Practical_modern_SCADA_protocols_-_dnp3,_60870-5_and_Related_Systems

378 Practical Modern SCADA Protocols: DNP3, 60870.5 and Related Systems
The panels below show an RTU from a reservoir. In this situation there are only a few
signals coming into the RTU and there is no PCL used. In other installations such as
borefield switchboards or pump stations, the RTU is mounted within a larger switchboard
and interfaces to a PLC.
Site components
The devices that can make up an RTU installation are:
• Sealed box (eg IP65)
• Main switch and circuit breakers
• Power supply
• Batteries
• PDS RTU
• Instruments or similar devices
• Radio and aerial
• Cables and ducting
• Communication device (eg PSTN modem)
The following panel shows how PDS communication ports are used in this installation.
Various ports on the PDS telemetry processors are provided for RTU communications.
The PDS serial ports, DIAG and Ports 0 and 1 (plus 2 & 3 on the PDS104), may be used
for any of the following purposes. Configuration settings need to be appropriate for these
modes to be used and not all combinations of these functions are possible as each port can
only perform one operation at a time.
• Connection to a PSTN data modem or data radio
The PDS RTU Radio port handles low speed data communications on
standard voice radio channels, but data radio and PSTN data modems require
a serial connection
• Connection to a MODBUS device or other brand of PLC
PLCs and other similar devices must be connected through a serial port
eg RS-232, RS-422 or RS-485 communications to PLC devices (eg using
MODBUS protocol)
• Other connections
There are a number of varied applications that also use serial ports:
eg Point-to-point communication between RTUs