M-Bus data logger for apartment buildings

How many meters add up?

A simple calculation for a building with 20 apartments: per apartment one electricity meter, one heat meter, one cold and one hot water meter, that makes 80 meters. Add common areas, heat pump and photovoltaics. With around 85 meters, the building falls within the M-Bus licence for 120 devices.

One M-Center or several?

The bus line is decisive. If several buildings are on one plot and a line connects the distribution boards, one M-Center is enough as long as the number of meters and the bus load fit. If no line can be laid between the buildings, each building gets its own M-Center. The target systems then receive the values from several devices.

For the bus load, calculate with 1.5 mA per meter. At 230 V AC the M-Center supplies 450 mA continuous load, at 24 V DC up to 1.6 A. For 250 meters, therefore plan with 24 V DC.

What the electrical planner needs to provide

• Space for the M-Center on the DIN rail: 162 mm wide.
• Supply 230 V AC or 24 V DC.
• A network connection with internet in the same distribution board, for data export, time synchronisation via NTP and remote maintenance.
• M-Bus cable J-Y(ST)Y 2×2×0.8 mm to all meters, in star, tree or line, not as a ring.
• For electricity meters above 100 A: current transformers and the CT version of the meter.

Data for billing

Most billing service providers accept files. The M-Center exports one file per readout interval and meter as CSV or JSON via FTP, FTPS or SFTP. With the Advanced Exporter, the data can also be aggregated and processed and sent as CSV, JSON or Excel via (s)FTP, e-mail or MQTT.

For the EMU Professional II electricity meter, the M-Center also reads the load profile memory. It reads new meters completely once, about 8 days of load profile per hour and meter at a 15-minute interval. For the timestamps to be correct, the M-Center needs access to an NTP server.

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