M-Bus A network for measuring devices

M-Bus (Meter-Bus) is a European standard for remote reading of measuring devices. M-Bus is predominantly used in buildings, for example in electricity meters, gas meters, water meters or other types of consumption meters. It is also used for various sensors and actuators.

The data from the measuring devices are transported via M-Bus to a reading point. This can be either a manual reading station for one specific meter, or a collected reading central for several values from a building.

Benefits of using M-Bus
The main benefit of M-Bus is that it enables remote reading of metering devices which otherwise can be hard to reach. It also makes it possible to gather data from several measuring devices into a central SCADA system for example. This can help building owners streamline their energy consumption substantially.

History
M-Bus was developed by Professor Dr. Horst Ziegler of the University of Paderborn in cooperation with Texas Instruments Deutschland GmbH and Techem GmbH. The concept was based on the ISO-OSI Reference Model, in order to realize an open system which could utilize almost any desired protocol.

M-Bus and the OSI model
Since the M-Bus is not a network, and therefore does not need a transport or session layer, the levels four to six of the OSI model are empty. Therefore only the physical, the data link, the network and the application layer are provided with functions.

OSI Model Data unit Layer Standard
Host layers Data 7. Application EN1434-3
6. Presentation Empty
5. Session Empty
Segment/Datagram 4. Transport Empty
Media layers Packet 3. Network Optional
Frame 2. Data link IEC 870
Bit 1. Physical M-Bus

M-BUS FACTS
Network Type:    Serial Master/Slave communication system
Topology:    Star and bus topology
Installation :    Two-wire standard telephone cable (JYStY N*2*0.8 mm)
Data Rate :    300 - 9600 Baud
max. Stations:   

Up to 250 slaves

Data :    252 Byte per telegram
Network Features :   This bus fulfills the special requirements of remotely powered or battery driven systems, including consumer utility meters. When interrogated, the meters deliver the data they have collected to a common master, which can, for example, be a hand-held computer, connected at periodic intervals to read all utility meters of a building.

An alternative method of collecting data centrally is to transmit meter readings via a modem. Other possible applications in home electronic systems for the M-Bus are alarm systems, flexible illumination installations and heating controlling.

User Organization:   M-Bus Usergroup

Source: M-Bus.org and Wikipedia.
HMS solutions for M-BUS