Note: Since the GPS Offset and the TAI Offset have a fixed rela-
tionship, only the GPS Offset can be set. If only the TAI offset is
known, subtract 19 from it, in order to obtain the GPS offset.
Note that the data stream of GPS and several other external references includes
information about a pending Leap Second, and as such automatically corrects for
a Leap Second. Nevertheless, it is advisable to perform some testing in advance
to ensure all system components will adjust flawlessly. For more information, see
"Leap Seconds" below.
3.2.3 Leap Seconds
3.2.3.1 Reasons for a Leap Second Correction
A Leap Second is an intercalary
1
one-second adjustment that keeps broadcast
standards for time of day close to mean solar time. Leap Seconds are required to
synchronize time standards with civil calendars, thus keeping UTC time in sync
with the earth’s rotation.
Leap seconds can be introduced in UTC at the end of the months of December or
June. The INTERNATIONAL EARTH ROTATION AND REFERENCE SYSTEMS
SERVICE (IERS) publishes a bulletin every six months, either to announce a time
step in UTC, or to confirm that there will be no time step at the next possible
date. A Leap Second may be either added or removed, but in the past, the Leap
Seconds have always been added because the earth’s rotation is slowing down.
Historically, Leap Seconds have been inserted about every 18 months. However,
the Earth's rotation rate is unpredictable in the long term, so it is not possible to
predict the need for them more than six months in advance.
1
Intercalary: (of a day or a month) inserted in the calendar to harmonize it with the solar year, e.g., February
29 in leap years.
196
CHAPTER 3 • SecureSync 2400 User Manual Rev. 5.2
3.2 System Time
To Next Page
Loading...
