Thermocouple Types

Table of Contents

TYPE J THERMOCOUPLE (Iron/Constantan) #

Composed of a positive leg which is iron and a negative leg which is approximately 45 % nickel-55% copper. (Note – Constantan is Copper-Nickel.)

Type J Thermocouple Color Code

When protected by compacted mineral insulation and appropriate outer sheath, Type J is useable from 0 to 816°C, (32 to 1500°F). It is not susceptible to aging in the 371 to 538°C, (700 to 1000°F) temperature range. A drift rate of 1 to 2°C, (2 to 4°F) occurs with Type E and K in the 371 to 538°C, (700 to 1000°F) temperature range. This low cost, stable calibration is primarily used with 96% pure MgO insulation and a stainless steel sheath.

Thermocouple Grade- 32°F to 1382°F, 0 to 750°C

Extension Grade- 32°F to 392°F, 0 to 200°C

Reference Charts

TYPE K THERMOCOUPLE (Chromel / Alumel)200°C to +1260°C / -328°F to +2300°F #

Chromel {90% nickel and 10% chromium} Alumel {95% nickel, 2% manganese, 2% aluminium and 1% silicon}

Type K Thermocouple Color

 

Thermocouple Type K #

This is the most common thermocouple type that provides the widest operating temperature range. Type K thermocouples generally will work in most applications because they are nickel based and have good corrosion resistance.

  • Positive leg is non-magnetic (Yellow), negative leg is magnetic (Red).
  • Traditional base-metal choice for high temperature work.
  • Appropriate for use in oxidizing or inert atmospheres at temperatures up to 1260°C (2300°F).
  • Vulnerable to sulfur attack (refrain from exposing to sulfur-containing atmospheres).
  • Perform best in clean oxidizing atmospheres.
  • Not recommended for use under partially oxidizing conditions in vacuum, or when subjected to alternating cycles of oxidization and reduction.

Composed of a positive leg, which is approximately 90% nickel, 10% chromium and a negative leg, which is approximately 95% nickel, 2% aluminum, 2% manganese and 1% silicon.Type K Thermocouples are the most common general purpose thermocouple with a sensitivity of approximately 41µV/°C, chromel positive relative to alumel. It is inexpensive, and a wide variety of probes are available in its -200°C to +1260°C / -328°F to +2300°F range. Type K was specified at a time when metallurgy was less advanced than it is today, and consequently characteristics vary considerably between samples. One of the constituent metals, nickel, is magnetic; a characteristic of thermocouples made with magnetic material is that they undergo a step change in output when the magnetic material reaches its Cure Point (around 354 °C for type K thermocouples).

Type K Thermocouple ( Chromel/Constantan) #

Type K thermocouples usually work in most applications as they are nickel based and exhibit good corrosion resistance. It is the most common sensor calibration type providing the widest operating temperature range. Due to its reliability and accuracy the Type K thermocouple is used extensively at temperatures up to 2300°F (1260°C). This type of thermocouple should be protected with a suitable metal or ceramic protection tube, especially in reducing atmospheres. In oxidizing atmospheres, such as electric furnaces, tube protection is not always necessary when other conditions are suitable; however, it is recommended for cleanliness and general mechanical protection. Type K will generally outlast Type J because the JP wire rapidly oxidizes, especially at higher temperatures.

Type K Thermocouple Color Code

Temperature Range:

  • Thermocouple grade wire, −454° to 2,300°F (−270 to 1,260°C)
  • Extension grade wire, −32° to 392°F (0 to 200°C)
  • Melting Point, 2550°F (1400°C)
    Accuracy (whichever is greater):
    • Standard: ± 2.2C% or ±.75%
    • Special Limits of Error: ± 1.1C or 0.4%

Deviations in the alloys can affect the accuracy of thermocouples. For type K thermocouples the tolerance class one is given as ± 1.5 K between -40 and 375 °C. However, deviations between thermocouples coming from the same production are very small and a much higher accuracy can be achieved by individual calibration. Metallurgical changes can cause a calibration drift of 1 to 2°C in a few hours, increasing to 5 °C over time. A special grade of Type K is available that can maintain special limit accuracy up to ten times longer than the regular grade.

