(I) Switching quantity connection
When the PLC controls the inverter in a switching quantity manner, it is necessary to connect the switching quantity output terminal of the PLC with the switching quantity input terminal of the inverter. At the same time, the switching quantity output terminal of the inverter can also be connected with the switching quantity input terminal of the PLC to detect the state of the inverter. For example, in some small mechanical processing equipment, when the PLC is not used, the control can be performed by connecting switches to the forward, reverse and multi-speed control terminals of the inverter. When using PLC control, the connection is made like this. In actual applications, when the internal program of the PLC runs to close the internal hard contact of a specific terminal, it is equivalent to closing the external switch of the corresponding terminal of the inverter, thereby realizing the start, stop and speed adjustment of the motor. For example, in a simple material conveying system, the inverter is controlled by the switching quantity output of the PLC to realize the forward, reverse and multi-speed switching of the conveyor belt to meet different material conveying needs.
(II) Analog connection
When the PLC controls the inverter in analog mode, it is necessary to connect the analog output terminal of the PLC to the analog input terminal of the inverter. For example, since the Mitsubishi FX2N-32MR PLC has no analog output function, it is necessary to connect an analog output module (such as FX2N-4DA) to it, and then connect its output terminal to the analog input terminal of the inverter. In actual application, when the external switch of a specific terminal of the inverter is closed, the inverter starts the motor to rotate forward, and the digital data generated by the internal program of the PLC is sent to the analog output module through the connecting cable, which converts it into a voltage (analog quantity) in the range of 0-5V or 0-10V and sends it to the corresponding terminal of the inverter to control the frequency of the inverter output power supply, thereby controlling the speed of the motor. The advantage of this control method is that it can make the speed of the motor change continuously and realize stepless speed change. For example, in a machine tool processing system that requires precise speed control, the motor speed can be adjusted in real time according to the requirements of the processing technology through analog control, thereby improving the processing accuracy and quality.
(III) Communication connection
Single inverter: When a single inverter is connected to the RS485 communication of PLC, the sending terminal (+/-) of one device should be connected to the receiving terminal (+/-) of the other device, and the receiving terminal (+/-) should be connected to the sending terminal (+/-) of the other device. For example, in an independent automated production unit, PLC controls a single inverter through RS485 communication to achieve precise speed regulation and control of the motor, improve production efficiency and product quality.
Multiple inverters: The RS485 communication connection between multiple inverters and PLC can realize the operation of multiple inverters controlled by one PLC. RS485 communication is a communication method widely used in industrial control at present, with strong anti-interference ability, and its communication distance can reach tens of meters to thousands of meters. RS485 communication can not only connect two devices for communication, but also connect multiple devices (up to 32 devices in parallel) to form a distributed system for mutual communication. For example, in a large industrial production workshop, a PLC can connect multiple inverters through RS485 communication to control different production equipment respectively, realize centralized management and control, and improve production efficiency and management level.
