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Type K Thermocouple - Temperature Sensors / Probes

Type K - Nickel-Chromium vs Nickel-Aluminium

Thermocouple Type K, generally referred to as Chromel-Alumel, is the most common thermocouple in use today. Type K thermocouples are designed primarily for general temperature measurements in normal atmospheres. Maximum continuous temperature is about 1,100°C, although above 800°C oxidation increasingly causes drift and decalibration. For short term exposure, however, there is a small extension to 1,200°C. The device is also suitable for cryogenic applications down to -250°C.

Although theType K thermocouple is widely used because of its wide temperature range and cheapness, it is not as stable as other base metal sensors in common use. At temperatures between 250°C and 600°C, but especially 300°C and 550°C, temperature cycling hysteresis can result in errors of several degrees. A Type K thermocouple should not be used in reducing atmospheres unless protected by a suitable sheath and whilst Type K thermocouples are popular for nuclear applications because of its relative radiation hardness, Type N is a better choice for those applications.

Type K Thermocouples - Typical Constructions and Styles

Type K Mineral Insulated
Thermocouples

Type K Thermocouples with Mineral Insulation

Rugged sensors, ideal for most applications. Vast choice of terminations e.g. pot seals, cables, connectors, heads etc.

Type K Swaged Tip
Thermocouples

Fast response thermocouples ideal for industrial and other applications.

Type K Miniature
Thermocouples

Type K Thermocouples in Miniature Styles

Ideal for precision temperature measurements where minimal displacement and a fast response is required.

Type K Heavy Duty
Thermocouples

For industrial applications such as furnaces, kilns, ovens, boilers, flues etc. Many types of sheath material available.

General Purpose
Type K Thermocouples

Type K Thermocouples in different styles

A wide range of thermocouples to suit many applications. Hand held, surface, bayonet, bolt, patch styles etc.

ATEX/IECEx Approved
Type K Thermocouples

Type K Thermocouples with ATEX/IECEx certification

A large range of thermocouples with a variety of terminations such as pot seal, terminal heads etc.

Type K - Technical Data

Conductor Combination		Approximate generated EMF change in µV per ºC change (referenced to 0ºC) at:			Approximate Working Temperature Range		Initial Calibration Tolerances to ASTM E-230 (whichever is greater)		Thermocouple Output Tolerances to IEC 60584-1
+ Leg	- Leg	100ºC	500ºC	1000ºC	ºF	ºC	Standard	Special	Type	Class 1	Class 2	Class 3
NICKEL - CHROMIUM Also known as: Chromel™, Thermokanthal KP, NiCr, T1, Tophel™	NICKEL - ALUMINIUM (magnetic) Also known as: Ni-Al, Alumel™, Thermokanthal KN™, T2™, NiAl™	42	43	39	32 to 2300	0 to 1260	±2.2 or ±0.75%	±1.1 or ±0.4%	Temperature Range Tolerance Value Temperature Range Tolerance Value	–40°C to +375°C ±1.5°C 375°C to 1000°C ±0.004 ⋅ [t]	–40°C to +333°C ±2.5°C 333°C to 1200°C ±0.0075 ⋅ [t]	–167°C to +40°C ±2.5°C –200°C to –167°C ±0.015 ⋅ [t]

1. The tolerance is expressed either as a deviation in degrees Celsius or as a function of the actual temperature.
2. Thermocouple materials are normally supplied to meet the tolerances specified in the table for temperatures above –40 deg C. These materials however, may not fall within the tolerances for low temperatures given under Class 3 for Types T, E and K thermocouples. If thermocouples are required to meet limits of Class 3, as well as those of Class 1 and/or Class 2, the purchaser should state this, as selection of materials is usually required.

What Color is Type K Thermocouple Wire?

IEC 60584-3 provides tolerances and identification for a common international system for thermocouple wire identification and tolerances based essentially on thermoelectric emf as opposed to a datum of the emf of the thermo elements against platinum. Tolerances are defined as the maximum allowable deviation in microvolts, caused by the introduction of extension or compensating extension wire into the circuit. Color codes and tolerances are well established in the United States and have been in use as a national standard for years. In other parts of the world, there are alternative color code systems and tolerances, either in use, or in the process of being implemented. One such color code system is that established by the IEC.

In the United States, color codes and tolerances are defined in ANSI 96.1 (1982) and ASTM E-230. Extension wire and compensating extension wire is indicated with the letter “X” after the thermocouple type per these standards. The color code for thermocouple grade wire includes a brown overall jacket whereas the color code for thermocouple extension wire typically includes an overall jacket in the color of the positive wire. For some insulations, colors may appear as a stripe or trace strand. High temperature braided insulation is not normally color coded.

The table below shows the color coding adopted by the ASTM and IEC. Please click here for all thermocouple wire colour codes.