Technical data

Installation & Operation Manual GM-TTT
Page 66
After a setting has occured, the amount of time code deviation with respect to "real time"
depends upon the accuracy of the crystal (of the GM-TTT or the sync-generator):
Deviation by frames:
with an accuracy of after one day after 30 days
10
-8
0,02 0,65
10
-7
0,2 6,5
10
-6
2 65
To achieve target 3, the GM-TTT should be synchronised either to a stable seconds pulse of
the receiver clock or - if the time code has to be generated in-sync with the video signal - the
sync generator has to be externally coupled to real time, i.e. by using a 10MHz clock. This will
avoid any frame jumps caused when the real time is transferred to the time code (please also
refer to the chapter entitled “Real Time Coupling of Time Code and Video“). In this case the
moment of time (every second, every day...) of the time adoption is only relevant with respect
to the time jumps caused by a leap second or by the start/end of DST:
• Leap second: A leap second is only precisely generated (as a forecast) in the "every
second" setting mode, provided that the leap second was announced. Remark on the leap
seconds: The leap seconds were firstly inserted on January 1
st
1972. According to the
instructions of the IERS (International Earth Rotation Service), the leap seconds are
generally inserted by the end of the year or mid-year as the last second of December 31
st
or June 30 in UTC, i.e. on January 1
st
at 1:00 o'clock CET or on July 1
st
at 2:00 o'clock
CEST. The leap second is the 60
th
second of an hour; to supply the leap second, the GM-
TTT generates the 59
th
second twice, i.e. the time sequence in summer is as follows:
Real Time Time Code of the
GM-TTT
July 1
st
1:59:59 CEST 1:59:59:23
1:59:59:24
July 1
st
1:59:60 CEST ← leap second 1:59:59:00
1:59:59:01
etc.
1:59:59:23
1:59:59:24
July 1
st
2:00:00 CEST 2:00:00:00
• Start/end of DST: The DST switchover is only exactly generated (as a forecast) in the
"every second" setting mode or when the automatic DST mode of the internal clock is
activated. This requires that the switchover is announced in the "every seconds" setting
mode. It further requires that the difference between OFFSET 1 and OFFSET 2 has been
correctly selected for the time zone, which is generally + or - one hour (ZONE menu). The
GM-TTT will generate the following frame sequence during a switchover to (example):
CEST: 01:59:59:23 CET: 02:59:59:23
01:59:59:24 02:59:59:24
03:00:00:00 02:00:00:00
03:00:00:01 02:00:00:01
etc. etc.