Helium sensor

[doublesunder]

Whats the average life expectancy ? Is 10 yrs expectable, or should it be changed more frequently ?

[kdupreez]

What analyzer and what sensor do you have?

Unlike oxygen sensors that are basically electro-galvanic fuel cells and chemically wear out, He Sensors uses thermal conductivity to test content, so I would assume its probably 5-10 years in normal expectancy.

That said, I have a DiveSoft Trimix analyzer that uses the speed of sound, so there is no sensor to change and measurement is almost instant and doggone accurate.

K

[boydski]

Whats the average life expectancy ? Is 10 yrs expectable, or should it be changed more frequently ?

The published life expectancy for an Analox Helium Sensor is 10 years. Mine is about 9 years old and is still going strong.

[CaptnJack]

No change in mine and its 6yrs old.

[Waynne Fowler]

What analyzer and what sensor do you have?

Unlike oxygen sensors that are basically electro-galvanic fuel cells and chemically wear out, He Sensors uses thermal conductivity to test content, so I would assume its probably 5-10 years in normal expectancy.

That said, I have a DiveSoft Trimix analyzer that uses the speed of sound, so there is no sensor to change and measurement is almost instant and doggone accurate.

K

I've never heard of such a thing. I'd sure dig it if you could pm me some info on that one.

Thanks!

[loanwolf]

If you are in the market the Divesoft and the new Analox that use sound are more or less permanent. They can also take some water but not a full flood of it.

Anyone know of any others using the sound trap?

[kdupreez]

You can buy the DiveSoft analyzer from GolemGear..

Its a pretty decent little machine with tough machined all aluminum body design and super bright OLED screen!

http://www.golemgear.com/p-395-divesoft ... r-kit.aspx

I'll have it with me at Cove2 every Wednesday for the WWW dive, if you want to check it out.

K

[camerone]

The way helium cells measure content is by thermal conductivity, as has been noted. The circuit used is called a Wheatstone Bridge - http://en.wikipedia.org/wiki/Wheatstone_bridge. Other than electrical failure of the circuit/meter/etc, there's just two ways that a helium sensor can fail:

• Heating element burnout - the wire resistance element inside the helium cell can wear out. It's a thin platinum wire, and is basically like an old-school lightbulb with a filament
• Helium loss - helium can leak out of the ampule over time, due to any number of reasons...helium can do some weird things and will leak out of the strangest bits and pieces...that's why it's often used for leak detection. Leaking of helium changes the thermal conductivity of the sensor cell. For a while, you can correct with the offset knob, within some limited parameters.

The most common failure is the first item...like a lightbulb it burns out. It'll be blatantly obvious when it does, as no adjustment of the zero knob will fix the reading.

The second case above is pretty rare, but can happen. Think about how you're using the meter - you should really not be using it to measure completely unknown mixes...unless you're sure it's working right. When I measure something I've blended in the garage, I've definitely got an idea in my mind, from the calculations, where the mixture should be. The reading on the meter should confirm what I already know. If it's wildly off, I either screwed up mixing, or the cell's gone south. The former screw up is far more likely, unless the unit's sustained some serious physical damage and cracked the sensor.

So, don't waste time or money changing out the helium sensor until it quits working on you...it's not like an oxygen sensor where the electrolyte has a fixed life span before the chemical reaction consumes it completely.

[doublesunder]

What analyzer and what sensor do you have?

Unlike oxygen sensors that are basically electro-galvanic fuel cells and chemically wear out, He Sensors uses thermal conductivity to test content, so I would assume its probably 5-10 years in normal expectancy.

That said, I have a DiveSoft Trimix analyzer that uses the speed of sound, so there is no sensor to change and measurement is almost instant and doggone accurate.

K

Oxycheq analyzer, about 3-4 years old . Intermittently shows say 40% on a known gas of 45%. Testing wasnt on recently mixed tanks.

[CaptnJack]

How was the known 45% made, is that just determined via another analyzer? Does its intermittent performance have any relationship with the flow meter you're using?

[doublesunder]

How was the known 45% made, is that just determined via another analyzer? Does its intermittent performance have any relationship with the flow meter you're using?

Not only the 45%, just a example of the 5% bounce. I can turn it off and then back on when it changes, then everything is back to normal. It then reads 45% correctly with no problems until the next instance.