Test: NKE-Watteco ModBus Bridge

December 12, 2018

The nke Watteco ModBus RS485 Bridge collects data from ModBus RTU devices and transmits them to a LoRaWAN network. The Bridge can also send control data to connected Modbus devices and thus influence their behavior.

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Product name: MODBUS RS485 BRIDGE LORAWAN
Category: Sensors
Manufacturer nke Watteco
Rue Gutenberg
ZI Kerandré
56700 Hennebont

 

The most important features at a glance

  • Class A LoRaWan device
  • configurable transmission cycle
  • supports ABP and OTAA
  • Physical interface: RS485 – 2 cores – protection against overvoltage
  • RS485 terminator can be activated on the board
  • RS485 data rate (kbps) 1.2 / 2.4 / 4.8 / 9.6 / 19.2 / 38.4 / 57.6 / 115.2
  • RS485 protocol: Mode RTU, Bridge works as ModBus master
  • Can manage several devices connected via RS485
  • All ModBus parameters can be configured via downlinks
  • Periodic wake up to read/write ModBus register
  • Optional: wake up via external signal to read/write ModBus register
  • Buzzer for auditory feedback to the user during configuration
  • Internal antenna

Unboxing: housing and processing

Like most nke Watteco sensors, the bridge sits in a sturdy and fire-retardant UL94-V0HB / IP61 enclosure. The dimensions are 84x82x85mm. The housing can be mounted on a standard DIN rail using the 2 screws supplied. A 3.6V / 3600mAh lithium battery is integrated. The bridge can also be operated via external 9V-24V 100mW. connections

Connections

Connection of the NKE Modbus Bridge

Two terminals are available for connection with the ModBus device. Here, the two wires of the RS485 interface are connected. If required, a terminating resistor can be activated. In addition, there is an on/off switch on the board as well as a magnetic contact for remote activation from outside.

Configuration and operation

The bridge can be configured completely via LoRaWAN downlinks – as it is usual with nke Watteco. The Bridge acting as the ModBus Master bridge allows multiple devices connected to the RS485 link to be managed. There are 8 possible configurations of the ModBus device address, ModBus registers and function codes.

As soon as the configuration has been completed, the bridge sends the stored ModBus request to the corresponding ModBus address in order then to send the received response data (ModBus Answer Frame) via LoRaWAN to the server. This happens in the stored intervals. In return, the server can also downlink the bridge to describe a register/coil/inputs of a Modbus device.

In both cases, the bridge does not interpret the ModBus request/response but transmits the data between the connected device and the server.

The standard communication parameters of the bridge are:

  • 9,600 Bauds
  • 8 Data bits
  • 1 Stop bit
  • Parity: none

If you want to change the speed of the RS485 interface to 115200 Bauds, send the following command to the bridge:

0x 11 05 80 06 00 00 22 11 52 00

Whether the communication parameters are configured correctly and whether the physical connection to the ModBus device works can be tested quickly with a direct reading of registers. With the following command, the Modbus device with device ID “01” reads out the first 3 registers from address 200:

0x 11 50 80 07 00 06 01 03 00 C8 00 03

The answer should look like this:

0x 11 01 80 07 00 01 00 41 09 01 03 06 08DB 0411 0414

wherein the marked bytes contain the values of the respective registers.

If the query was successful, it can now be stored persistently in the bridge as follows:

0x 11 05 80 07 00 00 41 06 01 03 00 C8 00 03

Now you have to set an interval for the automatic reports. For an automatic reporting interval of 5 minutes, the following command is sent:

0x 11 06 80 07 00 00 01 41 80 02 80 05 01 00

The bridge’s response to successfully saving the interval looks like this:

0x 11 07 80 07 00 00 00 01

From now on, the bridge will read the first 3 registers from address 200 every 5 minutes and send it to the server. An example payload of these automatic messages looks like this:

0x 11 0A 80 07 00 01 41 09 01 03 06 08D9 0410 040F

where the marked bytes contain the values of the 3 ModBus registers. In this case decimal: 2265 from register 200, decimal 1040 from register 201 and decimal 1039 from register 202.

The configuration examples shown here utilize one of 8 possible memory locations. Another 7 configurations with different ModBus requests and intervals can be set.

Conclusion

The bridge meets our expectations for the nke Watteco sensors. The case is stable and functional. The device could be configured as described in the documentation and sent the desired register values from our connected ModBus device to the server at regular intervals. The data format used is flexible but requires technical knowledge to be able to create ModBus requests yourself. We really like the support of other serial devices on the roadmap of the MoBus Adapter. The only thing that we found missing is the optional connection for an external antenna.

Reference

SmartMakers is an official nke Watteco distributor.
The device is now available in our IoT LPWAN Shop.

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