PLC connect with Frequency Inverter

There are three main ways to connect PLC with inverter:

① Control by switch mode

② Control by analog mode

③ Control by communication mode

(I) Hardware connection of PLC controlling inverter by switch

Inverter has many switch terminals, such as forward, reverse and multi-speed control terminals. The inverter can be controlled by connecting switches to these terminals. When PLC is used to control the inverter, it is necessary to connect the switch output terminal of PLC to the switch input terminal of inverter.

In order to test certain states of inverter, the switch output terminal of inverter can be connected to the switch quantity input terminal of PLC at the same time.

(II) Hardware connection of PLC controlling the inverter in analog mode

The inverter has some voltage and current analog input terminals.

Changing the voltage or current input value of these terminals can change the speed of the motor. If these terminals are connected to the analog output terminals of the PLC, the PLC can be used to control the inverter to adjust the speed of the motor.  The analog control function can make the speed of the motor change continuously (stepless speed change).

(III) Hardware connection of PLC controlling inverter by communication (taking RS485 as an example)

When PLC controls inverter by switch quantity, it needs to occupy more output terminals to connect the input terminals of corresponding functions of inverter in order to control the inverter forward, reverse and stop;

If PLC controls inverter by RS485 communication, only one RS485 communication cable (containing 5 core wires) is needed to directly send various control and frequency modulation commands to inverter. Inverter can perform corresponding function control according to the instructions sent by PLC through RS485 communication cable.

RS485 communication is a communication method widely used in industrial control at present. It has 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.

Of course there are other communication methods, such as PROFIBUS and Ethernet.