High-temperature resistant thermocouples are core temperature-sensing elements used in industry for measuring high-temperature media. Their typical continuous operating temperature exceeds 800℃, and some special models can measure ultra-high temperatures above 1800℃. Based on the Seebeck effect, they convert temperature signals into thermoelectric voltage signals, suitable for high-temperature applications such as metallurgy, petrochemicals, kilns, glass manufacturing, and nuclear power.

Classified by thermocouple type and material, common industrial high-temperature resistant thermocouples include Type K, S, B, R, N, as well as special high-temperature tungsten-rhenium thermocouples. Below are detailed parameters, features, and application scenarios for each type.

I. General Industrial High-Temperature Thermocouples

(800℃ ~ 1600℃ | for standard high-temperature conditions)

1. Type K Thermocouple (Nickel-Chromium – Nickel-Silicon, Type K)

Max temperature: Continuous 1200℃, short-term 1300℃ (thicker wire = higher heat resistance)
Key features: Best cost-performance, most widely used; large thermoelectric voltage, high sensitivity (41.4μV/℃); good linearity, easy to match instruments; excellent oxidation resistance, stable in oxidizing/neutral atmospheres; prone to corrosion in reducing atmospheres (requires protective tube).
Material: Positive pole NiCr9-10; Negative pole NiSi3-4
Main applications: Oxidizing high-temperature conditions such as metallurgical kilns, petrochemical heating furnaces, boiler flues, and heat treatment furnaces. It is the mainstream high-temperature sensor in industry, balancing accuracy and cost.

2. Type S Thermocouple (Platinum-Rhodium 10 – Platinum, Type S)

Max temperature: Continuous 1300℃, short-term 1600℃
Key features: Precious metal type; high accuracy (Class 0.25 / 0.5); excellent chemical stability, oxidation and corrosion resistance; stable long-term in high-temperature oxidizing atmospheres; small thermoelectric voltage, low sensitivity (9.5μV/℃); high cost; thin wire is brittle and easy to break.
Material: Positive pole PtRh10; Negative pole pure Pt
Main applications: High-precision high-temperature measurement, such as laboratory furnaces, glass kilns, metallurgical smelting furnaces, and standard temperature calibration devices. Commonly used for high-precision measurement above 1000℃.

3. Type R Thermocouple (Platinum-Rhodium 13 – Platinum, Type R)

Max temperature: Continuous 1300℃, short-term 1600℃ (same as Type S)
Key features: Precious metal type, performance better than Type S; thermoelectric voltage about 15% higher than S, slightly higher sensitivity; excellent oxidation and high-temperature corrosion resistance; better high-temperature stability; more expensive than S; only for oxidizing atmospheres.
Material: Positive pole PtRh13; Negative pole pure Pt
Main applications: Replaces Type S for higher-precision, demanding high-temperature oxidizing conditions, such as aerospace high-temperature component testing, high-end metallurgical furnaces, and precision ceramic sintering furnaces. Less common in China, widely used in Europe and America.

4. Type B Thermocouple (Platinum-Rhodium 30 – Platinum-Rhodium 6, Type B)

Max temperature: Continuous 1600℃, short-term 1800℃ (highest-temperature general industrial precious metal thermocouple)
Key features: Best high-temperature stability among precious metal types; extremely strong oxidation resistance, works long-term at 1600℃; negligible thermoelectric voltage at low temperatures (nearly zero below 50℃, no cold-junction compensation needed); low sensitivity (~3.4μV/℃); high cost.
Material: Positive pole PtRh30; Negative pole PtRh6
Main applications: Ultra-high-temperature oxidizing conditions, including metallurgical blast furnaces, cement rotary kilns, glass melting furnaces, and aero-engine combustors (1200℃~1600℃). The most reliable high-temperature precious metal thermocouple in industry.

5. Type N Thermocouple (Nickel-Chromium-Silicon – Nickel-Silicon-Magnesium, Type N)

Max temperature: Continuous 1200℃, short-term 1300℃ (same as Type K)
Key features: Upgraded version of Type K; stronger high-temperature oxidation resistance; much better thermoelectric voltage stability above 1000℃ (no “high-temperature aging” of K); good linearity; sensitivity close to K (39.5μV/℃); slightly higher cost than K, still cost-effective.
Material: Positive pole NiCrSi5; Negative pole NiSiMg4
Main applications: Replaces Type K for long-term stable oxidizing conditions above 1000℃, such as petrochemical cracking furnaces, heat treatment furnaces, and ceramic kilns, solving K-type drift at high temperatures.

II. Special Ultra-High-Temperature Thermocouples

(1600℃ ~ 2800℃ | for extreme high-temperature conditions)

Tungsten-Rhenium Series Thermocouples

(Type WRe3/25, WRe5/26, etc.)

Max temperature: Continuous 2000℃, short-term 2800℃ in vacuum/inert atmosphere; continuous 1800℃ in reducing atmosphere (oxidizes rapidly in air, not usable in oxidizing conditions)
Key features: Refractory metal type; highest temperature limit; large thermoelectric voltage, high sensitivity; small size, fast response; poor oxidation resistance; must be used in vacuum, hydrogen, argon, or inert/reducing atmospheres with ceramic protection tubes.
Material: Positive pole WRe alloy (e.g., WRe3); Negative pole WRe alloy (e.g., WRe25)
Main applications: Extreme ultra-high-temperature measurement, such as metallurgical vacuum melting furnaces, aerospace high-temperature testing, nuclear reactors, and graphite electrode furnaces. The highest-temperature industrial thermocouple available.

III. Common Features & Selection Principles
1. Common Features

① Wide measuring range (800℃~2800℃) for various high-temperature environments.

② Simple structure (thermoelements + insulation tube + protection tube + connection head), vibration and shock resistant, suitable for harsh industrial sites.

③ Signal can be transmitted remotely; no external power needed; works with temperature transmitters and digital meters for automated measurement.

④ Heat resistance increases with thermoelememt wire diameter (thicker = higher continuous temp, slower response).

2. Core Selection Rules

① Atmosphere matching: Oxidizing/neutral → K/S/R/B/N; vacuum/inert/reducing → tungsten-rhenium.

② Temperature matching: Below 1200℃ → K/N (cost-effective); 1200~1600℃ → B (precious metal); above 1600℃ → tungsten-rhenium (special type).

③ Accuracy: High-precision calibration/lab → S/R; general industrial → K/N/B.

④ Cost: Prioritize nickel-based (K/N); use precious metals (S/R/B) or tungsten-rhenium only for ultra-high temp / high precision.

IV. Key Differences from Medium-Low Temperature Thermocouples

High-temperature thermocouples use high-temperature alloys, precious metals, or refractory metals for thermoelements, with protection tubes made of high-temperature ceramics (alumina, corundum), high-silicon cast iron, etc.

Medium-low temperature types (E/J/T) mostly use copper-based or copper-nickel alloys, with maximum temperature below 800℃, unsuitable for high-temperature conditions.

High-temperature models are mostly assembled types with rugged structure; medium-low types can be made as thin-core armored types for faster response.