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

Anton Lundin glance at acc.umu.se
Thu May 11 05:37:08 PDT 2017

On 11 May, 2017 - Jef Driesen wrote:

> On 2017-05-10 15:43, Anton Lundin wrote:
> >>>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.
> That makes sense!
> >>(*) 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.
> My only concern here is that if the info is useless, like those zero
> millivolt values when external O2 sensor monitoring is disabled, the
> we better don't report them at all. But if that's not the case, then
> it's of course fine to keep reporting them.
> >>>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
> >places.
> I replaced your patch with your latest version, and updated the rest
> of the series. Please have a look. If you are okay with the changes,
> I'll merge them to master.


You can add my Reviewed-by: Anton Lundin <glance at acc.umu.se> tag to the
patches if you like.

I think its a good idea to keep the O2 sensors behind the SENSOR_AVERAGE
ifdef for now, and try to figure out a nice scheme to expose both the
raw sensors and the "voted average" value as different things to the

The two other libdivecomputer backends emitting DC_SAMPLE_PPO2 are
diverite_nitekq_parser and the hw_ostc_parser. The HW values are raw
sensor values, but do you know what the diverite_nitekq_parser value


Anton Lundin	+46702-161604

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