A stopped DNP3 outstation clock: 54 events, one timestamp
Most clock checks need a reference: a time write to compare with, or a clock read. When nobody syncs the outstation there is no reference, and many tools say nothing. A stopped clock still leaves a mark that needs none: different events, arriving minutes apart, with the same timestamp.
The setup
RTU 3, six points, polled for 45 minutes. Its clock stops for almost 20 minutes in the middle of the capture, the way a failing RTC does, and starts again. The master writes the time once at startup and never again.
What the capture shows
| 45 minutes | Value |
|---|---|
| Events stamped 12:15:06.126 | 54 |
| Time over which they arrived | 19 min 46 s |
| Median apparent event delay | 7.8 min |
| Worst apparent event delay | 20.0 min |
- Every one of the 54 events is a real change with a correct value. Only the time is wrong, and it is wrong in a way no network can produce: the timestamp stands still while the changes keep arriving.
- In the SCADA's sequence of events the 54 collapse into one instant, sorted by whatever the historian uses to break ties. The order of operations in those 20 minutes is lost.
- The apparent delays (up to 20 minutes) are a symptom, not a measurement: they grow because the clock stands still.
What to check
- Look for runs of distinct events with identical timestamps. Two or three can be a coincidence on a fast burst; dozens over minutes are a stopped clock.
- Note when the run starts and ends: that is when the RTC failed and recovered, useful for the hardware report.
- A clock that stops and restarts is usually an RTC or its backup supply. A clock that only moves when it is written is a firmware that does not run the RTC at all.
Try it on your own capture
ComputingSphere DNP3 flags a stopped outstation clock from distinct events stamped alike, with when it started and how long it lasted, even when the capture has no time sync to compare against. It only reads what already went over the wire. This capture is among the examples of every free account, to reproduce every number here; or upload your own: the Free plan covers 1,000 messages a month.