Poor man's trimix sensor

[parabuzzle]

So, as I was building my O2 sensor I got to thinking. "I could build an He sensor"

The problem is the actual helium sensor module seems to cost the same as a newborn child. So my mind wandered off a bit and I got to thinking that I could buy a nitrogen sensor module for pretty cheap ~$80.

What if I built a nitrogen sensor just like my oxygen sensor and measured my mix for O2 and N2... then I could assume the final percentage was He. I know it sounds scary to assume things about life support but I am also taking in to consideration that I am filling the tanks myself and know that I am filing with nitrox and helium.

So what do you think...

I put my O2 sensor on the tank and it reads 25
Then put my N2 sensor on and it reads 50
So... my mix must be 25/25/50 O2/He/N2

Or does that sound too scary to even try?

-Mike

 

[Van Isle]

Logic sounds good to me.

I've read that folks BITD mixed trimix with just an O2 sensor: PP blend in O2, check it, He, check it, top with air, check for O2.

Helium is not life support per se and the FHe is far less critical than FO2.

I wonder why no one else seems to have glommed on to this idea? When we do our normal calculations (for nitrox or trimix) we "assume" the remainder to be N2, why not the other way?

Disclaimer: I have no idea what I am talking about. I'm not even a certified diver. :shocked2:

VI

 

[elan]

So, as I was building my O2 sensor I got to thinking. "I could build an He sensor"

The problem is the actual helium sensor module seems to cost the same as a newborn child. So my mind wandered off a bit and I got to thinking that I could buy a nitrogen sensor module for pretty cheap ~$80.

What if I built a nitrogen sensor just like my oxygen sensor and measured my mix for O2 and N2... then I could assume the final percentage was He. I know it sounds scary to assume things about life support but I am also taking in to consideration that I am filling the tanks myself and know that I am filing with nitrox and helium.

So what do you think...

I put my O2 sensor on the tank and it reads 25
Then put my N2 sensor on and it reads 50
So... my mix must be 25/25/50 O2/He/N2

Or does that sound too scary to even try?

-Mike

You would only know you are filling it with helium just because you trust your provider, that would be your weakest link.

Yeah assuming things is scary.

 

[elan]

I wonder why no one else seems to have glommed on to this idea? When we do our normal calculations (for nitrox or trimix) we "assume" the remainder to be N2, why not the other way?

I guess we can safely assume N2 as we know that's the only gas (in meaningful quantities) besides O2 exists in the air we pump in. You do not actually know that you are pumping He insides. The fact it is written on the invoice and on the tank does not really mean it's He inside

 

[fdog]

Getting a reading on a helium meter doesn't assure that there's helium in the mix, either....it just means there's something triggering the helium sensor.


When receiving a T of helium, the plain old take a lungful and try the squeeky voice test has been a standard for years. Beyond that, I give it a check with an oxygen meter to make sure it isn't balloon grade, and trust the grade to the labeling.

Back to the OP, I am curious about a nitrogen-specific sensor cell. I have seen such solid state sensors, but they were in the range of thousands of dollars. Is it possible you've mistaken the N-33 sensor cell as a nitrogen gas specific sensor? It is actually an oxygen sensor.


All the best, James

 

[parabuzzle]

Thanks for the input everyone. I'm just throwing ideas out there.

fdog - here is the link for the Teledyne R-33N: R-33N Nitrogen Sensor [OSR-R33N] - $98.00 : OxyCheq - DiveOps, Analyzers and Scuba Diving Equipment

which states:

This maintenance free, sealed, electrochemical cell is specific to nitrogen, insensitive to flow rate, and has a 90% response in less than 10 seconds. At the end of its life, the cell is discarded and replaced like a flashlight battery.

-Mike

 

[fdog]

Mike, after reading the link you posted, I had to do a double-take too!

However, the Teledyne part you reference is an oxygen sensor. It's biased towards accuracy at a low % O2 reading; this allows it to produce Nitrogen % readings by subtraction.


All the best, James

 

[Van Isle]

Ahhh! Foiled!

VI

 

[parabuzzle]

Ahhh! Foiled!

VI

Tricky Tricky.

Bad marketing text.

 

[elan]

Getting a reading on a helium meter doesn't assure that there's helium in the mix, either....it just means there's something triggering the helium sensor.

It does, with the accuracy provided by the tool and measurement methodology, providing the tool is in working condition, verified in accordance with the schedules calibrated, and the measuring procedures are followed.