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B-5
NI PXI-6683 Series User Manual
The NI PXI-6683 Series uses the time of day information transmitted as BCD to synchronize its
internal timebase. If the IRIG-B signal includes the year, then it also uses that information to
synchronize its clock. Otherwise, it gets the year from the host computer. The NI PXI-6683
Series disregards the rest of the information contained in the IRIG-B signal. Therefore, when
configured to synchronize to IRIG-B AM, the NI PXI-6683 Series supports IRIG-B 12X
(200-04 standard) , and when configured to synchronize to IRIG-B DC, it supports IRIG-B 00X
(200-04 standard).
The following assumptions are made regarding the received IRIG-B signal. All conditions must
be met for the NI PXI-6683 Series to be able to synchronize accurately:
•
Seconds begin every minute at 0, increment to 59, and then roll over to 0.
•
Minutes begin every hour at 0, increment to 59, and then roll over to 0.
•
Hours begin every day at 0, increment to 23, and then roll over to 0.
•
Days begin every year at 1. Days increment to 365 in non-leap years, or to 366 in leap years,
and then roll-over to 1. Leap years must be supported. Valid values for year are 01 to 99,
inclusive. Years are assumed to be in the XXI Century. For instance, year
09
represents
2009. If the year is not supplied (sent as
00
), the OS system time is read and the year is
derived from it.
To achieve proper synchronization of the NI PXI-6683 Series ensure that the IRIG-B source used
conforms to the requirements listed above. Note that most IRIG-B sources conform to these
requirements.