Shearwater Perdix AI

[rhwestfall]

poking the bear is pointless....

 

[scubadada]

poking the bear is pointless....

I'm sorry

 

[dmaziuk]

And so why do some divers choose to install both?

Why people do anything? Apparently the ones living in this state don't even know how they voted recently and need a recount to confirm their wish for "not a politician insider" did indeed come true. Who knows what kind of electrical activity goes on between their ears... What matters is that if the ability to correctly guesstimate their gas consumption was sufficient, they would not need to install either. Presumably "some divers" don't believe that math is all you need, quite the opposite.

 

[stuartv]

But is cylinder/cylinders dependent, right?

No. If you suck down 50 psi in a minute, at 33' depth, your SAC is 25 psi/min, regardless of your cylinder size. 100 psi in a minute at 99', still 25 psi/min, when corrected to 1 ATA.

You only need cylinder size to calculate RMV (the actual surface volume of the gas consumed). 25 psi/min from an AL80 is a lower RMV than 25 psi/min from an HP120.

 

[scubadada]

No. If you suck down 50 psi in a minute, at 33' depth, your SAC is 25 psi/min, regardless of your cylinder size. 100 psi in a minute at 99', still 25 psi/min, when corrected to 1 ATA.

You only need cylinder size to calculate RMV (the actual surface volume of the gas consumed). 25 psi/min from an AL80 is a lower RMV than 25 psi/min from an HP120.

That was exactly my point, SAC does not really tell you what your gas consumption is and how that relates to you available gas. RMV will do that.

 

[scubadada]

That was exactly my point, SAC does not really tell you what your gas consumption is and how that relates to you available gas. RMV will do that.

Beating yet another dead horse, I will stop.

 

[Compressor]

I got a big laugh out of the manual just released when I saw this on page 4.

 

[AJ]

Honestly, I don't understand how any device that displays one's tank pressure (SPG or AI) could ever be viewed as a gimmick?

Sorry, English is not my native language and it is not easy for me to express want I want to say.

To me AI is a gimmick, it does not add any functionality that's not already there. Even an SPG is optional. A usefull optional, but when it breaks there's no problem or even danger as I can do without. Let's not forget not so long ago they used J-valves with pull rod and did not even have an SPG. They survided their dives did'nt they? According to some these days you're gonna of you don't know your GTR. How can this be?

What I can not do without is knowing how much gas to start with, time underwater and current depth. Anyone of these three missing could cause serious problems. What I am reading in this topic is that people are totally relying on computers to keep them save instead of thinking about whats really keeping them safe: their brains! No computer can make a diver safe, a thinking diver is a safe diver. Does the new Perdix help in this respect: no nore than the old and trusted Perdix, Petrel 1 and 2.

DTR, SAC, AI, sorry to me it's not important to know underwater. And it should not matter to any diver to be safe in any circumstance. But that's my opninion on this matter and I will refrain from further comments because it we won't change each others opinion on this matter I'am afraid. I wish everyone much fun with their new computer (really mean that) but please don't forget it's just a computer, a dumb machine. It can't make the right descisions for you.

 

[Centrals]

I got a big laugh out of the manual just released when I saw this on page 4.View attachment 386821

Won't be able to do that on every 1st stage which only has one HP port eg Apeks DS-4.
No wonder I never interested on AI because I love my DS-4 and spg.

 

[Kevrumbo]

My AI transmitter has 2 O-rings. One on the battery port and another in the HP port. The current battery in mine is the original. 2 years old now and hasn't needed to be changed yet.

My SPG has at least 3 O-rings plus the chance of the HP hose itself getting damaged.

It takes longer for me to reach past a deco bottle, unclip my SPG hold it up, read it, and re-clip it than it does for my computer to regain synch with the transmitter on the rare occasion that I look at it and it has lost synch with the transmitter.

Stuart, you describe once again in using WAI to compensate for a tech dive skill problem. I can check my SPG, unclip/clip from left hip, past two AL80 deco bottles faster than you can button press through your AI display menus to read a GTR/SAC rate function.

I reckon they haven't learned to fully trust the AI yet. Or they already had an SPG and they think SPGs are reliable enough to warrant having the redundancy in spite of the extra failure points.

I only have an AI transmitter on my rec reg set - no SPG. For rec diving, I think one SPG is perfectly adequate.

I have an SPG on my left post tech reg and an AI transmitter on my right post. I would be comfortable taking off the SPG, but I keep it so that if I ever have to shut down the right post I will still have a working SPG for the gas I am breathing. I also use it to cross check my AI every now and then, to confirm my AI and my SPG both are working correctly. 2 SPGs is one and one is none, right?

I use one SPG to confirm what I know about my remaining pressure over five or ten minute intervals, and have Gas & Deco Plans written out on Wetnotes as needed for reference & back-up. Any manifold post shutdown for me means to abort the dive. If I shutdown the right post, I still have SPG function which is fine; a left post shutdown idles the SPG function -I can manage without it since I'm ending the dive anyway, heading up to my deco stops as needed, and I have a buddy for a redundant gas source as needed.

My opinion: Because some people whose posts carry the weight of a big number in their profile keep posting (over and over ... and over ... and over) things that imply that if you use AI you are either dumb, lazy, or poorly trained - without actually substantiating those implications. Others want the thread to have counterbalancing points of view on record for the possible benefit of future readers.

It does seem rather pointless, doesn't it?

Clearly you are when you post dumb mistakes like the following:

No. If you suck down 50 psi in a minute, at 33' depth, your SAC is 25 psi/min, regardless of your cylinder size. 100 psi in a minute at 99', still 25 psi/min, when corrected to 1 ATA.

You only need cylinder size to calculate RMV (the actual surface volume of the gas consumed). 25 psi/min from an AL80 is a lower RMV than 25 psi/min from an HP120.

Stuart, RMV means Respiratory Minute Volume, so "25 psi/min" cannot be correct because you're referring to a Pressure rate. In other words you've got the wrong unit dimension.

The example I believe you're trying to make is:

For every 100 psi in your cylinder, an AL80 will provide 2.6 cubic feet of air, while a HP120 will provide 3.5 cubic feet. (These are referred to as GUE Imperial Unit tank factors: AL80 is 2.6cf/100psi; HP120 is 3.5cf/100psi).

That was exactly my point, SAC does not really tell you what your gas consumption is and how that relates to you available gas. RMV will do that.

@NWGratefulDiver had a better explanation describing this:
A good analogy is the gas gauge in your car. If you take two cars with exactly the same miles per gallon (your RMV/volume SAC rate), and put different size tanks in them, the gas gauge will show different values as you drive. If both cars get 25 miles per gallon and you drive 100 miles, both cars will use 4 gallons of gas. But if one car has a 20-gallon gas tank and the other has a 10-gallon gas tank, the former will show that it still has 3/4ths of a tank of gas, while the latter has only a half-tank. They didn't change their gas consumption rate at all ... what changed was the relative measure of how much gas they actually consumed, because the size of their tanks is different.

So the lesson is: your Volume Sac Rate or RMV is consistent across all tank sizes & capacities, but it is your Pressure Sac Rate that will change with the sizes & capacities of the cylinders that you actually use. . .