NT18B07 with WAGO PFC100 PLC and CODESYS: Real-World Modbus RTU Troubleshooting

Introduction

Integrating RS485 temperature acquisition modules into industrial PLC systems is a common requirement in automation, equipment monitoring, and industrial IoT applications.

The Eletechsup NT18B07 7-channel RS485 NTC temperature acquisition module is designed for applications that require multi-channel temperature measurement and serial communication.

A discussion on the WAGO Automation Community provides a useful real-world example of the challenges engineers may encounter when connecting the NT18B07 to a WAGO PFC100 PLC running CODESYS 3.5.

Original engineering discussion: Modbus RTU with PFC100 750-8112 (CODESYS 3.5)

1. The Integration Scenario

In March 2026, an engineer reported attempting to connect an Eletechsup NT18B07 to a WAGO PFC100 controller, model 750-8112, using Modbus RTU over RS485.

The engineer had already verified that the NT18B07 could be addressed and its register values read using a USB-to-RS485 adapter and PC-based Modbus testing software.

However, the WAGO PLC reported a Modbus response timeout.

This is an important distinction: successful communication with a PC test tool does not automatically guarantee successful communication with a PLC. The serial interface, protocol settings, register configuration, and physical-layer implementation must all be compatible.

2. Troubleshooting Points Discussed by the Engineering Community

The discussion covered several useful areas for industrial communication troubleshooting.

RS485 Interface Configuration

The WAGO PFC100 serial interface must be configured for the correct electrical mode. Community members initially suggested verifying that the port was assigned to RS485 rather than RS232.

The original poster subsequently confirmed that RS485 mode had already been selected.

Modbus Address and Communication Parameters

The discussion also highlighted the importance of matching the Modbus device address and communication settings between the PLC and the temperature acquisition module.

The engineer initially tested address 3 and later changed to address 1 after resetting the device. Address 1 was then confirmed as the configured address on both sides.

Diagnostic Tools in CODESYS

Community members suggested using the FbMbMasterSerial function block from the WagoAppPlcModbus library to obtain more detailed diagnostic information.

They also discussed inspecting raw serial communication data and using a simple register-reading test to isolate communication problems.

RS485 Termination and Signal Quality

Another contributor investigated whether the termination resistors and connector arrangement might be affecting communication.

The discussion compared different termination arrangements and highlighted the importance of suitable cable termination and signal biasing.

These suggestions are troubleshooting possibilities, not proof that the NT18B07 itself was responsible for the timeout. The available discussion does not establish a definitive root cause.

3. Why This Matters for Industrial Automation

For industrial engineers, the case illustrates several practical considerations when integrating a Modbus RTU temperature acquisition module into a PLC-based system:

• Verify serial interface configuration before investigating application logic.

• Confirm the slave address and serial communication parameters.

• Check register addressing and supported Modbus function codes.

• Use diagnostic tools to distinguish communication failures from incorrect application data.

• Verify the RS485 wiring, grounding, termination, and biasing requirements for the actual hardware configuration.

Following a systematic process can make troubleshooting more efficient when connecting third-party Modbus devices to PLC platforms.

4. Potential NT18B07 Applications with PLC Systems

Once communication has been correctly configured and validated, a multi-channel temperature acquisition module can be considered for applications such as:

Industrial equipment monitoring: Collect temperature readings from several locations and make them available to PLC logic or an HMI.

Electrical cabinet monitoring: Monitor selected cabinet or equipment temperatures and provide readings for alarms or maintenance systems.

Environmental control: Supply temperature measurements to automation systems controlling ventilation, cooling, or other environmental equipment.

Industrial IoT data acquisition: Provide temperature data to compatible gateways or supervisory systems that can communicate with the module through Modbus RTU.

Actual integration depends on the target PLC, communication hardware, register map, and application requirements.

5. Further Community Development

The WAGO thread continued beyond the initial troubleshooting attempts. On June 1, 2026, a community contributor shared a CODESYS 3.5 SP21 Patch 3 project example using the WagoAppPLCModbus library for serial communication.

This is a potentially useful reference for engineers developing their own Modbus RTU applications. However, the shared example should not be presented as a verified NT18B07 integration project unless compatibility has been independently tested.

Conclusion

The WAGO PFC100 and NT18B07 discussion demonstrates the practical engineering work involved in integrating Modbus RTU temperature acquisition devices into industrial control systems.

For automation engineers evaluating the Eletechsup NT18B07, the discussion offers useful troubleshooting references covering serial interfaces, Modbus configuration, diagnostics, and RS485 physical-layer considerations.

Product information: Visit Eletechsup to learn more about the NT18B07 and other RS485-based data acquisition modules.