The constant pressure water supply system based on PLC design

1 introduction usually water system in high water consumption, water pressure of water supply pipeline will drop, can't meet the needs of users; Water consumption is low, the water pressure of water supply pipeline will rise, beyond the needs of users, this situation is not only waste the energy, but also disrupt water pipe and water facilities, caused economic losses. Of water supply system, pressure regulating method is relatively backward, commonly used water tower secondary water supply and adjusted by the methods such as frequent start-stop motor. The money is more, covers an area of big, prone to failure; The latter will consume large amounts of electric energy, will also affect other electrical equipment connected to the electricity grid, repeatedly start-stop devices will shorten its service life [ 1] 。 Considering some disadvantages of the current water supply system in the actual application, the design of water supply system on the premise of high efficiency and energy saving, water stability, adopts PID closed-loop control method, improves the accuracy of the system. In order to guarantee the safe operation of the equipment, and using the PC monitor to the system. Its working principle is the use of frequency conversion technology, the combination of PLC and pressure sensor, complete water pumps in variable frequency power supply and power frequency power, the automatic conversion between the pipeline pressure stability near the set value, so as to achieve the design requirements of constant pressure water supply [ 2] 。 2 system overall design and work principle of system design goal is to achieve the requirement of the water, so regulating object is flow, but the pump will be decided the height of the water in the flow, its detection and adjustment is not easy to do. When the water supply system, pipeline network of water pressure depends on the size of the relationship between water supply and water. At the time of water supply is greater than the water consumption, water pressure of water supply pipe will be increased, at the time of water supply is less than water, water pressure in water supply pipeline will drop, at the time of water supply is equal to the water consumption, water pressure of the water supply pipe remains constant. So, in the control flow, we are going to the water pressure as control reference variable. Control system structure is shown in figure 1. Figure 1 structure system based on PLC internal PID control system of frequency conversion constant pressure water supply mode, the application of three cycle running of the pump and the variable frequency power supply and power frequency power conversion between to complete the process of constant pressure water supply, 1 # and 2 # pump as the main supply pump, 3 # pump as the standby pump. The control flow chart is shown in figure 2. Figure 2 control system structure of the system using the PID closed-loop control mode, USES pressure sensors measure the pressure in the pipeline, and then to turn pressure into electrical signals, feedback and PID controller, and through calculated deviation, use frequency converter to change the pump rotation speed; In residents' water consumption increases, the water pressure of water supply pipeline will less than the pressure setting, the output frequency of frequency converter get bigger, increasing the pump rotation speed, thus increasing the water supply, when 1 # of pump speed reaches limit, and the water pressure is less than the pressure setting of water supply pipeline, the 1 # water pump will automatically switch to the by the state of frequency conversion work under the condition of power frequency, 2 # pump frequency conversion work, if the water pressure is greater than the pressure setting of the pipe network, 2 #, dropping speed pump frequency is reduced, when reduced to lower limit pipe network pressure is greater than the pressure setting, 1 # pump stops, the 2 # pump frequency conversion work, the pipe network pressure is about to reach the pressure setting, the pump speed change slows down until the speed change, no longer to make constant water pressure on the pressure setting of water supply pipeline, so as to achieve the requirement of stable water supply pressure. 3 system is mainly composed of the hardware design of PLC CPU, memory, I/O mouth, peripheral programmer and power, etc [ 3] 。 The CPU is composed of registers, controller, and unit, it is PLC used to complete the information operation unit; Used for data storage, system program and user program, etc. ; Digital and analog I/O ports for the scene handling, testing equipment and implement equipment connection, PLC controller input port including three input forms, respectively, and ac/dc input dc input, ac input, the output form contains thyristor, transistor and relay type; PLC power supply is not only to provide the main power supply to PLC, at the same time provide the stable operation of the PLC's internal components required for direct current (dc), as the internal components as a member, read on.
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