[PATCH] Visualisation of individual oxygen sensor data for CCR dives

Anton Lundin glance at acc.umu.se
Wed May 10 06:43:10 PDT 2017

On 10 May, 2017 - Jef Driesen wrote:

> On 2017-05-10 11:33, Anton Lundin wrote:
> >On 10 May, 2017 - Jef Driesen wrote:
> >>I've implemented the scaling factor now. See attached set of
> >>patches. It took me a bit longer than expected because there were a
> >>few cases where the ppO2 still ended up being zero. And that turned
> >>out to be for dives without external O2 sensors enabled (e.g. fixed
> >>setpoint mode). But the tricky part was that the external PPO2 bit
> >>seems to be reversed. According to the documentation [1] external
> >>PPO2 is 1 and internal PPO2 is 0. But based on the data I have, it
> >>seems to be the opposite.
> >>
> >>BTW, I wonder if we should ignore the setpoint value when external
> >>O2 sensors are used? Are setpoint still used in such case?
> >
> >Do we have any data from a Shearwater running as solenoid controller?
> >
> >Ex. On the JJ-CCR's they use a Shearwater Petrel with sensors which
> >controls the o2 solenoid to try to get the o2 sensor values to match
> >your configured setpoint.
> I have data from several Petrels, but I have no idea how they were
> being used. Is it possible to detect this somehow based on the data
> itself?

Might be some bits there indicating that, but none that I know off.

> >That said, I think setpoint values are still interesting to see, to
> >validate how well the controller did manage to try to keep the o2 close
> >to the setpoint.
> After looking at the data, I had the impression that the setpoint
> value is "unused" because it seems to just contain some "dummy"
> value (for example the last used value, or some default value).
> I'll illustrate with an example dive from Steve's Petrel (*). This
> dive has a fixed setpoint of 0.70 on every sample, but the ppo2
> values range from 0.32 to 1.74!

This sounds like a mCCR. Then its up to the diver to press a button
until the ppo2 matches what the diver would like to have.

> (*) I can send you the data if you want to take a look. I don't know
> if Steve is okay with sending his dives to a public mailinglist, so
> I didn't attach it to this email.
> To me that doesn't look like the dive computer is even trying to
> keep the ppo2 close to the setpoint. At least not to the setpoint
> value that's stored in the sample. Hence my question whether this
> value is relevant or not?

I think so.

My guess is that the setpoint is what the computer will continue to use
as its ppo2 value if it looses the connection with the sensors.

Its better to expose the information to the user, and let the user
ignore/delete it if they don't care about it.

> >Attached is the last iteration I did of the sensors patch. It has some
> >minor differences from the one you included, but most of them
> >isn't that
> >relevant.
> The part where you add 1024 to the calibration value is actually
> worse then the original version where you only did that if the value
> is smaller than 1000. It works (although not perfect) for the
> Predator, but it breaks for the Petrel because it doesn't need any
> correction at all. The variant with the if < 1000 works for the
> Petrel because the values are always greater than 1000, and also for
> some Predators, but not all because sometimes the values are greater
> than 1000 too. So if you want to do it correctly, then you would
> need to check on the model as I did in the third patch. If you want,
> I can move that code from the third patch to the second one.
> The SENSOR_AVERAGE is maybe a good idea to keep around. Might come
> in handy once we have a way to communicate the type of value (sensor
> vs average/voted).
> >The only relevant information is that the adc offset value is probably
> >in 0.025 mV as unit.
> >Thats party based on the information in
> >https://www.shearwater.com/wp-content/uploads/2016/07/O2-Offsets-Public-Notice-RevA.pdf
> The info in the comments is indeed useful knowledge, but since we're
> not using the adc values, it's pretty pointless to store them in the
> parser struct. It's just a waste of space there. I know it's only a
> few bytes, but I see no good reason to clutter the code with unused
> stuff.
> >The only real comment about the code is that I would have liked to see
> >the calibration factor kept as a int, and just change the unit factor
> >from .00001 to .000022, between the models.
> What would be the advantage of that? That would mean yet some other
> field to store the scaling factor, or doing some "if (model ==
> PREDATOR)" when calculating the ppo2. Now it's just done once in
> advance, making the conversion from millivolt to ppO2 independent of
> the model. I'm even tempted to pre-multiply the value with the
> 100000.0 factor too, to get rid of an extra

I'd store it as a separate calibration factor unit. Anyway, if you
multiply the calibration factor with 2.2 as of now, its better to
include the 1/100000 factor to, rather than having them in two separate


Anton Lundin	+46702-161604

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