General Measure Technology Co. Ltd. (China) -  In this tutorial, we explain how to establish communication between the GMT-X4 instrument and the Modbus Poll software using the Modbus TCP/IP protocol.

Communication interfaces supported by GMT-X4

The GMT-X4 offers multiple communication options, including:

• Serial interfaces (RS232 and RS485)
• CAN communication
• Ethernet communication (Modbus TCP/IP)
• Fieldbus communication, such as PROFINET, EtherCAT, Ethernet/IP and CC-Link IE

This demonstration focuses specifically on Modbus TCP/IP communication through the Ethernet interface of the GMT-X4.

Hardware setup

Begin by connecting the Ethernet port of the GMT-X4 to your computer using a standard network cable.

Communication configuration

1. Local IP address

From the main screen of the GMT-X4, press Enter to access the Calibration Menu.

Press the Right key to open the Communication Parameter Menu. Use the Down key to select 4. TCP-IP, then press Enter.

Select 4.1 [Local IP] and use the Up/Down keys to assign an IP address that corresponds to the host computer.

Press Enter to save the setting.

(Tip: Check the IP address of your computer and ensure both devices are on the same network segment. The IP shown in the video is for demonstration purposes only.)

2. Subnet mask

Press the Down key to select [Subnet Mask], then press Enter.

Adjust the subnet mask using the Up/Down keys so it matches your network configuration.

Press Enter to confirm.

(Tip: Verify the subnet mask of your computer. Both devices must be within the same network segment. The value shown is for reference only.)

3. Gateway

Press the Down key to select [Gateway] and press Enter.

Use the Up/Down keys to configure the gateway according to your network environment.

Press Enter to confirm.

(Tip: Make sure the gateway setting matches your local network.)

4. Connection 1

Select [Connection 1] and press Enter.

4.1 Port number

Choose 4.4 [Port Number] and set the value using the Up/Down keys.

The default port number is 502.

Press Enter to confirm.

(Tip: The default TCP port is 502. Ensure this matches the setting on the host computer.)

4.2 Communication protocol

Press the Down key to select [Communication Protocol], press Enter, and choose Modbus/TCP.

Press Enter to confirm.

4.3 Double word mode

Press the Down key to select [Double Word Mode], then press Enter.

Select the required data format. The default setting is AB-CD.

Press Enter to confirm.

4.4 Continuous transmission protocol

Since this example uses Modbus/TCP, which is not a continuous transmission protocol, the Continuous Sending Interval does not need to be configured.

(Tip: This setting helps prevent communication errors caused by excessive transmission speed and should only be adjusted when required.)

If additional connections (Connection 2 through Connection 6) are needed, repeat the same configuration steps used for Connection 1.

PC software configuration

Once the instrument settings are complete, configure Modbus Poll on your computer as follows:

Open Modbus Poll and select Connection → Connect.

Set the parameters to match the GMT-X4 configuration:

• Connection Type: Modbus TCP/IP
• IP Address: Same IP address as configured on the GMT-X4
• Server Port: 502

Click OK to establish the connection.

When communication is successful, the LAN indicator on the GMT-X4 will blink, confirming normal data exchange.

The weight value displayed on the GMT-X4 will correspond to the data shown in Modbus Poll.

Watch the video to see the full process.

This concludes the setup of Modbus TCP/IP communication between the GMT-X4 and Modbus Poll. In the next video, we will demonstrate communication between the GMT-X4 and a PLC using the PROFINET protocol.