The Difference Between DL/T645、DLMS and Modbus-RTU
I. Core Positioning & Formulation Background
The origins and target industries of the three protocols are entirely distinct, which determines their core design directions：
II. Comparison of Technical Characteristics
The three protocols vary greatly in communication mechanisms, data structures, and flexibility:
1. Communication Architecture & Topology
DL/T645:
Only supports a master-slave architecture (1 master station + multiple slave stations). Slave station addresses are fixed (usually 6-digit BCD codes, e.g., electricity meter addresses), and multi-master or peer-to-peer communication is not supported. The topology is limited to bus-type (e.g., RS-485), mainly adapting to the simple "one-master-multi-slave" networking for meter reading scenarios.
DLMS:
Supports both master-slave architecture (mainstream) and peer-to-peer architecture (optional), adapting to more complex energy networks. The topology is flexible and can be based on RS-485, Ethernet (DLMS/IP), or wireless (GPRS/LoRa) technologies, meeting the hybrid networking needs of multi-energy equipment.
Modbus-RTU:
A typical master-slave architecture (1 master station can connect to up to 247 slave stations), with slave station addresses ranging from 1 to 247 (single-byte addresses). The topology is primarily bus-type (RS-485) but can be extended to Ethernet via gateways, focusing on the "centralized control" scenario for industrial equipment.
2. Data Encoding & Frame Structure
The frame format of a protocol directly affects data transmission efficiency and compatibility：
3. Functionality & Data Interaction Capabilities
The functional design of the three protocols revolves around their core scenarios, with obvious differences:
DL/T645:
Functions are highly specialized, covering only the core needs of electricity meters, such as:
Reading electricity quantity (active/reactive), voltage, current, and power;
Setting meter addresses, time, and tariff rates;
Remote power cutoff/restore (electricity usage control).
It does not support custom functions, has poor expandability, and is only suitable for electricity meters.
DLMS:
Functions are standardized and universal, enabling multi-energy data interaction based on the "COSEM object model." Core functions include:
Reading multi-type energy data (usage and parameters of electricity, water, gas, heat);
Event logging (e.g., meter faults, power outage events);
Security authentication (encrypted transmission, access permission control, compliant with the EU Measuring Instruments Directive (MID)).
It supports custom COSEM objects, can adapt to new types of energy equipment, and has strong global compatibility.
Modbus-RTU:
Functions are minimalist and universal, defining only 4 core operations (no business logic binding):
Reading discrete inputs (e.g., sensor switch status);
Reading holding registers (e.g., device operating parameters such as temperature and rotational speed);
Writing to holding registers (e.g., controlling frequency converter speed, valve opening);
Reading/writing coils (e.g., controlling device startup/shutdown).
It has no built-in business functions; register mapping is completely defined by users, making it suitable for all industrial control scenarios.
III. Industry Adaptation & Compatibility
DL/T645:
Regional Restriction: Mandatorily implemented only in China’s power industry; rarely supported by foreign equipment.
Device Restriction: Only compatible with electricity meters that meet Chinese standards; cannot be used for water/gas meters or industrial equipment.
Compatibility: Electricity meters from different manufacturers can communicate seamlessly as long as they comply with DL/T645, ensuring interoperability within China’s power system.
DLMS:
Global Compatibility: Widely adopted in Europe, Asia, and other regions; compliant with international standards (IEC 62056), enabling cross-border and cross-manufacturer interoperability (e.g., a European gas meter and a Chinese electricity meter can communicate via DLMS).
Multi-Energy Adaptation: Unified protocol for electricity, water, gas, and heat meters, supporting integrated energy management (e.g., a single system monitors all household energy consumption).
Regulatory Compliance: Meets strict metering regulations in regions like the EU (MID) and North America, making it the first choice for global energy metering projects.
Modbus-RTU:
Industry Universality: The "de facto standard" in industrial automation; supported by almost all industrial equipment manufacturers (e.g., Siemens, ABB, Omron).
Cross-Device Compatibility: A sensor from Brand A, a PLC from Brand B, and a frequency converter from Brand C can communicate via Modbus-RTU as long as they support the protocol.
Limitation in Metering: Lacks standardized energy data models; if used for metering, users must independently define register mappings (e.g., which register stores electricity quantity), leading to poor interoperability between different metering devices.
IV. Summary of Key Differences
To quickly distinguish the three protocols, the following core points can be used:
In practical applications, the choice of protocol depends on regional requirements, industry scenarios, and device types:
-For electricity meter projects in China: Prioritize DL/T645.
-For global multi-energy metering (e.g., international smart city projects): Choose DLMS/COSEM.
-For industrial automation (e.g., factory production lines): Modbus-RTU is the most cost-effective and compatible option.
Wuxi Zhongyi Smart Technology Co., Ltd. focuses on the development and manufacturing of smart water meters, energy meters, gas meters, covering more than 90 countries around the world. If you are interested in smart energy meters, please contact Zhongyi Smart!
