Ian Loke

I ran npm install on a Raspberry Pi 4, the same one I’d set up as an edge gateway with OPC UA and MQTT, and watched the terminal scroll. Node-RED, plus three protocol modules for Siemens S7 PLCs, OPC UA, and Modbus. When it finished, I counted.

IEC 62443 defines four Security Levels for industrial control systems. At the highest level — SL-4, protection against state-sponsored attacks with extensive resources — the standard calls for unidirectional data flow enforcement. Not a firewall rule. Not a software policy. Hardware-enforced, physically one-way communication.

Every factory faces the same question: how do you get sensor data from the shop floor to the systems that need it? The answer is never one protocol. It’s two — MQTT for vertical data flow to IT systems, and OPC UA for horizontal integration with SCADA and HMI on the plant floor.

In my previous post, I shared the importance of setting tag limits to prevent bad data from causing issues in SCADA systems. Now, let’s talk about another essential safeguard — clamping values.

Since WinCC Unified V17, users have been able to set upper and lower limits for tags to ensure the value stays within a defined range. This feature is essential for preventing invalid inputs and protects connected devices from unexpected inputs.

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