Application of PLC in motor control of water industry
The programmable controller (PLC, Programmable Logic Controller) is an automatic control device manufactured by microcomputer technology. He is based on sequential control, supplemented by loop adjustment, and can perform functions such as logic judgment, timing, memory and arithmetic operations.
With the development of PLC technology, its functions are more and more, the integration degree is getting higher and higher, the network function is getting stronger and stronger, PLC and network technology formed by PLC and upper PC networking are widely applied to industrial automation control. The PLC integrates three electric and one, has good control precision and high reliability, making PLC become the pillar of modern industrial automation. PLC manufacturers and models, a wide variety, different models of self-contained systems have different programming languages and methods of use. This paper intends to use the OMRONC20p PLC produced by Japan Lishi Company to design several PLCs in the control of three-phase asynchronous motors. Compared with the traditional relay control, it has the advantages of fast control speed, high reliability and flexibility. It can be used as a reference for college students to learn PLC control technology, and can also be used as an automatic control circuit for industrial motors.
2PLC application in motor control [1~3]
2.1 Forward and reverse control of three-phase asynchronous motor
Required that when the forward rotation button is pressed, the motor rotates continuously, and the reverse button does not work (interlock). Press the stop button to disconnect the power from the motor. Press the reverse button to continuously reverse the motor. effect. Figure 1 shows the schematic diagram of the forward and reverse control of a three-phase asynchronous motor.
2.2 Y-△ start of three-phase asynchronous motor
When the start is required, the motor is connected to the Y type, and after a period of time, it is automatically converted into the △-shaped operation. After the Y-shaped disconnection is required, the △ shape can be started to prevent the Y-shaped unbroken Δ-shaped start to cause a short circuit of the power supply. Figure 2 shows the schematic diagram of the Y-△ start control of the three-phase asynchronous motor.
2.3 Three-phase asynchronous motor time control
After requesting the first motor M1 to start for 5s, the second motor M2 is automatically started. Only after the second M2 stops, after 5s delay, M1 automatically stops. Figure 3 shows the schematic diagram of the time control of a three-phase asynchronous motor.
3 program write and run
联 After connecting the PLC to the programmer and turning on the power, the PLC power indicator lights up, and the programmer switch is turned to the “PROGRAM” position. At this time, the PLC is in the programming state. The programmer displays PASSWORD! At this time, press the Clr key and the Montr key in sequence until the screen displays the address number 0000, and the program can be input.
Before entering the program, you need to clear the contents of the memory, and then press Clr, Play/Set, Not, Rec/Reset and Montr to clear all the programs. According to the above three kinds of control ladder diagrams or program instructions, three kinds of control programs are written into the PLC. When the above three parts of the program are input into the PLC machine, use the up and down direction keys to read the written program. If the program is wrong, the insert command can be used. And delete instructions to modify the program.
After the program input is correct, connect the PLC external wiring and the main circuit line according to Figure 1 (a) and (c) respectively to realize the motor forward and reverse control. According to Figure 2 (a) and (c) connect the line to realize the motor Y-△ start , according to Figure 3 (a) and (c) connecting lines to achieve motor time control. This design can input all three kinds of control circuit programs at one time, and control three kinds of circuits at the same time. When running, press SBF, SBR motor starts up and down, press SB1, SB2 controls motor Y-△ start, press SB3 The SB4 motor starts in sequence, does not interfere with each other, and works with half the effort. It realizes one PLC to control multiple circuit forms at the same time.
