The World's Most Popular Thermocouple
The Type K thermocouple (Chromel-Alumel) is the most widely used thermocouple in industrial temperature measurement. With a usable range from -200°C to +1260°C, Type K covers the majority of industrial, laboratory, and process control applications. Its combination of broad range, reasonable accuracy, and relatively low cost makes it the default choice for general-purpose temperature measurement.
Thermometrics manufactures Type K thermocouple assemblies in mineral-insulated metal-sheathed (MIMS) construction with grounded, ungrounded, and exposed junction options. Available in a wide range of sheath materials, diameters, and lengths with various termination styles including connectors, connection heads, and bare wire leads.
- Positive leg: Chromel (90% Nickel, 10% Chromium)
- Negative leg: Alumel (95% Nickel, 2% Manganese, 2% Aluminum, 1% Silicon)
- Temperature range: -200°C to +1260°C
- Standard tolerance: ±2.2°C or ±0.75% (whichever is greater)
- Special tolerance: ±1.1°C or ±0.4% (whichever is greater)
- Sensitivity: approximately 41 µV/°C at mid-range
Color Code
ANSI (US): Yellow (+) / Red (-), Yellow jacket
IEC (International): Green (+) / White (-), Green jacket
Connector color: Yellow (ANSI), Green (IEC)
Type K Specifications
| Parameter | Value |
|---|---|
| ANSI Designation | Type K |
| Positive Conductor | Chromel (Ni-10%Cr) |
| Negative Conductor | Alumel (Ni-2%Mn-2%Al-1%Si) |
| Temperature Range | -200°C to +1260°C |
| Standard Tolerance (ASTM E230) | ±2.2°C or ±0.75% (whichever is greater), 0°C to 1260°C |
| Special Tolerance (ASTM E230) | ±1.1°C or ±0.4% (whichever is greater), 0°C to 1260°C |
| EMF at 0°C | 0.000 mV (reference) |
| EMF at 100°C | 4.096 mV |
| EMF at 500°C | 20.644 mV |
| EMF at 1000°C | 41.276 mV |
| EMF at 1260°C | 51.000 mV (approx) |
| Seebeck Coefficient | ~41 µV/°C (at 20°C) |
| Recommended Atmosphere | Oxidizing, inert; avoid reducing, sulfurous |
| Maximum Wire Size | 8 AWG |
| Extension Wire Type | KX (Chromel-Alumel extension grade) |
Type K EMF vs. Temperature
Reference EMF values at key temperature points per NIST ITS-90 thermocouple reference tables. Reference junction at 0°C.
| Temperature (°C) | EMF (mV) | Temperature (°C) | EMF (mV) |
|---|---|---|---|
| -200 | -5.891 | 400 | 16.397 |
| -100 | -3.554 | 500 | 20.644 |
| 0 | 0.000 | 600 | 24.905 |
| 20 | 0.798 | 700 | 29.129 |
| 100 | 4.096 | 800 | 33.275 |
| 200 | 8.138 | 1000 | 41.276 |
| 300 | 12.209 | 1200 | 48.838 |
Available Configurations
MIMS (Standard)
Mineral-insulated metal-sheathed construction with MgO insulation compacted within a seamless alloy sheath. Our standard configuration for maximum durability and performance. Available in 304 SS, 316 SS, 321 SS, and Inconel 600 sheaths from 1/16" to 3/8" diameter.
Exposed Junction
Junction extends beyond the sheath for sub-second response time. Ideal for gas stream temperature measurement, wind tunnel testing, and applications where the fastest possible response outweighs the need for mechanical protection. Not suitable for liquid immersion or corrosive environments.
Dual Element
Two independent Type K junctions within a single sheath. Provides redundant measurement for safety-critical applications or allows simultaneous measurement at the same point with separate instruments. Available in any junction/sheath combination.
Fast Response
Miniature diameter (1/16" and 1/8") sheaths with grounded junctions for the fastest MIMS response times — typically 0.3–1.5 seconds in moving liquid and 3–8 seconds in still air. Ideal for batch process monitoring and injection molding.
Type K Applications
Type K is the general-purpose workhorse of temperature measurement, suitable for the vast majority of industrial applications within its -200°C to +1260°C range.
Important: Avoid Reducing Atmospheres
Type K thermocouples are not recommended for use in reducing or sulfurous atmospheres, or in vacuum above 1000°C. In reducing environments, the chromium in the Chromel leg can be preferentially oxidized (a phenomenon known as "green rot"), causing significant measurement drift. For reducing atmospheres, consider Type N or noble metal types (R, S, B).
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