Demodulated Irig-B; Irig-B Implementation; Figure 56: Gps Satellite Timing Signal - GE MiCOM P747 Agile Technical Manual

Chapter 7 - SCADA Communications
13

DEMODULATED IRIG-B

IRIG stands for Inter Range instrumentation Group, which is a standards body responsible for standardising
different time code formats. There are several different formats starting with IRIG-A, followed by IRIG-B and
so on. The letter after the "IRIG" specifies the resolution of the time signal in pulses per second (PPS). IRIG-
B, the one which we use has a resolution of 100 PPS. IRIG-B is used when accurate time-stamping is
required.
The following diagram shows a typical GPS time-synchronised substation application. The satellite RF signal
is picked up by a satellite dish and passed on to receiver. The receiver receives the signal and converts it
into time signal suitable for the substation network. IEDs in the substation use this signal to govern their
internal clocks and event recorders.
Satellite dish
V01040

Figure 56: GPS Satellite timing signal

The IRIG-B time code signal is a sequence of one second time frames. Each frame is split up into ten 100
mS slots as follows:
● Time-slot 1: Seconds
● Time-slot 2: Minutes
● Time-slot 3: Hours
● Time-slot 4: Days
● Time-slot 5 and 6: Control functions
● Time-slots 7 to 10: Straight binary time of day
The first four time-slots define the time in BCD (Binary Coded Decimal). Time-slots 5 and 6 are used for
control functions, which control deletion commands and allow different data groupings within the
synchronisation strings. Time-slots 7-10 define the time in SBS (Straight Binary Second of day).
13.1

IRIG-B IMPLEMENTATION

Depending on the chosen hardware options, the product can be equipped with an IRIG-B input for time
synchronisation purposes. The IRIG-B interface is implemented either on a dedicated card, or together with
other communication functionality such as Ethernet. The IRIG-B connection is presented by a connector is a
BNC connector. IRIG-B signals are usually presented as an RF-modulated signal. There are two types of
input to our IRIG-B boards: demodulated or modulated. A board that accepts a demodulated input is used
where the IRIG-B signal has already been demodulated by another device before being fed to the IED. A
board that accepts a modulated input has an on-board demodulator.
To set the device to use IRIG-B, use the setting IRIG-B Sync cell in the DATE AND TIME column.
The IRIG-B status can be viewed in the IRIG-B Status cell in the DATE AND TIME column.
232
GPS time signal
Receiver
GPS satellite
IRIG-B
IED IED
MiCOM P747
IED
P747-TM-EN-1
P747-TM-EN-1.1