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Thermocouple Colour Codes & Tolerances

 
[ Thermocouple Colour Codes & Tolerances ]

Thermocouple temperature sensors can be made with various conductor materials for different temperature ranges and output characteristics. Over the years these have been standardised with defined temperature difference vs millivolt output relationships.

These established thermocouple “Types”, e.g. “Type K”, (sometimes confusingly referred to as “thermocouple calibrations”) are not compatible with each other and must have their own connecting cables and measurement instruments configured for that Type. Because of the way thermocouples work it is paramount that polarity (connection of positive to positive and negative to negative) is always followed through all connections.

Thermocouple Extension & Compensating Cable Colour Codes

The table below shows the most commonly encountered colour codes used on thermocouple leads and connectors. These are used to identify the Type and positive and negative wires. It is important to recognise the unfortunate use of the same colours for outer sheaths and connectors on different thermocouple types under different standards. Other colour coding systems also exist but are not shown below, these include French, German and Japanese.

Thermocouple
Type
IEC* / British
(IEC 60584-3:2007 / BS EN 60584-3:2008)
ANSI / American
(ANSI MC96.1 / ASTEM E230)
Former British
(BS 1843:1952)
Former Sheffield
(Bastardised system, 1950 onwards, developed by Land Pyrometers Ltd)
Type E
N/A
Type J
Type K
Extension
Type K
Compensating
Same as above.
Same as above.
Type N
N/A
Type R & Type S
Type T
N/A
Type B N/A. Uses uncompensated (copper) cable. Connectors are often white.

*IEC Intrinsically Safe Circuits have a blue outer insulation sheath (instead of the same colour as the inner positive insulation sheath).

Thermocouple Temperature Ranges

The table below shows the defined temperature ranges for thermocouple types. The IEC standard defines Class Tolerances for initial accuracy over a given temperature range. Outside these temperatures the manufacturing accuracy is unknown and if a thermocouple is used outside these temperatures it may de-calibrate (permanently lose accuracy) at a much faster rate.

Thermocouple
Type
Temperature Range (°C)
Short Term Use Continuous Use Class 1 Tolerance* Class 2 Tolerance* Class 3 Tolerance*
Type E −40 to +900 0 to +800 -40 to +800 -40 to +900 -200 to +40
Type J −180 to +800 0 to +750 -40 to +750 -40 to +750 N/A
Type K −180 to +1300 0 to +1100 -40 to +1000 -40 to +1200 -200 to +40
Type N −270 to +1300 0 to +1100 -40 to +1000 -40 to +1200 -200 to +40
Type R -50 to +1700 0 to +1600 0 to +1600 0 to +1600 N/A
Type S −50 to +1750 0 to +1600 0 to +1600 0 to +1600 N/A
Type T −250 to +400 −185 to +300 -40 to +350 -40 to +350 -200 to +40
Type B 0 to +1820 +200 to +1700 N/A +600 to +1700 +600 to +1700

Thermocouple Tolerances: IEC 60584-2:1982 / BS EN 60584-2:1993
*Thermocouples of this tolerance class can be used outside this range, but no tolerance is defined outside these limits.

