Remote Auomation and Montoring PLC or RTU

7/30/2019 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 commun ications examp les: TBox MS

PSTN

Modem

GSM

Modem

GPS

Receiver


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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

Remote Auomation and Montoring PLC or RTU

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