FEATURE REQUEST - Ability to set PSI or BAR on per-device basis

[ringmod65]

While I prefer to have pressure in my back, stage, deco, dil and bailout bottles communicated to me in PSI, I would really like to be able to read the pressure of my rebreather O2 bottle in BAR.

As far as I can tell this is currently not possible.

Thank you.

 

[Wibble]

Please excuse my ignorance, but why do you use Bar only on O2? Seems a very esoteric requirement.

The settings are global in that you choose all Bar or PSI and the user interface does the conversion.

 

[ringmod65]

Please excuse my ignorance, but why do you use Bar only on O2? Seems a very esoteric requirement.

The settings are global in that you choose all Bar or PSI and the user interface does the conversion.

I’m originally from the US and have been diving OC for the better part of 40 years now so I am very fluent in dealing with PSI under most circumstances.

When I was recently trained on my Choptima (my first rebreather), I was surprised that the included SPG was in BAR, but it was explained to me that this was because O2 consumption calculations are simpler in BAR, which I indeed find to be the case. I don’t know enough about other types of rebreathers to know whether they ship with O2 SPGs in BAR or PSI.

To wit, from the current Choptima user manual, page 15:

“A compact SPG on a braided Stainless Steel HP hose is included to monitor oxygen tank pressure. A BAR gauge is used to help simplify gas consumption calculations.”​

As an example of how BAR simplifies O2 consumption calculations, there is this from the AP Diving website:

“The INSPIRATION xpd's 3 litre onboard oxygen cylinder charged to 200 bar will provide: 3 x 200 = 600 litres O2. At the average consumption rate of 1 litre/min - this offers about 600 minutes or 10 hours of diving from each INSPIRATION 3 litre gas fill.”​

I have grown quite used to using BAR rather than PSI in this one specific circumstance and would like the readout on my wrist to match that on the physical SPG of my Choptima O2 reg, which I sometimes have a hard time reading due to its location.

I understand that a valid argument is to be had that mixing BAR / PSI in tx displays could lead to confusion, but it would actually make things easier for me as I have my SWIFT xmitrs clearly labelled on my Shearwater computers (e.g. "D1" for my dilout, "O2" for my O2 bottle, etc.)

Danki!

 

[inquis]

If you're used to Imperial, there's little need to fight that. You're using a metabolic rate around 5 psi per minute in that 3L cylinder, or more conveniently a metabolic tank factor of 0.2 min/psi. I suspect you can drop a zero and double far more quickly than you can multiply by 3 (as is required with metric). 3000 psi -> 300 doubled -> 600 mins.

Or if you're already used to volumetric tank factors in terms of "per 100 psi", that 3 L has a metabolic tank factor of 20 min per hundred psi (hpsi). Double & add a zero to 30 hpsi = 600 mins.

 

[ringmod65]

If you're used to Imperial, there's little need to fight that. You're using a metabolic rate around 5 psi per minute in that 3L cylinder, or more conveniently a metabolic tank factor of 0.2 min/psi. I suspect you can drop a zero and double far more quickly than you can multiply by 3 (as is required with metric). 3000 psi -> 300 doubled -> 600 mins.

Or if you're already used to volumetric tank factors in terms of "per 100 psi", that 3 L has a metabolic tank factor of 20 min per hundred psi (hpsi). Double & add a zero to 30 hpsi = 600 mins.

This is super helpful. Thank you!

 

[inquis]

I forgot to mention, the volumetric tank factor in liters per psi is the same numeric value (0.2 L/psi). If you burn 450 psi during a 100 min runtime, that's 4.5 psi/min -> 4.5 * 0.2 = 0.9 L/min O2 consumption rate.

 

[covediver]

Have you conisdered a gage calibrated in both BAR and PSI?