EMU M-Center: M-Bus and Modbus data logger

The M-Center is a data logger and protocol gateway for the 35 mm DIN rail. It reads meters over M-Bus, Modbus RTU and Modbus TCP, stores the values locally and passes them on to control systems, billing software or the cloud.

Meters with M-Bus to EN 13757, Modbus RTU over the two RS-485 interfaces, and devices with Modbus TCP on the network. Drivers are stored for common third-party makes, so that after the scan the devices deliver values with no manual mapping.

230 volts AC with at least 1 ampere, or 24 volts DC with at least 4 amperes. The higher current draw at 24 volts comes from the M-Bus supply being drawn from the same source.

It states how many meters the licence unlocks. An M-Center 20 reads 20 devices. Meters connected beyond that are not read, but still load the M-Bus with their current. That has to be taken into account in the bus load calculation.

It is 162 millimetres wide and weighs around 400 grams. The permissible temperature range is 0 to 55 degrees Celsius; it is installed in the distribution board on the DIN rail.

In Switzerland. Development, PCB assembly, final assembly and testing all take place here, and technical support comes from Baar in the canton of Zug.

No. Operation runs entirely through an HTML5 web server in the browser, locally in the distribution board or remotely. No installation on the laptop is needed.

The LAN port obtains its address by DHCP and can be reached through the host name mcenter-<MAC>.local. There is also a service port with the fixed address 169.254.254.1, through which the device stays reachable even without a DHCP server.

User name admin, password 123. This password has to be changed on first access. In installations with remote access that is the single most important measure against unauthorised access.

By an automatic scan for primary and secondary addresses. 2400 baud is recommended for the scan, because practically all M-Bus devices handle that rate and it offers the greatest range.

The read timeout on the M-Bus is 3000 milliseconds. If a device does not answer within that time, it is marked as unreachable and the cycle carries on.

Admin, operator and user. This separates who may configure, who may operate and who may only view data – useful where an operator and a service provider share the same installation.

Up to 250 M-Bus slaves through the integrated level converter. The supply is decisive: at 230 volts AC the master delivers 450 milliamperes continuously and 600 milliamperes at peak, at 24 volts DC up to 1.6 amperes. A standard slave draws around 1.5 milliamperes.

Number of devices times unit load. A device with one unit load draws 1.5 milliamperes; some meters take two or more loads. The total has to stay below the master’s continuous rating, with a reserve for the switch-on moment.

Up to 5000 metres at 100 nanofarads per kilometre and a maximum loop resistance of 90 ohms. J-Y(ST)Y 2×2×0.8 millimetres is recommended, screened where possible. The connections are polarity-independent.

With a 2×0.8 millimetre cross-section and 2400 baud, around 1 to 1.5 kilometres is realistic. The actual range depends on baud rate, cable capacitance and the number of devices.

Star, tree and line, including mixed. A ring topology is not permitted, because the return path short-circuits the bus and no longer allows unambiguous signal propagation.

First check the bus load, then the device’s baud rate and the secondary address. The most common causes are an overloaded supply, a device with a differing baud rate, and duplicated primary addresses.

The M-Center has two RS-485 segments with up to 32 devices each. Splitting across two segments helps to separate long cable runs and differing baud rates.

1200 metres total length at most, with the main segment not exceeding 700 metres. Stubs should be kept short, because they cause reflections.

A 120 ohm termination resistor goes at the far end of the segment. At the M-Center itself the termination is already present internally and must not be added again.

Yes. The M-Bus and the two RS-485 segments work in parallel. Mixed installations with M-Bus heat meters and Modbus electricity meters are the normal case.

MQTT with configurable topics and QoS as well as TLS, BACnet IP with BBMD function, OPC UA, Modbus TCP, an API, (s)FTP and email. CSV, JSON and Excel are available as data formats. MQTT, BACnet IP, OPC UA and the Modbus TCP conversion require a licence.

The M-Center maps the meter values it has read onto registers of its own. The register list can be viewed and exported in the web interface. A typical entry is register 6004, function code 0x03, data type uInt64, unit Wh, OBIS code 1-0:1.8.1.

Every object handed over receives an instance number through which the control system addresses it. If the control station is in a different subnet, the BBMD function takes over the forwarding of broadcast messages.

MQTT 3.1, 3.1.1 and 5. Topic structure and QoS are freely configurable, and the connection to the broker can be encrypted with TLS.

The read cycle can be set from 15 minutes to 672 hours. Short cycles run on a fixed grid at the full quarter-hour, i.e. at :00, :15, :30 and :45, which keeps the values of different devices comparable in time.

Following the pattern <device ID>-<secondary address>-<yyyyMMddhhmmss> with the extension of the chosen format, that is csv, json or xlsx. That simplifies automatic further processing in the target system.

The free exporter is limited to 3 devices with 10 values each. Larger installations need the corresponding licence.

MQTT, BACnet IP, OPC UA and the Modbus TCP conversion, as well as the number of devices that can be read. Which licences an installation needs follows from the meter list and the target system.

Eight inputs and outputs that are configured in pairs. They need a supply of their own of at most 36 volts DC and record, for instance, pulse outputs from meters with no bus interface.

Class A with 5 to 14 volts DC and class B with up to 25 volts DC. The class has to match the connected meter, otherwise pulses are not detected or are counted twice.

It stores load profiles in the M-Center. The function requires EMU Professional II meters, because only these hold the load profile in the device. If the connection fails, the M-Center retrieves around eight days of missing data per hour.

Through Device Management in Joulio-Web. For this the M-Center connects to the update servers menderv4.joulio.energy, mender.joulio.energy and mcenter.update.joulio.energy over ports 80, 443 and 9000. These connections have to be allowed in the firewall.

Device Management in Joulio-Web can create backups of the configuration and restore them onto a replacement device. A backup is recommended before firmware updates and before larger changes.

The manual describes a recovery over USB. Beforehand the LED codes on the front show which state the device is in and help to narrow things down.

Yes, optionally through a built-in LTE modem with a SIM card. The connection state is shown in the interface. That is the usual solution for installations with no network connection on site.

Change the default password, assign user roles, enable only the services needed, run MQTT with TLS, and do not expose the web interface unprotected to the internet. For remote access a VPN is the safe route.

Yes. It reads the individual parties’ sub-meters, stores the values and hands them over for billing, for instance to Joulio-Web or a third-party system. The M-Center does not produce the bill itself.

Several end consumers appear to the grid operator as a single end consumer. The legal basis is Articles 17 and 18 of the Energy Act in the version in force since 1 January 2025. The association organises the internal allocation itself.

An LEG under Articles 17d and 17e of the Electricity Supply Act has existed since 1 January 2026. Every participant is equipped by the distribution grid operator with a smart metering system, which forms the basis for billing towards the grid. The M-Center supplies the values behind the connection point.

Yes, if their values are used for billing. Electronic active energy meters must be re-verified every ten years under Article 6 EMmV. Responsibility for this lies with the operator of the installation, not with the distribution grid operator.

Yes. Drivers are stored for widely used M-Bus devices, which deliver values directly after the scan. Devices with no driver can be mapped manually through the raw data of the M-Bus telegram or through Modbus registers.