Both thermocouples and RTDs are temperature sensors used in industrial, commercial, and scientific applications—but they operate on different principles and have distinct characteristics that make them better suited to specific use cases.
1. Operating Principle
- Thermocouples generate a voltage based on the Seebeck effect—when two dissimilar metals are joined and exposed to different temperatures, a small voltage is produced that correlates to the temperature difference.
- RTDs operate based on the principle that a metal's electrical resistance changes predictably with temperature. Most RTDs use platinum wire for precise, repeatable resistance changes.
2. Accuracy and Stability
- RTDs are more accurate and stable over time, especially in the 0°C to 500°C range.
- Thermocouples are less accurate and may drift over time, but can still deliver consistent results in demanding conditions.
3. Temperature Range
- Thermocouples: Can measure extreme temperatures—typically -200°C to 1700°C, depending on the type.
- RTDs: Generally used in the -200°C to 600°C range, with the most accurate results below 500°C.
4. Response Time
- Thermocouples generally have a faster response time, especially when designed with fine-wire or exposed tips.
- RTDs are slightly slower, due to their construction and thermal mass.
5. Durability and Environment
- Thermocouples are more rugged and better suited for high-vibration, high-temperature, or chemically aggressive environments.
- RTDs are more fragile in comparison and typically used in controlled, clean, or lower-vibration environments.
6. Cost and Complexity
- Thermocouples are generally less expensive, especially in basic configurations.
- RTDs are generally more costly but offer better accuracy and long-term stability.
Typical Applications
| Thermocouples | RTDs |
|---|---|
| Engines & turbines | Laboratories |
| Furnaces & kilns | HVAC systems |
| Plastic molding | Food & beverage |
| Exhaust gas monitoring (EGT) | Pharmaceutical processes |
| Welding & metalwork | Precision Industrial Control |
Which Should You Choose?
Choose a Thermocouple if you need:
- High temperature range
- Fast response
- Rugged design for harsh environments
- Budget-friendly solutions
Choose an RTD if you need:
- High accuracy
- Excellent repeatability and stability
- Long-term measurement in clean, controlled environments
Need help selecting the right temperature sensor for your application?
Contact us now! We offer both thermocouples and RTDs, plus custom designs tailored to your needs.