An instrumentation chain is the linked path of sensors, wiring, signal conditioning, meters, and monitoring systems that converts a physical condition into usable data. In a power grid, that chain may start with a current transformer or other sensor and end in a relay, meter, historian, or control room display. Each stage has to preserve the meaning of the signal, not just carry electricity.
This matters in cybersecurity because attackers often target measurement before they target control. If they can tamper with wiring, corrupt calibration, inject noise, or spoof telemetry, they can hide abnormal conditions or create false ones. In industrial defense, the instrumentation chain is protected with physical security, tamper checks, redundancy, plausibility validation, and routine calibration. A trustworthy control system depends on trustworthy measurements, so the chain itself is a security boundary, not just a technical detail.