Feature request: variable out of water setpoint instead of fixed 0.19

[LFMarm]

All Shearwater CCR controllers have a dry setpoint of 0.19 to be used onland to prevent solenoid firing. This works well at sea level where pO2=0.21 bar but it becomes insufficient for any altitude above 810m / 2,660ft where atmospheric pO2 < 0.19 bar (e.g., everywhere here in Colorado). Given that all controllers have a pressure sensor, it would be great if this dry setpoint would be calculated based on the atmospheric pressure:

where Pe is what is measured by the computer and 90% is a factor to stay lower than atmospheric pO2 (90% is the same factor currently implemented 0.19/0.21=90%). For example with the computer measuring 820 mbar (typical atmospheric pressure at 1,600m), the dry set point should be 0.16 bar and this would prevent the solenoid firing given that atmospheric pO2=0.17 bar.

@Shearwater

 

[LFMarm]

If not implemented, anybody using the rebreather at higher altitude than 810m / 2,660ft will need to remove the SOLO battery or it will be drained because the rebreather will keep firing the solenoid to reach 0.19 bar (even with computers shut off).

 

[lostsheep]

Your solenoid fires even when the computer is off?

That doesn’t sound right

 

[LFMarm]

Your solenoid fires even when the computer is off?

That doesn’t sound right

It definitely fires with computer off if the last setpoint was either High SP or Low SP. This is a great safety feature to keep the electronics control the loop if the controller dies mid dive.

I have not tried with 0.19 before shutting off. Will report back

 

[lostsheep]

It definitely fires with computer off if the last setpoint was either High SP or Low SP. This is a great safety feature to keep the electronics control the loop if the controller dies mid dive.

I have not tried with 0.19 before shutting off. Will report back

Do I remember correctly you dive a Choptima?

Mine definitely does not fire when the handset is off.

 

[Wibble]

All Shearwater CCR controllers have a dry setpoint of 0.19 to be used onland to prevent solenoid firing. This works well at sea level where pO2=0.21 bar but it becomes insufficient for any altitude above 810m / 2,660ft where atmospheric pO2 < 0.19 bar (e.g., everywhere here in Colorado).

Interesting edge case for us sea level dwellers!

When diving with a hypoxic mix below 0.19 PPO2 you need to inject a bit of oxygen into the loop to bring the PPO2 up a bit. If Shearwater had an option to set the storage PPO2 lower than 0.19, it could be used in a potentially dangerous way by hypoxic mix divers. Although pulling a negative test often needs the controller to be turned off for the same altitude issue.

It definitely fires with computer off if the last setpoint was either High SP or Low SP. This is a great safety feature to keep the electronics control the loop if the controller dies mid dive.

I have not tried with 0.19 before shutting off. Will report back

How can the solenoid fire when the controller, the Shearwater Petrel, is switched off? By definition the controller controls the solenoid.

 

[LFMarm]

Do I remember correctly you dive a Choptima?

Mine definitely does not fire when the handset is off.

Indeed. I did some testing and it only fires either with controller on or if the last set point was Low or High SP (in this case it fires even with controller off).

 

[LFMarm]

How can the solenoid fire when the controller, the Shearwater Petrel, is switched off? By definition the controller controls the solenoid.

When the last setting from the controller is Low or High SP, if you disconnect or switch off the controller, the head continues to chase Low SP. My misunderstanding was that this happens also when your last setting is 0.19; that is not correct; when your last setpoint is 0.19, if you disconnect or switch off the controller, the head will not chase any setpoint.

 

[LFMarm]

When diving with a hypoxic mix below 0.19 PPO2 you need to inject a bit of oxygen into the loop to bring the PPO2 up a bit. If Shearwater had an option to set the storage PPO2 lower than 0.19, it could be used in a potentially dangerous way by hypoxic mix divers. Although pulling a negative test often needs the controller to be turned off for the same altitude issue.

This is also the case if you are at lower than sea level atmospheric pressure because your body is used to breathe lower pO2. E.g., if you are at 820 mbar (typical atmospheric pressure at 1,600m) you are breathing pO2=0.17 bar so a set point of 0.16 bar would still be safe (as safe as breathing 0.19 bar when you are used to 0.21 bar at sea level).

 

[lostsheep]

When the last setting from the controller is Low or High SP, if you disconnect or switch off the controller, the head continues to chase Low SP. My misunderstanding was that this happens also when your last setting is 0.19; that is not correct; when your last setpoint is 0.19, if you disconnect or switch off the controller, the head will not chase any setpoint.

My chop does not fire when the petrel 2 controller is off regardless of setpoint or altitude. I’ve had it to Tahoe which should have an ambient po2 around .18.