O2 sensor values on CCR dives

[Anton Lundin]

On 02 December, 2017 - Anton Lundin wrote:

> On 17 November, 2017 - Davide DB wrote:
> 
> > On 17 November 2017 at 19:10, Anton Lundin <glance at acc.umu.se> wrote:
> > > On 17 November, 2017 - Davide DB wrote:
> > >
> > >> Looking to one of my CCR dives (Petrel 2 controller) I realized that
> > >> Po2 values reported by Subsurface at the 6 meter stop are way higher
> > >> than those recorded and displayed by Shearwater Desktop.
> > >> I'm 100 sure that Shearwater Desktop shows correct values because I
> > >> perfectly remember O2 values I was seeing at 6 meter: I was never
> > >> never never over 1.6 for all the time.
> > >> According to Subsurface profile I was all the time at 6m over 1.6 with
> > >> spikes at 1.75.
> > >> Am I missing something?
> > >>
> > >> I chose a point in time (122' 50")and I attach three screenshots:
> > >>
> > >> Shearwater (which display only the AVG pO2)
> > >> Subsurface with single pO2 sensor display
> > >> Subsurface with AVG pO2 sensor display
> > >
> > > Could you dump the raw data from the device?
> > >
> > > It can be done using either dctool or using the predator protocol and
> > > creating a device dump.
> > >
> > >
> > > You could probably just send a log file of the download, I think I still
> > > got the tool to replay a log file as a download.
> > >
> > >
> > > Then I can take a look at the raw data to try to figure out what's going
> > > on.
> > >
> > >
> > > //Anton
> > 
> > 
> > After depleting one battery here are.
> > 
> > Dctool is a lucky process. 99% of the times I get errors like this:
> > 
> > [73.192176] ERROR: Failed to receive the response packet. [in
> > ../../source/src/shearwater_common.c:319 (shearwater_common_transfer)]
> > [73.192715] ERROR: Failed to download the dive. [in
> > ../../source/src/shearwater_petrel.c:266
> > (shearwater_petrel_device_foreach)]
> > [73.193107] ERROR: Error downloading the dives. [in
> > ../../source/examples/dctool_download.c:218 (download)]
> > [73.193712] INFO: Write: size=9, data=FF0105002E902000C0
> > 
> > Raw file for the dive attached
> 
> I've now looked at the data in the file, and the ppo2 values for the
> individual sensors are definitely bit high compared to the stored
> average value.
> 
> I'll take a look at the data to try to figure out what might be going
> on.

The ppo2 average calulated from our convertion of the mV values into
ppo2 values are out by a ppo2 of between 0.12 and .30, with a average of
0.19, so your keen observation is correct.


I saw something odd looking at that data. There's another calibration
value in the data, which we never figured out the meaning of.

In all other sample data its bin zero or low values like 2. In your data
its 255.

The thing is also that if i "correct" your mV values by about -8, the
data lines up pretty nicely, so there's some correcting needing to be
done.

Can you save the same dive from Shearwater Desktop so I can take a look
at the mV values they report there, so see of they are out by about -8
or so?


Your Sensor 3 reads a bit high towards the end of the dive, but you're
probably already aware of that.


//Anton

-- 
Anton Lundin	+46702-161604