In-depth Analysis of Multi-Device Connection and Shared Access Technologies for Modbus Converters

In the field of industrial IoT and automation control, modbus converters serve as the core hub connecting traditional serial devices with modern networks. Their multi-device connection capabilities and shared access mechanisms directly impact system efficiency and flexibility. This article will delve into two core questions—"Does the modbus converter support simultaneous multi-device connections?" and "How to enable shared access across multiple computers?"—through technical principles, typical application scenarios, and product implementations.

Analysis of Multi-Device Connection Capabilities in Modbus Converters

1.1 Hardware Architecture Determines Connection Limits
The multi-device connection capacity of a modbus converter primarily depends on its hardware design. Mainstream industrial-grade devices typically adopt the following architectures:

Multi-Serial Port Independent Channels: For example, PUSR's USR-N540 four-port RS485 Ethernet gateway utilizes four independently isolated RS485 interfaces for physical-layer multi-device connections, with each port supporting up to 32 nodes (compliant with RS485 standards). Theoretically, a single device can connect up to 128 terminals.

Shared Bus Design: Some lower-end products employ single-serial port time-division multiplexing technology, enabling multi-device connections through polling mechanisms. However, this approach suffers from cumulative communication delays and is only suitable for low-frequency data acquisition scenarios.

Typical Case Study: In a smart logistics center, the USR-N540 simultaneously connected the following devices via its four RS485 ports:

20 barcode scanners (Port 1)

15 electronic scales (Port 2)

8 automatic sorters (Port 3)

5 temperature and humidity sensors (Port 4)
The system operated stably, with data acquisition cycle errors below 50ms, validating the reliability of the multi-port independent channel design.

1.2 Software-Level Concurrent Processing Mechanisms
Modern modbus converters achieve software-layer concurrency through the following technologies:

Multithreaded Architecture: Each serial port is assigned an independent processing thread to prevent task blocking. The USR-N540, equipped with an ARM Cortex-A7 dual-core processor, supports up to 256 concurrent connection requests per port.

Data Buffering and Scheduling: Built-in large-capacity FIFO buffers (typically ≥8KB) combined with dynamic priority scheduling algorithms ensure high-priority data transmission.

Protocol Optimization: Dedicated acceleration engines for common protocols like Modbus reduce conversion delays. The USR-N540 achieves a Modbus TCP/RTU conversion delay below 2ms, a threefold improvement over traditional solutions.

1.3 Network-Layer Scalability
The following technologies break through single-device connection limits:

Virtual Serial Port Segmentation: A single physical serial port can be mapped into multiple virtual COM ports (e.g., USR-N540 supports 1:16 virtual segmentation), though this reduces individual channel bandwidth.

Multi-IP Binding: Assigning independent IP addresses to each serial port balances physical isolation with logical scalability.

Cascading Networking: Switch stacking technology enables the construction of clustered systems comprising multiple modbus converters. A large hydropower station deployed 20 USR-N540 devices to manage over 2,000 devices centrally, achieving 99.99% system availability.

Implementation Paths for Multi-Computer Shared Access

2.1 Direct Socket-Based Sharing Mode
Technical Principle: The modbus converter acts as a TCP server, with multiple computers connecting as TCP clients. Data distribution is achieved through custom protocols.
Implementation Highlights:

Port Listening Configuration: Set the USR-N540 to TCP Server mode in its management interface and specify a listening port (default 502 for Modbus TCP).

Client Permission Management: Control access via IP whitelisting and MAC address binding.

Data Broadcasting Strategy: Configure the modbus converter to actively push received data to all connected clients.

Typical Application: In an automotive production line testing system, three test workstations simultaneously accessed ECU data collected by the USR-N540. Custom protocols enabled:

Test command priority control

Data verification and retransmission mechanisms

Real-time status synchronization (delay <100ms)

2.2 Middleware Proxy Solution
Architectural Design: Deploy a dedicated proxy server as a data intermediary to enable:

Protocol conversion (e.g., Modbus TCP to OPC UA)

Load balancing

Historical data storage

USR-N540 Implementation Case:
In a steel plant blast furnace monitoring system:

One Windows Server was deployed as a proxy

The USR-N540 was configured as a Modbus TCP slave, with the proxy server acting as the master for polling data

Five HMIs and three MES workstations accessed data via the proxy

Achieved Results:

Access conflict rate reduced to 0.1%

Unified 500ms data update cycle

Support for disconnection caching and resumption

2.3 Database Sharing Mode
Implementation Steps:

The modbus converter writes collected data to an industrial database (e.g., InfluxDB, TimescaleDB)

Multiple computers retrieve data via SQL queries or API interfaces

Message queues (e.g., RabbitMQ) enable real-time data push

USR-N540 Optimization Features:

Direct MQTT protocol support for cloud platform data publishing

Built-in SQLite database for storing seven days of historical data

Python/C# SDKs simplify secondary development

Application Outcomes: After adopting this solution, a photovoltaic power plant achieved:

Data access latency reduced from seconds to milliseconds

Support for simultaneous historical trend queries from over 20 terminals

80% reduction in direct modbus converter access pressure

2.4 VPN-Based Isolated Access
Security Architecture:

Modbus converters deployed in industrial intranets

Secure tunnels established via IPSec/SSL VPN

Independent virtual IPs assigned to each remote computer

USR-N540 Security Features:

Support for OpenVPN client/server modes

Integrated SM2/SM4 encryption algorithms

Access log auditing capabilities

Implementation Results: A multinational corporation enabled secure remote access to serial devices across 50 global factories through VPN tunnels, with no data breaches reported.

