Re: Portable CO meter

[Eric Maxon <emaxon@megsinet.net>]

Phil Payne wrote:

> In message <3.0.2.16.19971201075635.3f1f0608@pop.flash.net> Tony Lum
> writes:
>
> > Phil, this may be rather extreme and requires modification of your
> exhaust
> > system. I read a article in EC mag about how Techtonics Tuning
> designed a
> > fuel enrichment device triggered by the WOT and temp sensor.  They
> were
> > able to measure fuel mixture by way of a "high" speed OXY sensor.  I
>
> > realize that your engine doesn't have one, but have you considered
> adding
> > one?  I read its quite easy to obtain the fitment, cut a hole in
> your
> > exhaust pipe, weld in the mount, and screw in the sensor.  You can
> use the
> > 3 wire kind to make sure it warms up fast.  Now with this sensor in
> place,
> > you can hook up all types of instrumentation.  How about a laptop
> with a
> > A-D coverter pcmcard and chart the output voltage vrs rpm etc, etc.
>
> Thought about that.
>
> As it happens, I have a redundant (but reliable and well-built) AST
> Premium PowerExec 386SX25 laptop with two PCMCIA slots.
>
> I've looked at a number of packages.  Farnell do an attractive one -
> an 11-channel A/D converter that plugs into the parallel port and
> uses cheap, nasty and probably very efficient DOS software.
>
> Experimentation is suspended while I get the car through its annual
> inspection.  It needs a new centre exhaust section, so I'm putting in
> a piece of cheap crap (rather than the real Audi part) so I can do
> some cutting and banging after the inspection is passed without
> damaging anything expensive.  But one reason for the 'portability'
> requirement is that I want to make measurements on a reasonable sample
>
> of cars - not just my own.
>
> --
>  Phil Payne
>  phil@isham-research.demon.co.uk
>  Phone: +44 385302803  Fax: +44 1536723021

   About 1 year ago, I bought a $250 (USD) CO meter, that was
manufactured in the UK and sold under the brand name "GasTester."  It
has proven to be almost completely useless.  It is based upon a cheap
tin oxide sensor that with proper firmware would be reasonably
responsive and *somewhat* accurate in measuring CO concentrations on the
order of about 100 to several thousand ppm, (about .0001 to .005
percent)  These sensors are used in household CO meters/alarm, (with
which I've done some reverse engineering work.)  Unfortunately, we're
talking about measuring far greater concentrations of CO-- a task these
cheap ($10) sensors just weren't designed to do, and simply can not do
well.  Even after proper warmup and "calibration", the measurement on my
meter fluctuates WILDLY.  I don't care if you had a CRAY III in your
back seat-- "you can't shine shit."  The CO concentration data you'll
get out of anything but a good quality infra-red gas analyzer ($750
minimum,) will be useless.  If you intend to service more than a few
Bosch fuel injected vehicles, the $750 price tag is well worth it-- I'm
still saving for one myself.  If you do discover a GOOD CO meter for a
reasonable price, that is not based upon a tin oxide sensor, I'd love to
hear about it.

Eric Maxon
emaxon@megsinet.net
Chicago, IL