NetMeter-OMNI-8C: Modbus



Requires administration privileges.

The NetMeter-OMNI implements a subset of the TCP/IP variant of the Modbus specification. Both Modbus Server ("slave") and Client ("master") mode are supported concurrently.

Modbus Server Mode

A Modbus Client device, such as a PLC or SCADA system, can query the NetMeter-OMNI through the Modbus Server API. In this mode, the NetMeter-OMNI will only respond on the Ethernet network when queried by a Modbus Client. When queried appropriately by a Modbus Client, the NetMeter-OMNI is capable of reporting a complete set of data representing the state of the inputs and counters etc.

Summary of Key NetMeter Modbus Server Features:

  • Modbus TCP server compliant with "Modbus Application Protocol Specification V1.1b" and "Modbus Messaging on TCP/IP Implementation Guide V1.0b"
  • Provides a complete set of data parameters including both the analog state and pulse counter value for each channel
  • Data available in both integer and floating point formats
  • Supports 2 concurrent Modbus TCP connections
  • Operates concurrent with the NetMeter-OMNI's advanced and user friendly web interface
  • NetMeter-OMNI web interface provides an online Modbus Map to simplify configuration of PLC/SCADA/BAS systems

Full Modbus Server operation is detailed in the following document:

User Manuals
Title Type Size Date Note
NetMeter-OMNI-8C Modbus Manual 263.7KB 2013-12-02

Modbus Client Mode

Note: Firmware build 0452 or higher is required to use the Modbus Client feature.

The Modbus Client Mode allows the NetMeter-OMNI to capture data from other Modbus TCP devices and log the data for display and download.

In order to use the Modbus Client Mode, it needs to be enabled by checking the Master Mode Enable under Modbus Master.

the other configuration settings are:

  • Refresh Period: How frequently to update the data from the external Modbus device.
  • Timeout Period: How long to wait for a response. This value may need to be tuned according to the expected latency of the response. On a local network, the response should be within milliseconds. However, latency will be higher when:
    • Modbus devices are not on the immediate local network (for example: via a WAN connection on another site)
    • The Modbus device is behind bridges such as a Modbus TCP to Modbus RTU serial bridge or via wireless bridges

Modbus RTU, HART, and other protocols may be supported using bridge devices to convert them to Modbus TCP.

Modbus Client Troubleshooting

The status of the Modbus Client is viewed under Modbus Master Status. Press Update Status to refresh the status.

When operating normally a green indicator for "Enabled" should be visible.

During normal operation, the Transfer Count value will increment every time a Modbus request is made.

If the Error Count for a particular channel continues to increase, then there may be a communications problem or wrong configuration. Verify the NetMeter-OMNI configuration for that channel. Also, confirm that you are able to query the device using Modbus Client software such as Radzio (free) or others. If other software cannot access the device from the same network using the same addressing, then the NetMeter-OMNI will also be unable.

For more information about how to configure the NetMeter-OMNI to capture data from Modbus sensors, see the Modbus section of the Sensor Configuration page