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The AC500 V3 supports the NTP and the SNTP protocol ((Simple) Network Time Protocol). Compared to SNTP, the NTP protocol achieves higher accuracy in time synchronization, meeting advanced requirements for accuracy and reliability of a PLC solution.

The S500 I/O modules do not support the functionality to create and transfer a timestamp with an event directly at the I/O channel. A workaround is using SoE logging (Sequence of Event) for a root-cause analysis. An ‎⮫ application example explains how events are processed.

The protocols NTP and SNTP provide the functionality to synchronize the clock of a PLC to an external time source.

A specification of the (S)NTP protocol itself can be found in the document RFC4330.

The following modes are supported by the implementation of the PLC:

The server and client implement the NTP protocol version NTPv4 , which is fully backwards compatible with NTPv3 and SNTP.

The function block PmNtpInfo can be used to read NTP client diagnosis information of the protocol.

Refer to the documentation of the library ABB_Pm_AC500.lib for further information.

Detailed information about the parameters for the NTP implementation used in AC500 V3 PLCs and how to diagnose possible NTP client synchronization errors are provided in the ‎⮫ application note.

  • If a high precision of system time is wanted, use a fully functional NTP server or at least an SNTP server with a high-precision time-source (e.g. DCF-77 receiver). Avoid cascading several levels of (S)NTP server / (S)NTP clients.

  • Client requests are normally sent at intervals depending on the frequency tolerance of the client clock and the required accuracy. However, under no conditions requests should be sent at less than one minute intervals (see RFC 4330). Keep that in mind when setting polling-interval of the (S)NTP client, especially if a huge amount of clients use one single server.

  • Be sure not to use broadcast or multicast addresses as server or backup-server since current (S)NTP implementation does not support manycast mode.

  • Most synchronization problems are caused by high root distance (combination of root dispersion and root delay) make sure that the server sends at max a distance of 3s or lower.