Protocol description

M bus(Meter-Bus) - communication protocol (European standard EN 1434/IEC870-5, EN 13757-2 physical and data link layers, EN 13757-3 application layer), based on the standard "client-server" architecture. One of the common data transfer protocols for a number of specific electronic devices, such as electric energy meters (electricity meters), thermal energy meters (heat meters), water and gas meters, some actuators, etc. Data is transmitted to a computer station (server) directly or through M-Bus bus hubs, signal repeater amplifiers.

The difference from the Modbus protocols, the RS-485 standard - other levels of logical signals, low data transfer rate (300 - 9600 bps), low requirements for the communication line, the ability to power devices from the M-Bus line, there are no polarity requirements. The protocol, due to a number of features, is not an industrial protocol, it is used only in those devices where low speed and even the loss of part of the transmitted data are not critical. The advantages of the protocol include minimal requirements for equipment, communication lines, simplicity and speed of implementation, installation, which makes it low-cost and economically attractive.

Some parameters of the M-Bus protocol

• transmission mode half duplex;
• data transfer rate 300-9600 bps (compatible with standard UART port speeds of PCs and microcontrollers, which are the source and receiver of data);
• logical unit +36V, current not more than 1.5 mA;
• logic zero 12..24V, current 10-11mA;
• cable type standard telephone (JYStY N*2*0.8 mm);
• line capacitance no more than 180 nF, resistance up to 29 ohms;
• transmission range, in a standard configuration, up to 1000 meters;
• the range of the slave device to the signal repeater is up to 350 meters;
• the number of devices on the line is up to 250.

A logical one is transmitted at a level of 36V, with the possibility of consumption from the current line up to 1.5 mA, a logical zero is transmitted at a voltage of 24V on the master device. To transfer a logical zero, the slave devices increase the current consumption to 10-11mA, the device detects a high current consumption and a decrease in voltage in the master line as a logical 0. In this, the transmission protocol is similar to 1-Wire, both in the way of data transmission and the ability to power devices from lines.

Notes on the term M-Bus

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See what "Meter-Bus" is in other dictionaries:

Meter bus- For similarly named bus technologies, see MBus. M Bus (Meter Bus) is a European standard (EN 13757 2 physical and link layer, EN 13757 3 application layer) for the remote reading of gas or electricity meters. M Bus is also usable for other types… … Wikipedia

Bus- Bus … Deutsch Wikipedia

BUS- Wappen Deutschlandkarte ... Deutsch Wikipedia

Teplopribor group of companies (GC) (Teplopribor, Prompribor, Teplokontrol, etc.)- these are devices and automation for measuring, controlling and regulating the parameters of technological processes (flow metering, heat control, heat accounting, control of pressure, level, properties and concentration, etc.).

At the price of the manufacturer, products are shipped both of our own production and of our partners - leading factories - manufacturers of instrumentation and automation, control equipment, systems and equipment for managing technological processes - process control systems (much is available in stock or can be manufactured and shipped as soon as possible) .

Dispatching with M-Bus and RS485

Below are two comparative examples of specifications for the dispatching of heat meters in an apartment building via a wired circuit using M-Bus and RS485 interfaces:

1. Commercial offer with M-bus

The object is an apartment building for 53 ultrasonic heat meters TSU-Du20:
1 entrance 10 floors, 1st floor non-residential premises, from floors 2 to 9, 6 apartments each, 2 water meters per apartment, 6 apartments on the 10th floor, 2 water meters per apartment

Type	Qty	Price per unit, rub.	Amount, rub.
Ethernet converter	1	9 350,00	9 350,00
IP power supply	1	3 630,00	3 630,00
Mbus / RS485 converter	1	7 160,00	7 160,00
Total:			20 140,00
Including VAT 18%			3 072,20

Total amount for CP with PC: 410,662.00 rubles.

Mbus based scheduling

2. Commercial offer with RS485 for the object

The object is an apartment building for 53 ultrasonic heat meters TSU-Du20:
apartment building, 1 entrance 10 floors, 1st floor non-residential premises, 2 to 9 floors, 6 apartments each, 2 water meters per apartment, 6 apartments on the 10th floor, 2 water meters per apartment.

Type	Qty	Price per unit, rub.	Amount, rub.
Ethernet converter	2	9 350,00	18 700,00
IP power supply	2	3 360,00	7 260,00
Total:			25 960,00
Including VAT 18%			3 960,00

Total amount for CP with PC: 451,462.00 rubles.
* — The system unit (computer-PC) is supplied at the request of the customer.

RS485 based scheduling

More information about interfaces and protocols

1. Difference between M-Bus and ModBas

M-Bus interface (Meter-Bus)- A physical layer standard for a field bus based on an asynchronous interface. Also under this name is understood the communication protocol used to communicate devices on this bus. The M-bus interface is mainly used for metering devices for electric energy (electric meters), thermal energy (heat meters), water and gas flow meters.

