1.5 hour timing error when using my RS offline

Technical Support
1

Hi Shaker friends,

Let me know if you have any suggestions RE:

I am trying to record subway trains in Brooklyn, NY, and to get near the trains I had to take our RS in Brooklyn (RBA72) offline for a few hours.

Attached is what we recorded. It looks to me like what I would expect for trains, and the timing between trains looks right to me, but:

The timing on the disk files during the time that the RS was offline is off by about 1.5 hours (early). We know the time those trains ran, so that’s what we consider to be “ground truth.”

After we put the RS back at it’s home site connected to internet, it shows the right time (and the time was right just before we unplugged it from internet).

So, my question is:

I would have expected the time to be right to within a few seconds when the RS was offline, but 1.5 hours seems like a lot to me.

Have any of you experienced a timing error that large when removing the RS from the internet for an offline experiment?

Any suggestions are welcome.

(I don’t have access to the log files because I am away from the RS’s home site. Will try to get access, but can’t say when.)

Alan Kafka

Geophysics, Earthquake Science, Environmental Systems, and Community Science for the Greater Good
http://X.com/Weston_Quakes
(in the process of transitioning away from X.com to BlueSky:
@alankafka.bsky.social on Bluesky)

subway_high_pass_25hz_2
subway_high_pass_25hz_1

1 Like
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This might be the explanation.
Yes, the subway location signals start at the same time as when we disconnected the RS from the internet.

RS tech experts does this seem right to you?

If yes, then it looks to me like we got some very interesting RS recordings of NY City subway trains :slight_smile:

Unknown
Unknown1125×1524 106 KB

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Hello kafka,

Yes, what is stated there is correct, and can be found here on our manual: NTP and GPS timing details

The sequence is the following (times are just for example):

  1. The Shake is connected to the internet, and time remains constantly updated via NTP
  2. The Shake is shut down at 12:00pm.
  3. The Shake is disconnected from the internet and brought to its recording location. This takes 1.5 hours.
  4. The Shake is turned on again, but is disconnected from the internet.
  5. If the time is not manually updated, the Shake time is still 12:00pm even if, in reality, it’s 1:30pm.
  6. The Shake will continue recording with the “wrong” timestamp until it is shut down again.
  7. When the Shake is reconnected to the internet, it will automatically update its time and thus display the correct timestamp.

We have a failsafe in place so that incorrectly timestamped data does not flow to our server, as described on the manual:

Data will still flow locally and use the system time for time stamping (It always uses the computer clock, whether NTP is running or not. The difference is if the clock disciplined by NTP). If there is no NTP, however, Raspberry Shake will recognize that the timing quality has been compromised and will not stream the data to the community server.

4

Excellent.

I will post our cool recordings of the subway trains sometime soon :slightly_smiling_face:

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Amazing news, we’ll be waiting for those!