Bacnet server descriptors are the Niagara components responsible for exporting station objects as BACnet objects. Each descriptor resides under the Export Table, and corresponds to a particular component, file, or history in the station.
You add, edit, and manage server descriptors using the different manager views of the Export Table. Each manager view simplifies
selection and enforces object ID instance rules. Server descriptors are automatically given Niagara names (upon creation)
using an <ObjectType>_<InstanceNumber> convention, for example: analogValue_1, trendLog_0, schedule_2, and so on (Figure 73).
Generally, it is recommended that you do not change the Niagara name of the export descriptor. If you wish to change the name
by which the object is known to BACnet clients, do this in the objectName property, which is initialized with the name of
the exposed component.
There are three categories of Bacnet server descriptors:
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export descriptor (for components, reflecting the Niagara station “object space”)
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file descriptor (for files)
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log descriptor (for histories)
In addition, as needed, you can add Bacnet export folders to organize Bacnet server descriptors.
Bacnet export descriptors include 15 different types to export different Niagara components, including Boolean, Enum, and Numeric points (read-only and writable), and various Schedule types. You add them using the Bacnet Export Manager view.
Externally, to another BACnet device, the exported BACnet object appears with properties that source from two different areas of the station. For example, each exported component (point or schedule) exports as a BACnet object with properties from the component itself, plus additional properties in its export descriptor.
You do not see export (component) descriptors in the other two export manager views (Bacnet File Export Manager, Bacnet Niagara Log Export Manager). Those views show other “non-component” server descriptors.
The different types of export descriptors include:
For additional details, see About Discover in Bacnet Export Manager, Add (and Edit) in Bacnet Export Manager and Properties of Bacnet export descriptors.
A Bacnet file descriptor exports a file under the station directory as a BACnet File object. You add file descriptors using the Bacnet File Export Manager view of the Export Table.
You do not see file descriptors in the other two export manager views (Bacnet Export Manager, Bacnet Niagara Log Export Manager). Those views show other server descriptors.
There is only one type: BacnetFileDescriptor. For more details, see About Discover in Bacnet File Export Manager and Properties of Bacnet file descriptors.
A Bacnet log descriptor exports a Niagara history as a BACnet Trend Log object. There are two different types of log descriptors:
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BacnetNiagaraHistoryDescriptor — Created when you select and add a “standard” Niagara history using the Bacnet Niagara Log Export Manager view of the Export Table. Note that the resulting exported Trend Log object is compliant only with the original “broken” specification for BACnet Trend Logs, which was superseded and fixed in Addendum B to the 2001 version of the spec,
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BacnetTrendLogDescriptor — Automatically created when you add a specialized BacnetTrendLogExt extension to a point. The resulting exported Trend Log object is fully-BACnet compliant with the 2004 version of the BACnet spec.
For more details, see About Trend Log exports.
You do not see log descriptors in the other two export manager views (Bacnet Export Manager, Bacnet File Export Manager). Those views show other server descriptors.