Syncing ResMed Airsense 11 with Wellue SleepU

[jsam]

I've seen several threads about the problem with clock drift on the ResMed Airsense devices and am trying to find the best solution for syncing with Wellue SleepU data, which I believe is correctly set to standard time by the phone app. Last night, I wrote down the exact standard time when I started the Airsense and then when I stopped it in the morning. But when I do this, the offsets to real time don't match. Specifically:

            Resmed        Reality            Offset
Start     23:10:42      23:09:00       -00:01:42
End       07:50:42      07:50:00       -00:00:42

In other words, it looks like the ResMed device gained an entire minute between 11pm and 8am.

Could that possibly be right? I would have expected any clock drift to be microseconds per day, not a whole minute per night.

Is there something I'm missing? Any suggestions for how to troubleshoot?

[Crimson Nape]

It takes up to a minute for all sleep parameters to start reporting.  This is because several parameters require data over the previous period to be used to calculate a result.  The same can be said for an oximeter and its results.  In order to sync the two devices closer to each other, it is best to import the CPAP data into OSCAR, then use the session times reported for the Wellue/Viatom data file(s).  Please read this Wiki if you are not aware of how to achieve this.

Wellue/Viatom Syncing Link:  Syncing your Oximeter times with OSCAR

- Red

[jsam]

Would you expect the offset to be the same every night, or does this process need to be repeated for each import? And for this to work, you need to start both devices nearly simultaneously, right? So you get the SleepU just about ready to put on the finger, then put your other finger on the CPAP, and insert the finger into SleepU just as you press the start button on the CPAP?

[Crimson Nape]

There isn't an exact time lag for the oximeter. The CPAP is usually around 41 to 45 seconds for all parameters to initiate reporting. I usually start the oximeter and when I see it display the time, I start the CPAP. The exact syncing of the two devices is pointless because there will be a time difference between the inhalation anomaly occurrence and any reported change to the oximeter.

- Red

[jsam]

There isn't an exact time lag for the oximeter.  The CPAP is usually around 41 to 45 seconds for all parameters to initiate reporting.   I usually start the oximeter and when I see it display the time, I start the CPAP.   The exact syncing of the two devices is pointless because there will be a time difference between the inhalation anomaly occurrence and any reported change to the oximeter.

- Red

But if you start the CPAP once the oximeter displays a time, does that mean the CPAP and oximeter will be 41-45 seconds out of sync due to the reporting delay? Or does the session start time stamp go with the "start" button even if data comes in 45 seconds later?

I understand that exact sync is impossible/useless, but I am trying to make sure the anomolies reported by CPAP are at least in approximately the same region as those reported by the oximeter.

[Crimson Nape]

The CPAP's starting time is closer to the initial start, as opposed to the oximeter's starting time. Try this, start the oximeter and record its clock's display time. Let the oximeter run for at least a few minutes. Now, terminate the recording session and look at the binary file's name for the starting time. You should see a difference. This difference is not repeatable from session to session.

- Red

[jsam]

If the oximeter start time is not repeatable from session to session, how do you know how to adjust it to more closely match the CPAP? I understand the suggestion to rename the binary file to match the CPAP session start time, but doesn't that fail to take into account the oximeter start delay?