Shearwater Perdix AI

[Compressor]

Even an SPG is optional.

I don't know AJ. Should we dive with no SPG? Should we all go back to the J valve? Why not use the computer, your spg and your situational awareness to make a safe dive. A diver should avoid OOA situations. The SPG and an AI DC help.

 

[stuartv]

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.

...

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

Wow. You are not just making a habit of being wrong, you are addicted to it!

There is no button pressing or scrolling required to see SAC on a Perdix AI.

And, what I said about 25 psi/min from an AL80 is a lower RMV than 25 psi/min from an HP120 is exactly and perfectly correct. If you don't understand that, maybe you should find a new tech instructor and engage him for some remedial classroom work on basic gas planning. Or maybe you just need a remedial class on reading and comprehension. Hard for me to say.

 

[Kevrumbo]

. . .And, what I said about 25 psi/min from an AL80 is a lower RMV than 25 psi/min from an HP120 is exactly and perfectly correct. If you don't understand that, maybe you should find a new tech instructor and engage him for some remedial classroom work on basic gas planning. Or maybe you just need a remedial class on reading and comprehension. Hard for me to say.

Hard for you to say, because you don't know what you're talking about.

• You have an inconsistent mathematical construct in terms of units: you cannot assign a unit of Volume to a value of Pressure. "25 psi/min" is not a Respiratory Minute Volume (RMV) term.

• Also a given RMV or volume SAC rate is consistent across all tank sizes so your argument, "25 psi/min from an AL80 is a lower RMV than 25 psi/min from an HP120 is exactly and perfectly correct", is not only exactly wrong & incorrect, but makes absolutely no sense.

Using a different cylinder doesn't change the gas consumption rate RMV at all --but what changes in regard to comparing an AL80 and a HP120 tank is the relative measure of how much gas is actually consumed with respect to their capacities, because the sizes of the tanks are different.

What you probably mean and could not properly convey @stuartv 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.

It's even easier to understand in the metric system:
an AL80 is called a 11L (11 liters/bar) cylinder,
and a HP120 is called a 15L (15.3 liters/bar) cylinder.
For every one bar of pressure, an AL80 provides 11 liters and a HP120 provides 15.3 liters.

" Wow @stuartv -You are not just making a habit of being wrong, you are addicted to it! . . .If you don't understand that, maybe you should find a new tech instructor and engage him for some remedial classroom work on basic gas planning. Or maybe you just need a remedial class on reading and comprehension. . ."​

 

[AJ]

I don't know AJ. Should we dive with no SPG? Should we all go back to the J valve? Why not use the computer, your spg and your situational awareness to make a safe dive. A diver should avoid OOA situations. The SPG and an AI DC help.

Ok, last response. Should we go back? Please no! Should we do what some stupid computer tells us to do without questioning? Heaven forbid no!!!!! Don't get me wrong, I like my SW a lot, I like my SPG too, I like even AI Perdix, but I won't get in trouble if they fail during a dive. Reading quite some posts here I get the feeling people are relying on instruments to make decisions for them like: "oh my, my GTR tells me its time to go up" or "wow, my SAC is really high I must slow down". For a REC diver this attitude imo is dangerous, for TECH divers it will quickly become deadly.

Maybe I misread some posts, but the trust some people put in their tools to make descisions for them concerns me a lot. For an analogy I have ABS, brake assistence, air bags, etc. on my car. Do I trust them: yes totally. Do I rely on them to keep me safe: no never! That is ultimately my own responsibility. Have I used these systemens: partly yes, wanted to know how for instance ABS feels, but thankfully have never needed them in a real situation. This is how I look at technology. It's great it's there, but you never rely on them to be safe.

 

[Joneill]

And so why do some divers choose to install both?

redundancy... why would that be a bad thing? I already have an SPG on my reg and will keep it - but will likely now clip it off on my lower D-ring as it will purely be a backup.

I don't know AJ. Should we dive with no SPG? Should we all go back to the J valve? Why not use the computer, your spg and your situational awareness to make a safe dive. A diver should avoid OOA situations. The SPG and an AI DC help.

My thoughts as well. Having only been a diver for 2 years now, I was not familiar with what a J valve was, but I found this very informative piece:

[URL/]
So, basically, the old way was to check your tank pressure before a dive, guesstimate what your gas consumption would be based on assumptions that might be wrong (due to changing conditions/an "off" day, etc.,) and then do mental math as your dive progressed (esp. if you did not dive a square profile) to further guestimate your gas? If you got it wrong, you'd notice difficulty in breathing at which point you'd reach back and pull on a lever and have 300 psi reserve to get to the surface (assuming the J lever did not accidentally get moved during your dive already)?

No thanks - I'll take an SPG or AI computer to allow me to monitor my tank pressure (and therefore my gas consumption) in real time throughout my dive so I can turn my dive and start my ascent well before I only have 300 psi left, regardless of what my SAC/RMV might be that day (as conditions, etc., can effect it).

For me, I picked up the Perdix AI to put my tank pressure on my wrist where I can see it along with all other dive info. I don't really care about GTR.

For those that want to dive without the "unnecessary" SPG, and rely on mental math: go ahead - it's a personal decision and more power to you if it works for you. However, for many others (like me), we'll use available, now proven technology to provide information that allows us to plan and manage our dives based on real time tank pressure data.

