Where possible create a concept for the time-of-day synchronization before the configuration. Make sure that you only use one time source for every station. It makes sense to have only one time source per subnet.
Note the mechanisms of time-of-day synchronization of the S7-1200 in the section Time-of-day synchronization with S7-1200.
NTP ‑ Network Time Protocol
With the NTP method, the CP or the CPU sends time-of-day queries to one or more NTP servers in the subnet (LAN). Based on the replies from the server, the most reliable and most accurate time is determined and the time of day on the querying module is synchronized. Any MMS time-of-day messages received are then ignored.
The advantage of NTP mode is that it allows the time to be synchronized across subnets.
In NTP mode, it is generally UTC (Universal Time Coordinated) that is transferred. This corresponds to GMT (Greenwich Mean Time).
The parameters described below are not available for all modules.
NTP server
You can configure the IP addresses of up to four NTP servers.
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Note S7-1500 CPUs as of version V1.8: Changing the NTP servers fro the user program For S7-1500 CPUs as of firmware version V1.8 you can change the addresses of 4 NTP servers with the instruction T-CONFIG (SFB 105) at runtime. The requirement for this is that you have configured at least one NTP server in the "Time-of-day synchronization" parameter group. The configured addresses of the NTP servers are overwritten by the IP addresses of the NTP servers in the instruction T_CONFIG. Even if only 1 NTP server was configured, up to 4 NTP servers can be programmed using the SFB. When necessary, the addresses of the NTP servers can be changed several times with T_CONFIG. The firmware version V1.8 for S7‑1500 CPUs is available with STEP 7 V13.0 SP1 Update 3. |
"Time zone"
The time offset from UTC can be set by configuring the local time zone.
"Update interval"
The interval specifies the time cycle of the time queries (in seconds). The value of the interval ranges between 10 seconds and one day.
If the "Time-of-day synchronization on the full minute" option is enabled, the cycle is automatically set to 60 seconds.
"Time-of-day synchronization on the full minute"
If the option is enabled, the synchronized time of day that the CP forwards to the CPU is adopted by the CPU precisely on the full minute.
If the "Time-of-day synchronization on the full minute" option is enabled, the parameter "Update interval" is automatically set to 60 seconds.
"Accept time of day from non-synchronized NTP servers"
If the option is enabled, the CP also accepts the time-of-day from non-synchronized NTP servers with stratum ≥ 15.
If the option is disabled, the CP does not accept the time-of-day from NTP servers with stratum ≥ 15. If the CP receives a time of day frame from an NTP server with stratum ≥ 15, the time of day of the CP is not set according to the frame. In this case, none of the NTP servers is displayed as "NTP master" in the diagnostics; but rather only as being "reachable".
"Forward time of day to station"
With CP 300/400 this option is enabled as default.
Some CPUs provide the option of requesting the time of day automatically from an NTP server. If the time-of-day synchronization is used by the CPU, you should disable the option described here on the CP. This avoids the time of day acquired by the CPU from the NTP server being overwritten again by the time of day received by the CP. Due to forwarding the time of day from the CP to the CPU there could be less accuracy in this case.