Suunto Cobra - remaining air time not working???

I noticed on my last three dives that the remaining air time function on my Cobra was either not working or began to work very late into the dive. The tank pressure function is working and everything else seemed fine. Max depth on these dives was 30 feet or less and often in the 20 ft range... Anyone know if this phenomena is indicative of imminent failure or is something else going on???

TIA

Mark

I'm no expert so don't rely on my post alone but I have a Suunto Cobra and have never found the remaining airtime to be reliable. Seems to fluctuate a lot and sometimes gives me times that I know can't be right. I don't look at it, I just watch my psi. If everything else on the computer is working fine I'd recommend ignoring it and just watching your psi, but maybe someone else knows better than me.

O, and I should mention that I actually love my Cobra, just don't like the airtime.

If you dive shallow depth, it may take the computer several minutes to calculate your air remain time because you're not using up a lot of air like you would at depth.

Just a guess, because you don't say what's displayed when air time isn't:

I notice you're nitrox certified. I'll guess you've set your Cobra to Nitrox mode.
In Nitrox mode, the %O2 is displayed instead of remaining air time until the remaining air time is under 30 minutes. See the manual section 3.4.2, page 29, middle of page.

If that's not it, what is displayed when air time isn't?


neutrallybuoyant, the air time goes to zero at 500 psi, not zero. Also, the time is deliberately pessimistic with regard to changes in consumption rate; dropping fast as consumption rate rises, increasing more slowly as consumption rate drops. See 3.3.3 on page 21. In general I agree, I use PSI mostly, but I look at the air time to see if there's something I don't expect that I should focus on.

As for fnfalman's comments, could be, although it sounds like a couple of minutes is all that you'd expect. The manual (3.3.3) says
Anytime you enter into a dive, the remaining air time calculation begins. After 30 - 60 seconds (sometimes more, depending on your air consumption), the first estimation of remaining air time will be shown ...

"... either not working or began to work very late into the dive." doesn't sound like that, but I guess there could be room to interpret it that way.

reefduffer:

neutrallybuoyant, the air time goes to zero at 500 psi, not zero. Also, the time is deliberately pessimistic with regard to changes in consumption rate; dropping fast as consumption rate rises, increasing more slowly as consumption rate drops. See 3.3.3 on page 21. In general I agree, I use PSI mostly, but I look at the air time to see if there's something I don't expect that I should focus on.

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Also remaining air time fluctuates quite a lot with depth, the same PSI will last twice as long at 5m vs 20m for example.

sydney-diver:

......the same PSI will last twice as long at 5m vs 20m for example.

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of course

mark01:

I noticed on my last three dives that the remaining air time function on my Cobra was either not working or began to work very late into the dive. The tank pressure function is working and everything else seemed fine. Max depth on these dives was 30 feet or less and often in the 20 ft range... Anyone know if this phenomena is indicative of imminent failure or is something else going on???

TIA

Mark

Click to expand...

Hi Mark,

I am having a problem that is very similar to yours with my cobra. Same depth range, but occurring at the end of my dives. Early/mid dive, it performs normally,

Couple hundred hours diving with Cobra's, and I do know how the remaining air time varies. This change, is recent and abnormal. The first stage of my reg is working great, so there is no problem with air delivery to the computer. Changed out the battery even though I still had 4 bars. Connected an analog SPG to the reg and they seem to be getting the same PSI readings. There is no problem with the depth readings, I know the dive site like the back of my hand.

Mark:

Air time is shown in min, and only up to 99 (2 digits) on all Suunto products. Thus if you dive very shallow the remaining air time will be more than 99 min on a full tank, resulting in a - (dash) being displayed. Same for NDL at shallow depths.

Reefduffer, in rereading the manual, I found the info you quoted. My Cobra is, in fact, set in Nitrox mode. What was showing in the left middle window on the dives is the 21% I have it set at as I was using air on these dives. Thanks for the assist!