Siemens Commissioning PC Stations C79000-G8976-C156-07 - Manual (Page 195)

15 Symbol File Configurator Too
195
Commissioning PC Stations - Manual and Quick Start
Release 5/2005
C79000-G8976-C156-07
15.2 The Meaning of Symbols
Definitions
The terms listed below are important in conjunction with the Symbol File
Configurator:
Term Meaning
OPC ItemID The OPC ItemID is the identifier of a process variable used
by the OPC server.
An ItemID is transferred by the OPC client to the OPC
Server to identify a process variable and is unique for the
OPC Server.
It is either a symbolic name or a runtime name.
Symbolic name A symbolic name is an OPC ItemID that was generated by
the Symbol File Configurator. In a hierarchically structured
name space, a symbolic name is made up of the names of
the hierarchical levels and the actual symbol.
Example:
Plant_Packing.Conveyor.Limit_Switch
Runtime name A runtime name is an OPC ItemID that contains protocol
and address information to allow the assignment and that is
accepted directly by the OPC Server without the use of a
symbol file. Using the Symbol File Configurator, a symbolic
name is assigned to a runtime name.
Examples:
S
DP:[CP.5613]Slave1M003_IB0
S
FMS:[Connection1]14
S
S7:[S7_1.Connection]MW5
Accessing Process Variables using Symbols
An OPC client normally accesses process variables using ItemIDs that contain
address information. It is, however, also possible to access the variables using
symbolic names that can be structured hierarchically.
These names that are independent of the protocol and device are known as
symbols. In contrast, the variable names that include information about the
communications path and type in their syntax are known as runtime names.
Example of a symbol: Conveyor_1.drive_1.lim_switch
Example of a runtime name: S7:[Connection_1]EX3.1