MODBUS Client

The MODBUS Client Plugin for OXYGEN is an extension for the popular OXYGEN measurement software to read data from Modbus devices. This allows the user, to use Modbus devices as data sources.

Features:

  • Reading Data from Modbus TCP Devices

  • Support of various data types (int, float, …)

  • Support of different scaling modes (linear and sunspec)

  • Independent definition of register and endpoints for simple reuse

  • Per endpoint definable refresh rate

Known Limitation:

  • No support of RTU

Concept

  • TCP Endpoint: An Endpoint is a Node with a unique IP address and port an can hold one to many devices.

  • Device: Is the representation of a physical modbus device. It is described by its UNIT_ID.

Datatypes and scaling

The Plugin supports two different types of data scaling:

  • const_linear: Linear scaling with factor and offset

  • sunssf: Variable scaling with another register value, compatible with the sunspec scaling (INT+SF)

Constant linear scaling

Typically, the linear scaling is used for converting the binary data to physical values. Output Value = read_value * scale + offset

Example:

read_value = 2314
scale = 0.1
offset = 0
output_value = 2314 * 0.1 + 0.0 = 231.4

SunSpec scaling

Within Solar inverters, the sunssf scaling is often used. It is defined by Sunspec. In this case, a separate register is read, which holds the actual scaling value. This specific value is an ex-ponent of 10. Output Value = read_value * 10^scale_reg_val

Example:

read_value = 2314
scale_reg_val = -1
output_value = 2314 * 10^-1 = 231.4

Activate a MODBUS client

  • Start OXYGEN (if not already started)

  • Open the channel list

  • Press “+” add channel

  • Select MODBUS Receiver in the Data Input section (see in Fig. 1)

MODBUS_set_client

Fig. 1 Activate and MODBUS client in OXYGEN

  • Load a XML Document with the Device and Network description

  • Adapt settings if necessary (e.g. load only selected channels, change IP-address, Unit Id)

  • Click “Add”

The following modbus client properties (see in Fig. 2) are loaded based on the imported .xml.

MODBUS_set_client_properties

Fig. 2 Imported modbus client properties

  • Host IP

  • Port

  • Polling rate - polling rate of the modbus client.

  • Response timeout - time before a disconnect warning is triggered. Modbus: unable to connect to ‘’IP-address’’