What is a Type K Thermocouple? - Technical Information
Type K - Nickel-Chromium vs Nickel-Aluminium, IEC 60584-1
Thermocouple Type K, also referred to as Chromel-Alumel, is the most common thermocouple in use today mainly because it is reliable, inexpensive, has a wide temperature range and is reasonably accurate. 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.
Type K thermocouples 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.
What are typical Type K thermocouple sensor styles?
Type K Mineral InsulatedThermocouples
Rugged sensors, ideal for most applications. Vast choice of terminations e.g. pot seals, cables, connectors, heads etc.Type K Swaged TipThermocouples
Fast response thermocouples ideal for industrial and other applications.
Type K MiniatureThermocouples
Ideal for precision temperature measurements where minimal displacement and a fast response is required.
Type K Heavy DutyThermocouples
For industrial applications such as furnaces, kilns, ovens, boliers, flues etc. Many types of sheath material available.
General PurposeType K Thermocouples
A wide range of thermocouples to suit many applications. Hand held, surface, bayonet, bolt, patch styles etc.
ATEX/IECEx ApprovedType K Thermocouples
A large range of thermocouples with a variety of terminations such as pot seal, terminal heads etc.
Type K - Technical Data
What are the conductors of a Type K Thermocouple?
The positive conductor of a Type K thermocouple is NICKEL - CHROMIUM which is also known as: Chromel™, Thermokanthal KP*, NiCr, T1* and Tophel™, whilst the negative conductor is NICKEL - ALUMINIUM (magnetic which helps with identification) and is also known as: Ni-Al, Alumel™, Thermokanthal KN™, T2™, NiAl™.
How accurate is a Type K Thermocouple?
There are a few factors to consider when quoting the accuracy of a thermocouple, such as the tolerance class of any cables or connectors and the accuracy of the associated indicators or instrumentation. The following accuracy figures are for the thermocouple material that we use in the manufacture of our thermocouple sensors and correspond to the output tolerances stated within IEC 60584-1:
We offer UKAS accredited thermocouple calibration and other services to prove the accuracy of complete thermocouple probes and systems.
What is the temperature range of a Type K Thermocouple?
The design of any specific thermocouple sensor has an influence on the temperaure range of the sensor. Things such as sheath diameter and sheath material can be a limiting factor as well as associated cables, connectors, sealants etc. The following ranges are for the thermocouple material used in the manufacture of our thermocouples: Continuous: 0ºC to +1100ºC and Short Term: -180ºC to +1350ºC.
What is the output from a Type K Thermocouple?
A Type K Thermocouple generates an EMF according to the differential in temperature between the measuring junction and the reference junction. A detailed explanation can be found in our guide to how a thermocouple works. The specific EMF change per ºC in accordance with IEC 60584-1 can be found on our Type K Thermocouple Output Table, however, some approximate generated EMF change in µV per ºC change (referenced to 0ºC) are as follows: at 100ºC = 42µV, at 500ºC = 43µV and at 1000ºC = 39µV.
What is the Colour Code for a Type K Thermocouple?
The most widely used colour code for Type K thermocouple cable is to the international IEC 60584-3 standard where the outer sheath is green, the positive NiCr conductor is also green and the negative NiAl conductor is colour coded white. Sometimes in the UK, American ANSI colours may be found which have a yellow outer sheath and yellow and red conductors as shown below. The colours of connectors for both match the outer sheath colour. You may also come across some old redundant colours such as the old BS1843 standard and these are shown in the table below:
| Thermocouple Type |
Extension and Compensating Cable Type | International Colour Code to IEC 60584-3 | American Colour Code to ANSI/MC96.1 |
Redundant national colour coding for thermocouple cables | |||||
|---|---|---|---|---|---|---|---|---|---|
| Extension Cable |
Compensating Cable |
Thermocouple Cable Colour | Intrinsically Safe Colour | Connector Colour | |||||
| BS 1843 | DIN 43714 | NFC 42324 | |||||||
| K | KX |  |
 |
 |
 |
 |
 |
 |
|
| KCA | |
||||||||
| KCB | |
 |  | ||||||
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