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Raven CDMA User Guide for Verizon, version 2.23 33
Modbus/BSAP Configuration
Telemetry
Telemetry is an automated communications process by which data is collected from
instruments located at remote or inaccessible points and transmitted to receiving
equipment for measurement, monitoring, display, and recording. Transmission of
the information may be over physical pairs of wires, telecommunication circuits,
radios or satellite.
Remote Terminal Unit (RTU)
Modbus was originally designed to be used in a radio environment where packets
are broadcast from a central station (also called master or host) to a group of remote
units. Each remote unit, Remote Terminal Unit (RTU) , has a hexidecimal identifi
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cation number (ID). The first part of the broadcast packet contains an RTU ID
which corosponds to the ID of one of the remote units. The Modbus host looks for
the ID and sends to only the unit with the matching ID. The RTU would then reply
back to the central station.
The RTU connects to physical equipment such as switches, pumps, and other
devices and monitors and controls these devices. The RTU can be part of a net
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work set up for Supervisory Control and Data Acquisition.
Supervisory Control and Data Acquisition (SCADA)
Supervisory Control and Data Acquisition (SCADA) describes solutions across a
large variety of industries and is used in industrial and engineering applications to
monitor and control distributed systems from a master location. SCADA encom
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passes multiple RTUs, a central control room with a host computer (or network),
and some sort of communication infrastructure.
SCADA allows for “supervisory” control of remote devices as well as acquiring
data from the remote locations. Programmable Logic Controllers allow for a higher
degree of automated SCADA.
Programmable Logic Controller (PLC)
A Programmable Logic Controller (PLC) is a small industrial computer which gen-
erally monitors several connected sensor inputs and controls attached devices
(motor starters, solenoids, pilot lights/displays, speed drives, valves, etc.) according
to a user-created program stored in its memory. Containing inputs and outputs sim
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ilar to an RTU, PLCs are frequently used for typical relay control, sophisticated