Reference Charts

TYPE E THERMOCOUPLE (Chromel / Constantan) #

Composed of a positive leg, which is approximately 90% nickel, 10 chromium and a negative leg, which is approximately 95% nickel, 2% aluminum, 2% manganese and 1% silicon.

Type E Thermocouple Color Code

When protected by compacted mineral insulation and appropriate outer sheath, Type E is usable from 0 to 900°C, (32 to 1652°F). This Thermocouple has the highest EMF output per degree of all recognized thermocouples. If the temperature is between 316 to 593°C, (600 to 1100°F), we recommend using type J or N because of aging which can cause drift of 1 to 2°C, (2 to 4°F) in a few hours time. For applications below 0°C, (32°F), special selection of alloys are usually required.

Reference Charts

TYPE T THERMOCOUPLE (Copper / Constantan) #

(copper-constantan) type t thermocouples are suited for measurements in the −200 to 350 °C range. Often used as a differential measurement since only copper wire touches the probes

Type T Thermocouple Color Code

When protected by compacted mineral insulation and appropriate outer sheath, Type T is usable from 0 to 350°C, (32 to 662°F). Type T is very stable and is used in a wide variety of cryogenic and low temperature applications. For applications below 0°C, (32°F) special selection of alloys are usually required.

Reference Charts

TYPE N THERMOCOUPLE (Nicrosil / Nisil) #

Type N (Nicrosil/Nisil) (nickel-chromium-silicon/nickel-silicon) thermocouples are suitable for use between -270 °C and 1300 °C owing to its stability and oxidation resistance. Sensitivity is about 39 ?V/°C at 900 °C, slightly lower compared to type K.

Type N Thermocouple Color Code

When protected by compacted mineral insulation and appropriate outer sheath, Type N is useable from 0 to 1260°C, (32 to 2300°F). Type N was developed to overcome several problems inherent in Type K thermocouples. Aging in the 316 to 593°C, (600 to 1100°F) temperatures is considerably less. Type N has also been found to be more stable than Type K in nuclear environments.

Reference Charts

TYPE B THERMOCOUPLE (Platinum / Rhodium) #

Composed of a positive leg which is approximately 14% chromium, 1.4% Silicon and 84.6% Nickel, a negative leg which is approximately 4.4% Silicon, 95.6% Nickel.

Type B Thermocouple Color Code

When protected by compacted mineral insulation and appropriate outer sheath, Type B is usable from 871 to 1704°C, (1600 to 3100°F). Also easily contaminated, and damaged by reducing atmospheres. The same protective measures as shown above apply to type B Thermocouples.

Reference Charts

TYPE S THERMOCOUPLE (Platinum / Rhodium) #

Composed of a positive leg which is approximately 70% Platinum, 30% Rhodium and a negative leg which is approximately 94% Platinum, 6% Rhodium.

Type S Thermocouple Color Code

When protected by compacted mineral insulation and appropriate outer sheath, Type S is usable from 0 to 1482°C, (32 to 2700°F). Easily contaminated. Reducing atmospheres are particularly damaging. Type S should be protected with gas tight ceramic tubes, a secondary tube of porcelain and silicon carbide or metal outer tubes, as conditions require.

Reference Charts

TYPE R THERMOCOUPLE (Platinum / Rhodium) #

Composed of a positive leg which is approximately 70% Platinum, 30% Rhodium and a negative leg which is approximately 94% Platinum, 6% Rhodium.

Type R Thermocouple Color Code

When protected by compacted mineral insulation and appropriate outer sheath, Type R is usable from 0 to 1482°C, ( 32 to 2700°F).Type R has a higher EMF output than type S. Also easily contaminated, and damaged by reducing atmospheres. Type R should by protected in a similar fashion as Type S.

Reference Charts

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