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GPS Time-Sync Protocols

The IRIG-B time code provides 1 ms resolution and is widely used by electric utilities and others, especially in the United States.   Devices which support IRIG-B include:

  • STR-100 Satellite Time Reference
  • CyTime SER-3200/2408 Event Recorders
  • Power quality meters (various models)
  • Overcurrent protective relays (various models)


IRIG-B is an older time-distribution protocol used to synchronize power system devices that do not support PTP (IEEE 1588), such as relays and meters.   The IRIG time codes were developed by the Inter-Range Instrumentation Group (IRIG), part of the Range Commanders Council (RCC) of the US Army.   The standard was first published in 1960 and has been revised several times.  The latest version is "IRIG Serial Time Code Formats," IRIG standard 200-04, updated in September, 2004.

IRIG-B (IRIG time code B) has been widely used in the electrical power industry.   IRIG-B has a pulse rate of 100 pulses-per-second to communicate the full date and time over its one-second time frame.   It contains time-of-year and year information in a BCD format, and (optionally) seconds-of-day in SBS.   Prior to the 2004 revision, year information was not part of the IRIG standard.   Instead, IEEE Standard 1344 prescribed a means for encoding the year in unused control bits, commonly known as "IEEE-1344 Extensions."

IRIG-B is typically distributed as a DC level shift (DCLS), pulse-width coded signal (“unmodulated IRIG-B”) or as an amplitude-modulated signal based on a sine wave carrier with a frequency of 1kHz (“modulated IRIG-B”).   The IRIG 200-04 standard does not define specific signal levels or implementation details, but IRIG-B is typically distributed as an unmodulated TTL-level signal (5 Vdc) over shielded twisted-pair or coaxial cable.