GE PACSystems RX7i, Руководство пользователя

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Chapter 5. Ethernet Global Data
GFK-2224Q January 2017 87
SNTP Broadcast and Multicast Operation Mode
The Ethernet Interface will synchronize to a remote SNTP timeserver after receiving two broadcast clock values
within a 150-second period. The Station Manager can be used to view server status information.
SNTP Unicast Operation Mode
In this mode, the module tries to request the time from a time server to synchronize the clock. You can
configure a maximum of two time servers: One for Primary Time Server and another for Secondary Time Server.
Based on the configuration parameters, the Ethernet module first polls the Primary Time Server and
synchronizes the clock. If the Primary Server does not respond to the requests, it switches to the Secondary
Server and polls it for updated time. This process repeats until it synchronizes to one of the time servers. Polling
rate and timing for switching from one server to another server are defined as user-configurable parameters.
For parameter definitions refer to Appendix A, “Configuring Advanced User Parameters.”
Multiple SNTP Servers (Applies only to SNTP Broadcast and Multicast Mode)
To guard against loss of SNTP timing messages, multiple SNTP timeservers can be tracked on a network. An
Ethernet Interface can maintain timing information from up to four total SNTP timeservers at a time. Each
server assigns a stratum number that determines its priority. The Ethernet Interface uses the message from the
server with the lowest stratum number until communication with that server is lost. Then the server with the
next lowest stratum number becomes the server of choice and the Ethernet Interface synchronizes to it if it
receives two of its timing messages within a 150-second period. A server is considered "lost" if more than 150
seconds elapse between timing messages.
Local Time and Daylight Saving Time Corrections
Versions 6.20 and later of the Ethernet interface support the ability to specify an offset to the Coordinated
Universal Time (UTC) to correct for local time zone and daylight saving time (DST). You can specify the DST
start/stop times and offset from local standard time, as well as the local time offset from the UTC. The specified
correction is applied to all modes of SNTP communications (Broadcast, Multicast and Unicast).
The default SNTP operation is
no correction
for local time or DST. Local time and DST corrections must be
enabled via AUP. For local time correction and DST parameters, refer to Appendix A, “Configuring Advanced
User Parameters.”
Loss or Absence of SNTP Timing Signals
If an Ethernet Interface is configured for SNTP, but does not receive two timing messages from an SNTP
network timeserver within a 150-second period, the following will happen:
▪
A fault entry will be placed in the PLC Fault Table.
▪
A fault entry will be placed in the Ethernet Interface's exception log. This log can be read using the Station
Manager.
▪
The Status word within a consumed exchange will indicate new data with a value of 3, instead of the
normal 1 value, indicating that SNTP is selected, but the Ethernet Interface is not synchronized to an SNTP
server. This Status word value can be obtained from the PLC register configured for the particular
exchange.
Note: The SNTP error condition is considered the least important of all possible error codes.
Therefore, if another error condition exists, its status code will appear in the Status word
instead of the SNTP error code.
Upon loss or absence of synchronization, the Ethernet Interface’s built-in clock will operate as follows:
▪
If the Ethernet Interface, after its last power-up/restart cycle, has never received an SNTP server's timing
message, it will continue to use the PLC CPU's local clock value that it received at power-up/restart for its
time base.
▪
If the Ethernet Interface has been synchronized to an SNTP server but lost its signal, it will use the most
recently received SNTP time message as its time base.