What is the difference between M-Bus and Modbus ?
M-Bus (“Meter-Bus”) is a new European standard for remote reading of heatmeters and it is also usable for all other types of consumption meters as well as for various sensors and actuators.
With its standardization as a galvanic interface for remote readout of heat meters this bus wins a great importance for the energy industry as relevant users.
The remote reading of heat meters can take place in different ways, beginnig with the classical method – manual reading by the personnel of the providers – up to the remotely controlled collection of all the meter values for a complete housing unit. The latter is a logical continuation/extension of the technical development of consumption meters and is realizable with the help of the M-Bus.
Here some substantial characteristics of this interface are mentioned regarding their new possibilities:
The data (e.g. heat consumption) are read out electronically
At one single cable, which connects to a building controller all consumption meters of a housing unit can be attached
All meters are individually addressable
Apart from the availability of the data at the controller also a remote reading is possible
A set of advantages arise, both for the supply enterprises, and for their customers:
The reading is fast and avoids reading errors
The data being present in machine-readable form makes the further processing easier.
A remote readout saves personnel expenditure, avoids unnecessary penetration into the private sphere of the inhabitants and permits to mount meters in places which are difficult to access.
Short reading intervals are possible, which reduces the problems with tenant change or tariff amendments
Due to the short reading intervals statistical data can be obtained, which can be used as a base for network optimization
The standardisation of the m-bus results in further technical possibilities. In particular devices of different manufacturers can be operated on the same bus; the users are free therefore in the choice of the manufacturer. On the other hand, a stimulation of the market can be expected, also regarding other m-bus based counters, so that with the very variable configuration options even difficult problems can be solved.
In the development of the m-bus also economic and technical aspects of the interface have been considered, that are relevant for everyday use.
These are essentially:
Large number of connectable devices
Possibility for network expansion
Fail-safe characteristics / robustness
Minimum power consumption in the meters
Acceptable transmission speed
None of the many already existing bus systems was able to fulfill all these constraints. Now with the M-Bus as a new standardized interface for the reading of consumption meters, an optimal compromise between price and performance can be offered.
For more information, please visit http://www.m-bus.com/
Modbus is an open serial communications protocol. It was developed in 1979 for use with Programmable Logic Controller (PLC) devices, and is now widely used for connecting many types of industrial electronic devices connected on different types of networks.
Modbus is used extensively for a number of reasons, including the following:
- Modbus is an open-source protocol, meaning that it can be included in a wide range of device types from any equipment vendor
Modbus uses a simple message structure, making it less difficult to deploy. Modbus might require just a matter of days to implement, a big improvement over the months of work that might be required to learn and deploy other protocols
Modbus moves raw words and bits, and it has very few restrictions
Modbus Utilizes Serial or Ethernet Connections
The Modbus protocol can be used with two types of serial connections, both RS-232 and RS-485. Some versions of Modbus can also be sent over Ethernet or TCP/IP. These Modbus communications are packed as a single bit, or 16-bit word packets.
Modbus is not part of a physical layer on a network, as with some other protocols. Modbus communications are transferred on top of physical layers, enabling it to be utilized on many different types of networks. This non-physical layer property makes Modbus an application layer protocol.
Two Variants of the Modbus Protocol
There are two variants of the Modbus protocol that travel over serial connections. One of these is Modbus RTU. This variation is more compact, and uses binary communication. In this format, data transmissions are always followed by a cyclic redundancy check checksum, which are used to detect transmission problems.
The second variant is Modbus ASCII. This version is more verbose, and it uses hexadecimal ASCII encoding of data that can be read by human operators. A different type of checksum, the longitudinal redundancy check checksum, takes place after Modbus ASCII data transmissions. Modbus ASCII is the less secure of the two variants.
As it is also less efficient than Modbus RTU, operators should only utilize Modbus ASCII for the transmission of data to devices which do not support the Modbus RTU format. Modbus ASCII can also be useful when RTU messaging cannot be properly applied.
Modbus is a “Master/Slave” Protocol
Modbus communications take place between a centralized master and up to 247 connected electronic devices on a single network. The design is commonly referred to as a “master/slave” protocol, because the system “master” requests information from connected devices, which are referred to as “slaves”. Slave devices only send information to the master in response to these requests, and do not operate autonomously. The master can also write information to the slave devices, but the slave devices cannot write information to the master.
When a slave device transmits a communication to the Modbus master, it begins the message with a unique address identifier. This is a number ranging from 1 to 247. This enables the master to identify which specific device is responding with the requested information.
For more detailed information, please visit https://www.automation.com/library/articles-white-papers/fieldbus-serial-bus-io-networks/introduction-to-modbus