Hypothetical - 2 AI transmitters instead of backup SPG?

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^That^

The first problem with having two transmitters is your backup system is poorly designed. The second problem is that if you're OK with continuing your dive on the one backup transmitter, then you should have been OK with diving on one single transmitter in the first place. So it's also overdesigned.
How, exactly, is having 2 transmitters a poorly designed backup for monitoring your tank level? I use 2 transmitters and 2 AI computers that each see both transmitters. If either a transmitter or a computer were to fail, I’m good and have no need to end my dive as would be the case if I had no backup.

Is it overkill? Maybe, but I had a Perdix AI and then bought a Teric and decided a backup is good to have as my diving is usually done in week long dive trips or live aboards. Life is too short to have to cut dives short or sit out dives due to possible computer or air monitoring issues. My setup avoids those concerns and works for me - dive as you like, but don’t preach your views to rest of us as fact.

I also don’t get how you can say continuing a dive on the backup means you didn’t need the backup in the first place?? That makes no sense - the backup means you don’t have to call the dive short if the primary fails - only in the highly unlikely event the backup also failed would you call a dive.
 
The second problem is that if you're OK with continuing your dive on the one backup transmitter, then you should have been OK with diving on one single transmitter in the first place. So it's also overdesigned.

I'm having serious problems with your logic which I consider faulty. In the event of a failure of the first transmitter, the diver continues their dive on their backup transmitter. The odds of the second transmitter failing at some point during the remainder of that dive is astronomically small as compared to the primary transmitter failing at some point during the course of many, possibly hundreds or even thousands of dives.

The first problem with having two transmitters is your backup system is poorly designed..

No, it isn't. Just because both backups are the same technology, possibly the same brand and model does not negate the fact that they are operating independently of one another.

Heck you could say "why dive doubles if both tanks are exactly the same", using that sort of faulty logic.
 
How, exactly, is having 2 transmitters a poorly designed backup for monitoring your tank level? I use 2 transmitters and 2 AI computers that each see both transmitters. If either a transmitter or a computer were to fail, I’m good and have no need to end my dive as would be the case if I had no backup.

Is it overkill? Maybe, but I had a Perdix AI and then bought a Teric and decided a backup is good to have as my diving is usually done in week long dive trips or live aboards. Life is too short to have to cut dives short or sit out dives due to possible computer or air monitoring issues. My setup avoids those concerns and works for me - dive as you like, but don’t preach your views to rest of us as fact.

I also don’t get how you can say continuing a dive on the backup means you didn’t need the backup in the first place?? That makes no sense - the backup means you don’t have to call the dive short if the primary fails - only in the highly unlikely event the backup also failed would you call a dive.

If I read the comment right about not needing it is that ,,,,,there is a difference between necessity and nice to have. Putting 10 psi transmitters on a rig and having one fail is not a condition that says end dive. For a single tank and no overhead a spg and a xmitter is over kill per the necessities of the dive An spg is really a non breaking device unlike the hose attached to it. With a xmitter it is ""nice to have"" the additional data on the computer that requires the xmitter but that data also is not necessary for the dive. having the primary reg fail is a problem so you need a backup. nothing fancy just something that will give you air while you end your dive. He who said that if you was able to do the dive on only the backup then it wasnt needed is correct. Your concept of using 2 xmitters is IMO somewhat flawed. the primary device (if the xmitter) is the one you would use because of the computer data available and the one you use to get your psi from the puter rather than another source. IMO the SPG should be the primary and your xmitter be the secondary. My reason is that the additional info from the puter is not necessary to the dive. loss of the xmitter takes away nothing. Using 2 xmitters is using one device to backup the other that has the same design flaws as it does. Use the SPG as primary for the dive and the xmitter for the sole source of PSI for record keeping functoins the computer supports. loss of the computer function in this regard is not a vital loss. The xmitter should have a primary purpose of supporting logging and a secondary purpose as a backkup of the primary PSI source. The SPG would have a primary purpose of showing PSI which controls end of dive or turn tjme and no secondary purpose. If your SPG goes out you end the dive because the backup is battery operated and has its problems that do not exist with a mechanical device.
 
I'm having serious problems with your logic which I consider faulty. In the event of a failure of the first transmitter, the diver continues their dive on their backup transmitter. The odds of the second transmitter failing at some point during the remainder of that dive is astronomically small as compared to the primary transmitter failing at some point during the course of many, possibly hundreds or even thousands of dives.



No, it isn't. Just because both backups are the same technology, possibly the same brand and model does not negate the fact that they are operating independently of one another.

Heck you could say "why dive doubles if both tanks are exactly the same", using that sort of faulty logic.
both xmitters are subject to joint failure because you probably changed both batteries at the same time. same device technology same flaws and probably set up to both fail at the same time.
 
both xmitters are subject to joint failure because you probably changed both batteries at the same time. same device technology same flaws and probably set up to both fail at the same time.

Oh, thanks for the clarification. Before I read your post I had no clue that batteries are always going to fail at exactly the same moment.

In my case, as I would expect with lots of other divers, my dive computer indicates low battery so I'd have more than enough warning to change one or both batteries, as the low battery indicator will illuminate at a point where there is still sufficient battery power remaining for a few more dives.
 
both xmitters are subject to joint failure because you probably changed both batteries at the same time. same device technology same flaws and probably set up to both fail at the same time.

This is nonsense. It is just like saying car 4856 and car 4857 will fail in order because that is the same order they came off the production line in. All mechanical device failure is modeled as probabilistic, there is an increasing probability of any particular component failing over time, but probabilities are just that, probabilities, not guarantees. Reliability Centered Maintenance (RCM) uses these probabilistic models to derive service schedules for equipment. Electronics are not much different.
 
This is nonsense. It is just like saying car 4856 and car 4857 will fail in order because that is the same order they came off the production line in. All mechanical device failure is modeled as probabilistic, there is an increasing probability of any particular component failing over time, but probabilities are just that, probabilities, not guarantees. Reliability Centered Maintenance (RCM) uses these probabilistic models to derive service schedules for equipment. Electronics are not much different.

No it is not if a battery lasts 40 dives and you change them at the same time the batteries should both fail ABOUT the same time. this is not magic science. And that goes for the batteries in the computers and the xmitters. What you cant say is that the battery cover seals will fail together.
 
Oh, thanks for the clarification. Before I read your post I had no clue that batteries are always going to fail at exactly the same moment.

In my case, as I would expect with lots of other divers, my dive computer indicates low battery so I'd have more than enough warning to change one or both batteries, as the low battery indicator will illuminate at a point where there is still sufficient battery power remaining for a few more dives.

the words same time does not mean down to the milisecond. Next in you logic. I dont know of many that would have 2 xmitters going to 2 computers both of which is monitoring both xmitters. I have seen folks with 2 xmitters going to 2 computers each one monitoring one xmitter.
 
No it is not if a battery lasts 40 dives and you change them at the same time the batteries should both fail.

Yeah sure if both batteries last 40 dives then both batteries will fail on the 40th dive. No one can argue that.
 
No it is not if a battery lasts 40 dives and you change them at the same time the batteries should both fail ABOUT the same time. this is not magic science. And that goes for the batteries in the computers and the xmitters. What you cant say is that the battery cover seals will fail together.
Try again - both of my computers and transmitters don’t just spontaneously drain their batteries with no warnings! It’s actually quite easy to see the state of charge on the computers and the transmitters warn you when the batteries are low - they won’t just die mid-dive (actually good for a few dives after a warning). So your concerns are really baseless...
 
https://www.shearwater.com/products/swift/

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