L-VIS User Manual
110
LOYTEC
Version 6.2
LOYTEC electronics GmbH
9.5.6.1 Internal Trends
Whenever a normal data point is connected to the trend control, the control itself will
record the data received from the data point and store it in the file system when the option
Preserve Data
is set. In this mode, there are a number of settings regarding data recording
and storage which are not applicable to external trends, explained in the next section. It is
possible to mix internal and external trending in one control.
When recording data locally, the control is able to generate three data recordings and
display three curves per connected data point: the minimum value, maximum value, and
average value. To do this, the control scans all incoming value updates between two shift
operations. From this data, it calculates the minimum value, the maximum value, and a time
weighted average value and adds this data to the appropriate data recording.
NOTE:
The average value calculated during each shift interval is the time weighted average of all
input values received during that time frame. For example, if the input has a value of 0 for
the duration of 9 seconds and a value of 20 for the duration of 1 second, the time weighted
average value for these 10 seconds will be 2, because (0*9s + 20*1s) / 10s = 2. In contrast,
the time independent arithmetic average value would be 10 (0+20)/2.
9.5.6.2 External Trends
Since version 4.3.0 of the device firmware, it is possible to use the trend control to display
trend data recorded by an external device or trend data source. In this case, the trend control
itself does not record any data on its own. Instead, it fetches records from a trend service
and displays this data. This is the recommended way to use trend controls. In many
applications, trending will and should be done on an external controller device anyways.
LVIS or LWEB should act as a client only, fetching the recorded data from the controller to
display it in the trend control.
Trend services like these are represented by a special type of data point called trend point.
Such a data point may represent a local trend (recorded on the same device, but not by the
trend control itself), or data located on a different device on the network.
When such a trend data point is attached to a trend control, the control will scan the trend
and display the first curve mentioned in the directory of the trend service. Note that most
trend data points represent the recording of only one curve. In case of a trend data point
which is known to contain more than one data recording, the trend will show the trended
data points as child points. Selecting and attaching one or more of the child points to the
trend control will show the corresponding curves. This is currently available for local trends
and for remote trends accessed via OPC from a LINX device whose configuration was
imported.
9.5.6.3 Trend Control Options
Regarding color, the trend control is one of the more complex controls to configure, since it
supports a large number of colors. The following colors may be set for trend controls on the
Color
property page: