Flowing from west to east, across the heart of China is the Yangzi River. It is the longest river in China and the third longest river in the world.
Originating in Tibet, it flows past the construction site for the world's largest dam, the Yangtzi River Three Gorges Dam, into the Pacific Ocean at the city of Shanghai. Raw water is collected from the Yangzi, filtered and purified and then sold to Tap Water Factories such as the Taihe Water Factory in Shanghai.
In 1995, Shanghai Taihe Tap Water Manufacture Ltd. began construction of the Taihe Water Factory. Phase I of the project established a SCADA system for the factory consisting of an ABB Modcell Multiloop Controller/Processor communicating with Modbus and ABB proprietary network, ICN.
Clean water could then be pumped through a series of pipes to supply the daily tap water needs for over 43,000 Shanghai residents.
"When the factory was established," said Alex Xu, Manager for Shanghai Yuandong Science & Technology Ltd., (SYST) the System Integrators. "It used a SCADA system only to supervise the working processes without any control functionality."
In any water system, as complex as this one, the water flow can vary dramatically from hour-to-hour and day-to-day, depending on domestic demand cycles and the more unpredictable aspects such as rainfall and storms. This makes it essential that the Master Control System be equipped, not only with monitoring capabilities, but control as well.
"The second phase of the project planned to add control ability to the plant," said Xu. "But they found it impossible since the substations were communicating as slaves, thus couldn't exchange data and information between each other. The main problem was that data exchanged between the slaves needed to be accomplished through the master node. As long as a personal computer carried out the master task, we could not count on its performance, steadiness and security. Use of a PLC instead of the PC was preferred."
In order to add the control needed Xu added an Allen-Bradley PLC5/20E with Ethernet capabilities. However, since the original SCADA system was ABB communicating with Modbus, an interface was needed to allow the Modbus end devices to communicate with the A-B processor. The solution Xu found was the Modbus Communication Module made by ProSoft Technology, Inc.
Designed to fit in an Allen-Bradley 1771 PLC rack, the module contains two active serial ports, each supporting RS-232, RS-422 and RS-485, supports full radio, modem and multi-drop and is configured using simple ladder logic. Since the module communicates over the backplane, needing only standard ladder programming, it provided highly configurable Modbus Master and Slave capability to the existing A-B PLC.
"It was the first time Shanghai Yuandong Science and Technology had used our 3100-MCM module," said Lenus Hong, Regional Sales Manager for ProSoft Technology. "But it certainly wasn't the last. They also installed the module in the control system for the compressors in the Shanghai General Motors Plant. Since the MCM module fits directly into Allen-Bradley's PLC5 racks, in both instances, it provided a seamless integration of technologies."
"The 3100-MCM module played an important role in the second phase of this project," said Xu. "Without the ProSoft module, this phase could not have been realized."
When asked what the deciding factors were in choosing the ProSoft module for this project, Chen Zong-Liang, General Manager for SYST said, "Ease of operation, higher profits and ease of implementation...all of the above."
The second phase was completed in May of 1999.
A Unique Partnership
This unique partnership of integrated technologies between Rockwell Automation and ProSoft Technology has enabled SCADA systems around the world to gather data and control operations in a multitude of plants just like the Shanghai Wastewater Plant and the Taihe Water Factory.
"The 3100-MCM Modbus module was also used at the Xin Ning Wastewater Plant in Suzhou, China," said Hong. "According to Rockwell Automation-Shanghai, the customer needed to collect data from Diris Power Meters which have embedded Modbus communications. They elected to use the 3100-MCM module which allowed them to collect 30 parameters from the power meters instead of 3 parameters they would have gotten using Analog I/O. The bottom line is, our interface module made more data available for better control and monitoring."
"We take great pride in our ability to help Rockwell Automation interface with alternate networks," said Doug Sharratt, CEO for ProSoft Technology, Inc. "We have been able to provide a number of solutions for the water/wastewater industry in China. We are currently presenting SCADA solutions in conjunction with Rockwell on two other large water projects. One is a wastewater treatment plant involving ten pumping stations using our MVI56-101S module interfacing Allen-Bradley's ControlLogix to the IEC870-5-101 protocol. The second is a water transportation project on China's Yellow River, using one of our ProLinx Communication Gateways to interface Allen-Bradley's PLC5 processors to DNPNET."
The seamless integration of Rockwell Automation and ProSoft Technology is helping China realize its goal of enough clean, fresh water for all of its citizens.
"China has its problems," said Xu. "But it has faced these problems and is attempting to tackle them. Sometimes the progress may be a little slow and seem small, but it is steady and good willing. As the international community continues to give real help and useful advice, things will go better, smoother and expeditious."