Section C Standard Displays
C-14
C 4 Trend Display
C 4.1 General description - trend display
The development of process variables for a period of time can be graphically displayed with the
Trend Display. Up to six process variables can be depicted in each trend display. The number of
trend displays per operator station is unlimited.
A trend display can be used to show either the data captured by a trend data acquisition block
or any process variables.
If a trend data acquisition block is used, up to six values are logged with their respective time
stamps and placed in a buffer memory with 200 values per signal and, if required, transferred to
the operator station for Long Term Archival (see Engineering Reference Manual, Functions
and Function Blocks, Acquisition blocks).
Any six variables from the Freelance system may be specified for configuring a free trend dis-
play. An additional variable with the data type DATE&TIME can also be configured for each pro-
cess variable. The value of this variable is used as a time stamp for the process value.
If no separate time-stamp variable is specified, then for variables from a Freelance process
station the associated system variable <resource_name>Date.Time is used; in the case of
variables read from an OPC server into the Freelance system, on the other hand, the OPC-
server time stamp that was supplied with them is used.
In order to use a free trend display a gateway station of type 'TRN gateway' must be configured
in the project tree. (see Engineering Manual, System Configuration, Project Tree).
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