Case Study: Using MODBUS communication, this example demonstrates how a PLC can control a frequency converter 's start/stop, forward/reverse rotation, and frequency modification. It also involves reading the converter's output voltage, output current, and output frequency.
I/O allocation:
Hardware wiring:
As shown in the wiring diagram: both the run command and the frequency set command are sent to the frequency converter via communication. A 10V voltage signal is output through the analog output channel and connected to the potentiometer. By rotating the potentiometer, the 10V voltage signal can be adjusted so that the analog input channel 1 can obtain a voltage signal that changes from 0 to 10V. Then, the obtained digital quantity is converted into the frequency of the frequency converter and sent to the frequency converter via communication.
Communication cable making:
Next is the construction of the communication cable between the PLC and the frequency converter. Connect pin 3 on the PLC port to pin 2 (485+) on the frequency converter, and pin 8 to pin 7 (485-) on the frequency converter.
Inverter SCI Communication Parameter Table:
The inverter parameters are set as follows:
F00.10 =2; SCI communication mode frequency setting
F00.11 =2; Start/stop motor via SCI communication.
F17 . 00=1; 1-8-1 format, even parity, RTU, 1 start bit, 8 data bits, 1 parity bit
F17.01 =4; baud rate set to 19200bps
F17.02 =1; Inverter address is 01
F17.03 =150; Inverter local response time
F17.04 =0; Inverter does not detect communication timeout.
F17.05 =0; Inverter does not detect communication errors.
F17.09 =01; Write function parameters for communication mode to EEPROM.
Inverter parameter register address:
Control command and operating frequency setting register address:
For example, the register address controlling the nameword is 0x3200, which is a hexadecimal number. Converted to decimal, this is 12800. Since the starting address of the register is 40001, 12800 + 1 = 12801. And since the type is type 4, a 4 is added to the prefix, so the addr address should be 412801. Other register addresses follow the same logic.
PLC and Hypurmont frequency converter communication program writing:
Main program
