System Overview ProSafe-COM 3.00
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7
Time distribution and synchronisation
7.1 Realisation of functions
This chapter describes the time aspects in ProSafe-COM. The two basic functions of ProSafe-COM in
relation to time are:
•
Time distribution
•
ProSafe-PLC event time stamp correction
7.2 Time
distribution
Function
Within a DCS system data is acquired at multiple locations. Data is acquired by the ProSafe safety
system, but also by various other instruments that monitor and control the production process.
Acquired events are time-stamped and stored in the sequence of events list. Both ProSafe-COM and the
CENTUM CS3000 / VP DCS system (or other DCS system) record a sequence of events. For these
sequence of events to be fully integrated, the time-stamping must be synchronised. Only in an integrated
system, synchronised sequence of events causes and effects can be traced back in the right way.
Realisation
Time distribution requires a time master. Other systems must be time slaves to this time master. The time
master can be realised as follows:
•
When ProSafe-COM is connected to V-net and CENTUM CS3000 / VP, the V-net time master is
the time master for ProSafe-COM. ProSafe-COM is the time master for ProSafe-PLC and
ProSafe-SLS.
•
When ProSafe-COM is not connected to V-net, the time master for ProSafe-COM is the DCS that is
connected via Modbus. Again, ProSafe-COM is the time master for ProSafe-PLC and ProSafe-
SLS.
•
When ProSafe-COM is running stand-alone, then ProSafe-COM is the time master. ProSafe-COM
is the time master for ProSafe-PLC and ProSafe-SLS.
7.3 ProSafe-PLC event time stamp correction
Function
Earlier versions ProSafe-PLC (before October 2001) did not support time synchronisation in the
millisecond domain between the ProSafe-COM system clock and the CCMs (times could differ seconds).
So the events emerging from different CCMs could not be directly sorted in the ProSafe-COM event list.
Dedicated event time stamp correction mechanisms of ProSafe-COM compensated for the differences in
absolute time in the connected CCMs.
There were two possibilities:
a) ProSafe-COM sent a synchronisation pulse each minute to calculate all CCM clock deviations with
respect to the ProSafe-COM clock.
b) A GPS clock provided a sync pulse each minute, which enabled ProSafe-COM to calculate the CCM
clock deviations with respect to the absolute time.
The current version of ProSafe-PLC has the possibility (using time sync function blocks) to keep CCM
clocks synchronised within a millisecond and all CCMs synchronised with the ProSafe-COM clock within 5
to 25 milliseconds. Event time stamp correction is no longer needed when an accuracy of 25 millisecond is
sufficient.
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Copyright Yokogawa Europe Solutions B.V.
TI48J01A00-00E Oct 2010
