Large wastewater treatment operations, comprising widely spread plants, generate vast quantities of data, which have to be processed using sophisticated control and automation techniques. The Waste Water Treatment Plant Association of the City of Hamburg is one of the most complex in Germany, with 32 separate operational installations. Each year it treats an average of 150 million cubic metres of wastewater. The entire operation is controlled via KH-Automation Projects' PMSXpro central control system. Automation technology is by Mitsubishi Electric with Melsoft software supplying continuous programming from master level to PLC.
Wastewater plants have strict regulations to guarantee quality control and precise documentation. For this reason it is essential to ensure that the following requirements are fulfilled:
* Centralised control of all operations.
* Vertical and horizontal data-throughput and continuous connection throughout the hierarchies.
* Strict data consistency throughout all software tools.
* Standardised software tools according to IEC 1131 3 norm.
The management system
PMSXpro includes all components required for measurement, display, alarm-function, protocol functions and archiving of process data for surveillance, control and operation of the plant.
Mitsubishi Melsec QnAS Series controllers are used for the automation functions of the water treatment plant. The Melsoft software is suitable for engineering applications down the line and is integrated into the entire system.
Programming and project planning of the controllers is centrally handled by Mitsubishi's GX IEC Developer. This software has a future oriented program structure and offers a tracking function and integrated analysis of the networks, enabling plant staff to locate malfunctions, minimise downtime and reduce the total cost of ownership.
The GX IEC Developer offers a number of features including:
* Choice of programming language by the programmer.
* Function units encapsulated in function blocks to provide secure and re-usable codes.
* Fast, intuitive configuration of controller components.
* Special test and debugging tools for control of the network.
The top/down architecture and structured programming provide realtime information to the operating staff.
Management of data
Since the wastewater treatment process has to be modified continuously to satisfy legal and ecological requirements, it is essential that all modifications can be initiated and managed from a central point.
Data consistency at the Hamburg plant is guaranteed by the software tool, MXChange, which organises the entire data management of the plant. The system was developed by Mitsubishi Electric and, in collaboration with KH-Automation Projects, modified for PMSXpro so that a full data consistency could be realised throughout all levels and software packages.
The platform consists of the MXChange server, a database where all connected programmes and software tools have access. Once a variable or object such as a drive is defined by the master system the data is made available throughout the whole plant and can be accessed from any location in the plant. The parameters for the designated drive are set in the master system and relevant data is automatically adapted in the QnAS Controller. No manual adjustment is necessary.
MXChange offers horizontal and vertical continuity. Controllers of the Mitsubishi Melsec Series allow engineering modifications and extensions on all automation levels - from the central engineering station and master PLC to the lowest slave PLC.
Based on the number of different I/Os and the program memory in the single Mitsubishi PLCs, the operators of the WWTP can adapt the system to the requirements of the cabinets. A single engineering tool is required for all controller types.
Network technologies
The master system is connected to the automation stations via 100 Mbit/s Ethernet with TCP/IP Protocol. The redundant network Melsecnet takes over connection of the master controllers to the subordinated slave controllers. It offers high security with easy installation and programming. With the MXChange concept, transparent access from Ethernet to Melsecnet can be realised. In the start up phase of the Hamburg WWTP, more than 70 Mitsubishi Electric controllers were used. This number will increase with further development of the project.
Plant expansion
To accommodate future expansion of the water treatment plant, each local process station is assigned a technological unit (process island). This station functions both as server and client, and with the subordinated Melsec controller, forms an integrated, homogeneous automation system. It collects and processes engineering data, is responsible for data pre-processing, alarming and archiving of process variables. The plant has unlimited operational functionality and the current decentralised system-topology will not require any extension or exchange of existing hardware components.
The software architecture and PMSXpro control system described above are particularly well suited for widely spread plant operations with high data volumes, for example, breweries; petrochemical, water treatment and power plants; and the building automation and automotive industries. To date, over 4,1 million Mitsubishi Melsec PLC systems have been installed worldwide.
For further information, contact Karen Heitmuller, Circuit Breaker Industries, 011 928 2000, [email protected]
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