Base Metal Thermocouples
Types J, K, T, E
Most common thermocouples for industrial and general-purpose applications. Inexpensive, widely available, suitable for temperatures up to 1300 °C. Different types optimized for specific temperature ranges and atmospheres.
Thermocouple Specifications
IEC 60584| Type | Positive (+) | Negative (-) | Color (IEC) | Color (ANSI) | Range ( °C) | Notes |
|---|---|---|---|---|---|---|
| J | Iron (Fe) | Constantan (Cu-Ni) | White/Black | White/Red | -40 to 750 | Reducing atmospheres, oxidizes above 500 °C |
| K | Chromel (Ni-Cr) | Alumel (Ni-Al) | Green/White | Yellow/Red | -200 to 1250 | Most common, oxidizing atmospheres |
| T | Copper (Cu) | Constantan (Cu-Ni) | Brown/White | Blue/Red | -200 to 350 | Cryogenic to moderate, moist atmospheres |
| E | Chromel (Ni-Cr) | Constantan (Cu-Ni) | Violet/White | Purple/Red | -200 to 900 | Highest output (mV/ °C), oxidizing |
Important Notes
- • Type K: Most widely used (60%+ of applications); general purpose
- • Type J: Limited to 750 °C; iron leg oxidizes rapidly above 500 °C
- • Type T: Best for cryogenic (-200 °C) and moist/corrosive atmospheres
- • Type E: Highest sensitivity (~68 μV/ °C); good for low-temperature precision
Noble Metal Thermocouples
Types R, S, B
Platinum-based thermocouples for high-temperature applications. Excellent stability and accuracy but expensive. Used in laboratories, heat treatment, and high-temperature processes up to 1700 °C.
Thermocouple Specifications
IEC 60584| Type | Positive (+) | Negative (-) | Color (IEC) | Color (ANSI) | Range ( °C) | Notes |
|---|---|---|---|---|---|---|
| R | Pt-13%Rh | Platinum (Pt) | Orange/White | Black/Red | 0 to 1450 | High accuracy, oxidizing/inert |
| S | Pt-10%Rh | Platinum (Pt) | Orange/White | Black/Red | 0 to 1450 | Similar to R, slightly lower output |
| B | Pt-30%Rh | Pt-6%Rh | Gray/White | Gray/Red | 200 to 1700 | Highest temperature, no cold junction needed |
Important Notes
- • Types R/S: Nearly identical; Type S slightly less sensitive but more stable
- • Type B: Unique - generates negligible voltage below 50 °C, no cold junction needed
- • Contamination: Platinum contaminated by base metals; use protection tubes
- • Cost: 10-20× more expensive than base metal types
Refractory Metal Thermocouples
Types N, C, D, G
Special-purpose thermocouples for extreme temperatures and harsh environments. Types N (Nicrosil-Nisil) as alternative to Type K. Tungsten-rhenium types (C, D, G) for vacuum/inert atmospheres up to 2300 °C.
Thermocouple Specifications
IEC 60584| Type | Positive (+) | Negative (-) | Color (IEC) | Color (ANSI) | Range ( °C) | Notes |
|---|---|---|---|---|---|---|
| N | Nicrosil (Ni-Cr-Si) | Nisil (Ni-Si-Mg) | Pink/White | Orange/Red | -270 to 1250 | Type K replacement, better stability |
| C | W-5%Re | W-26%Re | - | Green/White | 0 to 2300 | Vacuum/inert only, very high temp |
| D | W-3%Re | W-25%Re | - | Green/White | 0 to 2300 | Similar to C, slightly different output |
| G | Tungsten (W) | W-26%Re | - | - | 0 to 2200 | Vacuum/hydrogen, extreme temp |
Important Notes
- • Type N: Direct replacement for Type K; better stability above 1000 °C
- • Types C/D/G: Tungsten-rhenium; MUST use in vacuum, hydrogen, or inert gas
- • Oxidation: Tungsten oxidizes rapidly in air above 500 °C - will fail
- • Insulation: Use alumina or beryllia protection tubes for refractory types
Color Code Comparison
IEC 60584 vs ANSI MC96.1
Critical difference between IEC (international) and ANSI (US) color standards. IEC uses positive leg color + white; ANSI uses positive leg color + red negative. Mismatched colors cause reverse polarity and measurement errors.
Color Code Standards
IEC 60584 / ANSI MC96.1| Type (Standard) | Positive (+) Color | Negative (-) Color | Notes |
|---|---|---|---|
| Type J (IEC) | Black | White | IEC 60584-3 standard |
| Type J (ANSI) | White | Red | ANSI MC96.1 standard |
| Type K (IEC) | Green | White | Most common internationally |
| Type K (ANSI) | Yellow | Red | US standard, different from IEC! |
| Type T (IEC) | Brown | White | Cryogenic applications |
| Type T (ANSI) | Blue | Red | US standard |
| Type E (IEC) | Violet | White | High sensitivity |
| Type E (ANSI) | Purple | Red | US standard |
Important Notes
- • CRITICAL: IEC and ANSI colors are DIFFERENT - verify standard before wiring!
- • IEC rule: Positive leg = colored; Negative leg = WHITE
- • ANSI rule: Positive leg = colored; Negative leg = RED (always)
- • Type K example: IEC = Green/White; ANSI = Yellow/Red - completely different!
- • Polarity check: Use magnet (Type K positive is slightly magnetic) or voltmeter with heat