Note:
Since the
GPS Offset
and the
TAI Offset
have a fixed relationship,
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. Never
theless, 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.
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, NetClock will automatically change these offsets by the proper amount, no
matter which timescale is currently being used by the system.
As of 2017 the GPS to UTC Offset is 18 seconds. The last Leap Second occurred on December
31, 2016.
NetClock can be alerted of impending Leap Seconds by any of the following methods:
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.
3.2 System Time
CHAPTER
3
•
NetClock User Reference Guide
Rev.
16
155
Содержание NetClock 9400 Series
Страница 2: ......
Страница 4: ...Blank page II NetClock User Reference Guide...
Страница 16: ...BLANK PAGE XIV NetClock User Reference Guide TABLE OF CONTENTS...
Страница 42: ...BLANK PAGE 1 11 Regulatory Compliance 26 CHAPTER 1 NetClock User Reference Guide Rev 16...
Страница 160: ...BLANK PAGE 2 17 Configuring Outputs 144 CHAPTER 2 NetClock User Reference Guide Rev 16...
Страница 238: ...BLANK PAGE 3 5 Managing the Oscillator 222 CHAPTER 3 NetClock User Reference Guide Rev 16...
Страница 462: ...BLANK PAGE 446 NetClock User Reference Guide...
