Type N for above 1000 °C, Type T below zero, Type J for reducing atmospheres.
| Type | Alloy Pair | Range | Sensitivity | Accuracy | Oxidation | Cost | Best For |
|---|---|---|---|---|---|---|---|
| K | Chromel / Alumel | −200 … +1370 °C | 41 µV/°C | ±1.5 °C | Good (clean air) | $ | General purpose, furnaces, kilns |
| N | Nicrosil / Nisil | −270 … +1300 °C | 39 µV/°C | ±1.5 °C | Excellent (no green rot) | $$ | High-temp, vacuum, aerospace |
| J | Iron / Constantan | −40 … +750 °C | 55 µV/°C | ±1.5 °C | Poor above 550 °C | $ | Plastics, food, HVAC, reducing atm |
| T | Copper / Constantan | −200 … +350 °C | 43 µV/°C | ±0.5 °C | Good (moist environments) | $ | Cryogenic, pharma, autoclave |
| E | Chromel / Constantan | −200 … +900 °C | 68 µV/°C | ±1.5 °C | Good | $ | High-sensitivity, non-magnetic |
Selection quick guide
Work through three questions in order:
- How hot does it get? Above 1000 °C → Type N, or a noble metal above about 1200 °C; below → any base-metal type can be considered.
- Does it go below zero? Type T for accuracy (±0.5 °C), Type E for the largest signal (68 µV/°C). Both are non-magnetic.
- What is the atmosphere? Reducing → Type J at moderate temperatures, Type N above 800 °C. Avoid Type K in low-oxygen service above 800 °C.
Above 1000 °C?
Use Type N or Type R/S/B (noble metal). Type K drifts above 1000 °C in oxidising atmospheres. Type N was developed specifically to solve this.
Below zero?
Type T is the most accurate below 0 °C (±0.5 °C). Type E has the highest signal (68 µV/°C) for cryogenic instrumentation. Both are non-magnetic.
Reducing atmosphere?
Type J handles reducing atmospheres better than K. Type N avoids the green-rot problem entirely. Avoid Type K in low-oxygen environments above 800 °C.
Frequently Asked Questions
Which thermocouple type should I use above 1000 °C?
Type N for base-metal work, or a noble-metal Type R, S or B above roughly 1200 °C. Type K drifts in oxidising atmospheres above 1000 °C, and Type N was developed specifically to solve that.
What is the most accurate thermocouple type below zero?
Type T, at ±0.5 °C. Type E gives the highest signal, 68 µV/°C, for cryogenic instrumentation. Both are non-magnetic.
Which type is best for reducing atmospheres?
Type J handles reducing atmospheres better than Type K, and Type N avoids the green-rot problem entirely. Avoid Type K in low-oxygen environments above 800 °C.
How do the five base-metal types compare on sensitivity?
Type E is highest at 68 µV/°C, then J at 55, T at 43, K at 41 and N at 39 µV/°C. Higher sensitivity gives a larger signal for the same temperature change, which helps in electrically noisy installations.
Bottom line: Pick the type from three questions. Above 1000 °C, Type N — or a noble metal above about 1200 °C. Below zero, Type T for accuracy and Type E for signal. In a reducing atmosphere, Type J at moderate temperatures and Type N above 800 °C. Everything else is served by Type K.