industrial instrumentation basics

RTD 3-Wire vs 4-Wire: Understanding Lead Wire Compensation Ask any technician why an RTD needs three or four wires instead of just two, and you'll often get a vague answer like "for accuracy." That's true, but it skips the actual reason — and understanding the real mechanism behind it is what lets you diagnose a drifting temperature reading instead of just replacing a perfectly good RTD because the number looks slightly wrong. This article breaks down exactly what lead wire resistance does to your reading, and how 3-wire and 4-wire configurations each deal with it differently. The Core Problem: An RTD Is a Resistance Measurement An RTD (Resistance Temperature Detector) works on a simple principle: its resistance changes predictably with temperature. A standard Pt100 reads 100.00 ohms at 0°C, and that resistance climbs in a well-defined, repeatable curve as temperature rises. To find the temperature, the instrument measures the RTD's resistance and converts...