Sorry, I was cryptic - my bad.
What I was referring to is well known in the gas detection field - there is a base assumption: you assume you know the contents of the gas being surveyed.
A gas meter is not capable of telling you what gas is being metered - only that it is being triggered. That trigger may (or may not) be the gas that the sensor was calibrated against.
If it is the appropriate gas, then you get a reading, in % or ppm or ppb or whatever. If it isn't, then you are in risk of being fooled into thinking that a gas is there (which really isn't there, eh?).
Here's an example:
Take your oxygen meter. It contains an electrochemical cell that has a little chemical reaction when in contact with an oxidizing gas. The chemicals are optimized for O2. We detect this by measuring the electrical signal from the reaction. So far, so good.
But what about, say, Chlorine gas? This too, is an oxidizer, and will mimic the reaction of oxygen. Or, fumes from Nitric Acid (also an oxidizer). ....You get the picture.
<<Hazmat team enters unknown atmosphere. "Hey, look at this...the meter says a bit of elevated oxygen levels, that's all...!" Thinking there isn't any contaminant, the team removes their SCBA masks, and drops from exposure to chlorine gas....>>
Of course, it is possible to obtain a meter that positively identifies a gas, usually by means of peering into the atomic structure. You can get a used NMR for about $30,000. Or, a helium-specific mass spectrum analyzer for only $15,000.
Returning to the question of helium, there are any variety of gases I can pass through the typical GFM thermal mass flow meter thaat will "trigger" a reading. Hydrogen or argon come quickly to mind. They will not read out in their correct percentage; but, they will trigger the sensor.
So, simply getting a reading on a helium meter is not assurance that it really is helium, which is all I was really trying to say.
All the best, James
What I was referring to is well known in the gas detection field - there is a base assumption: you assume you know the contents of the gas being surveyed.
A gas meter is not capable of telling you what gas is being metered - only that it is being triggered. That trigger may (or may not) be the gas that the sensor was calibrated against.
If it is the appropriate gas, then you get a reading, in % or ppm or ppb or whatever. If it isn't, then you are in risk of being fooled into thinking that a gas is there (which really isn't there, eh?).
Here's an example:
Take your oxygen meter. It contains an electrochemical cell that has a little chemical reaction when in contact with an oxidizing gas. The chemicals are optimized for O2. We detect this by measuring the electrical signal from the reaction. So far, so good.
But what about, say, Chlorine gas? This too, is an oxidizer, and will mimic the reaction of oxygen. Or, fumes from Nitric Acid (also an oxidizer). ....You get the picture.
<<Hazmat team enters unknown atmosphere. "Hey, look at this...the meter says a bit of elevated oxygen levels, that's all...!" Thinking there isn't any contaminant, the team removes their SCBA masks, and drops from exposure to chlorine gas....>>
Of course, it is possible to obtain a meter that positively identifies a gas, usually by means of peering into the atomic structure. You can get a used NMR for about $30,000. Or, a helium-specific mass spectrum analyzer for only $15,000.
Returning to the question of helium, there are any variety of gases I can pass through the typical GFM thermal mass flow meter thaat will "trigger" a reading. Hydrogen or argon come quickly to mind. They will not read out in their correct percentage; but, they will trigger the sensor.
So, simply getting a reading on a helium meter is not assurance that it really is helium, which is all I was really trying to say.
All the best, James
