Thermocouple vs RTD vs Thermistor
Thermocouples, resistance temperature detectors (RTDs), and thermistors are the three dominant contact temperature sensors. They differ in temperature range, accuracy, linearity, cost, and response. This guide compares them side by side and explains when each is the right choice.
Side-by-Side Comparison
| Characteristic | Thermocouple | RTD (Pt100) | Thermistor |
|---|---|---|---|
| Principle | Seebeck EMF from dissimilar metals | Resistance change of pure platinum | Resistance change of a semiconductor |
| Typical range | −270 to +2315°C | −200 to +850°C | −50 to +300°C |
| Accuracy | Good (±0.5 to ±2°C class) | Excellent (±0.1 to ±0.5°C) | Excellent in a narrow band |
| Linearity | Non-linear (polynomial) | Nearly linear | Highly non-linear |
| Sensitivity | Low (µV/°C) | Moderate (~0.385 Ω/°C) | Very high |
| Response time | Fast (small junction) | Slower (larger element) | Fast |
| Excitation | Self-powered | Requires current source | Requires current source |
| Long-term stability | Moderate; drifts with use | Excellent | Good to moderate |
| Relative cost | Low | Higher | Low |
| Governing standard | ASTM E230 / IEC 60584 | IEC 60751 / ASTM E1137 | Manufacturer-specific |
RTD figures are for the common platinum Pt100 (100 Ω at 0 °C, temperature coefficient α = 0.00385 Ω/Ω/°C) per IEC 60751. Thermistor ranges vary widely by part; the values shown are typical for general-purpose NTC devices.
Which Sensor for Which Job
Choose a Thermocouple
- High temperatures above ~600°C
- Wide range in one sensor
- Rugged or vibration-prone environments
- Fast response, small size, low cost
- Furnaces, kilns, engines, heat treating
Choose an RTD
- Highest accuracy and stability
- Moderate range (−200 to +850°C)
- Repeatable, drift-sensitive processes
- Lab, pharma, and process control
- When linearity simplifies the system
Choose a Thermistor
- Narrow range near ambient
- Very high sensitivity needed
- Low-cost consumer and medical devices
- Point sensing where size matters
- Not for high-temperature work
Rule of Thumb
If the application exceeds 600 °C or demands ruggedness, use a thermocouple. If it sits within −200 to +850 °C and accuracy and repeatability dominate, use an RTD. If it lives near room temperature and needs high sensitivity at low cost, use a thermistor.