Air integration for tech dives

[Tracy]

Because you believe the gauge if that's all you have in the first place. So if the transmitter dies, now the SPG is all you have. What is the difference?

Because you now have something telling you different. The transmitters lose connection when the tank is empty. You have a gauge telling you it is empty and another telling you it isn't.
If you only have a gauge telling you it is full, you would assume it to be correct unless you have reason to doubt it. The transmitter failing is your reason to doubt it.
That is why you don't gain redundancy by running two.

 

[Tracy]

With only 2 pressure reading sources prone to failure, you are correct, however, you really have 3 sources. giving you two verifiable systems.
Your AI, Your SPG and, consumption. Consumption is a definite (you will consume gas)

The general consensus for having a single pressure reading device is; Diver checks on surface, tank reads full, diver dives. If during the dive, the diver notices that the pressure isn't going down, diver knows there is an issue with the gauge or the manifold is shut. This works with one device prone to fail and one definite (gas is consumed during dive) for one verifiable system.

This is similar to SCR where one O2 sensor is fine since you have a device prone to fail and a definite FO2 to reference it to. (one verifiable system)

Adding AI with an SPG and having a failure, leaves you at any one of the configurations you recommend, The important part is that the definite is still available and to the attentive diver, it will be.

If AI fails you wont have conflicting readings, you wont have anything at all. If by some oddity the AI sticks, (I'm not sure this is possible) it will not reflect consumption, just like the gauge.
If the gauge fails, you will know because it is stuck and not reflecting consumption. A diver being able to catch this has been beaten to death and the diver should be able to do so.


Similar in SCR, if you add backup computer with a singe sensor in addition to the original, you now have 2 sensors, which for CCR rebreathers is a no no, but since you really have two independent systems that can be referenced to a definite, it can be done and adds redundancy that is usable. If one sensor fails, a flush can verify the good sensor and the computer with the bad sensor can be switched to OC bailout (fixed FO2) and the dive could continue with redundancy since two computers, one with O2 sensor and one with fixed FO2 is considered safe.

In essence AI and a SPG, referenced to assumed consumption give the diver two verifiable systems and the diver can dive with.

We are on the same page. But knowing that an empty tank will not transmit, you have a gauge actively saying you are out of gas.
Basically it adds something, but also nothing.
I would just run the transmitter. The gauge is now an added failure point.

 

[jlcnuke]

We are on the same page. But knowing that an empty tank will not transmit, you have a gauge actively saying you are out of gas.
Basically it adds something, but also nothing.
I would just run the transmitter. The gauge is now an added failure point.

While I get what you're saying in theory, in practice you're not going to go from 2,000 psi on gauge and 2k on the transmitter with no battery low warning/indication to 3 minutes later having 1,900 psi on the gauge and the transmitter not giving an indication and realistically then believe that your gauge is incorrect because the transmitter isn't saying the same thing. In practice, neither indication exists in a vacuum. If I was diving that configuration, I'd be perfectly content to continue the dive using the SPG as the sole pressure indication as there wasn't a reasonable expectation that the indication it is giving is faulty and the logical conclusion is the transmitter has failed.

I'd personally only run the transmitter as the gauge is a redundancy I don't think is necessary and adds a failure point that you don't need. I wouldn't run two SPGs for redundancy in case one of those pressure indicators broke, so I similarly wouldn't run two transmitters or a transmitter and an SPG at the same time. If someone would run two SPGs though, then replacing one or both with transmitters would seem to fit their diving philosophy on redundancy. If someone wouldn't run two SPGs, running two transmitters or a transmitter and SPG together doesn't make much sense to me though.

 

[tursiops]

Because you now have something telling you different. The transmitters lose connection when the tank is empty. You have a gauge telling you it is empty and another telling you it isn't.
If you only have a gauge telling you it is full, you would assume it to be correct unless you have reason to doubt it. The transmitter failing is your reason to doubt it.
That is why you don't gain redundancy by running two.

The transmitter turn off when the tank is empty. They can lose connection at any time, but rarely do. If the tank is empty you don't need any kind of gauge to tell you that.
I simply do not agree with your logic. Sorry.

 

[boulderjohn]

How would it save a dive? If the gauges don't read the same, you don't know your gas and you turn your dive. If you have one that fails, you don't know your gas and you turn your dive.

You don’t have a backup, you have conflicting information. Conflicting information means you don’t know your gas and you turn the dive.

It is not that you have conflicting information. If you entered the water and saw that one gauge was reading one thing and the other was reading another, then you would have conflicting information because you would not know which to believe.

If, on the other hand, both gauges were reading the same throughout the dive and then one suddenly quit entirely, you do not have conflicting information, because you know which one is wrong and which one should be believed.

 

[Cio]

We are on the same page. But knowing that an empty tank will not transmit, you have a gauge actively saying you are out of gas.
Basically it adds something, but also nothing.
I would just run the transmitter. The gauge is now an added failure point.

I love the convivence of AI but do not trust it enough to fully commit.

I do agree that there is an added failure point, but I am willing to live with it since a total failure of the HP hose is not as bad as the total failure of an LP hose and if I detect a small leak in the beginning of a dive, I'll fix it and get back into the water. It is a compromise.

 

[PfcAJ]

Because you now have something telling you different. The transmitters lose connection when the tank is empty. You have a gauge telling you it is empty and another telling you it isn't.
If you only have a gauge telling you it is full, you would assume it to be correct unless you have reason to doubt it. The transmitter failing is your reason to doubt it.
That is why you don't gain redundancy by running two.

Obviously not a transmitter fan, but there’s a third point you’re not considering.

What *should* the gauge say? If you just start the dive and the transmitter fails, if the SPG reads full then it’s working. You can extend that to all phases of the dive.

Your pressure should never be a surprise when you look at your gauge, AI or analog.

 

[stuartv]

Because you now have something telling you different. The transmitters lose connection when the tank is empty. You have a gauge telling you it is empty and another telling you it isn't.
If you only have a gauge telling you it is full, you would assume it to be correct unless you have reason to doubt it. The transmitter failing is your reason to doubt it.
That is why you don't gain redundancy by running two.

This is incorrect. If your transmitter dies, your (Shearwater) computer will not show that your tank is empty. It will show "COMMS" (telling you that you have lost communication to your transmitter). If your tank does actually go to empty, then it will show 0 for the tank pressure for several minutes before the transmitter automatically powers down (when the computer will then switch to showing COMMS).

You do not get conflicting info (when a transmitter dies). You get no info at all (from the transmitter), which is not the same thing.

If the computer shows 0 psi and an SPG shows some other number, it's most likely that the SPG is stuck and the tank is at 0. Regardless, it's pretty darn easy to tell at that point which one is correct....

 

[Whitrzac]

All of this is assuming a shearwater AI setup is less reliable than a spg. Which any tech diver knows is BS but won't admit too as they glance over at their box of broken SPGs

 

[Tracy]

It is not that you have conflicting information. If you entered the water and saw that one gauge was reading one thing and the other was reading another, then you would have conflicting information because you would not know which to believe.

If, on the other hand, both gauges were reading the same throughout the dive and then one suddenly quit entirely, you do not have conflicting information, because you know which one is wrong and which one should be believed.

You are 100% correct.
So at that point you advocate to carry on with the dive with a known failure?
Speak into the mic.

Exactly. The protocol doesn't change. You turn the dive.