Why Connect Modbus RTU to the Cloud?
Modbus RTU remains the most widely used field protocol in global industry, found in tens of millions of devices: variable-frequency drives, programmable logic controllers, energy meters, power quality analyzers, temperature and pressure sensors, and photovoltaic inverters. However, this serial protocol from the 1970s was not designed for the Internet.
Connecting this equipment to the cloud provides immediate benefits:
- 24/7 remote monitoring without the need for on-site visits
- Real-time alerts for threshold exceedances or anomalies
- Historical data and trends for preventive maintenance
- Automated reporting for compliance and energy audits
- ERP/CMMS integration via REST API or webhooks
Architecture of a Modbus RTU Gateway to the Cloud
The gateway physically connects to the RS485 bus as a Modbus master. It cyclically polls the slaves according to a configurable setup (list of registers, addresses, polling frequency), converts the values into JSON/MQTT messages, and transmits them to the cloud.
RS485 Devices Eziwan Cloud Gateway
──────────────── ───────────────── ──────────────
Drive ──┐ ┌─ Modbus RTU master MQTT broker
Compteur ──┤── RS485 ──┤ Polling registres → Dashboard
PLC ──┘ └─ 4G / Ethernet Alerts / API
Key architectural features:
| Parameter | Typical Value |
|---|---|
| Physical Interface | 2-wire RS485 (A/B) or RS232 |
| Baud Rate | 9,600 / 19,200 / 38,400 bps |
| Parity | None (8N1) or Even (8E1) |
| Cloud connection | MQTT TLS over 4G LTE |
| Polling interval | 1 s to 15 min (configurable) |
| Local buffer | 72 h of data |
Configuring Modbus Registers to Be Read
The gateway allows you to precisely configure which registers to read on which slaves. Each measurement point is defined by:
- Slave address (1 to 247)
- Register type: Holding (FC03), Input (FC04), Coil (FC01), Discrete Input (FC02)
- Register address (0 to 65535)
- Data type: INT16, UINT16, INT32, FLOAT32, BOOLEAN
- Scale factor and offset for conversion to physical units
- Label / tag for the dashboard (e.g., "active_power_kW")
This configuration is performed through the Eziwan cloud interface, without physical access to the installation—ideal for remote or hard-to-reach sites.
MQTT Transmission: QoS, TLS, and Retention
Once the logs have been read, the gateway publishes the values to an MQTT broker (Eziwan Cloud, AWS IoT Core, Azure IoT Hub, or self-hosted Mosquitto). Best practices:
- QoS 1 (at-least-once) to ensure delivery despite network outages
- TLS 1.3 required to encrypt the connection
- Client certificate authentication (x509) for gateway identity
- Hierarchical topic:
site/zone/equipement/tagto facilitate filtering - JSON payload with ISO 8601 timestamp, value, and unit
Typical Industrial Use Cases
Modbus RTU → cloud connectivity has applications across many industries:
Energy and Utilities
- Remote meter reading for electric meters (Eastron SDM, SOCOMEC, Carlo Gavazzi)
- Generator and inverter monitoring
- Low-voltage distribution panel monitoring
Industrial Production
- Monitoring of variable-frequency drives (Schneider ATV, Danfoss, ABB)
- Control of compressors and pumps
- Monitoring of industrial furnaces and ovens
Water and Sanitation
- Remote monitoring of pumping stations
- Measurement of flow, pressure, and level
- Remote fault detection
OT/IT Security: The Zero-Trust Approach
Connecting OT (Operational Technology) networks to the Internet introduces cybersecurity risks. The Eziwan approach applies zero-trust principles:
- Outbound connection only — the gateway initiates the tunnel; no inbound ports are opened
- Network segmentation — the OT network (RS485) remains isolated from the IT network
- Certificates per device — each gateway has a unique cryptographic identity
- Signed OTA updates — it is impossible to install unauthenticated firmware
- Logging — all connections and anomalies are logged