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9 Time Synchronization
9.4 External Time Synchronization via Fieldbus
In these cases, SICAM P850/P855 is not synchronized anymore. The device uses the internal clock (on milli-
seconds time basis) and the last valid drift. After the programmable time delay, the device reports "Clock Error",
see chapter 14.
Switching Back from the Secondary to the Primary NTP Server
While the device is synchronized by the secondary NTP server, it continues to cyclically poll the primary NTP
server. The device will only switch back to the primary NTP server if it receives correct time information and if
none of the criteria for Redundant NTP Servers are fulfilled anymore.
NOTE
Chapter 2 of the system manual SICAM P850/P855 7KG85xx, order number E50417-C1040-C482, provides
information on the data format.
9.4
External Time Synchronization via Fieldbus
The external time synchronization via fieldbus is used if the device is connected to the systems control via pro-
tocol Modbus RTU or IEC 60870-5-103 using the RS485 interface.
The time information can also be transmitted from the systems control via Modbus TCP or IEC 61850 using
Ethernet interface. When using the Ethernet connection, Siemens recommend, however, to synchronize the
device from an NTP server, see chapter 9.3.
When using the external time synchronization via fieldbus, the client should send a message containing the
time information to the device in 1-minute cycles.
The time synchronization error using the Modbus RTU or IEC 60870-5-103 protocol is ±20 ms max.
NOTE
chapter 2 of the system manual SICAM P850/P855 7KG85xx, order number E50417-C1040-C482, provides
information on the data format.
9.5
Internal Time Synchronization via RTC
Besides external time synchronization, the internal time synchronization is also possible using the battery-buff-
ered RTC (Real Time Clock). SICAM P850/P855 features a quartz oscillator for this purpose.
The time offset of internal time synchronization is 86 ms/day maximum. Due to the reduced accuracy, RTC
should only be used in case of failure or unavailability of the external time synchronization.
NOTE
chapter 2 of the system manual SICAM P850/P855 7KG85xx, order number E50417-C1040-C482, provides
information on the data format.
238
SICAM P850/P855, 7KG85xx, Device Manual
E50417-H1040-C482-A6, Edition 10.2018
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