Perdix AI question with 2 independant tanks

[Compressor]

Hello:
Something that I cannot figure out with my Perdix AI:
1. If I am diving with 2 tanks: Say Main back mounted tanks and a deco bottle.
2. They each have their own transmitters.

What is a good way to allow the Perdix AI to continue keeping track of my air consumption when downloading data to my logs? I see that in the manual it states: "GTR can only be based on one tank. The Surface Air Consumption (SAC) measurements are also based on the tank selected for GTR calculations."

Why am I asking: I want to extend dive time. I dive with Tank 1 then switch to deco bottle for continuation of dive.

I am in REC mode.

I have a feeling that I have to "setup the dive" in the Perdix prior to the dive.

Thank you.

 

[VWRdiver]

I use a Perdix with two transmitters with my sidemount setup, and Subsurface for my logging software.

The Perdix only displays SAC and GTR for one of the transmitters during the dive, but air consumption is captured for the gas from both transmitters when I import it into Subsurface.

One more note, the Perdix only supports up to two transmitters at this point.

 

[tursiops]

First, if you are using it to extend your dive it is a stage bottle. If you are using g it as an emergency supply if something goes wrong it is a pony bottle. If tou exceed NDL on a planned deco dive, THEN it is a deco bottle.
Second, you can't do what you want to do.
Third, just think of gas time remini g as being for that bottle.

 

[TheCoolBeans]

once you go into deco then GTR isnt displayed anyway so it makes no difference.
If you arent going into deco then presumably its just a really long, really shallow dive, in which case just surface when you get to your minimums.

 

[Compressor]

I am making 2-3 hours dives in shallow depths (<30 feet).

 

[ATJ]

I used to do exactly what you are saying very often with my Perdix AI when diving one of my favourite sites (22m for 90-150 minutes).

I'd dive with a 12.2L 232bar or 12L 300bar as my main tank and a 5L or 7L 232bar tank as my secondary tank. Separate regs and each set had a transmitter. I'd dive the main tank to 100bar than switch to the secondary and usually take it to 50bar (or less depending where I was in my dive) before switching back to the main tank to finish the dive. I switched at 100bar because if something was wrong with the secondary, I still had plenty of gas to finish the dive. Similarly, switching back at 50bar meant that I had enough gas to finish the dive if my main no longer worked.

When I used this configuration (in REC mode), I changed the AI Setup: AI Mode to T1&T2. For Bottom Row I have Center set to AI Mini and so when I switch to both transmitters, it shows the pressure of each tank and GTR (for the main tank only). However, during the dive I'd usually change the bottom row to have the full AI setup which takes the whole bottom row and displays both tank pressures and SAC/GTR for the main tank.

When I switch to the secondary tank, the displayed SAC drops to zero with the GTR extending until the SAC is at zero and then it also displays at zero. I really wish Shearwater would display the SAC and GTR for the secondary tank but they have chosen not to. As they display it for one and that display is wrong when you switch to the second tank, there is no reason they couldn't display it for both. Sure the SAC/GTR for the second tank would be wrong while using the main tank but what is the big deal?

I import my dives into Subsurface which correctly calculates the RMV (which they call SAC) once the appropriate tank sizes are added.

I have since changed to twin 10.5L 232bar tanks (because I needed even more time) but use the same regs and criteria for switching tanks.