When diving with an AI computer do you also use a Redundant/backup analog pressure gauge?

[Reef Madness]

Yes

 

[tursiops]

Edit: my feeling is a transmitter's info would be quite off if there's any issue with the pressure sensor.

Agreed. One of the advantages of digital! Usually a glitch in a bit causes havoc, not just a small error. By the way, the transmitter sends a check-sum, too; the computers appear to not display anything if the checksum test fails.

 

[Divin'Papaw]

I'm in the "yes, I do" camp. It is a personal choice. There are arguments on both sides. For me, I'm more comfortable with a backup SPG and have one on all of my regulator sets. YMMV.

ADDITION: I use a small brass analog SPG as my backup. It is the DGX thin SPG. Thin, light, large enough though to be easily readable, made of a nickel plated brass housing with an impact resistant polycarbonate plastic face cover. I keep it clipped off on one of my left d-rings, completely out of the way but accessible if needed. I also have a spare spool with me in my boat box at all times. I've had the spool o-rings start to leak a couple of times but always on the boat when charging the regulator. It is a 3 minute fix to pop in a replacement spool.

 

[tursiops]

I'm in the "yes, I do" camp. It is a personal choice. There are arguments on both sides. For me, I'm more comfortable with a backup SPG and have one on all of my regulator sets. YMMV.

It is truly a personal risk assessment.
An SPG has three o-rings (one on the hose end at the 1st stage, two on the swivel at the SPG), whereas a transmitter mounted on the 1st stage has just that one o-ring at the mounting point. The SPG failure mode is usually one of those two o-rings on the swivel, or the SPG itself. If it is the SPG failing, that is tricky to ascertain because maybe it just reads high, for example, from being bumped too hard. Conversely, the transmitter has a battery in a compartment that is sealed with one o-rings. The failure mode on the transmitter is usually the battery, or the o-ring sealing the battery; BOTH of these failure modes are -- I would argue -- user error, because the transmitter tells you the battery status and/or changing the battery annually is not that big a deal, and screwing up the battery seal o-ring is just plain error.
If you hate o-rings, you may opt for the transmitter. If you hate electronics/batteries, then you may opt for the SPG.
If you have a digital SPG, you sort of have the worst of both worlds.
For recreational diving, if your transmitter or SPG fails, it is not an emergency; it is just the end of the dive. You WILL know if the transmitter dies; so having an SPG in addition allows the dive to continue.
If your SPG fails, and that is all you have....you may not even know it, depending on how it fails.

 

[scubadada]

Hi @rfwoodvt

I've been diving a hoseless AI computer since 2010, 1724 dives, with a SPG and computer backup. I have used the SPG on 13 dives, 0.75%, and have never ended a dive or interrupted a series of dives. I have used the computer backup on just 2 dives.

Some of the problems were my fault, some were not:
Computer battery dead 2 dives
Transmitter battery dead 2 dives
Transmitter failure 5 dives
Transmitter not installed on reg set used 2 dives
Transmitter not installed on loaner reg set after 1st stage failure 1 dive
Transmitter battery dead 1 dive

To each their own, it's a personal choice

I forgot to say, I have also had 3 SPG leaks during this time period, all remedied by replacement of the spool. I carry a few extra spools in my save a dive kit, I have also helped others on several occasions. I carry extra batteries for my computer and for my transmitter. My backup computer these days is also AI and has a rechargeable battery. Two AI computers are no better than one when you let your transmitter battery go dead

 

[Belzelbub]

Agreed. One of the advantages of digital! Usually a glitch in a bit causes havoc, not just a small error. By the way, the transmitter sends a check-sum, too; the computers appear to not display anything if the checksum test fails.

Yep. Electronics tend to fail in ways that are unmistakable. I’ve had a failed transmitter. Bought it used, and just didn’t work. Tried battery change and reading with two different computers nothing. NO COMMS is pretty unmistakable.

Recently, I’ve also seen an intermittent issue with an SPG. Shallow dive, I checked it after about 15 minutes. It read 3000 PSI. I started with 3100-3200, so this didn’t seem right. I know I’m good for well over an hour at this depth, so not real concerned. I flicked it a few times and went back to work. Checked again a little later and it read 2000 PSI. This made a lot more sense. In that case, it was also obvious, but had it froze at around 1500, it might not have been quite so obvious.

 

[CuzzA]

No

 

[Hojo in SC]

Yes, for the same reason I wear 2 computers.

 

[Belzelbub]

Transmitter was the notorious SUUNTO. the electronic gear was MF metal detecting coils.

It’s almost always the Suunto. They seem to have a higher problem rate than others. A few brands have opted for some complexity, seemingly for the sake of complexity. Sleeping the transmitter if the pressure doesn’t change after a while. Switching transmission protocols above and below the water. Presumably, those are to save battery, or to improve transmitter range. They seem to be solutions in search of a problem.

By contrast, the PPS transmitter is relatively dumb. It turns on with pressure, and turns off when the pressure drops to something like 50 psi. I’ve been involved with electronics manufacturing, including failure analysis for many years. By a large margin, the majority of failures occurred during startup. Those on/off cycles and protocol switches seem to open up the chances for failure.

I change the battery in my transmitter annually, even though I know it still good. Cheap insurance to avoid a preventable problem.

If I dove with a Suunto, I might opt for an SPG as well. I might also opt for a redundant SPG if my typical dives were different. I typically dive off of private boats, so a failure is at most an interruption in a dive. I carry the tools to swap out, so one dive may become two, or shortened depending on the gas left. If I were to do more charters, I may think about an SPG, but not sure.

Looking at Scubadada’s results, only a few appear to not have been preventable. @scubadada for the 5 transmitter failures, did any occur during the dive? Or were they during power up?

 

[scubadada]

@Belzelbub

My transmitter failed. I lost 5 dives before I could get it replaced by Oceanic for $120.

You're right most were my fault, not all