DNP3 Time Synchronization
Key Takeaway
How DNP3 time synchronization works between master and outstation — LAN and non-LAN procedures, accuracy, GPS alternatives, and why timestamps matter.
Quick Answer
DNP3 includes built-in time synchronization where the master sets the outstation's clock. Two methods exist: non-LAN (measures round-trip delay to compensate for communication latency) and LAN (assumes negligible delay over Ethernet). Accurate timestamps are critical for event sequencing, production accounting, and regulatory compliance.
Why Time Matters
DNP3 events carry timestamps from the outstation's clock. Inaccurate time causes event sequence ambiguity (did the alarm trigger before or after the shutdown?), production accounting errors, and regulatory compliance issues in custody transfer measurement.
Non-LAN Time Sync
- Master sends a Delay Measurement request
- Outstation responds immediately
- Master calculates round-trip delay
- Master sends Write Time with compensation for half the measured delay
- Outstation sets its clock
LAN Time Sync
For Ethernet connections where delay is negligible, the master sends a Record Current Time request followed by a Write Time. No delay measurement needed.
GPS Alternative
For custody transfer and high-accuracy applications, GPS time receivers provide ±1 microsecond accuracy independent of master communication. Many RTUs (ABB Totalflow, SCADAPack) support GPS receivers for direct time synchronization.
SNTP/NTP
Ethernet-connected outstations can also synchronize via NTP/SNTP servers as an alternative or complement to DNP3 time sync.
Frequently Asked Questions
The master measures communication delay, then sends a time-write command compensated for half the round-trip delay. The outstation sets its clock from this corrected time.
Typically ±10-100ms over serial links. For higher accuracy, GPS time receivers provide ±1 microsecond independent of the master.