Note: Leap Seconds only apply to the UTC and Local timescales.
Leap Seconds do NOT affect the GPS and TAI timescales. However,
a Leap Second event will change the GPS to UTC, and TAI to UTC
time offsets. When a Leap Second occurs, SecureSync will auto-
matically change these offsets by the proper amount, no matter
which timescale is currently being used by the system.
As of 2018 the GPS to UTC Offset is 18 seconds. The last Leap Second occurred
on December 31, 2016.
SecureSync can be alerted of impending Leap Seconds by any of the following
methods:
GNSS Receiver (if available as an input reference): The GNSS satellite sys-
tem transmits information regarding a Leap Second adjustment at a spe-
cific Time and Date an arbitrary number of months in advance.
Input references other than GNSS: Some of the other available input ref-
erences (e.g., IRIG, ASCII, NTP) can also contain pending Leap Second noti-
fication in their data streams (see chapter below).
Manual user input: SecureSync can be manually configured with the date/-
time of the next pending Leap Second. On this date/time, the System Time
will automatically correct for the Leap Second (unless the System Time’s
timescale is configured as either GPS or TAI).
3.2.3.2 Leap Second Alert Notification
SecureSync will announce a pending Leap Second adjustment by the following
methods:
ASCII Data Formats 2 and 7 (among other formats) from the ASCII Data
option modules contain a Leap Second indicator. During the entire calendar
month preceding a Leap Second adjustment, these Formats indicate that
at the end of the current month a Leap Second Adjustment will be made by
using the character ‘L’ rather than a ‘_ ‘ [space] in the data stream. Note
that this does not indicate the direction of the adjustment as adding or
removing seconds. These formats always assume that the Leap Second will
be added, not removed.
NTP Packets contain two Leap Indicator Bits. In the 24 hours preceding a
Leap Second Adjustment, the Leap Indicator Bits (2 bits) which normally
are 00b for sync are 01b (1) for Add a Leap Second and 10b (2) for Remove
a Leap Second. The bit pattern 11b (3) indicates out of sync and in this con-
3.2 System Time
CHAPTER 3 • SecureSync 2400 User Manual Rev. 5.2
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