Thermocouples are one of the most significant temperature sensors used by various industries to measure temperatures with high accuracy and efficiency. Thermometer types vary through unique combinations of metals that affect temperatures, accuracy, and suitability in different conditions of different types. There are eight common types of thermocouples, namely: K, J, T, E, N, S, R, and B. The knowledge of differences between them will guide you to choosing the right one for your application.
Type K (Nickel-Chromium / Nickel-Alumel)
Temperature Range: -200°C to 1260°C (-328°F to 2300°F)
Accuracy: ±1.5°C or ±0.4%
Features:
- One of the most widely used types of thermocouples because of the benefit of versatility.
- Extremely effective in a very wide range of temperatures and best used in oxidizing environments.
- Suitable for general-purpose temperature measurement in industrial applications.
Type J (Iron / Constantan)
Temperature Range: -210°C to 760°C (-346°F to 1400°F)
Accuracy: ±2.2°C or ±0.75%
Features:
- Type J is best used in low temperature ranges.
- It is applied wherever the situation of oxidation is poor as the iron component tends to get rusted if exposed to high temperatures.
- It works pretty well with furnaces or applications that do not reach extreme heights in temperature.
Type T (Copper / Constantan)
Temperature Range: -200°C to 370°C (-328°F to 700°F)
Accuracy: ±1.0°C or ±0.75%
Features:
- Type T is very efficient in the measurement of low temperatures thus its preference in cryogenic application.
- It is suitable for oxidizing or reducing atmospheres and, therefore, found plenty of industrial applications.
Type E (Nickel-Chromium / Constantan)
Temperature Range: -200°C to 900°C (-328°F to 1652°F)
Accuracy: ±1.7°C or ±0.5%
Special Applications:
- Type E has a higher output (in millivolts) than most other types so is good for low-temperature applications such as cryogenics.
- It works well in both oxidizing and inert atmospheres.
Type N (Nickel-Chromium-Silicon / Nickel-Silicon)
Temperature Range: -200°C to 1300°C (-328°F to 2372°F)
Accuracy: ±2.2°C or ±0.75%
Features:
- Type N is more stable in high temperatures than Type K. Additionally, it gives greater resistance against oxidation.
- For industries where readings of high temperatures are required, it gives better performance in harsh environments.
Type S (Platinum Rhodium – 10% / Platinum)
Temperature Range: 0°C to 1450°C (32°F to 2642°F)
Accuracy: ±1.5°C or ±0.25%
Features:
- Type S has very high stability. It delivers accurate high-temperature applications, especially in laboratories and research environments.
- It is suitable for oxidizing atmospheres and has the characteristic of having high strength at high temperatures.
Type R (Platinum Rhodium – 13% / Platinum)
Temperature Range: 0°C to 1450°C (32°F to 2642°F)
Accuracy: ±1.5°C or ±0.25%
Features:
- Type R is similar to Type S, but with a slightly higher millivolt output.
- It’s designed for applications at high temperatures that are within an oxidizing atmosphere and typically used in various industrial processes.
Type B (Platinum Rhodium – 30% / Platinum Rhodium – 6%)
Range of Temperature: 0°C to 1700°C (32°F to 3092°F)
Accuracy: ±0.5%
Features:
- These are Type B thermocouples which can use for applications requiring extremely high temperature and are stable and accurate.
- However, they produce very low output levels at lower temperatures, thus limiting their use under those conditions.
Summary of Thermocouple Types:
- Type K: can measure across broad ranges of temperature; easily used in industrial applications.
- Type J: suitable for lowest temperature measurement, corrodes in an oxidizing environment.
- Type T: Suitable for cryogenic and low-temperature measurements.
- Type E: High output suitable for cryogenic and moderate temperature measurement.
- Type N: Increased stability than type K with better response at higher temperatures.
- Type S, R, B: High temperature application with excellent stability, often used in laboratories or industries that would require excellent precision.
Choosing the Right Thermocouple
The type of thermocouple that is chosen depends on the temperature range in which it is going to operate, environment (oxidizing, reducing, inert), and the accuracy level that one wants for some application. The industrial, laboratory, and cryogenic measurements all require different types of thermocouples to ensure the highest performance and reliability. Knowing these can help you find the right thermocouple for your needs.
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