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CPAP Time Drift
#1
CPAP Time Drift
Hi,

My Airsense 10 Autoset is 17 seconds ahead of the normal clock. From what I understand, the clock keeps on working, even when you are setting it, so it isn't possible to change it to be exact, so I probably need to use OSCAR's time drift option, however I am not sure if I should set it to +17 sec or -17 sec. Does this option tell OSCAR that my CPAP is 17 sec ahead (by telling +17), or does it tell OSCAR to take it back by 17 sec (hence - 17sec)

Thanks...
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#2
RE: CPAP Time Drift
What are you trying to sync your CPAP with? Previously, I set the device, like an oximeter or camera first, then used its time display to set the CPAP's time.
Crimson Nape
Apnea Board Moderator
www.ApneaBoard.com
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Useful Links -or- When All Else Fails:
The Guide to Understanding OSCAR
OSCAR Chart Organization
Attaching Images and Files on Apnea Board
Apnea Helpful Tips

INFORMATION ON APNEA BOARD FORUMS OR ON APNEABOARD.COM SHOULD NOT BE CONSIDERED AS MEDICAL ADVICE. ALWAYS SEEK THE ADVICE OF A PHYSICIAN BEFORE SEEKING TREATMENT FOR MEDICAL CONDITIONS, INCLUDING SLEEP APNEA. INFORMATION POSTED ON THE APNEA BOARD WEB SITE AND FORUMS ARE PERSONAL OPINION ONLY AND NOT NECESSARILY A STATEMENT OF FACT.
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#3
RE: CPAP Time Drift
I am using both a camera and an oxymeter, and I also have a digital clock close to my bed. The camera and the clock are connected to Internet, so they have exactly the same clock settings (down to the seconds). The oxymeter has the option to synchronize with the computer when  connected, so it also practically has the same setting. The only device which doesn't get this info is the CPAP device and while it is possible to set the time manually, you can only change the hours and minutes, and cannot change seconds, and also the clock doesn't stop when you are making the adjustment, so, it is only possible to get an accuracy of 1 minute but you won't be able to correct any inherent difference in seconds. So, having this option in the software is very useful, just slightly confusing on which way to go.
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#4
RE: CPAP Time Drift
As you have learned, the clock in a CPAP is a poor timekeeper.   The closest synchronization that I have achieved has been by setting the device first.  I then open the clock setting function on the CPAP.  I make sure the hour is correct, then set the minute value to one minute ahead of the device's time.  Wait until the device changes to the next minute and when it does, press the enter button to set the CPAP's time.  This will bring you to within a second or two.  

The only unknown variable is when you turn on the CPAP, when does it actually start recording the data. In testing, I've found that the Resmed A10, depending on the parameter, does not start reporting data until 15 to 55 seconds after initial power on. (This also explains why there are zero values in a lot of OSCAR's Minimum stats for some parameters.) This creates the question; "Is the reporting data displayed in real time or does it have a built-in latency from the CPAP processing the data?"

The above should be close enough for an oximeter because of the latency in its reporting of SpO2 data.  (The O2 level drops in the lungs, but it will not be sensed until the blood has traveled to the extremity having the sensor.) Your pulse rate while this is happening would probably add to the latency too. (just a guess)

For a camera, I employ an additional method.  After preforming the initial time sync, I then turn on the camera then the CPAP (It really does not matter which is first.)  At the exact time I turn off the CPAP, I signal the camera of this, then restart the CPAP.  This provides a definitive timestamp as to when the CPAP was stopped.  When analyzing the sleep data and video, look at the camera's time when you signaled the stop and at OSCAR's stop time.  The difference of these two times will be the offset (delta) between the two devices for that particular night.  You would use this time delta for a finer synchronization of the devices.  For an example, let's say the camera's time was 2 seconds behind the CPAP. When you see an event in OSCAR, you know to look at the video's frame 2 seconds before the event's time in OSCAR.

I hope the above may help you in your quest.

- Red
Crimson Nape
Apnea Board Moderator
www.ApneaBoard.com
___________________________________
Useful Links -or- When All Else Fails:
The Guide to Understanding OSCAR
OSCAR Chart Organization
Attaching Images and Files on Apnea Board
Apnea Helpful Tips

INFORMATION ON APNEA BOARD FORUMS OR ON APNEABOARD.COM SHOULD NOT BE CONSIDERED AS MEDICAL ADVICE. ALWAYS SEEK THE ADVICE OF A PHYSICIAN BEFORE SEEKING TREATMENT FOR MEDICAL CONDITIONS, INCLUDING SLEEP APNEA. INFORMATION POSTED ON THE APNEA BOARD WEB SITE AND FORUMS ARE PERSONAL OPINION ONLY AND NOT NECESSARILY A STATEMENT OF FACT.
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#5
RE: CPAP Time Drift
I don’t think OP has had an answer to  the question, so:

One can use the CPAP clock drift option to shift the graph to the left or to the right on the timeline. 

Use negative values for minutes and seconds to shift it to the left and use positive values to shift it to the right. 

I synch the flow graph as follows:

At the beginning of a session I will move my hand in synch with my breath up and down, and then I’ll hold my breath for 10 seconds, and hold my hand still.

Later I can use the timestamp of the camera and the flat flow line in the graph and my hand being still to find out how much the graph needs to be shifted.

(Don’t give the synch signals with your hand too soon, because the CPAP will not record the data immediately.)
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#6
RE: CPAP Time Drift
(01-11-2023, 06:00 AM)PjotterHasApn Wrote: and then I’ll hold my breath for 10 seconds, and hold my hand still.

Meanwhile I've changed my sync signal to around 5 seconds, so it doens't get picked up as an apnea event.
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