Trend diagrams

At a Glance

A trend diagram allows the graphic representation of a variable status, with the representative curve moving from right to left.

You are advised to limit the number of trend diagrams on a same page because their display decreases the system’s performance.

Only rectangular type objects can be used as trend diagrams.

Trend diagram parameter screen

Description

The table below describes the settings that you may define.

Attribute	Description
Sampling	Period in which a new value is added at the end of the diagram and the diagram is refreshed. Default value: 1 second. When the sampling period is given in seconds, values between 1 and 3600 are allowed. When it is given in milliseconds, the allowed range is 1 to 9999. Sampling periods below 100 ms produce a lot of windows messages and generate a high CPU load. Therefore only few diagrams with such small periods should be animated at the same time and long lasting actions like Build Changes should be avoided while diagrams are animated (see also the NOTE at the end of the table).
Definition	Length of value display. Each new value is represented by a right segment whose length is fixed by the definition. The definition is expressed in pixels between 1 and 20. The value by default is 2.
Line color	Color of the timing diagram’s right segments The colors palette contains 16 predefined colors and provides access to the extended colors parameter screen.
Threshold: minimum and maximum	Thresholds between which the value representation develops. For binary values, the thresholds must be 0 and 1.
Display period	This value is calculated. It depends on the size of the rectangle, the sampling value and the definition. The procedure is as follows: Period = Rectangle size / Definition x Sampling.

NOTE: Internally, for every diagram, a timer is started with the sampling period defined by the user. When the timer fires, the last value of the corresponding variable transmitted from the PLC is read and added at the end of the diagram. Such timers may not always fire exactly in equidistant periods (e.g. they may be delayed when a lot of tasks run in parallel on the PC). Therefore the displayed values may not represent the exact values in the PLC at the end of each sampling period.