Building a Better Mousetrap (O2 Analyzer)

[dmdalton]

canuckdiver once bubbled...
another idea for saving o2 sensors.....

I was thinking the other night that a good method for storing your o2 sensors would be to take an air-tight case (pelican case, or even tupperware) and add two small fittings, one an LP inflator fitting, and the other and overpressure valve, then fill the container with an inret gas like helium or argon? This would keep the o2 from affecting either side of the fuel cell, correct?


just a thought...

In a word "don't". This has been tired and it screws up the sensor. See O2 Hacker for the details.

Pill bottle and fridge have kept mine at 98% efficency for 3 years (Maxtex with 2 year warranty). Maxtex recommends replacing when they drop to 70% of original.

Dave D

 

[dmdalton]

Padipro once bubbled...
........I opened the first one and tried it out just this morning, the output from the sensor was so strong that I had to actually remove one of the fixed resisters that I had installed in order to use the brand new Teledyne sensor I had originally................

Something you may not realize is that different sensors put out different levels of voltage. If yours is set up for one that puts out 10 mv and you put in one that puts out 14 mv you will have to pull or change one of the fixed resistors to get it in range. This is why I like the trimmer pot instead of the fixed resistor.

Padipro once bubbled...
........ I tried the trimmer pot in the circuit instead of the fixed resister in the begining but it never seemed to work.............Scott

Don't know why it wouldn't work, resistance is resitance.

1) make sure that the trimmer pot will provide more resistance than is provided by the fixed resistor. If you need a 50K fixed resistor to read 20.9 on air when your potentiometer is in the middle position, then I would use a 100K trimmer pot.

2) solder in place of the fixed resitor (use an end tab and a middle tab to solder - not both end tabs).

3) set main pot to mid position

4) hook up sensor, expose to air (free air is fine, opinions to the contrary not withstanding) and turn unit on

5) adjust trimmer pot to get 20.9 on the display

6) close up case

7) analyze gas

8) pack vehicle

9) drink Diet Coke

10) go diving

Dave D

 

[Padipro]

I just received this response from Maxtec on storing the sensors in the refrigerator to prolong their shelf life.

"Scott,

We generally recommend that you only buy what you're using and maybe a back up. We can always overnight what you want. There are few times that we don't have stock for the product you need. But to answer your question, YES, refridgeration will prolong the life of your sensor. We keep our sensors on the shelf in a refridgerator. I cannot guarentee how much life that will give you but think of it like a battery. Our recommended shelf life is 6 months.

Best regards,

Luke"

Scott

 

[NAM001]

i got mne from oxycheq.com they seem to be good on prices. my kit was 100 and change the sensor is 65. he has sensors of all types for sniffers and rebreathers. his listings say what the voltave is 10-15-25 mv ect so a substitute can be found most of the listings say bla bla bla used in maxtor series ect. i keep the pakage label in the case with the sensor. if you need a sensor that uses -/- 10mv then he has one with a 5 year life. throw the fridge away. my variable pot is nearly full on with new batttery and sensor. have plenty of fine control. i think the resistor the pot REPLACES is r2 or r3 my kit did not say remove it as i can remember. there was a note sayng pic shows location of removed r2.

 

[NAM001]

padipro i saw the listing on e-bay those were 25 mv sensors. was going to get some but mine uses 10mv and the shelf life thing was the other reason i passed on them.

 

[Padipro]

The price was right as well as the timing, mine had just died and I needed a new one. The one I'm using is working great and the others are still in their factory packaging and in the frig. If the others don't work or don't last very long I think I still got my moneys worth.

Scott

 

[Aquamaniac]

Padipro once bubbled...
The price was right as well as the timing, mine had just died and I needed a new one. The one I'm using is working great and the others are still in their factory packaging and in the frig. If the others don't work or don't last very long I think I still got my moneys worth.

Scott

I just picked up 2 for $10 each...Bargain, even if I only get 6 months out of them.
Thanks Scott!

 

[NAM001]

that O2 sensors very in their output based on both the TEMPERATURE and HUMIDITY of the gas they are sampling!

If you think about what they are (fuel cells) it makes perfect sense.... Temperature changes the rate of reaction (and thus output) and so does humidity (by interfering with the access of the gas to the fuel.)

A few (but not many) sensors are temperature compensated, but I know of NONE that are humidity compensated (it would require active, powered circuitry to do so, and all the sensors I'm aware of in "common use" are simple fuel cells.)

Thus, when you calibrate, you should do so with a known gas that is as close to the sampled gas in both temperature and humidity as you can obtain in order to get the best possible results.

For most analyzer users, the simplest is a tank full of air (NOT free air, especially in Florida where humidity is often close to 100%!)

You will find that if you calibrate in "free air" and then sample 20.9% air from a tank that you just compressed that your calibration in "free air" results in an error that can be as much as 0.3-0.4%. While this is not outside of "safe" limits, it does give one pause if you want to be "dead nuts" on.

hello genesis

found a correction cal chart for humidity and temp in vance harlow's oxygen hackers companion. on page 126 it for wxamle says if it is 80 degrees and 70% humidity you need to cal free air at 20.4. thought this was neet and never thought about it till you brought it up. i am including this chart in my gear. if you want a copy ill send it to you or post as an attachment for all to use

thanks

KWS

 

[Padipro]

Here's the same type of chart, in color, if anyone wants it.

 

[dmdalton]

Here's the same type of chart, in color, if anyone wants it.

You will notice on that chart that there is not much of a swing in output over the range of temp and/or humidity. However, if you get the sensor it self chilled to the 15 degree level the output drops so much that you can't even "zero" the analyzer. Happened to us once 2 years ago. Had to warm the sensor up in the truck before we could analyze!

Dave D