Modbus protocol is an open communication protocol based on a master-slave architecture. It is widely used in industry to organize communication between electronic devices. It can be used for data transmission via serial communication lines interfaces RS-485, RS-422, RS-232, and TCP/IP (Modbus TCP) networks. There are also non-standard implementations that use UDP.
Do not confuse "MODBUS" and "MODBUS Plus". MODBUS Plus is a proprietary protocol owned by Schneider Electric. The physical layer is unique, similar to Ethernet 10BASE-T, half duplex over one twisted pair, 1 Mbps. The transport protocol is HDLC, on top of which an extension is specified for the transmission of MODBUS PDUs.

2. Difference between RS485/RS422 interfaces from RS232 and USB

a) RS-485 interface

RS-485 interface (English Standard Recommended 485), EIA-485 (Eng. Electronic Industries Alliance-485) is a physical layer standard for an asynchronous interface. Regulates the electrical parameters of a half-duplex multipoint differential communication line of the "common bus" type.

The RS-485 standard has become very popular and has become the basis for creating a whole family of industrial networks widely used in industrial automation.
The RS-485 standard uses a single twisted pair of wires to transmit and receive data, sometimes accompanied by a braided shield or common wire.
Data transmission in RS485 is carried out using differential signals. The voltage difference between conductors of one polarity means a logical unit, the difference of the other polarity is zero.

Since the RS485/422 interfaces are implemented on differential communication lines, their noise immunity is very good. Typically, cable management with a wave impedance of 120 ohms is used. Terminating resistors must be placed at the ends of the lines. RS485 lines can be up to 1 kilometer long.

RS422 interface is a "light" version of RS485. It has reduced transmitter output currents and therefore less load capacity. Data repeaters are used to improve these parameters.

The RS485 interface implements the main principle of data exchange. It can address up to 63 ports. Strictly speaking, RS422 is a radial interface, but many equipment manufacturers supplement it with trunking and partial compatibility with RS485 (with reduced load capacity parameters).

b) RS232 interface

RS232 interface built on unipolar data transmission lines. Therefore, its performance and maximum cable length are small. RS232 is used to connect peripheral equipment to control computers. RS232 is a radial interface, so there is no concept of an address. These factors improve the efficiency of the interface in data acquisition systems and with peripheral equipment.

c) USB interface

USB (u-es-bi, English Universal Serial Bus - “universal serial bus”) is a serial interface for connecting peripheral devices to computer technology. The USB interface has received the widest distribution and has actually become the main interface for connecting peripherals to digital home appliances.

The USB interface allows not only to exchange data, but also to provide power to the peripheral device. The network architecture allows you to connect a large number of peripherals even to a device with a single USB connector.

The article is devoted to the M‑Bus communication protocol designed to build an energy accounting system, the features of the M‑Bus architectural bus, and ADFweb equipment for M‑Bus networks.

Krona LLC, St. Petersburg

With all our love for freedom, we are already accustomed to the nets that entangle us. Networks of asphalt roads on the ground and wires in the air, the invisible Internet and a data collection system in production ... And each network has its own rules that allow you not to get lost in its intricacies, but to use it for your own good.

Why is another M‑Bus protocol needed? The community of computers involved in the energy metering process needs its own "game conditions", optimized for taking readings from meters. To control the consumption of energy resources, a specific network is needed - as simple and cheap as possible, allowing the connection of many slave devices to the master device, extending over several kilometers. All these tasks are served by a special protocol.

M‑Bus (“Meter-Bus”) is a European standard for building distributed data collection systems and commercial metering of energy consumption (heat, water, gas, electricity, etc.).

The M‑Bus standard is described and approved by the normative documents EN‑1434–3 (1997), GOST R EN‑143403-2006 dated 01.09.06. Today, this standard is supported by most of the leading manufacturers of energy metering devices and is increasingly being used to solve energy metering tasks in Russia.

The main advantages of the M‑Bus standard:

Ease of building a network;

High noise immunity;

The length of communication lines is up to several kilometers;

Simple network segmentation;

A large number of metering points;

Ease of phased expansion of the network;

Passive power supply of Slave devices;

Minimum costs for installation and operation of equipment.

M‑Bus architecture

The data transmission medium for the M‑Bus standard is a copper “twisted pair”, while there are no strict requirements for the network architecture. However, the developers of M‑Bus equipment do not recommend using a “ring” architecture, as well as using looped fragments for network segments.

But the architecture of the M‑Bus network can simultaneously include elements of the “bus” and “star” typologies, which allows you to create flexible and arbitrary network structures.

The protocol for data exchange between M‑Bus network devices is based on the “one Master – many Slave” principle. Each network segment requires only one Master device that sends requests and receives responses from Slave devices (maximum 250 devices for one segment). This completely eliminates the possibility of conflict situations within the M‑Bus network segment.

