Error low pp02 on recreational air

[crunchiespg]

i used my petrel for the first time today. just a few short dives in a shallow lake, max depth was 7, averaged around 4m metres for 30 minutes..
when surfacing, we didn't really do a safety stop as the entire dive was around 4metres apart from the one little dip to 7m.
on the surface my petrel came up "error low pp02" .. why was that?
I'm in recreational mode, using air. Haven't changed any settings other than the basics like units and the dive log number.. The high pp02 is at the default 1.4.

I also had an issue where the dives started so shallow the computer didn't recognise I was diving. How deep do you need to go for it to go into dive mode? Initially the lake is only about 2-3m deep so it didn't go into dive mode for at least 10 minutes below the surface.

On one dive the computer auto turned off just as I was entering the water. I turned it on but I think the depth registered the surface as actually being about 2m down. Because it didn't go into dive mode until I went down to about 3m and then it said I was at 1.5m.
thank you.

 

[tcoen]

Hi crunchiespg,

I posted this on the other thread as well, but I am re-posting here for completeness.

The cause for the low PPO2 message is the altitude at which you are diving. The default low PPO2 warning limit is 0.19 ata [atmospheres absolute]. Since PPO2 is ambient pressure multiplied bythe FO2 (21% for air), the PPO2 near the surface can easily fall below 0.19 near the surface.

For example, at 4500ft elevation the ambient pressure is about 0.85 ata, resulting in a PPO2 breathing air of 0.1785 ata.

The low PPO2 warning level can be adjusted, but unfortunately not when in the OC Rec mode. But you can adjust it in the OC tec mode, then switch back to OC Rec mode and the value will stick. Steps:
- Switch to OC Tec mode.
- Go to "System Setup->Adv Config->Adv Config 2"
- Change the OC Low PPO2 setting to something lower like 0.17
- Swtich back to OC Rec mode.

I hope this helps answer your question.

Best regards,
Tyler Coen
Shearwater Research

 

[rhwestfall]

again, a company that cares!!!!! Quick response, and an actual solution! Nice to know there is someone that cares after the sale. It is my hope that I should never need tech help, but if I should, this company is A+++++!

 

[crunchiespg]

Hi crunchiespg,

I posted this on the other thread as well, but I am re-posting here for completeness.

The cause for the low PPO2 message is the altitude at which you are diving. The default low PPO2 warning limit is 0.19 ata [atmospheres absolute]. Since PPO2 is ambient pressure multiplied bythe FO2 (21% for air), the PPO2 near the surface can easily fall below 0.19 near the surface.

For example, at 4500ft elevation the ambient pressure is about 0.85 ata, resulting in a PPO2 breathing air of 0.1785 ata.

The low PPO2 warning level can be adjusted, but unfortunately not when in the OC Rec mode. But you can adjust it in the OC tec mode, then switch back to OC Rec mode and the value will stick. Steps:
- Switch to OC Tec mode.
- Go to "System Setup->Adv Config->Adv Config 2"
- Change the OC Low PPO2 setting to something lower like 0.17
- Swtich back to OC Rec mode.

I hope this helps answer your question.

Best regards,
Tyler Coen
Shearwater Research

Thanks Tyler. So basically it's nothing to worry about.
What about the auto on /recognising when diving issue? The lake I was in simply takes a long time to get deep. So at least 10 minutes of dive wasn't registered.

 

[tcoen]

Regarding the start of dive depth, it is 1.6m, when the computer is already turned on. For a dive to start, must be below 1.6m for 8 consecutive seconds.

When the computer is off, the computer does not turn on until about 3m.

When diving at altitude, it is important to ensure the Petrel is turned on above the surface before starting the dive. This is to ensure the surface pressure is recorded properly. There is a 15 minute timeout that the Petrel shuts down. You can reset this countdown by pressing any button.

We are working on improvements for divers at altitude for the next firmware release:
- When turned-off will record recent history of surface pressure so that even if a dive starts with computer off, it will be able to determine the correct surface pressure. We will still recommend always turning the computer on manually before the dive to check setup.
- 15 minute turn-off countdown to be extended to 30 minutes.
- Reevaluating the 3m turn-on depth when starting off.

We appreciate hearing about any frustrations and difficulties as it helps us improve our products.

Best regards,
Tyler Coen
Shearwater Research

---------- Post added June 4th, 2015 at 06:47 PM ----------

A few quick clarifications to the above:
- The 15 minute inactivity shutdown is only when in surface mode. It will never shutdown during a dive, and the turn-off option is completely disabled during a dive.
- When starting a dive with the Petrel turned-off (which we never recommend), it doesn't turn on until 3m deep, and you must be below 3m for up to 45 seconds for it to turn on. As mentioned above, these numbers are being re-evaluated and may change.

Best regards,
Tyler

 

[crunchiespg]

Regarding the start of dive depth, it is 1.6m, when the computer is already turned on. For a dive to start, must be below 1.6m for 8 consecutive seconds.

When the computer is off, the computer does not turn on until about 3m.

When diving at altitude, it is important to ensure the Petrel is turned on above the surface before starting the dive. This is to ensure the surface pressure is recorded properly. There is a 15 minute timeout that the Petrel shuts down. You can reset this countdown by pressing any button.

We are working on improvements for divers at altitude for the next firmware release:
- When turned-off will record recent history of surface pressure so that even if a dive starts with computer off, it will be able to determine the correct surface pressure. We will still recommend always turning the computer on manually before the dive to check setup.
- 15 minute turn-off countdown to be extended to 30 minutes.
- Reevaluating the 3m turn-on depth when starting off.

We appreciate hearing about any frustrations and difficulties as it helps us improve our products.

Best regards,
Tyler Coen
Shearwater Research

Thanks Tyler. I did turn it on. But I guess I just hit the 15 min after sorting some stuff out on the surface. It turned off just as I started to sink. So I turned it back on but then it seemed off for that whole dive.
Those improvements sound like good ideas.

Thank you for the excellent timely responses. I'm glad I went with the petrel. It's great. And it was nice to receive it last week from my dive shop and the date of manufacture was only 3 days before I got it.

 

[Scared Silly]

FWIW when I first got my Petrel and being at 1500m I noticed this critical alert (critical alerts are red/warnings are yellow).

What is interesting is the error only shows up when in OC mode - it does not show up when in Rec mode. At least on the surface.

I got round the alert by changing the limit to be .18 cause that is what is approximately standard for 21% at 1500m.

Something I suggested some time ago for the manual was to add the following:

Why doesn’t my PPO2 reflect the O2 percentage when at attitude and on the surface?
The PO2 takes into account the altitude at which the computer was turned on. For example, if the altitude was 885 mBar or .87 ATA, then a 21% gas, thePO2 would display to .87 * .21 = .18.

Further, in OC mode, by default the PO2 displays in Flashing Red when less than 0.19 or greater than 1.65. (See Display Elements Description and Advanced Configuration 2 for more info).