remote automation and monitoring: plc or rtu. key points plcs and rtus are similar devices with...
Post on 26-Mar-2015
227 Views
Preview:
TRANSCRIPT
Remote Automation and Monitoring: PLC or RTU
Key Points
PLCs and RTUs are similar devices with somewhat differing functionality.
Key Points
PLCs are best suited for wired applications and high speed networks while RTUs are
most effective in wireless applications and operate well on both high and low speed
networks.
Key Points
The major differences between PLCs and RTUs are in remote communications and
data handling capabilities.
Key Points
Most RTUs provide significant data logging capabilities so that data is retained during communications outages or for reporting
purposes.
Key Points
RTUs offer sophisticated RTU to SDADA/DCS, RTU to IED and RTU to RTU communications:
ı Multiple SCADA protocols, proprietary and standard.ı Multiple IED protocols for instrumentation, field
controllers, meters, sensor networks, analyzers, etc.
ı Advanced peer to peer communications with store and forward as well as dynamic message routing capability.
Communications examples
Standard polling The master station continuously requests the real-time data values.
Exception reporting (RBE) The RTU is polled but only reports values that have changed since
the prior poll
Push Communications The RTU initiates messages on and event or time basis.
Peer to peer communicationsRTUs can communicate with the master station and also with each other (peer to peer) if there is a communications path.·
Communications examples
Store and forward communications
Messages can be passed on by one RTU to another for further process 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
Communications
Dynamic message routing
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 and messages 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 that master 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.
Key Points
Most RTUs provide fully integrated communications hardware in the form of dedicated communications modules (with options for communications redundancy)
or integral modems.
Integrated Communications
Integrated communications examples: Kingfisher
MC30 comms module with option field swappable option
cards
Integrated Communications
Integrated communications examples: TBox MS
PSTN Modem
GSM Modem
GPS Receiver
Integrated Communications
Integrated communications examples: TBox LT
Integral Modem
GSM
Spread Spectrum RadioPSTN
Full Function RS232
Integrated Communications Comparison
Rockwell MicroLogix Semaphore TBox
OR
Key Points
Low Power Operation
RTUs are available in low and ultralow power configurations that operate on batteries or solar power and extend the range of remote control and monitoring to sites without any infrastructure. Generally, PLCs are not low power devices.
Summary
Use a PLC in applications: In plant Remote with:
ı Wired Ethernet WAN ı Utility power or large solar
panelsı Serial communicationsı No legacy protocolsı Integral communications
equipment not required
Use an RTU in applications: Remote with:
ı No infrastructureı Multiple IED interfacesı Legacy protocol supportı Data logging or reportingı Complex communicationsı Multi media communicationsı Antenna height issuesı RBE or Push
communicationsı Integral packaging
When RTUs Should Be Used In Place of PLCsGray Matter Users Group
Day StephensCSE Semaphore Inc.
August 19, 2010
top related