Is my Cootwo Crazy: My o2 bottles have CO

[KenGordon]

My friend suggested I look over the Cootwo for signs of cracked solder joints, but that will require that I do some work to extricate the board that is held in not with screws, but with melted plastic standoffs. His theory is that there is voltage leakage from the o2 circuit that is bleeding into the CO side, and it might be the result of a damaged trace or cracked solder joint.

You also trying to transpose the technology for measuring one analyte (O2) to the technology for measuring another (CO). Don't do that.

I agree with these views, you can imagine a number of issues with bad earth paths or poor power supply design that will make the two readings interfere. I doubt the device was designed for high O2.

It seems unlikely that CO in pure O2 will be an issue, first it would have to be boosted with a badly maintained booster, secondly you are breathing it at a much lower pressure. Has it ever happened that this has resulted in CO poisoning?

 

[_Slacker_]

I agree with these views, you can imagine a number of issues with bad earth paths or poor power supply design that will make the two readings interfere. I doubt the device was designed for high O2.

It seems unlikely that CO in pure O2 will be an issue, first it would have to be boosted with a badly maintained booster, secondly you are breathing it at a much lower pressure. Has it ever happened that this has resulted in CO poisoning?

You are only thinking of the example of using the O2 for <20 ft on OC. This could lead to very bad things if it was used as an O2 bottle for a CCR.

 

[KenGordon]

You are only thinking of the example of using the O2 for <20 ft on OC. This could lead to very bad things if it was used as an O2 bottle for a CCR.

Would it? Has it ever happened?

Say on some 60 minute CCR dive you metabolise 60 l of O2. 60000 cc of o2. At 10ppm about 0.6 cc of CO. Less really because the loop will get dumped a bit now and again. 0.6 cc in a 5000 cc CCR loop is 120 ppm (quite bad). It takes the whole dive to get there and assumes all left over CO stays in the loop, but really there is considerable loop turnover. I tend to flush my loop with O2 for deco too, not because of this, just to get my ppO2 up. Worst way at 6m on 100% I get 16ppm of CO, at depth 13ppm.

At no point in my CCR training have I been told to test O2 for CO or any mitigation for CO.

My impression is that CO is mostly an issue in 3rd world resorts with badly maintained air compressors. If I had CO in my dil I would be more worried. 10 ppm there is immediately 60 to 70ppm at 60m.

This device seems to have been designed with the wary warm water holiday diver in mind. Does it measure both at the same time? Does it claim to cover all the way to 100% O2 while also measuring CO?

Obviously nobody want crappy gas, but I don’t think you get crappy gas when getting 100%.

Does anyone know how likely a booster is to burn its lube?

Edit, I just checked the Divenav manual and it makes no claims as to what range of O2 is ok.

 

[JahJahwarrior]

Keep in mind that I've owned this thing for about 3-4 years and have analyzed plenty of o2 bottles before without ever getting a CO reading. Actually never gotten over 1ppm on any tank regardless of o2 or he content. So I don't think it is a fundamental inability of the unit to work with high O2 gas content.

The only thing that has noticeably changed is time, the CO sensor is 1 year old and has not been calibrated since it was installed, and the unit has been bumped around the gear box more. As I mentioned, the Bluetooth connection failed to work for 11 months after getting the CO sensor replaced and firmware updated by manufacturer, but suddenly started to work a month ago. I had chalked it up to quirky Bluetooth software, newer iPhone and older Bluetooth chip, etc. But it could corroborate the idea that there is a hardware failure.

I don't expect lab grade precision--mentally I have decided that 1ppm is not significant and I would accept that is a precision/hardware limitation issue and not a risk. But if I'm getting 5ppm, 10ppm, etc, then even if I don't know for sure that it's really 10ppm and not actually 4ppm, I'm assuming it's measurable enough to pose a risk to me and I would dump the gas. I have a personal principle that I won't die due to something scuba related.

What threw me for a loop is that I assumed CO couldn't appear in my O2 because it's not run through a compressor. And the non O2 gasses all reported no CO. But my personal principle says not to dive with CO present, and I didn't want to rule out the possibility that I was wrong about whether CO could be caused by a Haskel.

I will try to take apart the Cootwo and look it over soon. I don't expect to find much. I did not top off my o2 bottles so I can try to re-sample the same gas incase I do find any solder connections that are clearly damaged and fix them. I will also look into getting bump gas and compare the CO values before calibrating, to known CO PPM gas, to see if there is a clear calibration fault. If neither of those give me a strong indication of what the issue is, then I will responsibly recycle the Cootwo and buy an analyzer with a more clearly pronouncable name.

 

[JahJahwarrior]

Finally picked up my bottle of 15ppm bump gas from Grainger. Put the board into a ziploc bag and filled it up with the 'danger gas, stupid thing read 2ppm co. Vented, tried again, similar results. Put it into CO calibration mode, span, 15ppm, 60 seconds later the COOTWO says calibration failed. Tried again, same results.

I don't particularly want to throw good money after bad by buying another CO sensor, but if I can find a dive buddy with one of these who will swap them out with me to see if it's the sensor or the board, just for curiosity sake, but for now I will keep an eye out for a good deal on a Palm or Analox or Oxycheq.

 

[wnissen]

Finally picked up my bottle of 15ppm bump gas from Grainger. Put the board into a ziploc bag and filled it up with the 'danger gas, stupid thing read 2ppm co. Vented, tried again, similar results. Put it into CO calibration mode, span, 15ppm, 60 seconds later the COOTWO says calibration failed. Tried again, same results.

I don't particularly want to throw good money after bad by buying another CO sensor, but if I can find a dive buddy with one of these who will swap them out with me to see if it's the sensor or the board, just for curiosity sake, but for now I will keep an eye out for a good deal on a Palm or Analox or Oxycheq.

Dang, well at least you know it's busted.