# Thermocouple Alloy Comparison

> Side-by-side comparison of all five standardised base-metal thermocouple types. Composition, temperature range, EMF output, oxidation resistance and relative cost.


> 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:

1. **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.
2. **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.
3. **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.