Precision Timing for Reliable Power.  Simplified.
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GPS Time-Sync Protocols

The DCF77 precision time protocol provides 1 ms resolution and is used in some power and automation applications.   Devices which support DCF77 include:

  • STR-100 Satellite Time Reference
  • CyTime SER-3200/2408 Event Recorders
  • PowerLogic CM4xxx meters by Schneider Electric
  • Power Xpert PXM4000/6000/8000 meters by Eaton
  • Quantum ERT PLC I/O cards by Schneider Electric


DCF77 is a precision time protocol used to synchronize power system devices in time-critical applications.   DCF77 was developed by the Physikalisch-Technische Bundesanstalt (PTB) in Braunschweig, Germany, the national institute for science and technology.   DCF77 is both a longwave time signal and a radio station used by the PTB to transmit a precision time signal. DCF77 stands for D=Deutschland, C=long wave signal, F=Frankfurt, and 77= 77.5kHz.

The DCF77 time synchronization output is a 24Vdc pulse-width modulated signal that provides a complete date/time string once every minute.  The signal contains a one-pulse-per-second component that is accurate to 100 microseconds in reference to UTC (Coordinated Universal Time).   Once each minute, a pulse-string is sent containing a BCD (Binary Coded Decimal) value for minute, hour, day, day of week, month, and year as well as other control parameters such as leap second and Daylight Saving Time (Summer Time).

Unlike IRIG-B—which is typically distributed at 5V—DCF77 is distributed at 24Vdc, making it more robust for daisy-chaining to numerous devices over much longer distances.   The time frame of DCF77 is one minute, compared with an update interval of one second for IRIG-B.  This limits demands on processor bandwidth without adversely affecting accuracy.  These characteristics make DCF77 an attractive solution for synchronizing power system devices which do not yet support PTP (IEEE 1588).