RTDs (Resistance Temperature Detectors) and thermocouples are two of the most widely used temperature sensors, but they differ significantly in terms of their operation, applications, and performance characteristics. Below is a detailed comparison between RTDs and thermocouples to help you understand their strengths, weaknesses, and ideal use cases

Temperature Range

• RTD:
  • RTDs typically have a temperature range of -200°C to +850°C (for platinum-based RTDs), though some special designs can extend this range further.
  • They are generally limited to mid-range temperatures compared to thermocouples.
• Thermocouple:
  • Thermocouples have a much wider temperature range, with some types (like Type K) covering -200°C to +1372°C, and others like Type R or Type S reaching over 1700°C.
  • Thermocouples are well-suited for extreme high temperatures.

Accuracy

• RTD:
  • RTDs are known for high accuracy, especially in the temperature range from -200°C to +600°C.
  • Typical accuracy is around ±0.1°C or better, depending on the quality of the sensor and the measurement system.
  • Because of the linear relationship between temperature and resistance, RTDs are very precise and stable.
• Thermocouple:
  • Thermocouples are less accurate compared to RTDs. Typical accuracy is about ±1°C to ±2°C or 0.75% of the reading, though it can vary with the type of thermocouple and the temperature range.
  • The accuracy of thermocouples can also degrade at higher temperatures and under conditions of oxidation or contamination.

Durability and Stability

• RTD:
  • RTDs are generally more stable over time and less prone to drift than thermocouples. However, they can be fragile and susceptible to damage from mechanical shock or vibration.
  • They are often encased in protective sheaths to improve durability.
  • RTDs are susceptible to mechanical stress and can degrade if exposed to rapid temperature changes or harsh environments (extreme vibrations, shocks).
• Thermocouple:
  • Thermocouples are more rugged and durable in harsh environments and can withstand high temperatures, vibration, and mechanical shock.
  • They are especially useful in applications where durability and reliability in extreme conditions are critical.
  • However, they may experience drift or reduced accuracy over time, especially at very high temperatures due to material degradation (e.g., oxidation).

Response Time

• RTD:
  • RTDs generally have slower response times compared to thermocouples due to their larger size and the need for electrical resistance measurements.
  • However, the response time can vary based on the sensor’s construction (e.g., thin-film RTDs have a faster response than wire-wound RTDs).
• Thermocouple:
  • Thermocouples have a faster response time because of their small size and direct measurement of the temperature difference.
  • They are ideal for dynamic temperature measurements where rapid changes are expected.

Summary Comparison