Failure of Wireless Air Integrated COmputer and SPG

[TheRedHead]

Dennis, my spg failed because of a blown o-ring and it happened on the boat when I turned on my air.

loosebits, even those of who dive with air integrated computers think about it, but that's because we've been taught or exposed to the concept. Most people don't learn gas planning in their classes.

 

[Rev. Blade]

People don't think about that even if they don't have an air integrated computer. I dive with a Suunto Cobra which is air integrated (but not hoseless) and I never look at that "feature." It's not accurate anyway because it bases it assumptions on your air consumption of the past 5 minutes and can't take into account any decreae/increase in depth.

It looks at your SAC, not just how many PSI you used. It actually could take into account your improved gas use as you'll need to accend. (How well it does it, I don't know.)

For one thing the Suunto computer assumes a maximum accent rate of 30 feet per minute. If you lag behind that, you're using gas it didn't count on. If you rise faster, you're flagged for accending too fast.

I like to dive with a cushion. Usually that means coming up with lots more than the 500 psi minimum. If my Suunto says I was into deco, it means I stay a few minutes past "clearing" the deco.

 

[Diver Dennis]

Thanks Red. I wonder if anyone has had one go bad at depth?

 

[TheRedHead]

It looks at your SAC, not just how many PSI you used. It actually could take into account your improved gas use as you'll need to accend. (How well it does it, I don't know.)

The weakness in the rate of sampling - every 5 minutes. I'm not so sure it does look at your SAC. It has no idea what size cylinder you are using. The SAC is calculated by the Dive Manager software. Even if it did calculate SAC based on some default tank size (and not display it), the air time remaining figure is always way off on my dives because the computer doesn't know my dive plan. The number of minutes it displays is always conservative bordering on nonsense. The Suunto's older deco model does not take into account deep stops although the new D6 and D9 models do.

 

[pakman]

The weakness in the rate of sampling - every 5 minutes. I'm not so sure it does look at your SAC. It has no idea what size cylinder you are using.

It doesn't need to know what cylinder you are using. It is, or at least in the case of Suunto's, calculating your air consumption by measuring the pressure drop over time. see below from the Vytec DS manual... but again, I don't go by that number...:shakehead

3.3.3. Cylinder Pressure Data
When using the optional wireless pressure transmitter the pressure of your scuba cylinder in bars [psi] will be shown digitally in the lower left corner of the display 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 in the left center window of the display. The calculation is always based on the actual pressure drop in your cylinder and will automatically adapt to your cylinder size and current air consumption. The change in your air consumption will be based on constant one second interval pressure measurements over 30 - 60 second periods. An increase in air consumption will influence the remaining air time rapidly, while a drop in air consumption will increase the air time slowly. Thus a too optimistic air time estimation, caused by a temporary drop in air consumption, is avoided.

The remaining air time calculation includes a 35 bar [500 psi] safety reserve. This means that when the instrument shows the air time to be zero, there is still about 35 bar [500 psi] pressure left in your cylinder depending on your air consumption rate. With a high consumption rate the limit will be close to 50 bar [725 psi] and with a low rate close to 35 bar [500 psi].

 

[TheRedHead]

It doesn't need to know what cylinder you are using. It is, or at least in the case of Suunto's, calculating your air consumption by measuring the pressure drop over time. see below from the Vytec DS manual... but again, I don't go by that number...:shakehead

How can it know your cylinder size? I could have 3000 psi in an AL 80 or an AL 40.

An increase in air consumption will influence the remaining air time rapidly, while a drop in air consumption will increase the air time slowly. Thus a too optimistic air time estimation, caused by a temporary drop in air consumption, is avoided.

To me, the above is just backwards. You're much more likely to have a temporary increase in air consumption than a temporary decrease. How does depth figure into this?

It can only measure psi used and not real SAC in cu ft per minute. I suppose it has some kind of formula to guesstimate it based on use of gas. It records the cylinder reading every 5 minutes in the downloadable dive profile. I know this because I hacked into the Access database.

It's never accurate in predicting gas consumption for me. And now I'm really curious about why...

 

[pakman]

How can it know your cylinder size? I could have 3000 psi in an AL 80 or an AL 40.
It's never accurate in predicting gas consumption for me. And now I'm really curious about why...

Think about it, cylinder size is irrelevant for the calculations the computer is doing. Let's say you use 10 bar in 5 min. Barring any changes in the usage during the sampling period, it will assume you will use 10bar every 5 min... Now that could be 10bars on a AL40 or twin AL80's. Doesn't matter. It's not calculating how much volume you are using up... The computer is calculating pressure every second for a 30-60sec period (in the case of the Vytec DS). So if it know how many bars/ psi you use, it can then calcuate how much air time you have left assuming everything stays the same (your consumption rate, etc...) Obviously its a simple calculation and as we all agree not something to base our dives on! Also note in the case of the Suunto, the time is calculated up to 35bar reserve. So even if it says zero, there's still air in your tank...

 

[loosebits]

Wow, look at all the people out there who don't understand the calculations their computer is doing.

This is a good discussion and I think it is applicable to a lot of areas in diving, specifically dealing with computers.

Does everyone out there with a Vytec, D9 or other computer that generates deep stops know what these stops mean? How many of you can whip out your tables (do you even own tables anymore?) and track your N2 loading? How about calculate your EAD (for all you nitrox divers) or your CNS% or the MOD of EAN34?

We should all be very comfortable with each and every one of these concepts. If we didn't have computers at all, everyone could answer any of these questions but now we put our brains to the side and let the computer do the diving for us.

Here's something for the vacation divers out there who either don't remember how to read tables or don't even own a set:

If you're on vacation and your computer floods, what would you have to do to safely get back in the water (assuming you haven't been diving with 2 computers)? Unless you have a set of tables with you (at least in the hotel) you'll have to wait 48 hours before you can rent another computer and start diving again since the rental computer doesn't know anything about all the previous dives. Now, if you have a set of tables with you (and you've actually been logging your profiles after every dive), you can go back and run the tables for all your dives and finish your dive vacation on tables.

I don't reef dive a lot (been to Cozumel 3 times I think) but I can't recall seeing people with more than one computer and I've never seen a set of tables. I know I've seen someone who locked their computer immediately go rent another one to replace it (don't remember if the operator told her that was a bad idea or not). She obviously didn't remember the concept of RNT from her OW class.

 

[Alucard]

Only a beginner here but I carry a set of dive tables in my logbook which is with me on the boat when I am going to do repetitive dives. If my DC fails on a dive, I will be thumbing the dive, then using the tables to plan my next dive, whether I have rented a new DC or not....

This is what we were taught in our SSI OW course - they spent a lot of time on the tables, running through quite a few example calcs.

 

[loosebits]

Only a beginner here but I carry a set of dive tables in my logbook which is with me on the boat when I am going to do repetitive dives. If my DC fails on a dive, I will be thumbing the dive, then using the tables to plan my next dive, whether I have rented a new DC or not....

This is what we were taught in our SSI OW course - they spent a lot of time on the tables, running through quite a few example calcs.

That's what I would expect from a newly carded diver... you still remember this stuff. I suspect many people don't (usually it's the divers out there with 100 dives or so). They don't practice their tables so they don't remember how to run them.

By the way, the woman who locked her Suunto Cobra said she'd never seen it go into deco so she didn't know what it meant. If you dive a computer with a simulate option, you ought to play around with it every now and then so you are familiar with what deco looks like and you know how to safely complete your dive. If you don't have a sim option, you ought to break out that manual every now and then. After a hundred hours on a computer without going into deco, how can you remember what deco looks like from when your first read the manual?