Application Of Omron Plc In Water Treatment Control System

The main control unit adopts C200HE PLC, which is a small and medium-sized PLC product of OMRON Company, and is convenient to realize the production site with excellent expansibility; it can further enhance the basic functions of PC, reliable and convenient data processing, and improve the work efficiency of the production site; CX-Programmer is a programming software developed by OMRON and applied to C200H PLC, which runs in Windows 20. In the operating system, it has friendly user functions in all aspects of automation engineering water treatment. It is committed to production site intelligence to enrich the software adapted to Windows. It has a wide range of units, and achieves the best control of water treatment for a variety of machinery and equipment.
1 Process Introduction
In this case, according to the water quality condition of raw water and the water quality requirement of boiler steam-water system for recharge water, the process of boiler recharge water treatment system is as follows:raw water→Raw water tank→Raw water pump→heat exchanger→Multimedia filter→Activated carbon filter→Reverse osmosis desalination system→middle water tank→Intermediate pump→Mixed ion exchange bed→Desalination tank→demineralized water pump→Main workshop. In addition, it includes filter backwashing system, mixed ion exchange bed regeneration system, dosing system and so on.
Raw water tank is used to store raw water into the system. Its purpose is to adjust the change of the inflow flow, prevent the fluctuation of the inflow from affecting the operation of the system, and ensure the stability of the inflow and water quality of the system.
Raw water pump is to provide sufficient raw water flow and pressure for the pretreatment system.
The function of heat exchanger is to keep the inlet water in a certain temperature range, so as to ensure the stability of the output of reverse osmosis system.
The function of multi-media filter is to remove impurities such as fine particles, suspended solids, colloids, organic matter and alum formed after adding medicine, so as to ensure the SDI (pollution index) of the effluent.≤4.
The function of activated carbon filter is to remove low molecular organic matter, free chlorine, and less odor, color and smell in water.
Reverse osmosis desalination system uses the characteristics of reverse osmosis membrane to remove most of the soluble salts, colloids, organic matter and microorganisms in water.
The middle water tank makes the reverse osmosis water producing side bear lower pressure, avoids the irreversible damage caused by back pressure of reverse osmosis membrane, cushions the pressure fluctuation caused by the valve switching of the back ion exchange system, and controls the start-up and shutdown of reverse osmosis through the liquid level of the middle water tank.
The function of the intermediate pump is to provide stable pressure and water quantity for the follow-up water treatment system.
The function of mixed ion exchange bed is to further remove the remaining ions in reverse osmosis water.
The desalted water tank is used to store the water produced by the system. Its purpose is to ensure the stability of the boiler water supply.
The function of desalted water pump is to provide stable pressure and water quantity for boiler system.

Fig. 1 Boiler recharge water treatment process
2. Configuration and description of control system
2.1 General Control Requirements and Functions
　　The requirement of automatic control system for boiler feed water treatment in power plant is to automatically control and adjust the water treatment process so that the treated water quality index can reach the required range. When the upper computer of water treatment control room gives instructions, the main working parameters (water quality parameters, flow rate, liquid level, etc.), operation status and main process curves in a certain period of time are uploaded from the site to the upper computer of water treatment control room.
The functions are as follows:
　　(1) Control operation: In the water treatment control room, the controlled equipment can be controlled online and real-time.
　　(2) Display function: real-time display of the operating conditions of the field controlled equipment and the state parameters of the field with graphics.
　　(3) Data management: According to the change speed and importance of different operation parameters, a production history database is established to store the original production data for statistical analysis. By comparing and analyzing the data in real-time database and historical database, some useful empirical parameters are obtained, which is helpful for optimizing control and displaying some necessary parameters and results into real-time pictures and reports.
　　(4) Alarm function: When the measured value of an analog quantity (such as flow, conductance, water level, etc.) exceeds a given range or when a certain switch quantity (such as motor start-stop, valve switch) changes position, different levels of alarm can be issued according to different needs. In addition, it can diagnose and alarm the PLC.
(5) Printing function: It can print reports and trends, and print all kinds of events and alarms in real time.

Fig. 2 Configuration of Boiler Recharge Water Treatment Control System
2.2 Programming Structure and Realization of PLC
2.2.1 According to the technological characteristics, this project adopts the form of subroutine call in the programming of PLC, which not only makes the program readable, but also shortens the scanning period of PLC program. Taking the control program of reverse osmosis desalination system as an example, according to the process requirements, the control program of reverse osmosis desalination system includes RO Soft operation, RO Standby, RO Running and reverse osmosis desalination system flushing. Wash control (RORinse). These four working conditions are unique at the same time. We can make them into subroutines and call them by RO. Reverse osmosis program (RO) and alarm program (Alarm), pump control program (PumpControl), analog processing program (AD003Setting), address conversion program (IOConvert), level interlock program (Level Interlock) as subroutines are called by the main control program (MainProgram), which greatly shortens the PLC. The scanning time is clear, and the control idea is clear, and the program is readable. Operators only need to issue simple instructions on the upper computer, such as soft-handed requests, operation requests, flushing requests, etc. The control program can control the field equipment according to the process requirements.

Fig. 3 Human-machine interface of control system

Figure 4. Program structure diagram of PLC
For the programming software CX-Programmer of OMRON PLC C200HE controller, subroutine calls can be realized by simple instructions. For example:
Write the following instructions in the main control program to invoke“0”Number subprogram:

stay“0”The following instructions are written at the beginning of the logo subroutine:

stay“0”The end of the sign subroutine writes the following instructions:

This completes the calling of the main program to the subroutine and the return of the subroutine.
2.2.2 The analog input module used in this project is AD003 of OMRON. The actual number of channels used in this module and the type of analog electrical signals can be flexibly configured by PLC instructions. In this example, 8 channels of each analog input module are configured in use state, and the analog signal type is configured in 4-20 mA. The instructions written in the Analog Processing Program (AD003Setting) are as follows:

2.2.3 for OMRON C200HE PLC For the analog input module AD003, when the 4~20mA signal from the meter is not in the range of 4~20mA (below zero or out of range), the AD003 module will convert the field analog value to more than 1000 (16-bit binary) The value of the number is correspondingly displayed on the host computer for the full scale value of the analog quantity. Causes display errors, causing operator misunderstanding. In order to avoid this phenomenon, we need to remove the interference signal out of the range (less than 0000 (4mA) and greater than 1000 (20mA)) in the program. The specific instructions are as follows:

2.2.4 For the address exchanged between OMRON PLC and host computer, it is suggested to put it in the main control program and convert it into HR data area format.
The operation system of this control system is stable and reliable. This system has greatly improved labor productivity. It has effectively solved many problems in production, such as reducing sudden faults in production process, shortening production preparation time and emergency repair time, reducing labor intensity of workers, and creating considerable economic and social benefits for the treatment of boiler supply water in power plants. The purpose of energy saving and consumption reduction is achieved.