Modbus-RTU ⇄ LTE Gateway — Product Specifications

1. Product Overview

The Modbus-RTU ⇄ LTE Gateway is an industrial cellular gateway that bridges legacy Modbus RTU (RS-485 / RS-232) devices with cloud and SCADA systems via LTE (4G) and IP networks. It provides secure, resilient telemetry, remote control, and edge processing for utilities, industrial automation, energy systems, water/wastewater, and building management.

2. Key Features

  • Protocol bridging: Modbus RTU Master/Slave ↔ Modbus TCP / MQTT / HTTP(S) / TCP / UDP
  • Cellular connectivity: LTE Cat-1 / Cat-4 / Cat-M1 / NB-IoT (model dependent)
  • Serial ports: 1–4 × RS-485 isolated ports (2-wire), optional RS-232
  • Edge processing: data filtering, scaling, mapping, alarms, aggregation, scheduling
  • Security: TLS 1.2 / 1.3, device authentication, firewall, VPN support (optional)
  • Device management: Web UI, REST API, MQTT configuration, remote OTA firmware update
  • Industrial design: wide temperature range, surge & ESD protection, DIN-rail mountable
  • Offline resilience: local data buffer with store-and-forward capability

3. Hardware Specifications

3.1 Interfaces
  • RS-485: 1–4 ports (2-wire), 300–921600 bps, opto-isolated (2.5 kV)
  • RS-232: Optional DB9 or terminal block (Rx / Tx / GND)
  • Ethernet: Optional 10 / 100 Mbps (RJ45)
  • Cellular: LTE module with SMA antenna connector, Nano-SIM, eSIM optional
  • USB: Micro-USB or Type-C (Debug / Console)
  • Digital I/O: Optional 2 × DI, 2 × Relay outputs
  • GPS: Optional module with SMA connector
3.2 Power
  • Input voltage: 9–36 V DC (wide range)
  • Power consumption: < 2 W idle, < 6 W peak during LTE transmission
  • Protection: reverse polarity and surge protection
3.3 Mechanical & Environmental
  • Enclosure: metal or industrial-grade plastic, DIN-rail mountable
  • Dimensions: approx. 110 × 85 × 32 mm (model dependent)
  • Operating temperature: −40°C to +85°C
  • Humidity: 5% – 95% RH, non-condensing
  • MTBF: > 100,000 hours (typical, model dependent)
3.4 Certifications
  • EMC: EN 61000 series
  • Safety: EN 62368 (or regional equivalent)
  • Telecom: CE / FCC (where applicable)
  • RoHS compliant

4. Software & Protocols

4.1 Modbus Support
  • Master and Slave modes
  • Function Codes: FC01, FC02, FC03, FC04, FC05, FC06, FC15, FC16
  • Baud rates: 1200 – 921600 bps
  • Parity: None / Even / Odd
  • RTU over TCP tunneling (optional)
4.2 Cloud & Network Protocols
  • MQTT v3.1.1 (QoS 0 / 1 / 2, TLS support)
  • HTTP / HTTPS with JSON payloads
  • TCP / UDP raw frame forwarding
  • SNMP read-only traps (optional)
4.3 Edge Logic & Configuration
  • Register-to-topic / URL / JSON mapping
  • Transforms: scaling, offset, unit conversion, bit extraction
  • Rules: threshold triggers, hysteresis, event deduplication
  • Scheduling: poll intervals from 10 ms to 24 hours
  • Persistent buffering for offline data
4.4 Management & Diagnostics
  • Web UI for local configuration and monitoring
  • CLI access via Serial or SSH
  • REST API for telemetry and configuration
  • Local and Syslog-based logging
  • Remote OTA firmware management

5. Security

  • TLS 1.2 / 1.3 encryption with CA certificates
  • Device authentication (credentials or client certificates)
  • Firewall and configurable port access
  • Signed firmware updates
  • Password-protected UI and tamper-resistant enclosure

6. Performance

  • Max concurrent Modbus slaves: typical 12 (model dependent)
  • Polling throughput: thousands of registers per minute
  • Latency: < 200 ms Modbus read-to-MQTT publish (network dependent)
  • Data retention: configurable local buffering (hours to days)

7. Typical MQTT Topic Structure

devices/{device_id}/modbus/{port}/{slave_id}/holding/{reg_addr}

8. Example JSON Device Configuration

{
  "device_id": "GW-1001",
  "serial_ports": [
    {
      "id": "RS485-1",
      "baud": 19200,
      "parity": "N",
      "slaves": [
        { "id": 1, "poll_interval_ms": 500, "registers": [{"addr":40001,"name":"energy"}] }
      ]
    }
  ],
  "mqtt": {
    "broker": "mqtt.example.com",
    "port": 8883,
    "topic_base": "devices/GW-1001",
    "tls": { "ca": "/etc/certs/ca.pem" }
  }
}

9. Accessories & Options

  • LTE antenna (SMA)
  • GPS antenna (optional)
  • DIN-rail mounting kit
  • External 12V / 24V power adapter
  • eSIM provisioning
  • Industrial I/O expansion modules

10. Deliverables & Documentation

  • Gateway hardware unit
  • Quick Start Guide and User Manual
  • API and MQTT topic documentation
  • Firmware update instructions
  • Compliance and test reports (on request)

11. Ordering & Part Numbers (Examples)

  • GW-RTU-LTE-CAT4-1R — Single RS-485, LTE Cat-4
  • GW-RTU-LTE-CAT1-4R — 4 × RS-485, LTE Cat-1
  • GW-RTU-LTE-NB-4R — 4 × RS-485, NB-IoT

12. Customization & Next Steps

  • Custom firmware and protocol translations
  • Custom enclosure, branding, and mechanical design
  • Cloud integrat