I. Introduction
In today's era of rapid economic development and ever-increasing national strength in China, the inclusion of the World Water Resources Organization (WRO) signifies that all sectors of Chinese society must rapidly align with international standards. Urban water supply is crucial to the vital interests of the people, economic development, and social stability. This article takes the Haicang Water Supply Project in Xiamen City as an example, combining the technological process to introduce the application of a PLC system in the automated control of the water plant. The plant covers an area of 400,000 square meters and has a water purification capacity of 60,000 tons, including the plant area, water source pumping station, and water distribution network. The entire water plant operates under fully automated control.
II. System Composition
The entire water plant automation system is divided into four workstations: a water source station, a chemical dosing station, a filter station (including four remote I/O points), and a water delivery pumping station. A central control room is located within the system. The entire water plant is centrally controlled and managed.
The main characteristics of tap water production processes are as follows:
(1) Each production process section is relatively independent, with many individual pieces of equipment.
(2) The amount of data collected is large. The entire system has more than 3,000 digital inputs and outputs and more than 1,000 analog inputs and outputs. There are many types of process parameters, including pressure, flow rate, temperature, differential pressure, liquid level, current, voltage, power, etc., but there are few production parameters related to upstream and downstream.
(3) Tap water production is continuous, irreplaceable and uninterrupted.
(4) The process sections are far apart, the equipment is scattered, and the networking is relatively complex.
Based on the above characteristics, and considering factors such as system reliability, stability, high speed, scalability, and user-friendly human-machine interface, we selected the enhanced PLC-5/30. The PLC-5/30 processor supports ladder logic, SFC (Sequential Flow Control), and structured text programming methods; it is compatible with the I/O of the 1771, 1746, 1791, and 1794 series, and with products on general-purpose remote I/O links that have built-in remote I/O adapters; it can extend local I/O communication through a parallel I/O link for high-speed processing applications; it can be remotely programmed and transmit signals using DH+ (Enhanced Data Highway) networks; and it has configurable RS-232-C/422-A/423-A ports for programming.
DH+ networks are among the most widely used industrial LANs in the world. They were the first control networks to provide remote programming, configuration, and troubleshooting for programmable logic controllers (PLCs). The successful application of various products supported by this network has proven its versatility. On a DH+ network, you can connect up to 99 DH+ links, each capable of transmitting data at a rate of 57.6 Kbit/s over twisted-pair cable, with transmission distances up to 10,000 feet. All parameters required by the production process in the system are acquired and controlled by the PLC ; the host computer serves only as the human-machine interface and performs subsequent processing of production data, greatly improving system reliability. This control scheme uses PLC-5/30 throughout, providing distributed control of the main production equipment while tightly connecting them via a network for centralized management, reducing the risk of failure and improving reliability.
The host computer monitoring software uses RSView32 software, which provides data acquisition, monitoring, and information management functions in the Microsoft Windows environment. It is designed for industrial applications with speed and reliability requirements. This software uses an open platform that provides you with Open Database Connectivity (ODBC) performance as well as OLE and DDE performance.
It includes a fully functional object-oriented graphical editor, as well as alarms, trend indicators, event detection, data logging, security measures, communications, and an open database with 150, 300, 500, or 32,000 tags. RSView32 software can be used in conjunction with device drivers and DDE drivers.
The lower-level machine uses RSLogix5 programming software, a 32-bit window-based ladder logic programming software package that runs on Microsoft's Windows 95, 98, and Windows NT environments. Combined with modern technology, it helps users improve performance, save time, and increase productivity.
The communication software between the host computer and the slave computer uses AB's RSLinx software, a true 32-bit product family that provides communication capabilities between workshop-level equipment and various application software. Besides supporting ockwe11 programming software, MMI software, combined software products, and DDE protocol communication software, it also supports many popular industrial application software developed through OEMs and VARS.
III. System Functions
The entire water plant can operate unattended thanks to its automated control system. The functions of the central control room can be summarized as follows:
Displays process flow diagrams, dynamic display of real-time data for the entire plant, and the working status of individual equipment and system status; automatic control of all equipment in the plant.
Provides both manual and automatic operation interfaces;
Enables visual and audio alarms;
Enables operation and system status recording, historical query, real-time curves, historical curves, and report printing;
Operator management.
IV. Conclusion
This project utilizes a distributed control system composed of an industrial computer and a PLC -5/30. It leverages the PLC's advantages of strong anti-interference capabilities, convenient networking, and suitability for industrial sites. The host computer enables control of all production equipment in the plant, as well as the setting, adjustment, and monitoring of process parameters, meeting the automatic control requirements of a large-scale waterworks. The entire solution is safe, reliable, economical, practical, easy to program, operate, and maintain, and has been successfully applied in the Haicang Water Supply Project Waterworks in Xiamen.
