homemade oxygen sensor

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i saw a contraption online that indicates how much oxygen is in a purged chamber. i wondered to myself why i couldn't use an automotive oxygen sensor to see how well a chamber is purged. i guess i need to learn just how car oxygen sensors work. do they have to be hot to work? are there any other limitations to them?any thoughts?Dynasty 200DXPassport plus w/ spoolmate 100victor 315c oxy/(act and prop)Miller digital elitemilwaukee power tools
Reply:Originally Posted by turki saw a contraption online that indicates how much oxygen is in a purged chamber. i wondered to myself why i couldn't use an automotive oxygen sensor to see how well a chamber is purged. i guess i need to learn just how car oxygen sensors work. do they have to be hot to work? are there any other limitations to them?any thoughts?
Reply:Yes, all oxygen sensors need to be heated to work.1 wire and 2 wire sensors, require an external heat source.  That's no good.3, 4, and 5 wire sensors have an internal heater (which you would have to supply with a separate source of power), but these are more $$, and the heater takes time to reach temperature (could be measured in minutes).Most oxygen sensors have a very narrow range of operation (especially the titania ones).They probably wouldn't indicate anything useful, since they'll switch from sensing fully rich, to fully lean, outside of the acceptable range you would consider as purged.Wide band zirconia sensors (5 wire type), might give a useful indication of purge quality, but these are the most expen$ive type of O2 sensor out there.
Reply:One other issue.  Oxygen sensor require a lot of heat to measure oxygen.  At the temperature most oxygen sensors run they are really reacting to CO levels.  There is an SAE paper on this.Another way to measure gas is specific heat.  Take a chamber of gas, heat it for a known number of seconds by something like fixed current across a resister.  If you can then measure the temperature change, you can get an idea what gases are in there.  So, pure Nitrogen or Argon will have one characteristic, air, will of course have another.  The professional sensors run a few thousand dollars and do exactly that.  Take about 20 seconds to do it.