Currently, frequency converters and PLCs are widely used in factory equipment control.
Frequency converters, as control devices for three-phase AC asynchronous motors, bring great convenience to the production site. They can not only adjust speed and torque but also save energy.
Before the advent of frequency converters, achieving these controls was extremely complex and costly.
A frequency converter, as a mature industrial control device, can operate independently or accept external control signals, such as PLC control, touch screen control, or host computer control.
This describes controlling a frequency converter; currently, the most widespread application is PLC control.
There are two main ways to control a frequency converter with a PLC. The first is to directly connect the PLC’s output points to the frequency converter’s start and stop signals. Simultaneously, the PLC can also output analog signals to adjust the frequency converter’s speed.
The first method is simple and straightforward to control; we only need to write the relevant program in the PLC to achieve relatively perfect control.
As shown in the diagram above, the PLC’s COM port and the inverter’s COM port need to be connected together.
This is crucial to ensure that the inverter can receive the signals output by the PLC.
The second way to control a frequency converter with a PLC is through 485 communication.
Using RS-485 communication to control frequency converters has several clear advantages.
Only two control cables are needed, and it can control multiple frequency converters simultaneously without interference.
Theoretically, one PLC can control 256 frequency converters simultaneously, but in practice, controlling 10 to 20 is no problem.
It can easily control the start and stop of frequency converters, adjust their speed, and read real-time data.
This includes, but is not limited to, current, voltage, frequency, current power, current speed, frequency converter temperature, and fault codes.
It can comprehensively display the current operating status of the frequency converters and monitor the operating status of multiple frequency converters simultaneously.
Therefore, RS-485 communication control is a very convenient control mode when multiple frequency converters are used simultaneously.
Post time: Jun-11-2026
