Shearwater Computers and CCR

[RobPNW]

Full disclosure- I know next to nothing about CCRs but I want to keep my options open to learn and use other equipment in the future.

I have been looking at the Teric and Perdix computers and when they list features about operating modes, I have seen comments such as "supports CCR bail out". To me, that implies that a diver is on CCR and something goes wrong and now they have to switch to their open circuit gear and the computer would accommodate that.

But I have not seen language to the effect that these two computers supports monitoring CCR diving in general. Is that true or am I missing something? Can I use one of these computers as my primary computer while diving on CCR? Or only when shifting over to open circuit from CCR?

I hope that made sense.

Thanks in advance,
Rob

 

[_Ralph]

The Perdix and Teric are for OC only. They do support CC diving (not familiar with the Teric feature set, so this part could be wrong), but not connected to a CCR ... in that you can set it to CC mode, and it will approximate what your unit should be doing for a set point.

You'll need a Nerd or Petrel (1/2) with the EXT (external) to actually talk/see what the CCR is doing.... Think of the Perdix/Teric as a backup bottom timer and a deco plan ....


_R

 

[Valyngar]

I use teric as backup computer for CCR. Primary computer which is also controller usually comes with rebreather (eccr new ones). It is usually Petrel2.

 

[KenGordon]

Full disclosure- I know next to nothing about CCRs but I want to keep my options open to learn and use other equipment in the future.

I have been looking at the Teric and Perdix computers and when they list features about operating modes, I have seen comments such as "supports CCR bail out". To me, that implies that a diver is on CCR and something goes wrong and now they have to switch to their open circuit gear and the computer would accommodate that.

But I have not seen language to the effect that these two computers supports monitoring CCR diving in general. Is that true or am I missing something? Can I use one of these computers as my primary computer while diving on CCR? Or only when shifting over to open circuit from CCR?

I hope that made sense.

Thanks in advance,
Rob

Shearwater supply computers and controllers to many CCR manufacturers, they will also sell you a Petrel or Nerd which can monitor the actual O2 mix in a CCR loop.

The various stand alone computers (regular Petrel, Perdix, Teric) can do the same job but assume that the ppO2 is being maintained by the CCR itself. This is necessary as what the ppO2 was on a dive prior to a failure make a bit difference to the deco required.

This means that through the dive the deco, NDL and time to surface numbers should be the very nearly same on both computers, assuming the same GF setting.

All computers which claim CCR support should be able to do this.

 

[happy-diver]

You can see the Petrel EXT down there on this chestmount rebreather that I built

tells you how much oxygen is lingering around the inside

of that round box down there with the wires poking out

as well as all the other dive information it tells you

Very good!

 

[Caveeagle]

There’s a lot going on here. A hardwired Petrel operates several eCCR units as a controller that monitors po2 levels and Controls setpoint for o2 injection. Until recently a Nerd2 was only capable of being a monitor that gives you a redundant view of PO2 levels and depth/deco data. *The O2ptimaCM is now capable of using a Nerd2 as a controller, but only if you get it set up with it as older Nerd2 are not upgradable.

Unwired Petrel/Perdix/Terics are much more than just a back up computer for open circuit bailout. (As stated above). Each has a “CCR mode”. In this mode, you can define Po2 setpoints that should mirror what the Petrel(controller) is set to. This will not normally be as accurate as the one that is actively tracking your actual po2 levels by reading the O2 cells. If you have a total system failure of your controller, your unwired backup will have a pretty good idea of what you have been diving and give you enough info to safely compete your dive, either on or off the loop.

 

[RobPNW]

Excuse my ignorance. Does a computer that fully supports CCR diving have to be physically connected to the rebreather?

 

[tbone1004]

Excuse my ignorance. Does a computer that fully supports CCR diving have to be physically connected to the rebreather?

there are 3 types of "CCR" computer.
Computers that support constant ppO2 mode and are not connected to a CCR. Perdix/Teric are good examples of this. They have a CCR mode that tracks your tissue loading as a function of constant ppO2, vs. a constant fO2 that is used for open circuit tracking.
CCR monitors-these computers have the ability to read some number of O2 sensors and track the ppO2 in real time. This is historically done through analog monitoring where the cells are plugged directly into the computer, a la Petrel EXT or DiveSoft Freedom and the computers are reading an analog mV signal that the cells are putting out. With CCR's that use digital communication, Poseidon Se7en/Shearwater DiveCAN/Liberty etc, the head has a board that does an analog:digital conversion and sends a digital signal to the computer.
CCR controllers-these are actually controlling the solenoid functions. This can be done fully integrated into the handset, think older Shearwater Predator controller, but is now almost exclusively done by control boards in the head itself, and the handset is communicating digitally to the head.

This article gives a good high level rundown on how digital communication is done in modern eCCR's. There are still a few holdovers of the old style eCCR, but they are not worth talking about IMO as they are obsolete.
What is DiveCAN® and why should I care? - Shearwater Research

 

[RobPNW]

there are 3 types of "CCR" computer.
Computers that support constant ppO2 mode and are not connected to a CCR. Perdix/Teric are good examples of this. They have a CCR mode that tracks your tissue loading as a function of constant ppO2, vs. a constant fO2 that is used for open circuit tracking.
CCR monitors-these computers have the ability to read some number of O2 sensors and track the ppO2 in real time. This is historically done through analog monitoring where the cells are plugged directly into the computer, a la Petrel EXT or DiveSoft Freedom and the computers are reading an analog mV signal that the cells are putting out. With CCR's that use digital communication, Poseidon Se7en/Shearwater DiveCAN/Liberty etc, the head has a board that does an analog:digital conversion and sends a digital signal to the computer.
CCR controllers-these are actually controlling the solenoid functions. This can be done fully integrated into the handset, think older Shearwater Predator controller, but is now almost exclusively done by control boards in the head itself, and the handset is communicating digitally to the head.

This article gives a good high level rundown on how digital communication is done in modern eCCR's. There are still a few holdovers of the old style eCCR, but they are not worth talking about IMO as they are obsolete.
What is DiveCAN® and why should I care? - Shearwater Research

Thanks Tbone. If I am understanding your reply correctly, I could use a wrist mounted computer such as the Shearwater Teric or Suunto DX, that operate based on a constant ppo2, assuming the CCR equipment continues to work properly and that assumption is correct? In other words, those computers do not really know what the actual ppo2 is in your gas at any given time and they assume that is it a specific value. If what I said is correct, how does a diver monitor the actual parameters in the breathed gas during the dive to make sure a malfunction has not occurred and the computer is calculating data based on accurate parameters?

 

[tbone1004]

@RobPNW correct. So if you tell the Teric that your setpoint is 1.1, then in order for it to actually give you some sort of useful deco information, you have to maintain a setpoint of 1.1. Doesn't have to be exact but you want say 1.05:1.15 which is a lot less difficult than it sounds.
The diver monitors the actual parameters via something that is attached to the computer. All of the breathers on the market now, to my knowledge have integrated decompression computers that are actively monitoring the cells, so they monitor in real-time, with real ppO2 data. Back in the day, they would just be monitors and you had to keep your ppO2 close enough to whatever value you told the computer.