Eaton Power Xpert PXM 4K Series User Manual
Also see for Power Xpert PXM 4000: User and installation manualQuick start guideUser and installation manual
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22. DNP3 Protocol PrimerPXM 4/6/8K DNP3 Ethernet Communications User Manual MN150005EN January 2017 www.eaton.com2.1.1 Master and Outstation DatabasesFigure 1 shows the master-outstation relationship and givesa simplistic view of the databases and software processesinvolved. The master is on the left side of Figure 1, and theoutstation is on the right side.A series of square blocks at the top of the outstation depictdata stored in its database and output devices. The variousdata types are conceptually organized as arrays. An array ofbinary input values represents states of physical or logicalBoolean devices. Values in the analog input array representinput quantities that the outstation measured or computed.An array of counters represents count values, such as kilo-watt hours, that are ever increasing (until they reach a maxi-mum and then roll over to zero and start counting again).Control outputs are organized into an array representingphysical or logical on-off, raise-lower, and trip-close points.Lastly, the array of analog outputs represents physical orlogical analog quantities such as those used for set points.Figure 1. Master and Outstation Relationship.The elements of the arrays are labeled 0 through N - 1where N is the number of blocks shown for the respectivedata type. In DNP3 terminology, the element numbers arecalled the point indexes. Indexes are zero-based in DNP3,that is, the lowest element is always identified as zero.Indexes are zero-based in DNP3, that is, the lowest elementis always identified as zero.Notice that the DNP3 master also has a similar databasefor the input data types (binary, analog and counter.) Themaster uses values in its database for the specific purposesof displaying system states, closed-loop control, alarm noti-fication, billing, and much, much more. An objective of themaster is to keep its database updated. It accomplishesthis by sending requests to the outstation asking it to returnthe values in the outstation’s database. This is termedpolling. The outstation responds to the master’s requestby transmitting the contents of its database. Arrows aredrawn at the bottom of Figure 1 showing the direction ofthe requests (toward the outstation) and the direction of theresponses (toward the master). Later, we will discuss sys-tems whereby the outstations transmit responses withoutbeing asked. |
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