IRIG-B is a serial time-code standard originally defined by the Inter-Range Instrumentation Group for coordinating time across US military test ranges. Decades later, it remains one of the most widely used time-distribution signals in electrical substations, protection and control systems, and SCADA infrastructure — largely because it is simple, robust, and doesn't depend on a packet network being up and correctly configured.
What IRIG-B actually carries
An IRIG-B signal encodes a complete timestamp — day of year, hours, minutes, seconds, and often a year and a straight binary seconds-of-day count — repeating once per second. A receiving device (a protection relay, a fault recorder, an RTU) decodes this continuous signal to keep its own clock synchronized, without needing to poll a server or maintain a network session. Because the format repeats every second and is self-contained, a device can recover full time information from the signal within a second or two of connecting.
B00x vs B12x — the format suffix
IRIG-B format names follow a numbering convention where the digits describe what the signal carries. The commonly seen distinction in the field is between the "B00x" family, which carries time-of-year information only, and the "B12x" family, which adds a Control Function field — additional encoded bits used to signal things like time quality, leap-second pending status, or daylight-saving state to the receiving device. Which variant a given piece of protection or SCADA equipment expects is determined by that equipment's own specification, so the time source and the receiving device need to agree on the exact format in use.
DC level shift vs amplitude-modulated
IRIG-B is distributed in two physical signal forms. DC level shift (sometimes written DCLS) is a straightforward digital pulse-width-coded signal — it's simple to generate, simple to decode, and works well over relatively short cable runs typical inside a substation control building. Amplitude-modulated (AM) IRIG-B carries the same time-code information modulated onto a 1 kHz sine-wave carrier. The AM form is more tolerant of longer cable runs and electrically noisy environments, which is exactly the environment a substation yard often is, at the cost of slightly more complex generation and decoding circuitry. Which form a given installation uses generally comes down to cable distance and the electrical environment between the time source and the receiving equipment, and many time servers and protection devices support both.
Why substations and SCADA still rely on IRIG-B
Modern protection relays, digital fault recorders, phasor measurement units, and RTUs frequently still specify a hardwired IRIG-B input alongside, or instead of, a network time protocol. There are practical reasons for this. A hardwired time-code signal does not depend on Ethernet infrastructure being correctly configured, does not require IP addressing or network security policy to reach the device, and continues to function even if the station's data network experiences a fault or misconfiguration. In a protection and control context — where correctly time-stamping a fault event, sequence-of-events record, or trip signal is central to post-incident analysis — that independence from the packet network is valuable in its own right, separate from whichever protocol (NTP or PTP) is also being used for IT-side time distribution.
IRIG-B alongside NTP and PTP
None of this means IRIG-B replaces network time protocols — most substations today run all three in parallel, from a single GPS-referenced time source: IRIG-B feeding legacy and protection-class equipment directly, NTP serving general IT and logging infrastructure, and increasingly PTP (often under the IEC 61850-9-3 or IEEE C37.238 power utility profile) for sampled-values and synchrophasor applications that need sub-microsecond accuracy. Our ORNATE 7000 TSDRNT is built for exactly this mixed environment — it outputs NTP/SNTP, PTP IEEE 1588, IRIG-B, 1PPS and serial time strings simultaneously from one GPS-disciplined reference, so a single time server can serve a substation's protection relays, its IT network, and any PTP-capable equipment without three separate boxes.
Choosing an IRIG-B source
When specifying a time source for IRIG-B distribution, confirm which format variant (B00x vs B12x) and which signal type (DC level shift vs amplitude-modulated) your downstream equipment expects, check cable-run distances against the signal type's tolerance, and confirm the time source itself is GPS or GNSS-referenced so the IRIG-B signal — and everything synchronized from it — carries a traceable, verifiable time base rather than a free-running local clock.
Distribution and signal integrity
Because IRIG-B is typically distributed over coaxial or twisted-pair cable rather than a switched network, signal integrity depends on the same fundamentals as any analog or digital signal run: cable quality, run length, grounding practice, and — in a substation yard specifically — electromagnetic interference from nearby high-voltage switching equipment. This is precisely why the amplitude-modulated form exists: encoding the time code onto a 1 kHz carrier makes the signal more resilient to exactly the kind of electrical noise a substation yard generates, at the cost of slightly more complex generation and decode circuitry compared with a straightforward DC pulse. On longer runs, or where a single time source needs to feed many devices, a distribution amplifier is commonly used to fan the IRIG-B signal out to multiple receivers without degrading the signal at each downstream point.
A standard that has outlasted its original purpose
IRIG-B's origins in military range instrumentation are largely incidental to why it remains in use today — the standard has persisted in power and utility applications because it solves a narrow, well-defined problem reliably: getting an unambiguous, self-contained timestamp to a device over a simple point-to-point or fan-out connection, without any dependency on network infrastructure, addressing, or protocol negotiation. As substations modernize toward IEC 61850 architectures and packet-based sampled values, IRIG-B increasingly sits alongside newer protocols rather than being replaced by them outright, precisely because that network-independence remains valuable for protection-class equipment even in an otherwise fully digital substation.
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ORNATE 7000 TSDRNT with IRIG-B output → ORNATE 7000 TSDR secure GPS time server → All products →