Ref ID : ADR233B/IM/CS
Rev No. : 05
ADR233B
IRIG-B Encoding
IRIG-B consists of 100 bits produced every second, 74 bits of which contain various time, date,
time changes and time quality information of the time signal. Consisting of logic ones, zeros and
position identifier bits, the time code provides a reliable method of transmitting time to
synchronize power equipment devices. There are three functional groups of bits in the IRIG-B
time code: Binary Coded Decimal (BCD), Control Functions (CF) and Straight Binary Seconds
(SBS). The BCD group contains time information including seconds, minutes, hours and days,
recycling yearly. The BCD time-of-year code (BCDTOY) reads zero (0) hours, minutes, seconds
and fraction of seconds at 2400 each day and reads day 001 at 2400 of day 365, or day 366 in a
leap year. The BCD year code (BCDYEAR) counts year and cycles to the next year on January
1st of each year and will count to year 2099. The (optional) SBS time-of-day code consists of
the total elapsed seconds, recycling daily. SBS reads zero (0) seconds at 2400 each day
excluding leap second days when a second may be added or subtracted. The CF group
contains year, time quality, leap year, pending leap seconds and parity. Other CF bits are
reserved for user-defined purposes, depending on application. Lastly, position identifiers
separate the various components of the IRIG-B time code.
IRIG-B Implementation
Typical techniques for transmission of unmodulated IRIG-B (DCLS) include:
5V signal over coaxial cable or shielded twisted-pair cable
Multi-point distribution using 24 Vdc for signal and control power
RS-485 differential signal over shielded twisted-pair cable
RS-232 signal over shielded cable (short distances only)
Optical fibre.
7.2 MODBUS
This section describes how the MODBUS standard is applied to the relay platform. It is not a
description of the standard itself. The level at which this section is written assumes that the
reader is already familiar with the MODBUS standard.
The MODBUS protocol is a master/slave protocol, defined and administered by the MODBUS
Organization. For further information on MODBUS and the protocol specifications please see
the Modbus web site (
www.modbus.org).
Overview: Physical Connection and Link Layer
For connecting on MODBUS use:
Rear serial port 1 - for permanent SCADA connection via Ethernet (RJ45/FO) port.
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