What products are involved?
SRV – Inline Viscosity Meter
What is the purpose of this article?
This article describes how to integrate the Rheonics Sensor Module Electronics (SME) via Modbus RTU with the CAN serial communication protocol, which is commonly used in industrial environments with high electrical noise for monitoring and control of variables.
Short answer: This guide shows how to convert Modbus RTU data from a Rheonics SME into CAN messages using a Waveshare RS232/485/422-to-CAN converter, and how to verify the resulting communication with a Kvaser USB-to-CAN interface and CanKing software.

TABLE OF CONTENTS

1. Overview

The Controller Area Network (CAN) is a serial communication protocol that uses a serial bus system to share information between electronic devices. Electronic modules can communicate over a single CAN interface instead of multiple input/output signal connections, which reduces wiring costs and allows operation without a "host" computer. All devices — also called CAN nodes — can read every message on the bus, but they identify messages using a message identifier (ID) rather than a device address.

In this application, the Modbus RTU data received from the Rheonics SME must be converted into CAN messages so that other CAN nodes on an industrial plant network can share the information acquired by Rheonics sensors, such as the SRV. This article demonstrates communication between a Rheonics SME and a second CAN node (a PC), using a Modbus RTU-to-CAN converter and a Kvaser USB-to-CAN interface.

Figure 1: Architecture of the Rheonics SME and industrial isolated RS232/485/422-to-CAN converter integration.

2. Wave Share RS232/485/422 to CAN Converter Configuration

To set up the converter parameters, connect the device to the PC through a USB-to-RS485 converter attached to the RS485 port. After identifying the assigned serial port (using Device Manager), download, extract, and open the WS-CAN-TOOL [1].

Figure 2: Connection diagram for converter configuration.

2.1 Configuration in WS-CAN-TOOL

  1. The software sets the parameters of the RS485 and CAN ports and the conversion mode. Select the identified COM port number of the converter, keep the remaining values at their defaults, and select Open Serial.
Figure 3: Establishing serial communication.
  1. Once the serial port is open, all device information is shown in the software after pressing Read Device Parameters. Change the serial parameters to match the Rheonics SME Modbus RTU port.
Figure 4: Reading Device Parameters.

Table 1: Modbus RTU default parameters in Rheonics SME

ParameterValue
Baudrate38400
ParityBitOdd
Databit8
Stopbit1

Apply the following settings:

  • CAN ID: the ID of the required device.
  • Frame Type: select Standard Frame (2.0A, compatible with the CANopen protocol). Extended Frame (2.0B) is also available and is compatible with the J1939 protocol.
  • Transform Parameters: choose the Modbus option.

Finally, click Save Device Parameters, then Restart Device. The next time the device needs to be configured, use the current baud rate, parity bit, and other active values to open the serial port — not the factory defaults.

Figure 5: Setting up RS232/485/422 to CAN conversion parameters.
  1. After the restart, check which LEDs are active on the converter. If the device is working correctly, the PWR LED lights up and the RUN LED blinks.
Figure 6: PWR and RUN LEDs when the device is functioning correctly.

2.2 Connection with Rheonics SME

Disconnect the USB-to-RS485 converter from the device. Using the wiring diagram below as a reference, connect the SME to the converter. The Rheonics SME ships with Modbus RTU enabled and configured with the default settings listed in Table 1. These settings can be changed in the Rheonics Control Panel (RCP). At this point, the Rheonics SME and converter can be integrated into a CAN network.

→ See: Modbus Organization partnership with Rheonics and Connecting Modbus RTU (RS-485) outputs for more information on Modbus RTU configuration.
Figure 7: Wiring diagram of RS232/485/422-to-CAN converter to Rheonics SME.

3. Testing the Conversion Using a USB to CAN Interface

The converter has two connectors: a USB Type-A port and a DB9 connector. To configure the interface, connect the USB port to the PC — this powers on the device. To configure the CAN channel, download the Kvaser driver for the interface model and the CanKing 7.5 software from the official Kvaser site [2].

Figure 8: Connection diagram for USB-to-CAN interface configuration and usage.

3.1 Configuration in CanKing 7.5.0 Software

  1. Select New Project.
Figure 9: Creating new project.
  1. In the Source menu, select CAN channel.
Figure 10: Creating CAN channel.
  1. If the driver is installed correctly and the device is connected, the software identifies the interface model automatically. Name the channel and select the bus speed configured in WS-CAN-TOOL — 250 kbit/s for this application — then create the channel.

Figure 11: Setting up CAN channel parameters.
  1. Create a Traffic Generator block in the Source menu.
Figure 12: Creating a Traffic Generator.
  1. Configure the CAN parameters as follows:
    • Constant Identifier: enter the CAN ID value set in WS-CAN-TOOL.
    • Interval: 3000 ms for this application (user-editable).
    • Data Length: 6 bytes. The software doesn't need the CRC bytes used in the Modbus RTU Command and Response Examples article, since the temperature median value is being requested here.
    • First Byte: 00, not 01 — the Modbus conversion mode treats this first byte as an indicator of whether the message is segmented, not as a device address.
Figure 13: Example of command for requesting data.
Figure 14: Setting up the CAN message parameters.
  1. Create a Workspace to view the sent and received data.
Figure 15: Creating a Workspace.
  1. In the Select View menu, click Message Trace.
Figure 16: Creating Message Trace.

3.2 Connection with RS232/485/422-to-CAN Converter

Using the wiring diagram below, connect the DB9 port to the converter.

Figure 17: Wiring diagram of USB-to-CAN interface to RS232/485/422-to-CAN converter.

4. Rheonics SME Data Integration

Once all devices are connected and configured, click the Start button to begin communication with the SME. Data received in CanKing appears in HEX format, so it must be converted before comparing it with RCP measurements.

Figure 18: SME data visualization using CanKing software.

After conversion, the hexadecimal value 0x4185002F (last 4 bytes) equals 22.73 in decimal — confirming the data was requested and transmitted successfully, with no communication or conversion errors. This process can be tested with different parameters and registers, as described in Modbus Input Registers.

Still have questions about integrating your Rheonics SME with a CAN network? Contact Rheonics Support for further assistance.

Further information

Modbus Communication

5. References