Product category:
Mid-range and Large PLCs
News Release from: Mitsubishi Electric Automation Systems | Subject: Q4AR PLC
Edited by the Engineeringtalk Editorial
Team on 09 August 2002
PLCs aid novel sewage-control scheme
With a central range of mountains and hills, the Isle of Man's varied landscape created unique problems for the Isle of Man Government's Department of Transport.
With a central range of mountains and hills, the Isle of Man's varied landscape created unique problems for the Isle of Man Government's Department of Transport They had the task of constructing a new sewage treatment plant to treat foul sewage flows from the whole of the Island as well as an associated sewage transmission main infrastructure system
This article was originally published on Engineeringtalk on 6 Aug 2008 at 8.00am (UK)
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Called the IRIS project, the major items involve a new sewage treatment works at Meary Veg and a transmission main system around the whole Island to pump sewage to the new plant.
This also includes tanks that would store sewage flows during storms to prevent overload at the treatment works.
The system requires careful management and control to ensure it interacts totally, preventing unwanted spillage of excess effluent into the sea.
A major challenge for the project was how to control and communicate with all the pumping stations and storage tanks around the Island, while linking the signals back to a single point at the Island's sewage treatment plant at Meary Veg.
The sland's physical topography was a major restriction to technology usage, as the mountains and hills prevented line of sight or low power radio communications.
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Speed was also critical to the project with the DOT requiring a one second response from any device such as a valve etc.
This high speed over long distances, plus the required determinism, eliminated networks such as Ethernet due to their high protocol overheads, lack of redundancy and non-deterministic nature.
To overcome this problem, a 90km fibre optic network was installed, together with the transmission mains, as the basis of the infrastructure backbone.
Mitsubishi's Q4AR PLC systems and MelsecNet 10 network (which can use fibre optics as a connection medium) was the only solution submitted that met the Isle of Man's criteria for data throughput, reliability, networking distance and medium redundancy.
The Mitsubishi solution also offered a cost effective redundancy to all the communication and data control sections of the transmission main, as well as offering unique control and monitoring possibilities.
The DOT also realised that, with Mitsubishi Electric, they would be working with a supplier who offered continuity of supply and backwards compatibility for up to 10 years on their automation products.
To achieve the required communication distances on some of the sections whilst maximising the speed of data throughputs, multimode to single-mode fibre optic convertors were used.
These convertors were supplied by Optical Sources (a specialist manufacturer of fibre optic connections and driver technologies) as part of Mitsubishi Electric's Melsmart initiative.
Mitsubishi works with third-party suppliers to offer best in class automation solutions tailored to meet the needs of their extensive customer portfolio.
Like the sewage transmission main system, the control and communication network is broken down into sections to create an easy control and monitoring topology.
Each control section (11 over the entire Island) is marshalled by a Mitsubishi Q4AR PLC system.
The dual redundant construction of all the elements on the Q4AR (including processing and data storage) provides increased localised data and control security on the system.
Each control section's Q4AR acts as a Master gateway to all the sub fibre optic networks that are used to connect all the remote assets such as pumping stations etc.
All the stations (32 in all) on the 'totally redundant' subnetworks are Mitsubishi Q2AS PLC systems.
All the section Q4ARs communicate to each other and to a central control and monitoring station at the Meary Veg sewage treatment works.
A Mitsubishi MX2000 32bit Scada system co-ordinates and controls the overall system.
The MX2000's visual display allows the engineering team to operate the whole IRIS project in a simple graphical format, giving them access to control the entire Island's waste water automated assets (including system data, alarms etc.) and provides secure storage to all past operation data.
As this is the first time a large Island's entire water treatment system has been completely networked, it was important for the DOT to have high network visibility.
This included all diagnostics, programming and error correction for the network, with associated PLC stations being monitored and performed on-line from Meary Veg.
Mitsubishi's IEC-61131 PLC programming software enables all the PLC programmes to be created with a recognised programming standard, allowing for easy creation and continuity of programming even between different programmers. Request a free brochure from Mitsubishi Electric Automation Systems ...
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