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5.8 Accuracy / synchronization loss
In synchronized state the deviation typically is lower +/-50 ms.
The movements continues running autonomously for 24 hours without synchronization
with
quartz accuracy. After that the clock signalizes synchronization loss by setting the hands to 12:00 po-
sition and waiting for renewed synchronization. The deviation without synchronization after 24 h is
typically lower +/-2 s (quartz accuracy: 20 ppm at room temperatures). Slave movements totally con-
tinue running for 48 hours without synchronization (timeout timeout slave).
Note:
The mentioned deviations depend on the accuracy and ability of the time source
(NTP server). NTP reception can be affected by network traffic and network devices
(hubs, switches, routers, firewalls, etc.).
5.9 Time source redundancy
The availability of the time source in the network can be enhanced by redundant installation of NTP
servers. Depending on the selected operation mode of the NBU 190 one of the following strategies is
recommended (also adequate for time zone servers):
5.9.1 NTP Client Unicast
Up to four different NTP server addresses can be provided to the NBU 190 by means of DHCP/
DHCPv6 or the PC tool MOBA-NMS. If three NTP requests stay unanswered by the current NTP
server the movement changes to the next server (if available). The duration until a change happens is
depending on the configured NTP request time interval (default: 3 x 10 seconds). After a reset the
movement sends the NTP requests to the first server.
5.9.2 NTP Client Multicast
Two NTP servers have to be installed sending out NTP packets on the same multicast address. The
sending intervals of the servers have to be chosen in a ratio that synchronization in normal operation
is done by the first server. Only in case of failure of the primary server the secondary server should
take over synchronization. The ratio of the number of transmitted packets between primary and sec-
ondary server should be about 4:1:
• Sending interval primary server: 1 packet / 1 minute
• Sending interval secondary server: 1 packet / 4 minutes
The selection of the server hence depends on the dominance of the server with the shorter sending
interval. If the primary server fails the secondary server thus becomes dominating.
5.10 MOBA-NMS (MOBATime Network Management System)
MOBA-NMS is a Java based PC program used for the configuration and status
requests of NTP movements. This software allows for a central configuration of
one or multiple devices.
Further informations, manuals and the software itself are available on our website
http://www.mobatime.com. These are also available on a USB stick (must be or-
dered separately).