DNP3 Tutorial Part 3: Understanding the DNP3 Object Library.

Previous Page: Part 2: How elements communicate.
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The DNP3 framework includes a library of objects that are used in SCADA systems. This library is available for downloading to members of the DNP Users Group. Visit www.dnp.org for more information. These objects include such things as Binary Inputs that are used to report gear assets that have two states. Power is on or off, or an access panel is open or closed are two such cases. Another common object is an Analog Input that is used to report characteristics that have a range of values. For example, exhaust fan speed can be anywhere from 40 to 400 RPM or main power can vary from 110 to 128 VAC.

This library makes it easy for the manufacturer to design the DNP3 Remote responder to use these common objects to report to upstream Masters. It also makes it easier for Masters to integrate the data collected from Remotes and present it for decision making.

Without this framework of common objects, manufacturers must develop their own model for reporting status and providing control capability. These models must then be 'compiled' into the Masters. Then converted into some kind of common objects for efficient management. Another tool often found in these more 'open' frameworks is a proprietary interface or translation module to access and control the Remote.

Objects in the DNP3 library are divided into Groups and Variations. For example, the Analog Input group has six variations to provide 16 or 32 bit integer or floating point values with or without a status bitmap. The Analog Event group has eight variations to provide 16 or 32 bit integer or floating point values with a status bitmap and with or without a timestamp. Note that the Analog Event group does not include variations without a status bitmap.

Next Page: Part 4: DNP3 Message Structure
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