Key Technical Challenges and Solutions

3.1 Concurrent Access Conflict Issues
Problem Manifestation: Simultaneous commands from multiple computers cause data corruption or device response abnormalities.
Solutions:

Time-Slice Polling: The USR-N540 supports configurable minimum communication intervals (e.g., 10ms) to prevent command overlap.

Token Ring Mechanism: Dynamic access rights allocation through custom protocols.

Priority Queuing: High-priority channels for urgent commands (e.g., USR-N540's prioritized Modbus exception responses).

3.2 Data Consistency Guarantees
Challenge Scenario: Simultaneous parameter modifications by multiple computers may cause state inconsistencies.
Countermeasures:

Atomic Operation Encapsulation: Parameter modifications are wrapped as indivisible TCP transactions.

Version Control Mechanism: The USR-N540 supports mixed use of Modbus function codes 0x06 (write single register) and 0x10 (write multiple registers) to ensure synchronized parameter updates.

ACK Confirmation and Retransmission: Critical commands implement automatic retransmission upon timeout.

3.3 Bandwidth Competition Optimization
Optimization Methods:

Traffic Shaping: The USR-N540 supports QoS policies to allocate bandwidth proportions for different services.

Data Compression: LZ4 compression improves text data transmission efficiency by 40%.

Edge Computing Preprocessing: Data aggregation and filtering at the modbus converter reduce invalid transmissions.

In-Depth Analysis of Typical Application Scenarios

4.1 Smart Manufacturing Workshop Equipment Networking
System Architecture:

Ten USR-N540 devices deployed across production lines

Each connects 8-12 devices (PLCs, sensors, robots, etc.)

Twenty HMIs and five MES workstations share access

Innovative Practices:

Hybrid "Master-Slave + Broadcasting" Mode:

MES workstations send control commands as masters

HMIs only monitor status data (via UDP broadcasting)

Dynamic Load Balancing:

Automatic port priority adjustment based on device communication frequency

Idle ports enter low-power mode automatically

Implementation Results:

25% increase in equipment utilization

60% reduction in fault location time

Annual maintenance cost savings of 180,000 RMB

4.2 Smart City Pipeline Monitoring System
System Characteristics:

500 remote terminal units (RTUs) report data via GPRS/4G

Municipal and district monitoring centers require simultaneous data access

7×24 reliable operation required

Solution:

USR-N540 as edge gateways:

Support 4G全网通 (4G full network compatibility) for local RTU data aggregation

Built-in 3G/4G signal strength monitoring with automatic switching

Dual-Server Hot Standby Architecture:

Primary and backup devices implement IP failover via VRRP protocol

Data synchronization delay <500ms

Hierarchical Access Control:

Municipal platforms have full data access rights

District platforms can only view devices within their jurisdiction

Operational Data:

99.98% system availability

99.999% data integrity

Mean Time Between Failures (MTBF) >50,000 hours

Product Selection Guide and Comparison

5.1 Core Parameter Comparison Table

5.2 Typical Product Analysis
USR-N540 Core Advantages:

Fully Isolated Design: Each RS485 port features independent optocoupler isolation with ≥2500V isolation voltage

Intelligent Anti-Interference: Built-in adaptive filtering algorithms suppress -15dB industrial noise

Ecosystem Compatibility: Provides Python/C#/Java SDKs for seamless integration with mainstream SCADA systems like ScadaBR and Ignition

Visual Diagnostics: Real-time display of port status, signal strength, and traffic statistics via LED indicators and Web interface

Field Test Data from a Chemical Enterprise:

Data bit error rate <10^-9 in strong electromagnetic interference environments (5V/m field strength)

12 months of continuous operation without failure, 5× more reliable than previous solutions (single-port devices from another brand)

80% reduction in annual on-site maintenance through SMS-based remote restart and configuration recovery

Future Development Trends

6.1 5G+TSN Converged Architecture
As 5G RedCap and TSN (Time-Sensitive Networking) technologies mature, modbus converters will evolve to:

Support 5G low-latency slicing (<10ms)

Integrate IEEE 802.1Qbv time-aware shapers

Enable deterministic network transmission for hard real-time motion control requirements

6.2 AI-Empowered Intelligent Operations
Edge AI chips will enable:

Communication quality prediction (based on SVM algorithms)

Anomaly pattern recognition (e.g., LSTM neural networks for detecting data mutations)

Adaptive parameter optimization (dynamic adjustment of buffer sizes, timeouts, etc.)

6.3 Digital Twin Interface Standardization
Future modbus converters will incorporate built-in digital twin model interfaces to support:

Virtual device state mapping

Predictive maintenance data output

Seamless integration with digital twin platforms like Siemens MindSphere

The multi-device connection and shared access technologies for modbus converters are evolving from simple protocol conversion to intelligent, highly reliable, and scalable solutions. Industrial-grade products like the USR-N540, through hardware isolation design, software concurrency optimization, and ecosystem compatibility enhancements, provide a solid foundation for device networking in smart manufacturing, smart cities, energy management, and other fields. With the integration of 5G, TSN, AI, and other technologies, modbus converters will continue to push performance boundaries and become critical infrastructure for the Industrial Internet.