8.3 Output Signal Description
67
8.3.2
Modulated and Unmodulated IRIG-B
Figure 8.2 illustrates the primary differences between modulated and unmodulated IRIG-B. You
will notice that the while modulated IRIG-B (B120) is distinctive because it uses a sinewave carrier
signal of 1 kHz, it is similar to unmodulated IRIG-B (B000) since the peak-to-peak values of the
carrier follow the same form as the digital waveform, where the information is contained.
Figure 8.2: IRIG-B Waveforms
8.3.3
IRIG-B IEEE 1344 Extension
As mentioned above, the IEEE 1344 enables extra bits of the Control Function (CF) portion of the
IRIG-B time code. Within this portion of the time code, bits are designated for additional features,
including:
•
Calendar Year (old method, now called
BCD
Y EAR
)
•
Leap seconds, and Leap seconds pending
•
Daylight saving time (DST), and DST pending
•
Local time offset
•
Time quality
•
Parity
•
Position identifiers
To be able to use these extra bits of information, relays, RTU’s and other equipment receiving the
time code must be able to decode them. Consult your equipment manual to determine if the IEEE
1344 feature should be turned ON in the Model 1094B. To view details of the IEEE Std 1344-1995,
please check with the IEEE.
NOTE
: To download a copy of of the IRIG-B 2004 specification, please use the link to the Arbiter
web site.
http://www.arbiter.com/catalog/timing freq index.php and click on IRIG-B.
8.3.4
1 Pulse per Second (1 PPS)
A one Pulse-Per-Second timing output signal is very simple in concept. It is a digital bit transmitted
every second with a pulse width of 10 milliseconds. Probably the most critical part of this signal
is that it is “on time” at the rising edge, compared with the signal from the Global Positioning