Connecting industrial equipment

How to connect equipment to Rela-ai

Rela-ai supports 8 industrial connection protocols: MQTT, HTTP, OPC UA, OPC UA via MQTT Gateway, OPC UA Reverse Connect, Modbus TCP, S7 (Siemens), and EtherNet/IP (Rockwell). The right choice depends on what the client has at their plant.

Connection options

Option 1: IoT sensors with MQTT (recommended)

If the client has IoT sensors with WiFi or network (temperature, humidity, vibration), they can publish data directly to an MQTT broker on the internet. Rela-ai listens automatically.

Advantage: No VPN needed, no firewall configuration, no port forwarding. The sensor publishes outward and Rela-ai listens.

IoT sensor → MQTT broker (internet) → Rela-ai (listens)

Option 2: IoT gateway at the plant (recommended for remote PLCs)

If the client's PLCs don't have native MQTT, install an IoT gateway at the plant. It's a small computer (Raspberry Pi, Siemens IOT2050, HiveMQ Edge, $50-300 USD) that:

1. Connects to the PLC via local network (OPC UA, Modbus, S7)
2. Reads data from the PLC
3. Converts data to OPC UA Pub/Sub JSON format
4. Publishes via MQTT to the internet
5. Rela-ai listens using "MQTT OPC UA Bridge" protocol

PLC (local network) → gateway (translates OPC UA → MQTT) → MQTT broker (internet) → Rela-ai

Advantage: The PLC is never exposed to the internet. Works with PLCs in any city or country without VPN.

We can:

• Recommend which gateway to buy for their PLC
• Provide MQTT broker configuration (URL, topic, credentials)
• Help remotely configure the gateway

Recommended gateways: Raspberry Pi + Node-RED ($50-80), Siemens IOT2050 ($200-300), HiveMQ Edge (free, software only), Secomea SiteManager ($400+, enterprise).

Option 3: OPC UA Reverse Connect (no gateway, no VPN) — Coming Soon

This option will be available soon. The architecture is designed and the parser/service code is ready. Production infrastructure deployment is pending.

How it works: In normal OPC UA, Rela-ai tries to connect to the PLC — but the firewall blocks it. With Reverse Connect, the direction is reversed: the PLC initiates the connection to Rela-ai. Since firewalls allow outbound traffic, the connection goes through without issues.

Normal mode:     Rela-ai → firewall ✗ → PLC  (blocked)
Reverse Connect: PLC → firewall ✓ → Rela-ai  (works)

PLC requirements:

• OPC UA Reverse Connect support (standard Part 7): Beckhoff TwinCAT 3.1+, Siemens via SIOTH Bridge
• Internet access (outbound traffic only, no port forwarding needed)
• Security certificate (Rela-ai generates it automatically)

How it will be configured (when available):

1. In Rela-ai, create a source with "OPC UA Reverse Connect" protocol
2. Rela-ai generates an endpoint and certificate
3. The client's integrator configures the PLC to connect to that endpoint
4. The PLC calls Rela-ai, the OPC UA session is established, and data flows

What's pending for production:

• Dedicated server with public IP and open TCP port (Compute Engine VM)
• Automatic source scanning from MongoDB
• Periodic re-scanning to detect new sources

Advantage: Zero additional hardware. Native OPC UA connection. The PLC just needs internet.

In the meantime: Use Option 2 (MQTT Gateway) which covers the same use case (remote PLCs) with an affordable gateway ($50-300 USD).

Option 4: HTTP from existing SCADA or software

If the client has SCADA, MES, ERP, or plant software with internet access, it can send alerts directly to Rela-ai via HTTP webhook.

SCADA/software → HTTP POST → api.rela-ai.io → Rela-ai processes

Advantage: Zero additional hardware.

Option 5: Automation integrator

If the client has an integrator company that installed their PLCs, they can configure the connection. We provide the technical specifications.

Which protocol to use

FAQ

Do I need a VPN to connect remote equipment? Not if you use MQTT, HTTP, MQTT Gateway, or Reverse Connect. These options work without VPN. You only need VPN for direct OPC UA, Modbus, S7, or EtherNet/IP connections without a gateway.

Can I connect a PLC in another country? Yes. With MQTT Gateway (option 2) or Reverse Connect (option 3), the PLC can be anywhere in the world — it just needs internet. Direct OPC UA would require VPN.

Who configures the client's network? The client's IT department or their automation integrator. We do NOT configure client networks or firewalls. We provide specs and support remotely.

What to ask the client?

1. "What brand of PLC or control system do you have?"
2. "Do you have IoT sensors already installed?"
3. "Do you have an IT team or integrator?"

With those 3 answers, we determine the best connection option.