Which interface suits what?
| Interface | Transmission | Typical use | Strength |
|---|---|---|---|
| M-Bus | 2 wires, line, star or tree | Billing in residential and commercial buildings | Power over the bus, free topology |
| RS485 / Modbus RTU | 2 wires plus reference ground, line | Control cabinet, industry, PLC | robust and very widespread |
| Modbus TCP | Ethernet | Control systems, SCADA, energy management | fast, several clients at the same time |
| BACnet | Ethernet (BACnet IP) or RS485 (MS/TP) | Building management | values describe themselves |
| LoRaWAN | Radio, 868 MHz | Retrofit without cables | no cabling, long range |
The table shows typical use. Which interface is right for your project depends above all on the target system: what the control system, the billing or the cloud can accept determines the route the data takes.
Line or protocol: what does each term describe?
Many terms describe only one layer. RS485 and Ethernet define how the bits travel over the line. Modbus and BACnet define what is in the telegrams. That is why there is Modbus over RS485 (Modbus RTU) and over Ethernet (Modbus TCP), and BACnet over both routes as well.
With M-Bus and LoRaWAN, transmission and protocol belong together: M-Bus is line and data format in one, and LoRaWAN always builds on the LoRa radio technique.
Several interfaces in one project
In practice, different worlds often meet: heat and water meters with M-Bus, power meters with Modbus and a building management system that expects BACnet. A data logger and gateway such as the EMU M-Center reads M-Bus, Modbus RTU and Modbus TCP and passes the values on via BACnet IP, Modbus TCP or MQTT.
The EMU Professional II power meter is available with M-Bus, RS485 (Modbus RTU), TCP/IP (Modbus TCP and MQTT) and LoRa. So the interface can be chosen to suit the project, not the other way round.