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how do I measure CO

Discussion in 'Embedded' started by goose, Oct 9, 2003.

  1. goose

    goose Guest

    Hello all

    Once again I humbly seek your assistance :)

    I would like to build a CO meter for when I do the service
    on my car. How does one measure carbon monoxide ?

    I've searched google until I exhausted every possible
    combination of keywords (+CO +Meter, +CO, +resistor, "measuring
    CO", "measuring carbin monoxide", etc).

    Anyone knows where I can find the relevant information ? what I would
    like is a simple component that will change resistance when the
    CO in the air around it changes. I dont need a linear change either,
    although one that has a linear change would be easier to code for.

    thanks in advance

    goose, Oct 9, 2003
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  2. goose

    Fred Guest

    I thought the CO meters measured thermal conductivity of the exhaust gas. I
    guess they use a hot wire with a known throughput of gas to cool the wire.
    The amount of cooling giving an indication of the CO level.
    Fred, Oct 9, 2003
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  3. CO can be measured with an optical system.
    There are CO absorbing wavelengths. A thermopile
    with such a filter does it.

    perkin-elmer selles the sensors

    Rene Tschaggelar, Oct 9, 2003
  4. goose

    Terry Guest

    goose threw some tea leaves on the floor
    CO percentage in parts per million is usually measured by pumping air
    containing CO after it has been filtered and cooled, thru a tube.

    Each end of the tube contains quartz windows and one end has a filament
    or heater glowing dim red which provides the light source.

    The other end has a chopper wheel which interrupts the light from
    reaching a thermopile sensor.

    Such instruments are very accurate but require regular calibration
    using *expensive* calibration gas that has been analysed in a lab.

    Such equipment usually costs around several thousand dollars
    Australian and also measures CO2, and oxygen percentages.

    A modern car will only output perhaps 10 ppm CO, while a old car from
    the 80's may output 700PPM or more.

    A cheap alternative may be a sensor built by "Figaro" but it won't be
    anywhere near as accurate.
    Terry, Oct 9, 2003
  5. goose

    Paul Kasley Guest

    What about starting with the guts out of a common $35 household CO
    Paul Kasley, Oct 9, 2003
  6. goose

    moocowmoo Guest


    Or get a ready made vehicle exhaust measuring system for £135 from
    http://www.gunson.co.uk and save yourself a lot of time and effort.

    moocowmoo, Oct 9, 2003
  7. goose

    Clint Sharp Guest

    Sounds like an old Andros 600 analogue bench you're describing here!
    Used in Sun DGA1800 analysers IIRC. Old tech, take a look at the Andros
    Microbench, LED source and <30s warm-up time. Fits in the palm of your
    hand (excluding pneumatics)
    Once every 30 days by the user and once a year by a UKAS accredited
    engineer for most equipment or never by the user and UKAS every six
    months to meet the requirements of the emissions test in the UK, the
    user cal gas is good for many hundreds of calibrations though and costs
    around a hundred UKP, the UKAS cal gas (probably from the same batch as
    the user gas) costs around twice that but is good for maybe a thousand
    calibrations due to the bottle size. Both are certified for only two
    years but will keep for many years if traceability isn't important
    Can be had second hand for under 300 UKP for a four gas analyser (CO,
    CO2, HC and O2, calculated Lambda)
    10 PPM is quite high, if the machines are to be believed a good, hot
    engine and Cat is under 5PPM IIRC.
    If the car is a non cat or an open loop management system then the CO
    measurement needn't be that accurate, a simple glass tube with the
    appropriate mechanical gas filtering can be used with an IR sensor and
    IR led to give a relative indication, it can even be fairly accurate if
    calibrated and temperature compensated.
    Clint Sharp, Oct 9, 2003
  8. goose

    Leon Heller Guest

    This is one way:


    It took me a few seconds to find it with Google.

    Leon Heller, Oct 9, 2003
  9. goose

    Terry Guest

    Clint Sharp threw some tea leaves on the floor
    So right!
    Yes, I did a lot of work on the Andros benches! Also the old Ausie Repco

    The Andros was my favourite, so easy to cal and so accurate.

    Here is a man who knows gas analysers folks!
    Plus there is some real junk about, especially benches made out of pvc,
    with nasty little vacuum pumps.
    So true, I was being generous :)

    I remember the company mechanic once informing me that their unit was faulty
    as a new Toyota (can't remember the model) wouldn't diplay any CO. Sure
    enough the gas analyser seemed to be totally dead CO wise. Our spare
    unit was the same, that car had so little CO we couldn't read it!
    Really? I haven't seen a solid state model, but then again I haven't
    worked in that area for a few years.

    Thanks for the update Clint:)
    Terry, Oct 10, 2003
  10. goose

    Guy Macon Guest

    http://www.veris.com/products/env/gas/cde.html sells one in the
    0-2000 ppm range, but it's +/- 20 ppm - good enough for finding
    the minimum as you adjust things on the engine, but not good
    enough to tell you whether you will pass the smog check.
    Guy Macon, Oct 10, 2003
  11. goose

    Chris Giese Guest

    I thought there was a related project in Popular Electronics
    years ago. The sensor was a heated pellet of tin oxide.
    Supposedly, it could detect any oxygen-reducing gas; not just CO.

    I don't know if these sensors are still the best way to go...?
    Chris Giese, Oct 11, 2003
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