DNP3 Tutorial Part 3: Understanding the DNP3 Object Library

The DNP3 framework includes a library of objects that are typically used in SCADA systems. This library is available for downloading to members of the DNP Users Group; visit dnp.org for more information. These objects include such things as Binary Inputs that are used to report equipment characteristics that have two states; power is on or off, an access panel is open or closed. Another common object is an Analog Input that is used to report characteristics that have a range of values; exhaust fan speed can be anywhere from 40 to 400 RPM, 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, frequently quite different one from another, must then be 'compiled' into the Masters and usually 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.