how do I measure CO

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.

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

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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.

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What about starting with the guts out of a common $35 household CO alarm?

------------------------------------------------------------------------ Paul Kasley, Beams Division / Controls Hardware Fermi National Accelerator Lab, PO Box 500, MS 360 Batavia, IL 60510

would

filament

[snip]

Or get a ready made vehicle exhaust measuring system for £135 from

and save yourself a lot of time and effort.

Peter

In message , Terry writes

Ruby/Mica in some analysers.

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

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

This is one way:

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

Leon

So right!

Yes, I did a lot of work on the Andros benches! Also the old Ausie Repco units.

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:)

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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.

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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...?