The following two parts are mainly checked:

① Temperature controller side:

A. Whether the communication wiring is correct. It is recommended to use shielded twisted pair for the communication line; Refer to the figure below for RS232 wiring:

B. Check whether the communication writing in the adjustment menu is set to On;

C. Whether the terminal resistance is used, generally 120 Ω is recommended;

D. Whether the baud rate, data bit, stop bit, communication protocol and unit number are set correctly (the MODBUS-RTU data bit and stop bit are fixed as 8 and 1).

② PLC side:

A. Whether the DIP switch of PLC or adapter is set correctly;

B. Whether the serial communication format (baud rate, data bit, stop bit) is set as the temperature controller;

C. Whether the program is edited correctly (mainly instructions and communication format);

D. Whether the terminal resistance of PLC is set to ON (SCB, SCU, communication adaptation);

E. Whether there is response code or response code after sending the protocol, check the error and no response code according to the temperature controller response code table, and check all the above settings and wiring