All Slave devices are connected in parallel to the Master device via the M‑Bus bus (twisted pair), while the polarity of connecting devices to the bus does not matter.

Data transmission via the M‑Bus is carried out in serial mode in both directions. The bus maintains a nominal voltage level from the Master device to provide power to the Slave devices. To transmit a data bit, the Master device changes the voltage level on the bus, which is perceived by all Slave devices. After recognizing its address in the request, the authorized Slave transmits data bits, changing the current drawn from the M‑Bus. These changes are read by the Master device.

The physical length of the M‑Bus is limited by the active resistance of the wires, which, due to the current consumption of the Slave devices, reduces the supply voltage in the network as it moves away from the Master device. The data transfer rate in M‑Bus networks is limited by the electrical capacity of the bus and ranges from 300 to 9600 baud. The limit on the number of Slave devices in one network segment is determined by the power of the voltage source of the Master device and the maximum addressing capabilities - up to 250 devices.

However, despite all the advantages of the protocol, its use in the dispatcher control systems of APCS and ASKUE has been difficult until recently for the following reasons:

A small selection of equipment for building M‑Bus networks was presented on the market;

This equipment was too expensive;

There was a lack of reference and technical documentation.

This situation changed with the appearance on the domestic equipment market of the company ADFweb, which specializes in the production of equipment for working with industrial protocols. At the end of 2010, the company introduced a line of equipment for M‑Bus networks. Information about these devices is presented in tables 1 and 2.

Recently, we have been paying great attention to the issues of connecting third-party devices to the ASUD-248 system.

This is due to the logical desire to integrate engineering subsystems that ensure the operation of serviced objects within the framework of a single system of dispatch control and management.

Connected devices can be, for example, heating and ventilation controllers, heat energy and water meters, various sensors, actuators, etc.

A third-party device connects to the ASUD-248 system via a specific physical interface, data exchange occurs according to a set of rules supported by the device: protocol.

Often they operate with the concepts of M-bus, Modbus, RS-485, Ethernet, Computer network, etc. - some of which define the physical interface for connecting devices, while others define a set of data transfer rules.

When communicating with design organizations, customers who are directly faced with the task of connecting third-party devices to ASUD-248, you often encounter confusion in the definitions of "interface", "protocol" and related issues, for example:

• "Modbus is an interface?"
• "Modbus and M-bus are the same"
• "The device has RS-485 - can it be guaranteed to be connected to the ACS?" etc.

It should be noted that in essence the terms "interface" and "protocol" express the same concept - a description of the procedure for the interaction of two objects. This fact, in our opinion, in the field of the topic under consideration, can also lead to some ambiguity.

Therefore, for definiteness, we will agree under the interface to understand the physical (hardware) interface - the data transmission medium. Under the protocol - a set of described rules for data transmission over a particular interface.

RS-485

RS-485 is an interface. It defines the requirements for the communication line (cables), regulates the electrical parameters of the communication line and other parameters associated with signal transmission from one device to another.

RS-485 says nothing about the rules for communicating between devices.

Therefore, the mere fact that a third-party device has an RS-485 interface is not enough for a guaranteed connection to the ACS. It is necessary to clarify the data exchange protocol.

RS-232

RS-232 is also an interface (similar to RS-485).

Modbus

Modbus is a communication protocol widely used in industry. It defines the rules for transferring data when devices interact.

We can implement dispatching and control of almost any device if it supports this protocol.

There are several modifications of this protocol:

• Modbus RTU.
• Modbus TCP/IP.
• Modbus ASCII (currently not supported in ASUD-248).

The word "Modbus" itself does not say anything about the interface between devices.

Modbus protocol can work over RS-485/RS-232 interfaces, computer network and others.

Therefore, if it is known that the device supports the Modbus protocol, it should be clarified what physical interfaces the device has and whether they are supported in ASUD-248.

For details on connecting devices that support Modbus, see

M bus

The situation is somewhat different with M-Bus.

First of all, it should be noted that despite the consonance in Russian transcription, M-Bus has nothing to do with the Modbus protocol.

The term M-Bus can simultaneously mean both a physical interface and a data transfer protocol.

Usually, M-Bus support is implemented only in metering devices: heat meters, electric meters, water meters, etc.

If it is indicated that the meter supports M-bus, you should always clarify what is meant:

• only physical interface
• physical interface and protocol (usually)
• protocol only.

Those. the device can support the M-bus protocol, but the connection interface is, for example: RS-485. Or the device has an M-bus interface, but the device developers have implemented their own exchange protocol. In this case, to connect to ASUD-248, it is necessary to agree on the exchange protocol.

