Configuration
4.12 Time-of-day synchronization
CP 1243-8 IRC
Operating Instructions, 02/2018, C79000-G8976-C385-03
101
Basics of time-of-day synchronization
With telecontrol applications that require time-of-day synchronization, you need to
synchronize the time of day of the CP regularly. If you do not synchronize the time of day,
there may be deviations of several seconds per day in the time information of the stations.
If security functions are activated, the module also requires the current time.
The CP can obtain the time of day from an external source, for the method see below. When
using an external time source, the connected S7 station can obtain the current time of day
both via the CPU as well as via a CP.
Note
Recommendation: Time-of-day synchronization only by 1 module
Only have the time of day of the station from an external time source synchronized by a
single module so that a consistent time of day is maintained within the station.
When the CPU takes the time from a CP, disable time-of-day synchronization of the CPU.
If you have the time synchronized on the CP and the CPU via NTP, when possible use the
same NTP server to maintain a consistent time of day within the station.
Time-of-day concept
Before configuring time-of-day synchronization specify the following:
●
Specify the time source in the network.
●
Specify the time master in the network.
●
Specify the network or networks via which the time of day will be forwarded by the time
master to the time slaves.
Synchronization method
The CP supports the following methods of time-of-day synchronization:
●
NTP / NTP (secure)
Network Time Protocol
Time-of-day synchronization only via Ethernet
The function is available only when telecontrol communication is disabled.
The secure method NTP (secure) can be used if the security functions are enabled. It
uses authentication with symmetrical keys according to the hash algorithms MD5 or SHA-
1. In the global security settings, you can create and manage NTP servers of the type
NTP (secure).
Recommendation with NTP:
Synchronization with an external clock at intervals of approximately 10 seconds is
recommended. This achieves as small a deviation as possible between the internal time
and the absolute time.