M-Bus (Meter Bus) is a communication protocol for data exchange. M-Bus is a European Standard (EN 13757) that describes remote meter reading. It defines a physical layer for meters to consume power from the communication line.
Metering devices include a unit load to define the amount of current consumed, where one unit load is defined as a current of 1.5 mA. If a device requires more than one M-Bus load, it is printed at the metering device itself (xUL, where x is an integer number) and in device documentation.
M-Bus is a reliable communication bus and can cover distances of several kilometers. Because of the physical communication definition and possibility to supply power to the metering devices, an estimation of distances for bus segments depends on resistance and capacitance of cable and devices and is complex. The European Standard EN 13757-2 contains several examples depending on communication speed, distance, cable diameter, and number unit loads, see Table 1. If the number of required M-Bus unit loads or distances exceeds the specification of the level converter, you can use an M-Bus repeater to increase number unit loads and distances.
Metasys network engines can integrate an M-Bus protocol application layer but do not provide the physical M-Bus connectivity. See Network Engine Commissioning for M-Bus Vendor Integration Application Note (LIT-12013149) . For connection of NxE/SNx to the M-Bus network, you require an external M-Bus level converter.
In Europe and Asia, three level converters and two M-Bus repeaters are available to use with Metasys SNC and SNE network engines.