 

[Joneill]

Ok, last response. Should we go back? Please no! Should we do what some stupid computer tells us to do without questioning? Heaven forbid no!!!!! Don't get me wrong, I like my SW a lot, I like my SPG too, I like even AI Perdix, but I won't get in trouble if they fail during a dive. Reading quite some posts here I get the feeling people are relying on instruments to make decisions for them like: "oh my, my GTR tells me its time to go up" or "wow, my SAC is really high I must slow down". For a REC diver this attitude imo is dangerous, for TECH divers it will quickly become deadly.

Maybe I misread some posts, but the trust some people put in their tools to make descisions for them concerns me a lot. For an analogy I have ABS, brake assistence, air bags, etc. on my car. Do I trust them: yes totally. Do I rely on them to keep me safe: no never! That is ultimately my own responsibility. Have I used these systemens: partly yes, wanted to know how for instance ABS feels, but thankfully have never needed them in a real situation. This is how I look at technology. It's great it's there, but you never rely on them to be safe.

I hear what you are saying and agree - I would never just blindly follow my computer for anything - we still need to know enough to ensure that what it is telling us makes sense.
In this case, I plan on using AI to provide a digital SPG on my computer along with some other data that can be useful both during and after the dive. However, I'm still turning and ascending based on preplanned tank pressures - so for the rec diving I do, I really don't need to worry about mental math on gas time remaining: if I see my consumption is higher, I'll turn sooner and ascend sooner. If I lose tank pressure data and SPG (unlikely), I'll start my ascent (with my buddy) immediately.

Different strokes for different folks - I just don't get (or like) the venom and condescending attitude some here (not you!) display on the topic of AI.

 

[Kevrumbo]

redundancy... why would that be a bad thing? I already have an SPG on my reg and will keep it - but will likely now clip it off on my lower D-ring as it will purely be a backup.

My thoughts as well. Having only been a diver for 2 years now, I was not familiar with what a J valve was, but I found this very informative piece:

[URL/]
So, basically, the old way was to check your tank pressure before a dive, guesstimate what your gas consumption would be based on assumptions that might be wrong (due to changing conditions/an "off" day, etc.,) and then do mental math as your dive progressed (esp. if you did not dive a square profile) to further guestimate your gas? If you got it wrong, you'd notice difficulty in breathing at which point you'd reach back and pull on a lever and have 300 psi reserve to get to the surface (assuming the J lever did accidentally get moved during your dive already)?

No thanks - I'll take an SPG or AI computer to allow me to monitor my tank pressure (and therefore my gas consumption) in real time throughout my dive so I can turn my dive and start my ascent well before I only have 300 psi left, regardless of what my SAC/RMV might be that day (as conditions, etc., can effect it).

For me, I picked up the Perdix AI to put my tank pressure on my wrist where I can see it along with all other dive info. I don't really care about GTR.

For those that want to dive without the "unnecessary" SPG, and rely on mental math: go ahead - it's a personal decision and more power to you if it works for you. However, for many others (like me), we'll use available, now proven technology to provide information that allows us to plan and manage our dives based on real time tank pressure data.

Then by that logic, you are best served by purchasing two wireless AI units/dive computers. By analogy, a satellite in orbit has two RF telemetry systems for primary and redundant back-up communication. Makes good sense for you...

A single SPG for both recreational and technical open circuit diving works for me. I don't worry about losing its function during the dive because in that case I'll simply end the dive, knowing I have enough remaining pressure to surface, or ascend to deco gas switch stop.

 

[Joneill]

Then by that logic, you are best served by purchasing two wireless AI units. By analogy, a satellite in orbit has two RF telemetry systems for primary and redundant back-up communication. Makes good sense for you..

A single SPG for both recreational and technical open circuit diving works for me.

That makes ZERO sense. I already have an SPG on my reg. I am adding the AI to have the tank pressure display on my wrist computer for CONVENIENCE (and for logging data). If the AI fails for some reason (unlikely with today's tech), I then have the SPG as a backup so I don't need to thumb my dive. Why would I buy another Perdix AI???

And please don't tell me what "makes good sense" for me as you obviously have not read what I've already stated as to my reasons for adding AI (or you don't accept it since it is not the way you think) - I have not and will not try to tell you what works for you.

 

[Kevrumbo]

That makes ZERO sense. I already have an SPG on my reg. I am adding the AI to have the tank pressure display on my wrist computer for CONVERNIENCE (and for logging data). If the AI fails for some reason (unlikely with today's tech), I then have the SPG as a backup so I don't need to thumb my dive. Why would I buy another Perdix AI???

And please don't tell me what "makes good sense" for me as you obviously have not read what I've already stated as to my reasons for adding AI (or you don't accept it since it is not the way you think) - I have not and will not try to tell you what works for you.

Because you need that digital display convenience, so you have one on your left wrist and one on your right wrist, and maybe purchase an Oceanic Data Mask receiver too so you'll have the display right in front of your face at all times, together with the double redundancy of your wrist AI/PDC's and their data logging functions (or something as absurd as @stuartv would post).

 

[Joneill]

Because you need that digital display convenience, so you have one on your left wrist and one on your right wrist, and maybe purchase an Oceanic Data Mask receiver too so you'll have the display right in front of your face at all times, together with the double redundancy of your wrist AI/PDC's and their data logging functions (or something as absurd as @stuartv would post).

Wow - you really are an arrogant, narrow minded person who only sees the world though your own needs - If it doesn't make sense to you, then it should not make sense to anyone. What a sad and miserable attitude.
I'd also suggest taking a reading comprehension course as I have clearly stated that AI is about convenience and not need. I'm sorry that obviously this concept is too much for you to deal with. Have a nice life as I won't respond directly to your senseless drivel and veiled insults anymore.