What is the difference between a PT100 (RTD) and a thermocouple?
Compare PT100 resistance temperature detectors (RTD) and Type J/K thermocouples by temperature range, accuracy, wiring compensation and industrial use.
What is the main difference between a PT100 and a thermocouple? A PT100 (RTD) measures temperature via the predictable electrical resistance of platinum (100 Ω at 0 °C), offering superior accuracy and long-term stability between -200 °C and +400 °C. A thermocouple (Type J, K, S) generates a millivolt (mV) signal across two dissimilar metals and excels at high temperatures (+400 °C to +1200 °C+) and fast-response surface/mold measurements.
PT100 vs Type J and Type K Thermocouple comparison table
| Criterion | PT100 (Platinum RTD) | Type J Thermocouple (Fe-CuNi) | Type K Thermocouple (NiCr-Ni) |
|---|---|---|---|
| Sensing Principle | Resistance change (100 Ω at 0 °C) | Seebeck thermoelectric voltage (mV) | Seebeck thermoelectric voltage (mV) |
| Operating Range | -200 °C … +400 °C (up to +600 °C special) | 0 °C … +400 °C (short-term +750 °C) | 0 °C … +1100 °C (up to +1200 °C) |
| Accuracy & Drift | High (±0.1 °C – ±0.5 °C; minimal drift) | Moderate (±1.5 °C – ±2.5 °C) | Moderate (±1.5 °C – ±2.5 °C) |
| Wiring | 2, 3 or 4-wire copper cable (3-wire standard for lead compensation) | 2-wire polarized Type J extension wire | 2-wire polarized Type K extension wire |
| Category Link | Temperature Probes | Temperature Probes | Temperature Probes |
Frequently asked questions
Why are PT100 sensors wired with 3 wires?
Because a PT100 changes by ~0.385 Ω per °C, lead wire resistance would cause a positive temperature error over long cable runs. The third wire allows the controller to measure and subtract lead resistance.