What is the purpose of this article?
This guide explains how to read data from a Rheonics SME via Modbus TCP with Node-RED and publish it to an MQTT broker (HiveMQ in this example). The main goal is to enable remote visualization of sensor data from any location. This is achieved by using cloud-based MQTT brokers for accessible data exchange and combining it with Node-RED, which is a flexible and user-friendly tool to read, process, and publish sensor data into an MQTT broker.


TABLE OF CONTENTS


1. Prerequisites

1. Rheonics SME electronics with Modbus TCP enabled

  • SME connects to the sensor probe and transmits the data using different industrial communication protocols. Modbus TCP protocol is used in this article.

2. Node-RED (Windows 10/11 or Linux)

  • A visual programming tool used to collect, process, and route data. In this case, it acts as an intermediary that allows sending sensor data to an MQTT broker. 

  • node-red-contrib-modbus: A Node-RED add-on that enables communication with Modbus devices. 

3. MQTT broker (HiveMQ in this article)

  • A cloud-based MQTT message broker acts as an intermediary between clients that send (publish) and receive (subscribe) data. In this case, it transmits the sensor data received from Node-RED to Ignition for remote visualization.


Following this architecture, data from Rheonics sensors can be sent to an MQTT broker to visualize readings in any MQTT-compatible platform such as Ignition SCADA.


Figure 1: Architecture of Rheonics, Node-RED, MQTT and Ignition integrationFigure 1: Architecture of Rheonics, Node-RED, MQTT, and Ignition integration


2. Obtaining Data in Node-RED

The goal is to obtain sensor data via Modbus TCP in Node-RED and send it to an MQTT broker. The completed Node-RED flow is shown below, and the following steps will explain how to build it.


Figure 2: Node-RED flow for sending data from Modbus to an MQTT

Figure 2: Node-RED flow for sending data from Modbus to an MQTT

2.1. Open Node-RED

1. After installing Node-RED correctly, in a terminal, paste the following command to start running Node-RED:


node-red


2. The terminal will display the corresponding version and indicate that Node-RED is running correctly. The server URL will appear after the Server now running at, in this case, http://127.0.0.1:1880/ 


Figure 3: Node-RED running in terminal

Figure 3: Node-RED running in a terminal


3. Paste the link in a browser to load the Node-RED editor.


Figure 4: Node-RED editor

Figure 4: Node-RED editor


2.2. Add a Modbus-Read Node

To obtain the sensors data through Modbus TCP, use the node-red-contrib-modbus module.

1. Drag a Modbus-read node onto the flow.

Figure 5: Modbus-Read node

Figure 5: Modbus-Read node


2. Double-click to configure:

  • Name: Viscosity (It is just the label of the node)
  • Function Code: FC4 - Read Input Registers
  • Address: 40 (viscosity register). The rest of the input parameters can be found in Modbus TCP - Input Registers
  • Quantity: 2 (float = 2 registers)
  • Poll Rate: 3s (depends on frequency of data reading desired)


Figure 6: Modbus-Read Node Configuration

Figure 6: Modbus-Read Node Configuration


3. Click on the Server field and press the plus to add a new Modbus TCP client. In this case, it corresponds to the SME:



Figure 7: Modbus Client Configuration

Figure 7: Modbus Client Configuration


2.3. Add a Function Node to Decode Float

The Modbus-Read node returns the values of the registers, which need to be transformed to obtain the value of viscosity. Add a function node to convert the 2 16-bit registers into a float value.

Figure 8: Function node

Figure 8: Function node


1. Drag a function node onto the flow.

2. Double-click on the node and add the following code to the On Message section. This allows to return the viscosity as a float.


let buffer = Buffer.alloc(4);

buffer.writeUInt16BE(msg.payload[0], 0);
buffer.writeUInt16BE(msg.payload[1], 2);

msg.payload = buffer.readFloatBE(0);

return msg;


Figure 9: Function Node - Float Conversion

Figure 9: Function Node - Float Conversion


2.4. Add an MQTT-Out Node

Add an MQTT-out node to publish the sensor data to the broker. In this case, HiveMQ broker. 


Figure 10: MQTT-out node

Figure 10: MQTT-out node


1. Drag an MQTT-out onto the flow. 

2. Double-click on the node to configure its properties

  • Topic: srv/viscosity (name of the topic where the viscosity data will be published)
  • QoS: 1 (this allows the message to be received at least once)

Figure 11: MQTT-Out Node Configuration

Figure 11: MQTT-Out Node Configuration


3. Add an MQTT broker by pressing in the plus next to Server to add the HiveMQ broker.


Figure 12: MQTT broker addition

Figure 12: MQTT broker addition


4. Next, the properties of the MQTT broker are filled as follow:

  • Name: Desired name for the broker

  • Server: HiveMQ Connection URL

  • Port: Port used by the broker

  • Use TLS: Enable if using encrypted communication

  • Protocol: MQTT V5


Figure 13: HiveMQ Broker Configuration - Connection Tab

Figure 13: HiveMQ Broker Configuration - Connection Tab


5. Go to the Security Tab on the HiveMQ Broker configuration and fill it with the credentials of the HiveMQ broker.

  1. Username: username credentials in HiveMQ broker

  2. Password: password credentials in HiveMQ broker


Figure 14: HiveMQ Broker Configuration - SecurityTab

Figure 14: HiveMQ Broker Configuration - SecurityTab


2.5. Deployment and Final Visualization of Node-RED flow

1. After adding correctly and configuring the nodes, press on the Deploy button to run the flow.

Figure 15: Deployment of Node-RED flowFigure 15: Deployment of Node-RED flow


2. The final flow looks as follow.

Figure 16: Complete Node-RED Flow for Modbus to MQTTFigure 16: Complete Node-RED Flow for Modbus to MQTT


3. Repeat the same procedure to obtain other parameters of the SME by modifying the address and topic.


3. Resources