O2 sensors.

[Woz]

Right I have called them and the D-05 (what gets fitted to inspos) are £28.93 + VAT with £6.50 carriage.
However if we can get a few of us together then the price drops to £24.59 + VAT for 10. I'll start another thread to see if we can get some interest.

[Finless]

Originally Posted by Woz

Right I have called them and the D-05 (what gets fitted to inspos) are £28.93 + VAT with £6.50 carriage.
However if we can get a few of us together then the price drops to £24.59 + VAT for 10. I'll start another thread to see if we can get some interest.

Wow, does that mean that I have, at last, actually been of some use .......possibly? To quote the Americans "awesome"!

I think my sensor has quite a bit of life left in it and it's not as if you can store the sensors for a year or two and then use them.

Wouldn't you be better off posting on RB website? Maybe they have an even cheaper source?

[Woz]

Originally Posted by Finless

Wow, does that mean that I have, at last, actually been of some use .......possibly? To quote the Americans "awesome"!

I think my sensor has quite a bit of life left in it and it's not as if you can store the sensors for a year or two and then use them.

Wouldn't you be better off posting on RB website? Maybe they have an even cheaper source?

Already posted on RBW. I'll see what happens.

[Finless]

Anyway, back to my original question - the best measurement is obtained from a "static" gas rather than a continually flowing gas?

[gibbon]

Originally Posted by Finless

Anyway, back to my original question - the best measurement is obtained from a "static" gas rather than a continually flowing gas?

AFAIK

The O2 cell burns O2 to create a voltage, if you seal the cell with a "sensor saver" or even a well fitting cap you will find that by the next day there is no O2 left inside the space of the cap... and hence no voltage output.

So if there is no movement of gas the cell will eat the O2 and give you a decending voltage...

However it is obviously a very small amount that the cell eats so as to be negligable in a "bag" of gas to be tested..

The cell is totally unaware of gas flowing or being static, it is simply reacting with those O2 molecules it comes into contact with and creating a proportional voltage to the partial pressure of O2.

IMO the best reading is given by providing a fresh source of gas flowing gently continuously over the sensor face (making sure that there is no increase in pressure due to the flow).

[Finless]

Originally Posted by jonny

AFAIK

The O2 cell burns O2 to create a voltage, if you seal the cell with a "sensor saver" or even a well fitting cap you will find that by the next day there is no O2 left inside the space of the cap... and hence no voltage output.

So if there is no movement of gas the cell will eat the O2 and give you a decending voltage...

However it is obviously a very small amount that the cell eats so as to be negligable in a "bag" of gas to be tested..

The cell is totally unaware of gas flowing or being static, it is simply reacting with those O2 molecules it comes into contact with and creating a proportional voltage to the partial pressure of O2.

IMO the best reading is given by providing a fresh source of gas flowing gently continuously over the sensor face (making sure that there is no increase in pressure due to the flow).

Doesn't gas flow imply an increased pressure? Wouldn't flowing gas expose the sensor to increased numbers of O2 molecules?

[gibbon]

Originally Posted by Finless

Doesn't gas flow imply an increased pressure? Wouldn't flowing gas expose the sensor to increased numbers of O2 molecules?

A low flow rate (flow restrictor giving 1 or 2 litre per minute) with a large exhaust gives negligable increase in pressure at the sensor surface.

The number of molecules available at the surface of the sensor will decrease (and in turn the ppO2) unless replaced with new molecules so you need some flow, but very little in reality which is why the plastic bag works.

The voltage produced by the cell is proportional to the ppO2 not the number of molecules passing over the surface in a given period of time... perhaps a chemist will be able to explain better how it actually works.