170 • SMP Gateway User Manual
Window Description
in the expression. Double-click on an item to insert it at the cursor location in
the expression window. The various operators are described in the sections
below.
Expression
(empty window at
the bottom of the
application
window)
Used to enter and edit the expression to be evaluated. You can type the
expression directly or use the memory-jogging windows described above.
The result of the evaluation of the expression is assigned as the value of the
calculated data point.
A calculated data point has the following properties:
Properties Description
Produced point Resulting data point.
Name Name of the calculated data point for which the expression is currently being
edited. This field cannot be edited. To edit an expression for another calculated
data point, close the editor and select another data point in one of the analog or
binary point pages in the Site view.
Description Optional space for you to type a description of the new point.
Timestamp Defines how the calculated data point is to be time-stamped. Specify "Server" if
you want the system time to be used as the timestamp, and specify "Triggered
point" if you want the timestamp to be the time of the point that triggered the
calculation.
By default, the calculated data point is time-stamped by the SMP Gateway.
Quality Specifies whether the quality of the calculated data point will always be good,
or will depends the quality of its source point(s)
If you select Use source quality, as soon as the quality of one of the source
points is bad, the calculated data point’s quality will also be bad.
Time-based Specifies whether the expression is to be evaluated on a periodic basis. The time
interval is then specified via the Time interval attribute. Normally, expressions
are not
evaluated on a periodic basis.
Time interval (ms) Specifies that the expression is to be evaluated every X milliseconds. This time
interval applies only if the Time-based attribute specifies "Yes". The minimum
value is 50 ms. If this condition is
By exception Specifies whether the expression is to be evaluated whenever there is a
transition on one of the data points or signals in the expression.
Specific trigger Specifies whether the evaluation of the expression is to be triggered by a single
data point ("Yes") or by any data point ("No") in the expression. This attribute
is ignored if By exception is set to "No".
Triggered by Used to specify the name of the data point or signal that will trigger the
evaluation of the expression. This attribute is ignored if Specific trigger is set
to "No".
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