter with bar graph display.

I would like to use this method to adjust the carburetors on my motorcycle,
but with the commercial system selling for just over $200, I would like to
roll my own.  The sensor sells for around $40 at the local auto parts store,
and I already own a VOM.

What I need to know is the electrical characteristics of the oxygen sensor.
What's the resistance or voltage output of the sensor when the fuel/air
mixture is correct (which I believe is 15 grams of air to 1 gram of fuel)?

The commercial oxygen sensor kit comes with a sensor, but if it is to be
installed in a car with fuel injection that already has a sensor installed, 
the existing sensor can be used instead of the sensor supplied with the kit,
which leads me to believe that the electrical characteristics of different
oxygen sensors are the same, regardless of manufacturer.


Robert Parnell
robp@attctc

smit@.ucalgary.ca (Theo Smit) (09/01/89)

In article <9187@attctc.Dallas.TX.US> robp@attctc.Dallas.TX.US (Robert Parnell) writes:
>
>Recently I saw an ad for an oxygen sensor that is used to adjust the air/fuel 
>mixture for an internal combustion engine.  It had a sensor that mounted in
...
>idea behind the device is that with a lean mixture more oxygen will remain in 
>the exhaust gases than with a rich mixture.
>
>The sensor that mounts in the exhaust system is a standard automotive part
>used in electronic fuel injection systems, and it's my guess that the small
>box is nothing more than an ohm or volt meter with bar graph display.
>
>What I need to know is the electrical characteristics of the oxygen sensor.
>What's the resistance or voltage output of the sensor when the fuel/air
>mixture is correct (which I believe is 15 grams of air to 1 gram of fuel)?
>
>Robert Parnell
>robp@attctc

Sounds like you're talking about the MicroDyno (I can't remember the mfg's
name). 
A standard automotive oxygen sensor has an active metal in a shroud which
sits in the exhaust stream. Free oxygen causes the sensor to produce a
potential difference between the case and the center lead; basically
it works like a battery. The active range for the sensor is from about 13 to
1, to 15.5 to 1. (I'm doing this from memory; a friend uses one of these
to set up the mixture on his turbo Corolla), with the output voltage range
from 0 (rich) to 1.0 V (lean). I think that at stoichiometric (14 to 1) the
output is about 0.6 V; the curve is not linear. The transient response of
the oxygen sensor is pretty good (in the tens of ms, I believe). 

The major problem with the unit is that using leaded gas (such as 100-130
aviation fuel :-) fouls the sensor and makes it unusable after some time.
Also, while 14 to 1 gives maximum efficiency and minimum emissions, this
is too lean for maximum power output. The air/fuel ratio for maximum power
from gasolines is around 12 to 1, which is outside the sensing range for
the device.

Still, the MicroDyno has proved a valuable analysis tool for carb jetting,
especially for getting rid of those part-throttle bogs.
Disclaimer: I'm not affiliated with the manufacturer of this thing, I've
only seen it used. Your mileage may vary.

Theo Smit