thermowell assembly

Thermocouple sensors with wide operating temperature range

A thermocouple sensor consists of two dissimilar metals, joined together at one end. This junction is where the temperature is measured. A small voltage is produced by the two metals, which can be measured and interpreted by a control system. The dissimilar metals are individually insulated, and an overcoat is present to maintain an intimate bifilar configuration. Our thermocouple sensors and assemblies are offered in a variety of standard styles to fit a wide range of applications. Class 1 thermocouples are built according to IEC584. Custom thermocouple solutions are available. We offer decades of experience designing and manufacturing custom sensing solutions.

Product Features:

Capabilities of TE's Thermocouple Portfolio
  • Wide operating temperature range
  • Relatively constant sensitivity over their entire range
  • Industry standard output signals
  • Most popular alloy types available
  • Wide range of sizes available, from micro to heavy industrial
  • Metal sheathing and industrial connection head options
  • Full range of motor/generator and plastic industry styles

Type K Thermocouple

Widest temperature range

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 a good corrosion resistance.

  • Positive leg in 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 (regrain from exposure to sulfur-containing atmospheres)
  • Performs 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.

Type J Thermocouple

General purpose applications (no moisture)

This is the second most common thermocouple. It is a good choice for general purpose applications, if moisture is not present.

  • Appropriate for use in vacuum, air, reducing, or oxidizing atmospheres to 760°C (1400°F) in the heavier gauge sizes.
  • The expected service life of the finer sized wires is limited due to the rapid oxidation of the iron wire at temperatures above 540°C (1000°F)
  • Avoid use in sulfurous atmospheres above 540°C (1000°F)
  • Limited subzero use due to rusting and embrittlement of the iron conductor
  • Positive (iron) wire is magnetic (white), negative is non-magnetic (red)

Type E Thermocouple

Highest output EMF

  • Neither wire is magnetic but negative wire is red, positive is purple
  • Recommended for use to 900°C (1600°F) in oxidizing or inert atmospheres
  • Appropriate for low temperature to about -230°C (-380°F)
  • Has the highest output EMF of any standard type
  • Vulnerable to sulfur attack, do not expose to this type of atmosphere
  • Performs best in clean oxidizing atmospheres
  • Not recommended (except in short periods) for use in:
    • Under partially oxidizing conditions
    • When subjected to alternating cycles of oxidation and reduction
    • In vacuum    

Type T Thermocouple

Appropriate for use to -200°C

  • Neither wire is magnetic but the negative wire is red, positive wire is blue
  • When used in air:
    • Moisture resistant
    • Very stable
    • Useful to 370°C (700°F)
  • Higher temperature use is possible when used in a vacuum, or in reducing or inert atmospheres
  • Appropriate for use down to -200°C (370°F). Special selection may be required of the materials.
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Temperature Ranges

Type Application Range Trade Names Color Code
K 95-1260°C (200-2300°F) Chromel / Alumel Red(-) / Yellow(+)
J 95-760°C (200-1400°F) Iron / Constantan Red(-) / White(+)
E 95-900°C (200-1650°F) Chromel / Constantan Red(-) / Purple(+)
T 0-350°C (32-660°F) Copper / Constantan Red(-) / Blue(+)

Tolerance Ranges

Initial Calibration Tolerances

Type Temperature Range Standard Limits Special Limits
K -200°C to 0°C* 
0°C to 1250°C
±2.2°C or ±2%*
±2.2°C or ±0.75%
N/A
±1.1°C or ±0.4%
J 0°C to 750°C
±2.2°C or ±0.75% ± 1.1°C or ± 0.4%
E -200°C to 0°C*
0°C to 900°C
±1.7°C or ±1%*
±1.7°C or ±0.5%
±1°C or ±0.5%*
±1°C or ±0.4%
T -200°C to 0°C*
0°C to 350°C
±1°C or ±1.5%*
±1°C or ±0.75%
±0.5°C or ±0.8%*
±0.5°C or ±0.4%

*Thermocouple wire is usually supplied to meet tolerances for temperatures above 0°C.  Special selection and testing may be required for these same materials in order for them to fall within the sub-zero tolerances given. 

Thermocouple Wire Temperature Limits

Wire Size Temperature Limit

The table below gives the recommended upper temperature limits for the various thermocouples and wire sizes.   These limits apply to protected thermocouples, that is, thermocouples in conventional closed-end protecting tubes (sheaths). 

 

Gauge K J E T
20 980°C (1800°F)  480°C (900°F)  540°C (1000°F)  260°C (500°F) 
24 870°C (1600°F)  370°C (700°F)  430°C (800°F)  200°C (400°F) 
28 870°C (1600°F)  370°C (700°F)  430°C (800°F)  200°C (400°F) 
30 760°C (1400°F)  320°C (600°F)  370°C (700°F)  150°C (300°F) 
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  1. Stator Temperature Sensor (English)

TE Connectivity's (TE) stator temperature sensors provide high stability for various applications including large motors.

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Frequently Asked Questions

Q: What are the advantages and disadvantages of grounded thermocouples? 

A:  A grounded junction puts the junction in contact with the packaging, protecting, metal case. This allows for a faster response time, however, a grounded tip is susceptible to electromotive forces in the environment, which might cause potential errors in the measurement. An ungrounded junction, therefore, is one without a contact with the metal case. Thus, have slower response time, but is less likely to provide erroneous readings. 
Read More: RTDs & Thermocouples FAQs