For more information on connecting M-Bus, see

The development of high technologies simplifies the work of modern services, including in the public sector. The need for a person to take readings from the meters and transfer them to the control point is completely eliminated by introducing the m-bus system, which organizes a full-fledged modern control center that receives readings automatically. The standard is approved by the normative documentation of 1997 EN-1434-3 and GOST of 2006 EN-1434-3-2006. The system has become widespread in Eastern and Western Europe. With its help, taking readings from water, heat, gas, electricity meters in residential and industrial buildings is organized.

Organization of a dispatch network for taking readings from meters

The European m-bus standard is a system for collecting data from energy metering devices. Using this standard, it is possible to organize the collection of data on the consumption recorded by meters from hundreds of devices. To do this, cable systems are laid - m-bus buses, to which the device is connected.

The m-bus system has clear advantages that allow it to be used to create appropriate dispatch networks:

• Ÿ stable transmission of information from a large number of non-initiative sources over distances up to several kilometers;
• Ÿ the system is inexpensive and does not require high costs for its installation and operation;
• Ÿ the system is easily restructured and supplemented with new data sources;
• Ÿallows to carry out a complete cut of the real state of meter readings, taking data simultaneously from many sources;
• Ÿeasy to take readings from devices located in hard-to-reach places;
• ŸThe system can be optimized according to customer requirements.

M-bus protocol

Data is transmitted over the system using an anti-jamming protocolm— bus. This protocol is used in the scheme one master - many slaves. Each network segment uses one master that sends requests and receives a response from each device. This scheme avoids network conflicts. Data is transferred over the bus in serial mode. To transmit a data bit, the master changes the voltage on the bus. Each of the devices listens for this signal, knowing which one is receiving the request. The device being accessed sends data bits in response, changing the bus voltage, which the master reads.

M-bus master

The m-bus master is the central device that controls the operation of the network. The m-bus master can be a computer or other device that saves data from devices and sends signals to read data. The m-bus master also powers the devices via a cable connection. The system can additionally include various sensors (pressure, temperature, smoke), which are also powered by the m-bus master.

Bus and hub in m-bus network

In the m-bus network it is possible to take data from a large number of devices. However, it is impossible to lay a cable from the server to each of the devices, so the network uses an m-bus hub that combines many devices and then connects directly to the dispatcher's computer or to the Internet. The hub also acts as an archiver. Without it, the m-bus system takes the current meter readings, and with the concentrator it is possible to take the readings stored by the device. This device is controlled from the dispatcher's computer and organizes the transfer of data from the devices, storing information from them and sending them on a signal to the control computer. There are hub models for 25, 60 or 250 subscribers. Hubs can act as a repeater, so it is possible to build a network of several hubs, which are subordinated to other hubs that have their own subscribers.

Data is transmitted via a copper twisted pair - m-bus bus. The device can be connected to the bus using a telephone cable 2x0.75 mm2, the length of which can be 1-5 meters. Depending on the remoteness of the dispatching computer, the RS232/USB interface is used to connect the hub to a computer or modem. Limitations on the length of transmission cables are due to the increasing resistance of the conductor, depending on the increase in length. Changes in the voltage level in the bus, which is a signal during data transmission, is difficult. The number of connecting Slave devices is also limited. The maximum number can be 250. How fast data is transmitted on the network depends on the electrical capacity of the bus. Usually it is in the range of 300-9600 bps.

Repeaters used to extend a network typically provide a visual representation of the network load. There is an indication on the devices, through which you can determine the operating mode and the possibility of adding devices. For example, on the Hydro-Center 60/250/Memory repeater, the m-bus indication can be in the following modes:

• Ÿgreen means up to half the tire load;
• Ÿyellow - the bus load exceeds 100%, the device is operational, but a warning is issued that it is unacceptable to supplement the network with more devices;
• Ÿred - this is a critical overload of the device. It needs to be rebooted and checked to see if it works.

Converters for m-bus network

The m-bus network interface uses 36V. Devices connected to the network, equipped with other interfaces (for example, RS232, RS485) operate at different voltage values, so special converters must be installed in front of them. Converting voltage levels. An example of such a device is the m-bus 10 converter. Such an m-bus converter allows you to connect up to 10 metering devices. It operates on the network as a master. The device contains indicator diodes that display the power status and data transfer mode. Also, converters are used in systems where it is necessary to convert and transfer data from a network that operates in m-bus to a system that transmits telemetry data, for example, SCADA. NPE-Modbus is used as such a device.

Meters with the possibility of data transmission over the network

Energy metering devices used in m-bus systems are equipped with a special module. Heat meters that include such a module can be of two types. In the first type, the m-bus module is built into the device; in the second type, it is optional. The module is a printed circuit board that supports the data transfer function. The presence of such a module must be noted in the device passport. The bus wires are connected to the meter screw contacts. The maximum possible diameter of connected wires is 2.5 mm, and the bus voltage is no more than 50V.