The timestamps don't tell the whole story (fixture inspection)

NoraAli0235 · 19 Jul 2026, 14:34 UTC

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NO
NoraAli0235
Our logs show a timeout during fixture inspection with Universal Robots UR5e, but I can't assign an acknowledgement to the right attempt. We're in a commissioning station recording job events, using a sample housing. Python, PLC and controller timestamps don't agree, and our application reused the job label after restarting. I'm trying to reconstruct what we actually know.

14 replies

FA
FarahBaker0504
Replying to NoraAli0235

@NoraAli0235 Can your application log identify where the process restarted? That would distinguish the reused labels within one source, even with mismatched clocks elsewhere.

8 points
NO
NoraAli0235
Replying to FarahBaker0504

Found it. I can split our Python log into two sessions. Still no attempt match for that PLC acknowledgement, though.

12 points
FA
FarahBaker0504
Replying to NoraAli0235

Start with the session split and each source's own ordering, leaving that acknowledgement unassigned. The timestamps beside those entries should establish a combined sequence.

6 points
OS
OscarAllen0271
Replying to FarahBaker0504

Those clocks disagree. Why would putting their timestamps beside the sessions establish an order across systems without an offset or matching exchange?

10 points
FA
FarahBaker0504
Replying to OscarAllen0271

You're right to challenge that. The timestamps can suggest matches, not prove them. Keep source order intact and label cross-system links uncertain unless there's supporting evidence.

17 points
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NoraAli0235
Replying to FarahBaker0504

@FarahBaker0504 I'll keep that acknowledgement unassigned. One tidy sequence would look nicer, but choosing the nearest request by timestamp would be a guess.

6 points
EL
EllaBennett0729
Replying to NoraAli0235

@NoraAli0235 My merged log fooled us after a machine clock adjustment. Keeping the original source order let us untangle our confidently wrong interpretation.

3 points
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NoahArcher0368
Replying to EllaBennett0729

Would monotonic time fix it? Or only inside one process?

8 points
FA
FarahBaker0504
Replying to NoahArcher0368

@NoahArcher0368 Use monotonic time for durations within a running process. It doesn't supply a shared clock across machines or restarts; keep session identity and wall-clock reference alongside it.

7 points
NO
NoraAli0235
Replying to FarahBaker0504

Stable job ID, separate attempt ID for each try? Is that what our reused label is missing?

5 points
FA
FarahBaker0504
Replying to NoraAli0235

That's the useful split. A job ties the work together; an attempt distinguishes each try. Record both with the event source and session.

9 points
OS
OscarAllen0271
Replying to FarahBaker0504

@FarahBaker0504 Does the documented PLC interface support a correlation value? Application identifiers alone won't create matching identifiers in another system's records.

4 points
NO
NoraAli0235
Replying to OscarAllen0271

Splitting the application sessions helps. I still can't assign the acknowledgement reliably, so our reconstruction remains incomplete.

16 points
FA
FarahBaker0504
Replying to NoraAli0235

@NoraAli0235 Clearer sessions help, and you're right that they don't supply the missing acknowledgement link.

18 points

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