M-Bus to MQTT gateway for meter data

Key facts

The M-Center is M-Bus master and MQTT client in one device and reads up to 250 M-Bus meters.

MQTT 3.1, 3.1.1 and 5 are supported, optionally with TLS and with QoS 0, 1 or 2.

Every value gets its own topic, either by register number or by OBIS code.

MQTT is enabled by licence, article number 210.300.03.

BACnet IP, Modbus TCP, OPC UA and the file export keep running in parallel.

What an M-Bus to MQTT gateway does

M-Bus to EN 13757 is a two-wire bus on which a master polls the meters one after the other. MQTT works the other way round: a client publishes messages to a broker, and every system that needs the values subscribes to them there. A gateway connects both worlds. It polls the meters at the set interval and publishes the values to the broker.

The M-Center takes on both roles and also stores the values in its internal 16 GB memory. If the broker fails, the readings remain in the device. The M-Bus readout interval is 15 minutes by default and can be set between 15 minutes and 28 days, individually for each meter if required.

How the topics are structured

The structure is fixed. Only the prefix at the start can be chosen freely:

<prefix>/emu/mcenter/<MAC of the M-Center>/meterreading/<meter serial number>/byregister/<register number>
<prefix>/emu/mcenter/<MAC of the M-Center>/meterreading/<meter serial number>/byobis/<OBIS code>

Part	Meaning	Example
Prefix	optional, set in the MQTT settings	house-a
emu/mcenter	fixed part
MAC	serial number or MAC address of the M-Center	10:2C:EF:12:34:56
meterreading	meter readings; configuration data appears under config/meterconfig
Serial number	serial number of the meter	24201234
byregister / byobis	value by register number or by OBIS code	0 or 1-0:1:8:1

For topics by OBIS code, enter the OBIS code for the required registers in the M-Center. This pays off as soon as meters from different manufacturers are involved: the import tariff 1 reading then ends up under the same topic ending for every meter, regardless of where the manufacturer places it in the telegram.

Before processing the data in a target system, look at the messages with an MQTT client, for example MQTT Explorer or mosquitto_sub -v -t '#'. This shows you the exact path and the content of the messages on your own broker.

Settings in the M-Center

Host name and port of the broker
User and password if the broker requires a login
Prefix for all topics, optional
MQTT version 3.1, 3.1.1 or 5
TLS for an encrypted connection. The «Insecure connection» option disables the check of certificate and host name. We recommend it for tests only.
Quality of Service 0, 1 or 2

Commissioning step by step, from the service port to the first message on the broker, is shown in our M-Center commissioning guide.

Which QoS level fits?

QoS	Delivery	When it makes sense
0	at most once, without acknowledgement	sufficient for most installations, lowest network load
1	at least once, with acknowledgement	when no message may be lost; duplicates are possible
2	exactly once	when the target system cannot handle duplicates; more network load

As the M-Center also stores all values, QoS 0 is usually enough for monitoring and dashboards. For billing we recommend the file export or reconciliation with the stored values.

Order numbers

Item	Article number	Shop
M-Center for 20 M-Bus devices	210.000.00	Shop: EMU M-Center 210.000.00 →
M-Bus licence 20 → 60 devices	210.020.01	Shop: M-Center M-Bus-Lizenz 20 → 60 Geräte 210.020.01 →
M-Bus licence 20 → 120 devices	210.020.02	Shop: M-Center M-Bus-Lizenz 20 → 120 Geräte 210.020.02 →
M-Bus licence 20 → 250 devices	210.020.03	Shop: M-Center M-Bus-Lizenz 20 → 250 Geräte 210.020.03 →
MQTT licence	210.300.03

Order online in the EMU Metering shop.

Frequently asked questions

Which MQTT brokers does the M-Center work with?

With any broker that supports MQTT 3.1, 3.1.1 or 5, locally in the building or in the cloud. You enter host name, port and credentials in the web interface of the M-Center.

Does the M-Center also read meters from other manufacturers?

Yes. The M-Center finds M-Bus meters from other manufacturers with the search by primary or secondary address and reads them using device drivers. Drivers can be imported, exported and adapted.

How often does the M-Center send the values?

Once per readout interval. The default is 15 minutes. Intervals from 15 minutes to 28 days can be selected, individually for each meter if required.

Do I need a cloud for MQTT?

No. The broker can run on the local network, for example on a server or on the home automation system. The M-Center only needs a network connection to the broker.

Can I use MQTT and BACnet at the same time?

Yes. The M-Center reads once and serves all target systems in parallel: MQTT, BACnet IP, Modbus TCP, OPC UA and the file export. Each protocol needs its own licence.

M-Bus to MQTT: meter data straight to your broker