Sensor life claims for oxygen analyzers

[2airishuman]

The Analytical Industries Palm D claims a typical sensor life of 36 months.

The Divenav Cootwo claims a typical (oxygen) sensor life of 12 months.

Do these reflect real differences in the useful life of the sensors, or just, um, marketing?

Is storing the analyzer in an oxygen-free environment a useful strategy for extending sensor life (e.g. in a barrier laminate bag with an oxygen absorber)?

 

[stuartv]

I can only give input on your last question and I believe the answer to that question is yes.

Other than the new Poseidon solid-state O2 sensors, all O2 sensors work by virtue of a chemical reaction inside the sensor that generates electricity. In simple terms, as the reaction occurs, the chemicals inside the sensor are used up. Eventually, they are all used up and the sensor no longer generates electricity so it has to be replaced.

So, if you protect the sensor by keeping it in an oxygen-free environment, those chemicals in the sensor are not consumed and remain ready for use somewhat indefinitely (not really - but much longer). When you put the sensor saver plug in an Analox, for example, it seals the chamber containing the sensor. The sensor "consumes" the little bit of oxygen that is trapped in there with it and then, practically speaking, goes dormant until you uncap it later in preparation for using it.

Regarding the first question, I guess I can say that I know different analyzers use different specific models of O2 sensor. So, it certainly seems possible that one analyzer could use a sensor that contains twice as much of the reactive chemical inside as another.

 

[packrat12]

2airishuman - One of the sensors that CooTwo recommends is a PSR-11-39-MD which is a common CCR sensor. The recommended replacement interval for CCRs is 12 months in use, 18 unused. CooTwo is probably just using those recommendations. The CCR divers are taking them out of their normal range so heat, the sensor response, voltage limiting plus lots of moisture are a real concern. This just does not apply to hand held sensors. The rebranded Analox Analytical Industries sensor is good for 36 months as an example. It is made by the same manufacturer but not going to be used in a CCR. It is not used in harsh environments.

As for sealing, the best statement I have seen comes from Dive Gear Express. It does not do much. The sensor is still aging even if not exposed to O2. While this is stated with CCR diving in mind, it applies to all sensors. I cap mine just to protect it from the environment around it.

 

[nadwidny]

As for sealing, the best statement I have seen comes from Dive Gear Express. It does not do much. The sensor is still aging even if not exposed to O2..

According to Teledyne, which is probably a more reliable source than DGE-

Can the shelf life of Micro-fuel cell sensors be extended by refrigeration?

No. The shelf life is primarily a function of oxygen exposure. For this reason most fuel cells are packaged in inert atmospheres which maximizes shelf life.

So a sensor that is stored in nitrogen, argon, or some other inert gas does seem to have a longer shelf life than one left exposed to O2.

 

[fmerkel]

stuartv and nadwidny have it right. O2 consumes the sensor and produces electricity. More O2 > faster consumption. If you have a sensor that is seldom used you can extend it a lot by sealing it off. You should also know the procedure for testing the limits which test the functional integrity of the cell.

(Note- pressure and high humidity affect the reading accuracy. If yours reads out to 1/10% that's pretty much LCD marketing. They are accurate about plus/minus 1% if accurately calibrated)

Fritz - Retired Respiratory Therapist. I used to work with these things all day long for years.

 

[kelemvor]

Sensors in handhelds can definitely last longer than a year. I had a 2 year old maxtec oxygen analyzer that was giving readings very close to my lds's maxtec. When I replaced it with a cootwo, the readings on the maxtec and cootwo were consistent with each other. I've not had an analyzer long enough for it to need a sensor replacement so far. Also, I store my analyzers in a ziploc type bag to limit how much oxygen (or co) they are exposed to. I assume at some point they'll use up all those gasses in the bag and stop degrading.

 

[packrat12]

stuartv and nadwidny have it right. O2 consumes the sensor and produces electricity. More O2 > faster consumption. If you have a sensor that is seldom used you can extend it a lot by sealing it off...

While the consumption part is true, I doubt that anyone is storing their sensor in much higher than 21% O2. That being the case, Analytical Industries states the following about sensor life: (They are the maker of the PSR-11-39-MD) "< 6 months at 25° C, from factory ship date to obtain the 60 months expected life in air. Note: The storage life can exceed the 6 months and or the temperature can exceed the 25 ° C (up to 40° C), but in either case the expected life will be reduced." - Simply put, their sensors are designed to be good for 5 years when exposed to air. Do you really want to try to exceed that? I also hope a Respiratory Therapist does not try to get more than 5 years out of a sensor... Can I see a medical malpractice suite here? Either way, the sensor is still aging and considering the electrolyte in the sensor, I would be concerned as it ages, passing tests or not.

So yes you can extend it's life, but should you? Does it do any good - No because it will typically will not out last the components and if it does, why bother anyway it is only <$100.

Best way to extend the life.... Take care of the sensor. Do not heat it up (leave in the car), do not drop it and do not freeze it..

 

[fmerkel]

Got to admit, since these things were used almost continuously, often in higher O2 situations they never approached anything like shelf life.
OTOH, I did say it was important to know HOW to calibrate the unit to make sure it was functioning properly. As long as it does that OK, it should work fine.

(Personal opinion - I seldom believe anyone's tech specs anymore until proven in the field by the people that will be using them. That's all the way from the ignorant and careless to the OCD and fanatic manual readers. You really get a different result than the engineers. Lord help you if the marketing people were involved in writing specs. How do you know?)

 

[Lorenzoid]

The Analytical Industries Palm D claims a typical sensor life of 36 months.

The Divenav Cootwo claims a typical (oxygen) sensor life of 12 months.

Do these reflect real differences in the useful life of the sensors, or just, um, marketing?

If it's just marketing, then I succumbed to the marketing in choosing a Palm D over the Cootwo.

 

[DiveNav]

......The Divenav Cootwo claims a typical (oxygen) sensor life of 12 months....

We do not manufacture the O2 sensors ourselves. We purchase them from a respectable manufacturer and we go by their recommendations (at least 12 months).
cootwo is designed to work with O2 sensors from different brands.
A customer could decide to mount in cootwo an O2 sensor with claimed longer life if s/he desires so.