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Q.series
Gantner Instruments Test & Measurement GmbH
Connecting the modules → Synchronization of several systems
4
In the variant with a master controller (an additional Q.pac mas-
ter controller is also possible) the first three methods transfer the
time stamp via an RS-485 link to the other Test Controllers and
achieve the best time synchronization with the smallest jitter
(approx. ±2 μs) between the individual modules, because the time
information passes simultaneously to all Test Controllers. The
absolute accuracy of the time information depends on the method
used. Configuration takes place using the test.commander pro-
gram, see Section 5.8.3.3, Synchronization, Page 97.
If you do not want to use or cannot use any time synchronization
lines, e.g. because the spacing of the systems is too large, you
must expect greater deviations. In the variant 2b the deviations
lie in the range from a few milliseconds up to about 100 millisec-
onds, but this depends on various factors, e.g. how often the time
information is received. In the variant 3b the time accuracy of the
GPS signal is decisive, which is only approx. 1 second absolute.
The fourth method uses, for example, the SNTP protocol (Simple
Network Time Protocol) used in the Microsoft Windows operating
system to transfer the date and time via Ethernet. However, the
individual Test Controllers must always query the time server in
order to be able to synchronize their times to the time server. The
achievable accuracy is therefore not as good as for the three
other methods. If required, you can also set up a (full) NTP time
server on a PC and synchronize it with a time server in the Inter-
net. You will find further information about this at
www.meinberg.de
(here you can also download a time server pro-
gram) and at http://www.pool.ntp.org. The time accuracy is then
only dependent on the response times in your network.
If you combine several synchronization methods, the best possi-
ble one is always used from those available:
1. Hardware synchronization
2. IRIG-B via time signal, e.g. DCF77
3. Time signal from GPS (NMEA-0183)
4. SNTP
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