DCS, PLC, and RTU.pdf
- 1. DCS, PLC, and RTU Common features and diffrences 1
- 2. Overview DCS,PLCs and RTUs shares same basic features with somewhat differing functionality. In this discussion ,we shall focus on hardware point of view, indicating common features and differences 2
- 3. Definitions Distributed Control Systems “A design approach in which factory or machine control is divided into several sub-systems, each managed independently by a unique programmable controller or other control system, yet all interconnected to form a single entity. Individual subsystems may be interconnected via communications networks.” o Patrick-Turner Industrial Automation Dictionary, 1996 3
- 4. Definitions (cont.) Programmable Controller “A solid state industrial control device, member of the computer family, designed specifically to be programmed to perform relay logic functions, timing, counting, arithmetic, and data manipulation, all for the purpose of implementing control over industrial machines and processes. The programmable controller consists of a central processor, memory system, input/output system, and power supply, all of which are designed to operate in harsh industrial environments.” o Patrick-Turner Industrial Automation Dictionary, 1996 4
- 5. Definitions (cont.) Remote terminal unit “A remote terminal unit (RTU) is a microprocessor-controlled electronic device that interfaces objects in the physical world to a distributed control system or SCADA (supervisory control and data acquisition) system by transmitting telemetry data to a master system, and by using messages from the master supervisory system to control connected objects.” o Wikipidea 5
- 6. Definitions (cont.) SCADA “Supervisory Control – “A control scheme whereby a computer or controller monitors and intermittently downloads programs, sets sub-goals, or adjusts control parameters of a lower level automatic controller.” Data Acquisition – “The process of collecting data from the system through some manual or automatic means for the purpose of producing printed reports for operating, supervisory, maintenance, or accounting disciplines.” o Patrick-Turner Industrial Automation Dictionary, 1996 6
- 7. Basic Hardware Platforms 7 Control Unit Output Circuits Work Memory Input Circuits Program Memory Power Supply Communication ports
- 8. Basic Hardware Platforms 8 Micro Compact Modular Control Unit Output Circuits Work Memory Input Circuits Program Memory Power Supply Comm. ports
- 9. Redundancy 1/12/2022 Southern Cairo Electricity Distribution Company, Cairo, Egypt 9 Simplex: Conventional PLCs ,RTUs, simple DCS Doublex CPU Hot standby : Siemens S7:400H, Schneider : Quantum 140 CPU 6xx,Allen Bradley : Redundancy module IOs :Allen Bradley: 1715 redundant Ios Triplex :Triconics, Hima Triconics
- 10. Redundancy 10 Hot standby structure example
- 11. Redundancy 11 Redundant IOs example
- 12. Environment resistance 12 Normal hardware : working temperature 0-55 degree Harsh environment : Part number ends with H or C for Schneider, Siplus series for Siemens. Working temperature : -40°C to +70°C. Coating provides protection against most, aggressive gas like H2S, conductive dust. IP65 : suitable for some DCS and PLC distributed IOs and RTUs installed in harsh environment.
- 13. PLC vs RTU 13 The major differences between PLCs and RTUs are in : remote communications and data handling capabilities. Low Power Operation Most RTUs provides a variety of wired and wireless communication support. Most RTUs provide significant data logging capabilities so that data is retained during communications outages or for reporting purposes. Most RTUs consumes low power compared to PLCs
- 14. PLC vs RTU (cont.) 14 RTUs offer sophisticated RTU to SDADA/DCS,RTU to IED and RTU to RTU communications: Multiple SCADA protocols, proprietary and standard. Multiple IED protocols for instrumentation, field controllers, meters, sensor networks, analyzers, etc. Advanced peer to peer communications with store and forward as well as dynamic message routing capability.
- 15. PLC vs RTU (cont.) 15 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 communications RTUs can communicate with the master station and also with each other (peer to peer) if there is a communications path
- 16. PLC vs RTU (cont.) 16 Store and forward communication Dynamic message routing
- 17. DCS vs PLC 17 Direct implementation of simple PID,Cascade , Ratio,Feedforward,etc. Possible implementation of advanced loop control : Multivariable loops,adaptive control,model predictive control,artificial intelligence based control (ex:fuzzy and neural based control) Handling of large number of loops
- 18. DCS vs PLC 18 Fixed Loop sampling time Easy changing of loop configuration by plant trained person Common database between Programming and HMI