External Time Synchronization Per Ntp - Siemens SENTRON PAC5200 Device Manual

9.3

External Time Synchronization per NTP

General
To synchronize the time via an external source, SENTRON PAC5100/5200 is equipped with an SNTP client
(SNTP = Simple Network Time Protocol) that can be connected to 2 NTP servers (NTP = Network Time Proto-
col), the primary and the secondary (redundant) NTP server.
The chapter 7.3.6.1 describes how to set the parameters of the 2 servers.
NTP is used for external time synchronization via Ethernet. The SNTP client sends a time request to the NTP
server once a minute. The time synchronization error is ±5 ms referred to UTC time of the NTP server.
The time stamp of the NTP server has a 64-bit format. Counting is accomplished in seconds and fractions of
seconds.
NOTE
The time format is described in detail in the RFC 5905 (Request for Comments 5905 for NTP).
Time Synchronization Procedure
The device was set to external time synchronization (Ethernet NTP) during the parameterization. After switch-
ing on or resetting the device, the FAIL bit is first set to "1" (=invalid) and the device sends a time request to
the NTP server. After receiving the time information from the NTP server via Ethernet, the FAIL bit is set to "0"
(=valid) and the internal timer (RTC) is updated. The SNTP client repeats the time request to the NTP server
cyclically once every minute.
If the primary NTP server fails (for example, no response to a request twice or one of the criteria at "Redundant
NTP server" satisfied) and if the secondary NTP server is operational (always polled in parallel), the device
switches to the secondary NTP server. The FAIL bit remains = 0. In this case, the operational indication "Pri-
mary NTP Server Error" is displayed, see chapter 14.1.
If the secondary NTP server is also invalid, the FAIL bit will be set to 1 after the programmable timer Error in-
dication after has expired, and the "Clock Error" indication is output.
Redundant NTP Servers
The time synchronization supports a primary and a secondary NTP server. Different IP addresses are set for
the two NTP servers, see chapter 7.3.6.1.
SENTRON PAC5100/5200 cyclically polls both NTP servers once every minute, but during normal operation it
is synchronized by the primary NTP server. The device automatically switches to the secondary NTP server if
one of the following criteria are met:
• No response from the primary NTP server to 2 successive requests
• The "Alarm" indication is set in the time information of the primary NTP server.
• The primary NTP server responds with 0.
• The message runtime in the network is > 5 ms.
• The stratum of the primary NTP server is 0 (unknown) or > 3.
Switching to the secondary NTP server is prevented if:
• The secondary server does not provide better time information (see criteria that initiate the switch from
primary to secondary NTP server; "Secondary NTP Server Error" indication was already output) or
• The secondary server has recently been available for less than 10 minutes.
SENTRON PAC5100/5200, 7KM5212/5412, Device Manual
E50417-H1040-C568-A1, Edition 03.2015
9 Time Synchronization
9.3 External Time Synchronization per NTP
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