Thermocouple Materials & Accuracy Tolerances

Thermo-
couple
Material
( + / – )
Class 1 Tolerance Class 2 Tolerance Class 3 Tolerance
Type E Chromel / Constantan -40 to +375 : ±1.5°C
+375 to +800 : ±0.4%
-40 to +333 : ±2.5°C
+333 to +900 : ±0.75%
-200 to -167 : ±1.5%
-167 to +40 : ±2.5°C
Type J Iron / Constantan -40 to +375 : ±1.5°C
+375 to +750 : ±0.4%
-40 to +333 : ±2.5°C
+333 to +750 : ±0.75%
N/A
Type K Chromel / Alumel -40 to +375 : ±1.5°C
+375 to +1000 : ±0.4%
-40 to +333 : ±2.5°C
+333 to +1200 : ±0.75%
-200 to -167 : ±1.5%
-167 to +40 : ±2.5°C
Type N Nicrosil / Nisil -40 to +375 : ±1.5°C
+375 to +1000 : ±0.4%
-40 to +333 : ±2.5°C
+333 to +1200 : ±0.75%
-200 to -167 : ±1.5%
-167 to +40 : ±2.5°C
Type R &
Type S
Platinum–Rhodium / Platinum 0 to +1100 : ±1°C
+1100 to +1600 : ±(1°C+0.003* (t°C-1100°C))°C
0 to +600 : ±1.5°C
+600 to +1600 : ±0.25%
N/A
Type T Copper / Constantan -40 to +125 : ±0.5°C
+125 to +350 : ±0.4%
-40 to +133 : ±1°C
+133 to +350 : ±0.75%
-200 to -67 : ±1.5%
-67 to +40 : ±1°C
Type B Platinum–Rhodium / Platinum–Rhodium N/A +600 to +1700 : ±0.25% +600 to +800 : ±4°C
+800 to +1700 : ±0.5%

Thermocouple Tolerances: IEC 60584-2:1982 / BS EN 60584-2:1993

Thermocouples & RTDs Accuracy Tolerance Comparison

The table below contains the manufacturing tolerances for different thermocouple types and Pt100s classes at different temperatures. These are ± (+/-) values, so a Class 1 Type K thermocouple at 500°C is ±2°C, so could read anything between 498°C and 502°C and be within manufacturing tolerance. But remember, with use thermocouples will de-calibrate and drift outside these tolerances, which is why calibration is so important.

Select Temperature Range:

  Thermocouple Pt100
RTD
Type: E J K N R & S T B
Class: 1 2 1 2 1 2 1 2 1 2 1 2 2 3 A B

Thermocouple Tolerances: IEC 60584-2:1982 / BS EN 60584-2:1993. RTD Tolerances: IEC 60751:2008 / BS EN 60751:2008

Thermocouple Extension & Compensating Cable Accuracy Tolerances

Thermocouple
& Cable Type
Cable Ambient Temperature Rating Tolerance (Constant µV / Example °C) Example Measured Temperature
Class 1 Class 2
Type E Extension (EX) -25°C to +200°C ± 120 µV / ± 1.5 °C ± 200 µV / ± 2.5 °C 500°C
Type J Extension (JX) -25°C to +200°C ± 85 µV / ± 1.5 °C ± 140 µV / ± 2.5 °C 500°C
Type K Extension (KX) -25°C to +200°C ± 60 µV / ± 1.5 °C ± 100 µV / ± 2.5 °C 900°C
Type K
Compensating A (KCA)
0°C to +150°C ± 100 µV / ± 2.5 °C 900°C
Type K
Compensating B (KCB)
0°C to +100°C ± 100 µV / ± 2.5 °C 900°C
Type N Extension (NX) -25°C to +200°C ± 60 µV / ± 1.5 °C ± 100 µV / ± 2.5 °C 900°C
Type N
Compensating (NC)
0°C to +150°C ± 100 µV / ± 2.5 °C 900°C
Type R
Compensating A (RCA)
0°C to +100°C ± 30 µV / ± 2.5 °C 1000°C
Type R
Compensating B (RCB)
0°C to +200°C ± 60 µV / ± 5.0 °C 1000°C
Type S
Compensating A (SCA)
0°C to +100°C ± 30 µV / ± 2.5 °C 1000°C
Type S
Compensating B (SCB)
0°C to +200°C ± 60 µV / ± 5.0 °C 1000°C
Type T Extension (TX) -25°C to +100°C ± 30 µV / ± 0.5 °C ± 60 µV / ± 1.0 °C 300°C
Type B (Copper / Uncompensated) 0°C to +100°C ± 40 µV / ± 3.5 °C 1400°C

Thermocouple Extension and Compensating Cables Tolerances: IEC 60584-3:2007 / BS EN 60584-3:2008