Use of o2 cell data in CCR dive logs

Willem Ferguson willemferguson at
Mon Oct 13 03:37:37 PDT 2014


On 13/10/2014 12:19, Paul Sargent wrote:
> I hope everyone will forgive a recent subscriber and lurker stating an 
> opinion, but I wonder if this is going down the wrong road. I promised 
> Dirk I'd get involved a while back and never did - so here goes nothing.
> You're assuming that the cell data provided in a CCR log is:
>     a) interpretable.
>     b) present.
> For example: If you get a log from a Shearwater predator or petral 
> (used on JJs, rEvos, etc) you'll find that the logged values are the 
> millivolt readings from the cells. You can only turn these into ppO2 
> readings if you also have the cell calibration data (Also in the 
> memory dump, but not in the CSV or XML exported by Shearwater 
> Desktop). You have to use the ppO2 value calculated by the computer 
> during the dive.
> Paul

Hope you do not mind me changing the topic title.

Thank you very much for your response. The philosophy here is to get the 
system working for a fully logged CCR system and then to expand this 
foundation to others. The Poseidon logs po2 values (as well as cylinder 
pressures!). The APD (which logs po2 pressures for 3 sensors) is 
probably next on the list, but carries a different type of complexity 
with it. The Shearwater would probably be number 3 on the list and a 
good amount of discussion is required to start on this. So you will hear 
a lot about logging Shearwater CCR dives.

One of the important things a CCR diver wants to know is to assess the 
accuracy of the oxygen management system. By how much did the sensors 
differ and when or where during the dive did significant differences 
occur? That is basic towards assessing the accuracy of the system and to 
detect cells that are starting to decay. Therefore the importance of 
recording sensor values if they are provided in the log file from a 
particular CCR system. The APD as well as the Poseidon vendor-supplied 
software allow this and one would like to make Subsurface as attractive 
as possible for CCR users by making this a real alternative to vendor 
software. Hope this makes sense.
Kind regards,

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