In modern metering devices (meters of electric energy, heat, water, gas), as a rule, proprietary protocols are used for data transmission. As a result, metering devices of different manufacturers become incompatible, and this not only complicates the modernization of systems, the introduction of innovations, but also deprives the market of energy metering systems of “free” competition.

The solution to this problem is the use of open protocols, for example, protocols that comply with IEC 62056 (DLMS / COSEM).

Links to published parts of a series of publications

1. DLMS / COSEM is an open protocol for exchanging data with metering devices. Part 1: Overview
2. DLMS / COSEM is an open protocol for exchanging data with metering devices. Part 2: interface classes, meter model

IEC 62056 General Information (DLMS / COSEM)

DLMS / COSEM is a stack-based protocol based on the concepts of the OSI model, regulating the exchange of data between metering devices and data acquisition systems, which is based on a client-server architecture. The fundamental specifications in this standard are DLMS and COSEM. The following is a brief description of these specifications.

DLMS stands for Distribution Line Message Specification and is an application layer specification that is independent of lower layers and, as a consequence, of communication channels. This specification was developed to standardize messages transmitted over distribution lines. In this notation, this standard is published under the number IEC 61334-4-41. Subsequently, the concept of DLMS underwent changes, and the abbreviation DLMS began to be deciphered as Device Language Message Specification. The purpose of the changes was to provide a unified environment for structural modeling and data exchange with metering devices. In its current form, the standard governs: remote reading of meter readings, remote control, as well as additional services for measuring any type of energy resource (electricity, water, gas,

COSEM stands for COmpanion Specification for Energy Metering and is a specification that reflects the interface model of metering devices, providing a representation of their functionality. The front-end model uses an object-oriented approach.

According to COSEM, a meter is a physical device consisting of logical devices . Each logical device has a unique identifier (globally) called the logical name of the device . The information contained in each logical device is accessible through interface objects . In turn, access to interface objects within a logical device is throughassociation objects . An association object provides information about resources available in a logical device depending on access rights.

Each interface object consists of attributes and methods. The attributes contain information about the object and the functionality that it represents. For example, for an object representing the "Measurement of the frequency of the electric network" functionality, the attributes will display information about the frequency value (for example, 50) and the unit of measure (for example, Hz). Methods, in turn, allow you to change or view values. For example, you can reset the values ​​of certain attributes using the Reset () method, if there is one in the corresponding interface object. Methods are optionally present in interface objects.

Interface objects that have common characteristics (the same attributes and methods) make up the interface class . The converse is also true, interface objects are instances of an interface class. An interface class is identified through two parameters: class identifier ( class_id ) and version ( version ). It is worth noting that each interface object, within the framework of the logical device, is unique and uniquely identifies information independent of the manufacturer of the meter, represented by this object using the logical name (the first attribute of any interface object), the class identifier and its version.

The DLMS / COSEM standard is fully described in the so-called four color books:

• The blue book describes the COSEM object model of the meter and the object identification system;
• The green paper describes architecture and protocols;
• The yellow book addresses all issues related to testing for compliance with the standard;
• The white paper contains a glossary of terms.

These books are available free of charge to all members of DLMS UA (User Association). For users who are not members of DLMS UA, excerpts from these books are available here .

Difference of the DLMS / COSEM standard from other standards for data exchange with metering devices

The most commonly used standard for exchanging data with metering devices is the FLAG protocol, standardized for electricity metering as IEC 61107. There are also other commonly used standards:

• The Euridis protocol is used mainly in France and is focused on transmitting twisted pair information. This protocol is standardized for use in the electric power industry, standard IEC 62056-31: 1999;
• MBUS protocol for heat metering, standardized by CEN TC 294 as EN1434-3: 1997;
• IEC 60870-5-102: 1996 protocol for transmitting integrated integrated values, standardized by IEC TC 57;
• The ANSI protocols C12.18 (optical port), C12.19 (utility tables), C12.21 (communication trough telephone modems) used in North America.

Here we will not make a detailed comparison of standards, but focus only on those key points that allow the DLMS / COSEM standard to fully satisfy the needs of the liberal energy market.

Firstly, DLMS / COSEM defines an interface model valid for any type of energy resource (electricity, gas, water, heat, etc.). Each interface object has a standardized unique identifier by which data is identified. This model is completely independent of those protocol levels that transport data. As a result, a system built on the basis of the DLMS / COSEM protocol is open for expansion by adding new interface classes and versions without changing the services providing access to the interface objects, while maintaining functional compatibility.

Secondly, the definitions of interface classes standardize a number of widely used metering device functionality: registration of consumption (electricity, heat, water, gas), tariff planning (implementation of multi-tariff metering devices), measuring the quality of electricity, etc. An unambiguous interpretation of the data is guaranteed by the fact that attributes of the interface class use clearly defined types (array, structure, boolean, integer, long, etc.) information about which, if necessary, is transmitted along with the data.

Thirdly, DLMS / COSEM provides controlled and secure access to information inside the meter for various participants in the energy market. DLMS / COSEM defines three levels of access to the meter, open access (none), password access (low level) and access with authentication (high level). In addition, information transmitted over communication lines can be encrypted, this is also regulated by the standard.

Fourth, since the interface model is completely independent of the communication environment, it is possible to use a wide selection of interfaces for data transfer without changing the interface model and data management mechanism in data acquisition systems. Today, serial interfaces and data transfer over the Internet are supported.

Fifth, unlike older protocols, where (for example, when using IEC 61107) special drivers for data acquisition systems were needed for each new measuring device, DLMS / COSEM allows creating unified drivers, through which it becomes possible to communicate with metering devices of different types from various manufacturers.

These unique combinations of features, which are not available in any other protocols currently known, make it possible to fully realize the idea of ​​a liberal energy market, make it competitive and open to innovations, and also simplify system modernization.