What is Wireless M-Bus?
Wireless M-Bus is the European radio standard water, heat and gas meters and heat cost allocators use to send their readings. It is why a meter in a basement can be read without anyone going down to it.
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The standard
Wireless M-Bus (also written wM-Bus, wMBus or Wireless MBUS) is defined in EN 13757-4. It is the radio counterpart of wired M-Bus: the same data format for meter readings, carried by radio instead of a two-wire bus.
In Europe it runs mostly at 868 MHz, a licence-free band. A meter wakes up, sends a short telegram with its current values and goes back to sleep, which is how a battery in a water meter lasts for its whole service life.
Modes: S, T and C
The standard defines several modes, and a meter uses one of them. S mode (stationary) sends rarely, at 868.3 MHz. T mode (frequent transmit) sends often, at 868.95 MHz, and is common in walk-by and drive-by reading. C mode (compact) uses the same frequency with a more efficient encoding, so a telegram is shorter and the battery lasts longer.
The number after the letter says which way data flows: T1 and C1 meters only transmit, T2 and C2 meters also listen for a short moment after each telegram. For fixed remote reading, one-way T1 and C1 meters are by far the most common.
OMS: making meters from different brands interchangeable
The Open Metering System (OMS) specification builds on EN 13757 and pins down the choices the standard leaves open: telegram layout, security profiles and how values are described. An OMS meter from one manufacturer can be read by any OMS receiver, which is what makes a mixed building of Kamstrup, Diehl and Axioma meters readable by one gateway.
Encryption and AES keys
Most meters encrypt their readings with AES-128. The telegram header — manufacturer, meter ID, type — stays readable, so a receiver knows which meter it heard, but the values need the meter’s own key. The key comes with the meter from the manufacturer or supplier and is entered once in the reading system.
In the Metbox platform the key is stored per meter; the gateway forwards the telegrams and the platform decrypts and decodes them, so a new key never means touching the hardware.
From walk-by to fixed remote reading
The same meters can be read two ways. Walk-by and drive-by reading collects telegrams with a handheld receiver on a route. Fixed reading puts a gateway in the building that listens all the time and sends every reading on over the mobile network, so the data arrives daily or hourly without a route at all.
A Wireless M-Bus gateway such as the Metbox Wireless M-Bus 230V is that fixed receiver: it hears every meter in range, of any brand, and sends the telegrams over 4G/LTE. Where there is no mains socket, the battery version does the same over NB-IoT.
Which meters speak Wireless M-Bus?
Most modern European water and heat meters and heat cost allocators ship with a Wireless M-Bus radio or offer it as an option, and many gas meters do as well. The list of Wireless M-Bus meters we have tested shows the models Metbox reads today, with the connection options for each.