BACnet_TrendLog
The BACnet_TrendLog object type (WinCC OA data point type) archives a property of a referenced object and, when predefined conditions are met, saves ("logs") the value of the property and a timestamp in an internal buffer for subsequent retrieval. The data may be logged periodically or upon a change of value. Each timestamped buffer entry is called a trend log "record". The referenced object may reside in the same device as the Trend Log object or in an external device.
Each Trend Log object maintains an internal fixed-size buffer. This buffer fills or grows as log records are added. If the buffer becomes full, the least recent record is overwritten when a new record is added, or collection may be set to stop.
The logging of the entries may be activated or deactivated at any time.
A protection against data loss of the recorded values provides the optional config entry userBitTrendLog, e.g. if a trend log object was deleted and thus also the stored values in the Log_Buffer property are not longer available (for further information see WinCC OA online help in the chapter "Possible Config Entries of the BACnet Driver").
Datapoint Type Name
BACnet_TrendLog
(Object/)Data point Type Structure
Faceplate
Tabs
The "Properties 1" tab shows the values of all properties of the BACnet object.
Figure: "Properties 1" tab of the TrendLog object
In the "Properties 2" tab the recorded values with timestamp from the logged buffer ("Log_Buffer" Property) are displayed in a list. These values can be exported to a CSV file in the /data project directory by clicking on the "Save to File" button.
The appropriate writing permission must be given to the /data directory. Otherwise an error message is shown in the log viewer.
By default the CSV file has the following format:
<obejct_name>_<logged_property>_<stajrt_time>_<end_time>.csv
The name can be changed in the text field at will.
With the aid of the spin buttons the number of the latest entries, which are shown in
the list, can be changed (by default 50; max. 200). The logged data is not displayed
until the 
button
was not clicked.
The buffer of a TrendLog object can be read out executing a single query on the Log_Buffer property (for single query see chapter "Definition of the peripheral address of the BACnet driver" of the WinCC OA Online Help). This is possible only for TrendLog objects which already exist in the BACnet device, but not for manually created TrendLog objects (the Log_Buffer property will not be updated).
In the "Trend" tab the logged records can be displayed in a trend.
For more information on tabs, see Tabs.
Available Symbols
In the upper area of the symbol (in the example below: "TrendLog") the name of the object ("Object_Name" property) is shown.
In the center area (in the example below: "Record A57") the name of the logged property ("Log_DeviceObjectProperty" Property) of the BACnet object is shown. If this area is displayed in a green color, then logging is active. If this area is displayed in a white color, then the logging is inactive.
The "TrendLog" label in the bottom area represents the name of the object type.
| Name | Usage | $ Parameter | Symbol |
|---|---|---|---|
| TrendLog | Object for logging the values of an object property. | DP |
|
