Remote Auomation and Montoring PLC or RTU
Transcript of Remote Auomation and Montoring PLC or RTU
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Remote Automation and Monitoring: PLC or RTU
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Key Points
PLCs and RTUs are sim i lar devices w ithsomewhat d i ffer ing funct ional ity .
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Key Points
PLCs are best su i ted for w ired app l icat ions
and high speed netwo rks whi le RTUs are
mos t ef fect ive in wireless appl ications and
operate wel l on bo th high and low speed
networks .
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Key Points
The major d i f ferences between PLCs and
RTUs are in remote commun ications and
data handl ing capabi l it ies.
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Key Points
Most RTUs provide sign i f icant data logging
capabi l i t ies so that data is retained dur ing
commun icat ions ou tages or for repo rt ing
purposes.
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Key Points
RTUs offer soph ist icated RTU toSDADA/DCS, RTU to IED and RTU to RTU
communicat ions :
Multiple SCADA protocols, proprietary andstandard.
Multiple IED protocols for instrumentation, field
controllers, meters, sensor networks, analyzers, etc.
Advanced peer to peer communications with storeand forward as well as dynamic message routing
capability.
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Communications examples
Standard po l l ing
The master station continuously requests the real-time data
values.
Except ion repo rt ing (RBE)
The RTU is polled but only reports values that have changed
since the prior poll
Push Communicat ionsThe RTU initiates messages on and event or time basis.
Peer to peer commun icationsRTUs can communicate with the master station and also with
each other (peer to peer) if there is a communications path.
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Communications examples
Store and fo rward commun icat ions
Messages can be passed on by one RTU to another for furtherprocess or forward transmission. This type of communication
can be used to extend the coverage of point to multipoint style
networks and also allows linear communications paths such as
along distribution or collection networks
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Communications
Dynam ic message rou t ing
RTUs are able to learn of changes to network routing and
dynamically change message routes. For example if primary
communications are radio via communications port 1 andmessages have been failing, the master station may use an
alternative communications path (via an intermediary RTU or
different network connection). If a new message from the
master station is received on backup PSTN communications
port 2 the RTU will change its routing information to reflect thatmaster station communications are now via port number two.
Some RTUs can also re-direct messages via alternative
message paths and ports based on message success/failure
statistics or by RTU configuration.
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Key Points
Most RTUs p rov ide ful ly integrated
commun icat ions hardware in the form o fdedicated commun icat ions modules (wi th
opt ions for communicat ions redundancy)
or integral modems.
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Integrated Communications
Integrated commun ications examp les: Kingf isher
MC30 comms module with
option field swappable optioncards
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Integrated Communications
Integrated commun ications examp les: TBox MS
PSTN
Modem
GSM
Modem
GPS
Receiver
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Integrated Communications
Integrated commun ications examples: TBox LT
Integral ModemGSM
Spread Spectrum Radio
PSTN
Full Function RS232
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Integrated Communications Comparison
Rockwell MicroLogix Semaphore TBox
OR
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Key Points
Low Power Operation
RTUs are available in low and ultralow power
configurations that operate on batteries or solarpower and extend the range of remote control
and monitoring to sites without any
infrastructure. Generally, PLCs are not low
power devices.
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Summary
Use a PLC in appl icat ions:
In plant
Remote with:
Wired Ethernet WAN Utility power or large solar
panels
Serial communications
No legacy protocols
Integral communications
equipment not required
Use an RTU in app l icat ions :
Remote with:
No infrastructure
Multiple IED interfaces Legacy protocol support
Data logging or reporting
Complex communications
Multi media communications
Antenna height issues
RBE or Push
communications
Integral packaging
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When RTUs Should Be Used In Place of PLCs
Gray Matter Users GroupDay Stephens
CSE Semaphore Inc.
August 19, 2010