Ed,
I am planning to do the same thing (when I get a little free time). I was able
to
find some good information on the net - I tried to find it now, but I am a
little
short on time however you might start with the VW info located at :
http://alicudi.usc.edu/~jan/cars.html . I think thiats where I found the info.
>From what I can remember:
- The O2 sensors generate a voltage voltage based on the ratio of Oxygen on
either
side of a platnium thingie. One side of this surface is exposed to outside
air,
the other side is exposed to exhaust gas. The voltage resposnse has a sharp
transition at stochiemetric(sp?) where the voltage output is about 0.7 volts.
- You are correct in that this sharp transition makes it very difficult to use
an
O2 sensor as a very good linear type measurement device, however the transition
does have some slope to it and therefore a little extrapolation is possible.
- The commercial units are basically just voltmeters to read the output of the
O2
sensor (some are meter typr outputs, some are LED outputs). The O2 sensor has a
high impedance which means that you can not use a regular VOM to read the
voltage,
it will load down the voltage to nothing. You have a couple of options: all (I
think) DVM (digital voltmeters) have high input impedance and would work. Or
you
could build an input buffer (op amp voltage follower, or FET input) to match to
a
meter.
- O2 sensors thread into a spark plug thread which is handy. One could go to
pep
boys and buy a "spark plug foul stopper" which is an adaptor which has matching
threads and weld this into the exhaust system. Or the O2 sensor could be
pushed up
the exhaust pipe. You seem to realize the benefit of a heated O2 sensor: these
things need to be preety hot to wrok. A non heated sensor needs to mounted
pretty
close to the head to get hot enough. A self heated sensor does not.
- Someone with multiple carbs needs to figure out how to make this work. If the
sensor can be placed in the exhaust of only one carb this is no problem. If
not
you have to figure things out.
- Leaded gas destroys O2 sensors
I plan to use one on old cars to set up carbs. I don't plan to make a dash
mounted
output, I will use a DVM instead - I figured that a DVM was a more useful tool
for
my purposes. I hope to have soome experience in about 2 months.
Good luck !
-Roger
Ed Mellinger wrote:
>
> Hi Folks -
>
> This might be a bit far afield for this list, but I'm wondering if
> anyone has advice or experience with the hobbyist grade exhaust gas
> analyzers that one sees advertised. I believe most of them are based on
> a self-heated O2 sensor, which gives kind of a trinary rich/stoich/lean
> indication... probably adequate for my purposes which are to set up
> carbs on old cars and bikes.
>
> Would welcome any comments on brands, cost effectiveness, etc.
>
> Ed Mellinger
> meed@mbari.org
>
> '59 XK150 FHC
> '49 HRD
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