Appendix Iii - Dnp Protocol; Introduction - Ametek TR-2100 Operation Manual

TR-2100 User Manual 79
Appendix III – DNP Protocol

Introduction

Distributed Network Protocol (DNP Version 3.0) is an industry standard specification for
SCADA communications between Master Stations, Host computers, Remote Terminal
Units, and Intelligent Electronics Devices (such as the TR-2100 Transient Recorder). It is a
public domain, non-proprietary protocol based on the IEC-870 standards, and is intended
primarily for use in SCADA-like systems.
DNP as a protocol provides efficient, robust data communications through a system of data
link CRCs (Cyclical Redundancy Checks) and confirmation messages. However, DNP is
much more than an error-detection-and-correction scheme. A DNP-compliant device, from
the protocol's point of view, is considered a group of data "objects", each of which contains
one or more "points". The DNP protocol specification defines the allowable object types
and what constitutes a "point" for that object type.
DNP is not intended to be a general-purpose two-way communications link. Rather, it is
highly optimized for SCADA and automation applications involving relatively small
amounts of near-real-time data that is often read by the DNP master once every several
seconds. In the case of the TR-2100, it is not used as a means of controlling or
reconfiguring the recorder.
The TR-2100 is able to communicate with Remote Terminal Units (RTUs) using the
Distributed Network Protocol (DNP). The available functions defined in V3.0 include
reading of:
1. Instantaneous RMS voltage or current levels of the Analogue Inputs
2. Analogue profile values; four points per analogue channel
3. Digital contact inputs; alarm or normal state
4. Recorder status events
The level of DNP support, data formats and data object types are contained in the Device
Profile Document. The interface uses the serial port at the rear of the recorder. This
assumes that an internal modem is installed in the recorder. Baud rates of 300 to 19,200 are
supported.
Note that the DNP refresh rate of the TR-2100 is 5 seconds. This means that the status of a
DNP point may not change for up to 5 seconds after its real-time occurrence. The DNP
Master should be instructed to read DNP data from the TR-2100 at a proportionate rate.