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Thermocouple Types in Detail
Common Thermocouple Types
This section outlines the standard and commonly used thermocouple types defined by IEC 60584-1. Each type features a unique combination of conductors suited to specific environments and temperature ranges. More detailed information is available on the individual thermocouple type pages linked below.
Type K - Nickel-Chromium vs Nickel-Aluminium
The most widely used industrial thermocouple (Chromel-Alumel), Type K is ideal for oxidising environments. Max continuous use is ~1100°C, with short-term tolerance to 1200°C. It's suitable down to -250°C but can suffer from drift between 250–600°C, especially during thermal cycling. While popular in nuclear settings, Type N is now preferred.
Type T - Copper vs Copper-Nickel
Type T (Copper-Constantan) is well-suited to laboratory and cryogenic applications (-250°C to 400°C). It offers excellent repeatability in the -200°C to 200°C range (±0.1°C), but the copper leg oxidises quickly above this range. Note: Type T and Type J alloys are not interchangeable.
Type J - Iron vs Copper-Nickel
Known as Iron/Constantan, Type J is suitable for reducing atmospheres, with a maximum continuous temperature of ~800°C (short-term: 1000°C). Below ambient temperatures, condensation can lead to rusting and embrittlement.
Type N - Nickel-Chromium-Silicon vs Nickel-Silicon
Designed as an advanced alternative to Type K, Type N (Nicrosil-Nisil) resists drift, oxidation, and magnetic instabilities up to 1280°C. Its superior repeatability and nuclear radiation resistance make it ideal for harsh, high-temperature environments. Standardised in 1986 (BS EN 60584-1 Part 8), it's now widely used and seen as a better choice than E, J, K, and T in many applications.
Type E - Nickel-Chromium vs Copper-Nickel
Also known as Chromel-Constantan, Type E provides the highest EMF output among common thermocouples. Its range spans -250°C to 900°C in oxidising/inert atmospheres. More stable than Type K, but Type N still ranks higher for long-term accuracy.
Type S - Platinum-10% Rhodium vs Platinum
Used in oxidising or inert atmospheres, Type S thermocouples are suitable for continuous use up to 1600°C (briefly up to 1700°C). High-purity alumina sheaths are typically required to avoid contamination and EMF degradation. Prolonged high-temperature use can lead to rhodium diffusion and output reduction.
Type R - Platinum-13% Rhodium vs Platinum
Offering slightly higher output and better stability than Type S, Type R is generally preferred for the same high-temperature applications. Performance and handling requirements are otherwise similar.
Type B - Platinum-30% Rhodium vs Platinum-6% Rhodium
Type B thermocouples can operate continuously up to 1600°C (short-term: ~1800°C). Though output is lower, cold junction compensation is often unnecessary due to negligible EMF below 50°C. Not typically used below 600°C.
Type C - Tungsten-5% Rhenium vs Tungsten-26% Rhenium
Used in vacuum, inert atmospheres, or dry hydrogen, Type C (formerly W5) offers high-temperature capability with linear EMF output. Recrystallisation above 1200°C can lead to brittleness.
Type A - Tungsten-5% Rhenium vs Tungsten-20% Rhenium
A variation of Type C, Type A extends the usable temperature range up to 2500°C under similar atmospheric restrictions.
Non-Standard Thermocouples
A range of specialised thermocouple types continue to serve niche or legacy applications. Key examples include:
- Type G (Tungsten vs Tungsten-26% Rhenium) and Type D (Tungsten-3% Rhenium vs Tungsten-25% Rhenium):
Both function up to ~2300°C (short-term: 2750°C) in vacuum or inert gases. Above 1800°C, rhenium vapourisation can occur. Suitable insulators include beryllia and thoria. - Iridium-40% Rhodium vs Iridium:
Usable in air without protection up to 2000°C (short-term). Batch calibration is required due to lack of standard tables. Embrittlement is a risk after prolonged exposure. - Platinum-40% Rhodium vs Platinum-20% Rhodium:
Offers higher temperature coverage than Type B (up to 1850°C short-term). No standard reference tables; batch calibrations typically available. - Nickel-Chromium vs Gold-Iron (Cryogenic):
Designed for use below 1K (better performance above 4K), this thermocouple is ideal for ultra-low temperature measurements. Reference tables are available from NBS and other sources.
Thermocouple Output Tolerances
Not all thermocouples match reference tables perfectly. IEC 60584-1 defines output tolerances for both noble and base metal thermocouples. These tolerances (see Table 3.3) apply to wires typically 0.1–3 mm in diameter and do not account for in-use calibration drift. Non-standard types are usually supplied with manufacturer-specific batch tables.
| Type | Tolerance Class 1 | Tolerance Class 2 | Tolerance Class 3 |
|---|---|---|---|
| Type K Temperature Range Tolerance Value Temperature Range Tolerance Value |
–40°C to +375°C ±1.5°C 375°C to 1000°C ±0.004 . |t| |
–40°C to +333°C ±2.5°C 333°C to 1200°C ±0.0075 . |t| |
–167°C to +40°C ±2.5°C –200°C to –167°C ±0.015 . |t| |
| Type T Temperature Range Tolerance Value Temperature Range Tolerance Value |
–40°C to +125°C ±0.5°C 125°C to 350°C ±0.004 . |t| |
–40°C to +133°C ±1.0°C 133°C to 350°C ±0.0075 . |t| |
–67°C to +40°C ±1.0°C –200°C to –67°C ±0.015 . |t| |
| Type J Temperature Range Tolerance Value Temperature Range Tolerance Value |
–40°C to +375°C ±1.5°C 375°C to 750°C ±0.004 . |t| |
–40°C to +333°C ±2.5°C 333°C to 750°C ±0.0075 . |t| |
– – – – |
| Type N Temperature Range Tolerance Value Temperature Range Tolerance Value |
–40°C to +375°C ±1.5°C 375°C to 1000°C ±0.004 . |t| |
–40°C to +333°C ±2.5°C 333°C to 1200°C ±0.0075 . |t| |
–167°C to +40°C ±2.5°C –200°C to –167°C ±0.015 . |t| |
| Type E Temperature Range Tolerance Value Temperature Range Tolerance Value |
–40°C to +375°C ±1.5°C 375°C to 800°C ±0.004 . |t| |
–40°C to +333°C ±2.5°C 333°C to 900°C ±0.0075 . |t| |
–167°C to +40°C ±2.5°C –200°C to –167°C ±0.015 . |t| |
| Type R and Type S Temperature Range Tolerance Value Temperature Range Tolerance Value |
0°C to +1100°C ±1.0°C 1100°C to 1600°C ±(1 +0.003 (t . 1100)°C |
0°C to +600°C ±1.5°C 600°C to 1600°C ±0.0025 . |t| |
– – – – |
| Type B Temperature Range Tolerance Value Temperature Range Tolerance Value |
– – – – |
– – 600°C to 1700°C ± 0.0025 . |t| |
600°C to +800°C ±4.0°C 800°C to 1700°C ±0.005 . |t| |
Table 3.3: Thermocouple Tolerances According to IEC 60584-1 (reference junction at 0ºC)
Note: The information in this guide is provided for general informational and educational purposes only. While we aim for accuracy, all data, examples, and recommendations are provided “as is” without warranty of any kind. Standards, specifications, and best practices may change over time, so always confirm current requirements before use.
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Further Reading
What are the various thermocouple types?
Explore the features and characteristics of the various thermocouple types
Thermocouple Output Tables
View EMF versus Temperature tables for all thermocouple types.
What are the thermocouple colour codes?
Explore thermocouple colour codes for cable and connectors.