B&B Electronics VFG3000 - Manual - Manual (Page 58)

U SING T IME M ANAGEMENT V LINX F IELDBUS G ATEWAY M ANAGER U SER M ANUAL
P AGE 42
selected, the unit’s Ethernet port must be configured to use DHCP, and the
network’s DHCP server must be configured to designate a server via option 42.
• The Enable GPS property is used to instruct the time client to use a GPS unit
connected via NMEA-0183 as an alternative method of obtaining the current
time. The unit may be connected to any serial port using the appropriate driver.
• The Frequency property is used to specify how often the Gateway should
attempt to synchronize its time by the methods enabled above. The Gateway will
always attempt to sync twenty seconds after power-up, and will then sync as
specified by this property. If a given attempt to sync fails, the unit will retry
every 30 seconds until it is successful. If both GPS and SNTP synchronization
are enabled, the SNTP will only be used if a GPS is not available.
L OG F ILE
• The Time-Stamp Using UTC property is used to instruct Fieldbus Gateway
Manager to base its event and data logging on UTC rather than on local time.
This produces log files which are more easily portable across time-zones, and
which do not suffer from discontinuities when switching in and out of Daylight
Savings Time. The setting is global, and will effect all log files within the
system.
S ELECTING AN SNTP S ERVER
When configuring the SNTP client, you have several options when selecting a server.
If you have a Windows- or Unix-based time server as part of your network infrastructure, you
should ultimately synchronize to this source to ensure enterprise-wide synchronization. If you
have several Gateways on the same network, though, you will find it better to nominate one
of these as the master device for the purpose of setting Daylight Savings Time, and then have
that Gateway alone synchronize to the enterprise time source. You can then configure the
other devices to synchronize to the master device, and enable the Linked DST facility to
propagate the Daylight Savings Time setting around your factory.
If you have no enterprise time source available, you may choose to nominate a single
Gateway as the point where an operator will set the time, and then have other Gateways
synchronize to that source. Alternatively, if your installation provides TCP/IP access to the
Internet via either Ethernet or a modem connection, you may configure the SNTP client to
synchronize to a public time server. An example of this would be 192.6.15.28, which is the
current IP address of a public time server provided by NIST. A list of other servers can be
found at…
http://support.microsoft.com/kb/262680
Note that since Fieldbus Gateway Manager uses an IP address and not a host name to
reference the SNTP server, it will lose connection with any server that is relocated to a new
network address. While such relocations are very rare, they are beyond your control and that
of B&B Electronics. The use of an enterprise time source which accesses its own source via
DNS is thus considered preferable!