SCADA Component:
Remote Station
Field instrumentation connected to the plant or equipment
being monitored and controlled are interfaced to the Remote Station to allow process
manipulation at a remote site. It is also used to gather data from the equipment and
transfer them to the central SCADA system. The Remote Station may either be an RTU (Remote
Terminal Unit) or a PLC (Programmable Logic Controller). It may also be a single board or
modular unit.
RTU versus PLC
The RTU (Remote Terminal Unit) is a ruggedized computer
with very good radio interfacing. It is used in situations where communications are more
difficult. One disadvantage of the RTU is its poor programmability. However, modern RTUs
are now offering good programmability comparable to PLCs.
The PLC (Programmable Logic Controller) is a small industrial computer usually found in
factories. Its main use is to replace the relay logic of a plant or process. Today, the
PLC is being used in SCADA systems to due its very good programmability. Earlier PCL's
have no serial communication ports for interfacing to radio for transferring of data.
Nowadays, PLC's have extensive communication features and a wide support for popular radio
units being used for SCADA system. In the near future we are seeing the merging of the
RTU's and the PCL's.
Micrologic is offering an inexpensive RTU for SCADA system wherein the PLC may be an
overkill solution. It is a microcontroller-based RTU and can be interfaced to radio modems
for transmitting of data to the CMS.
Single Board versus Modular Unit
The Remote Station is usually available in two types,
namely, the single board and the modular unit. The single board provides a fixed number of
input/output (I/O) interfaces. It is cheaper, but does not offer easy expandability to a
more sophisticated system.The modular type is an expandable remote station and more
expensive than the single board unit. Usually a backplane is used to connect the modules.
Any I/O or communication modules needed for future expansion may be easily plugged in on
the backplane.
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