introduction:
With the development of urbanization throughout the country, high-rise buildings are a more prominent feature, and they are getting higher and higher. Then a problem that follows is the problem of water supply. Both residential and office buildings are inseparable from water. So how to maintain a constant water supply pressure and improve the quality of water supply is very important, while also ensuring the reliability and safety of the water supply. But with the development and application of PLC, this problem has been solved, so let me introduce how PLC solves it.
1. Water supply method and control system1. This design consists of a main water supply circuit, a backup water supply circuit, a clean water tank and a pump room. Among them, the pump room is equipped with three pumps, and there are multiple electric gate valves or electric butterfly valves to control each water supply circuit and water flow. The control system adopts PLC. In order to prevent the system from powering the inverter back and damaging the inverter, the contactors KM1 and KM2, KM3 and KM4, KM5 and KM6 must be mechanically interlocked. The following figure shows the schematic diagram of the pump unit:
2. System control requirements
(1) The water supply pressure must be constant, and the fluctuation must be small, especially when changing the pump.
(2) According to the pressure setting, the 3 pumps adopt first-on and first-stop.
(3) In order to prevent a pump from running for a long time, it is necessary to set the running time. When the time is up, it will automatically switch to the next pump to prevent the pump from rusting if it is not used for a long time.
(4) It must have perfect protection and alarm functions.
(5) Manual function is required for maintenance and emergency.
(6) It has the function of anti-evacuation of the pool.
3. PLC selection
According to the system's requirements and functions in improving water supply quality and energy saving, a control system composed of Aoyuexin 200 series CPU224DPLC and frequency converters is adopted.
4. PLC I/O distribution
The system occupies 4 input points and 9 output points of the PLC. The figure below is the I/O allocation table
5. Schematic diagram of electrical control system
(1) Main circuit diagram
In the figure below, M1, M2, and M3 are three motors, AC contactors KM1--KM6 control the operation of the three motors, and KH1, KH2, KH3 are thermal relays of motors M1, M2, and M3.
(2) Wiring diagram of PLC (OYES cpu224C)
(3) Control circuit diagram
The electrical control route is shown in the figure below. In the figure, SA is the manual/automatic transfer switch; KA is the manual/automatic intermediate relay, when it is set to "1", it is manual, when it is set to "2", it is automatic, and KA sucks at the same time. In the manual state, the start and stop of the three pumps can be controlled by SB1---SB6. In the automatic state, the system automatically controls according to the PLC program. HL1---HL8 are indicator lights for various operations. The normally open contact of the intermediate relay KA is connected to I0.3 to control the start in the automatic state. In the automatic state, the three pumps can be switched and run orderly and smoothly under the control of PLC. KH1, KH2, KH3 are the normally closed contacts of the thermal relays of the three pumps, which can protect the motor from overcurrent.
6. System programming
The system program includes the main program and the start subprogram. The main program includes the adjustment program and the motor switching program. The start subprogram is actually a clearing program. When the PLC is powered on, first assign VB200, VB201, and VD260 to 0 as the middle Following the reset of M.
In the main program, T56 and T57 are the filter time relays for the upper and lower limits of the frequency converter frequency, which are mainly used to stabilize the system. VB200 is the pump number of the variable frequency pump, VB201 is the total number of pumps operating at power frequency, and VD260 is the time memory of the reverse pump.
Second summaryThe constant pressure variable frequency water supply equipment of this design is composed of PLC, frequency converter, sensor, low-voltage electrical control cabinet and water pump. For this design, it is tested in most high-rise building water supply systems, and some parts must be modified according to the site. This system can stably control three pumps under the control of Aoyuexin CPU224C, which fully meets the required control requirements. In the future, there will be more intelligent constant pressure control water supply systems, which are all built on the basis of PLC control. I hope everyone can communicate together so that PLC can solve problems for everyone in more fields and bring convenience to everyone's lives.
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