Constant pressure water supply system controlled b

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this paper introduces a programmable constant pressure water supply monitoring system that enables parents and children to exchange sequence controllers with each other. The operation principle of the system and the design method of constant pressure water supply are emphasized, and the program block diagram of automatic pressure regulation is given

keyword: frequency converter; Programmable controller; Control; Water supply system

1 Introduction

constant pressure water supply system is very important for some industries or special users. For example, in some production processes, if the tap water supply is under pressure for some reason or short-term water shortage, the classification of material testing machine may affect the product quality, and in serious cases, the product will be scrapped and the equipment will be damaged. For another example, in case of fire, if the water supply pressure is insufficient or there is no water supply, the fire cannot be extinguished quickly, which may cause major economic losses and casualties. Therefore, it is of great economic and social significance to adopt a constant pressure water blasting system in some water areas

in the old pressurized equipment, the constant pressure water supply is generally realized by starting or stopping the water pump of the pressurized station and adjusting the opening of the outlet valve. The control system adopts relay contactor to control the line. This system has complex lines, difficult maintenance and operation. Workers have to be on duty 24 hours, which is labor-intensive. Therefore, it is necessary to transform it and improve the automation level

the constant pressure water supply monitoring system introduced in this paper is used for a tap water pressurization station to quickly start the constant pressure water supply to produce the initial friction force control system on the clamping surface. FP3 programmable controller (PLC) produced by Panasonic Electric is used for control, and Yanhua industrial computer is used for monitoring. The degree of automation is high, and the whole working program is completed automatically, which can clearly display the real-time status of each equipment and automatically adjust the water pressure

the system is also equipped with a variety of protections, such as water pressure over limit alarm, valve fault alarm, water level over limit alarm and processing, water pump motor current over-current alarm and processing, etc

2. System structure and control requirements

constant pressure water supply system is composed of main water supply circuit, standby circuit, two clean water tanks and pump room group

among them, the pump room is equipped with a total of 6 150KW pumps from 1# ~ 6#. In addition, there are multiple (V1 ~ V23) electric gate valves to control each water supply circuit and water flow

the constant pressure water supply system is required to have the following basic operation functions

(1) when the municipal tap water pressure is higher than the set pressure by 21.56 × At 104pa, it is directly supplied by municipal tap water

(2) when the municipal tap water is lower than the set pressure, but not lower than the downpressure of 7.84 × At 104pa, the direct pumping pressurized water supply scheme is adopted. That is, gradually start two pumps to pressurize the pipe. When the municipal tap water is detected to be higher than the set pressure, it will be converted to municipal tap water for direct water supply

(3) when the tap water pressure is continuously lower than 2.94 × 104pa or when there is an exact negative pressure signal, it should be immediately converted to pumping water to pressurize, but at this time, it should ensure that the water level of the pool is higher than the minimum limit water level

(4) when direct pumping or pumping pool water pressurized water supply is adopted, the total outlet water pressure shall be automatically adjusted to the given value, and the adjustment error shall be less than or equal to ± 10%

3. PLC control system design

the constant pressure water supply system has many detection points and control quantities, which is a large-scale measurement and control system. According to its characteristics, we choose FP3 programmable controller of Panasonic electric as the control device. Compared with other programmable controllers, this controller has some obvious advantages. For example, FP3 adopts modular design, which can be flexibly assembled according to actual needs, and is easy to use. I/o distribution adopts free programming mode; Large capacity, the amount of program is only limited by the scanning cycle, and the scanning cycle can be changed within a certain range; With a/d, d/a, pulse output, position control and other advanced units, it can realize "shared memory"; There are also some special functions

the structure of the constant pressure water supply PLC system is shown in the imaginary box in Figure 1. The system includes a power supply unit, a CPU unit, a host computer connection unit, as well as i/o unit and a/d unit. The upper computer adopts Advantech industrial computer ABB configuration software, and the upper computer connection unit passes C/Font net adapter communicates with it. The industrial control computer monitors the whole system, and the display shows the structure of the whole pressurization system, the real-time status of each valve and water pump, reads out each water pressure and flow, the opening of the valve, the water level of the pool and other parameters, and has various alarm real-time displays and fault records

the system has both analog input and switching input. Analog quantity is input through a/d module, with 27 channels in total. I/o has 96 points each

4. PLC software design

according to the constant pressure water supply operation requirements, the PLC control system should monitor the municipal tap water and the water supply port at any time to decide whether to start the pump, or whether to adopt the direct pumping and pressurization scheme or the pumping pool water pressurization scheme. The program of the control system is complex. In the control process, the automatic regulation of water pressure at the water supply port is one of the important and distinctive design parts. Here, the software design to realize the function of automatic constant pressure is emphatically introduced

because the water supply system has long pipes and large pipe diameters, and the opening, closing and pipe pressurization of valves are slow, the system is a large lag system. At the same time, because the transformation is based on the old equipment and the existing equipment should be used, the speed regulation and pressure regulation are not used, but the following methods are used to regulate the water pressure. First, the water pressure deviation is divided into four sections, namely 10%, 20%, 30%, 40%. When the detected deviation is small, the output control quantity (increment of butterfly valve) is small, and the operation cycle is also large; When the deviation is large, the output control quantity is large and the operation cycle is small, so that it can quickly reduce the deviation and avoid excessive overshoot. In addition, when the deviation is less than or equal to ± 10%, add fuzzy control, and determine whether to adjust the opening of the butterfly valve according to the value of D ek=ek-ek-1, so as to further reduce the error and ensure the error requirement of less than or equal to ± 10%. When the valve opening cannot be adjusted to make the deviation enter the allowable range, the water pressure shall be adjusted by starting or stopping one or more water pumps. Through the combination of such various methods of adjusting water pressure, the water pressure at the outlet can be adjusted satisfactorily

5. Conclusion the PLC constant pressure water supply monitoring system designed in this paper has been successfully applied to an industrial area. The operation results show that the system fully meets its design requirements, with convenient operation, strong reliability, complete data, timely monitoring and so on

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