If you’ve ever worked with a thermocouple, you’ve probably wondered about its colour code.
As Process Parameters explains (ProcessParameters.co.uk), each thermocouple has a colour code that you can use to identify the type of thermocouple it is, its temperature range, and its calibration value.
This post will show you how to interpret the colour code and how it relates to the temperature range of the thermocouple.
Type J Thermocouple
International Electrotechnical Commission (IEC) has set the colour code for J type thermocouple as follows:
Positive Lead – Black insulation
Negative Lead – White insulation
The jacket insulation and thermocouple connector housing are also black.
The temperature range for type J thermocouple grade wire is between -210 and 760 °C, while that of an extension wire is from 0 to 200°C.
According to the American National Standards Institute (ANSI) standard, the colour code of type J thermocouple is white insulation for the positive lead and red insulation for the negative lead, both enclosed by a black jacket.
The British Standard (BS 1843) for J type thermocouples is a black jacket, yellow insulation for the positive leg and blue insulation for the negative lead. The German standard is also relatively common. The postive and negative legs are red and blue, respectively, the jacket insulation is blue. This colour code causes confusion because it is identical to the American ANSI colour code for T-type thermocouples. However, you can differentiate between the two using a magnet. Type J has a strong magnetic positive lead, while type T has no magnetic conductors.
Type K Thermocouple
The IEC colour coding for K type thermocouple is:
Positive Lead – Green insulation
Negative Lead – White insulation
The jacket insulation and thermocouple connector housing are black.
Type K thermocouple can measure a wide temperature range (-27- to 1260°C); hence, its everyday use in nuclear applications due to its relative radiation hardness and oxidising atmosphere.
According to USA’s ANSI colour coding, the positive and negative legs have yellow and red insulation, respectively, while the jacket insulation is yellow. For British (BS 1843), the colour coding is brown insulation for the positive leg and blue insulation for the negative lead. The jacket insulation is red. German standard colour coding for K type thermocouple is; green insulation for the jacket while the positive and negative legs have red and green insulations.
Type T Thermocouple
T type thermocouple has a smaller temperature range of -210 to 760°C. the international colour coding for T type thermocouple is:
Positive Lead – Brown insulation
Negative Lead – White insulation
The jacket insulation and thermocouple connector housing are brown.
Type T thermocouple legs are not magnetic. However, it is the only thermocouple with a copper conductor. The U.S colour codes for this thermocouple are blue insulation for the positive conductor, red for the negative leg and blue jacket.
As for British BS 1843, the jacket insulation is blue, while the positive and negative conductors have white and blue insulations.
Type N Thermocouple
The N-type thermocouple is relatively new to the market. However, it is highly stable and reliable. Its maximum continuous operating temperature can reach 1260°C. Its temperature range is between -270 and 1260°C.
According to IEC colour coding, type N thermocouples have; pink jacket insulation, pink positive lead insulation and white negative lead insulation. ANSI colour codes are orange insulation for both the jacket and positive leads, while the negative lead has red insulation. With British’ BS 1843, type N thermocouple is assigned orange for positive leg and jacket insulation and blue for the negative conductor.
Type E Thermocouple
This thermocouple has a high EMF output and can measure temperatures between -270 and 870°C. IEC’s colour code for E type thermocouple is purple insulation for positive leg, jacket and thermocouple connector housing and white insulation for the negative leg.
American ANSI also assigns purple insulation for positive leg and jacket but the negative lead is assigned red insulation. British BS 1843 assigns brown colour for positive leg, blue for negative leg while and brown for the jacket insulation.
R/S Type Thermocouple
IEC colour code:
Positive Lead – Orange insulation
Negative Lead – White insulation
Jacket – Orange insulation
ANSI colour code:
Positive Lead – Black insulation
Negative Lead – Red insulation
Jacket – Green insulation
BS 1843 colour code:
Positive Lead – White insulation
Negative Lead – Blue insulation
Jacket – Green insulation
R/S type thermocouples can measure temperatures ranging from -50 to 1480.
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