Thermocouples

Thermocouples are sensors that measure temperature by detecting the voltage difference between metals or alloys. They consist of two wires of dissimilar metals joined at one end to form a sensing junction. Thermocouples are very rugged and inexpensive to replace in most cases. At EUSTIS/Pyrocom, we manufacture various types of thermocouple assemblies, available to meet nearly all industrial and scientific temperature range requirements.

Flexible Thermocouples For Industrial Applications

Thermocouples are available with flexible or “soft wire” insulations for applications requiring high levels of versatility, including surveys or portable industrial applications. Tube and wire-sheathed thermocouples are designed for mechanical strength or hold at the insertion point into machine processes such as plastic injection molds and food applications. The thermocouples in this section are considered low-temperature thermocouples at 900°F (482°C) and below. Insulations available are:
  • Fiberglass 900°F (482°C)
  • PFA Teflon® 500°F (260°C)
  • FEP Teflon® 400°F (204°C)
Additional insulations are available that are not listed in this section of the catalog (see Wire section).
Industrial Thermocouple Performance Specifications
Thermocouples can operate at temperatures from -454°F (-232°C) to 4,200°F (2315°C) and perform in extremely rugged applications. They respond quickly to temperature changes and are physically small and self-powered. Thermocouple accuracy has been established into standard limits of error (+ 2.2°C) or .75%, whichever is greater, and special limits of error (+ 1.1°C) .4%, whichever is greater.

Thermocouple Cold Junction Compensation

Thermocouples require a temperature reference to compensate for unwanted electromotive force (EMF) at ambient temperature. Traditionally, reference to 0°C was accomplished by an ice bath where the positive and negative legs were immersed in the bath. This method is impractical in most cases. Today, temperature controllers, thermometers, indicators, recorders & transmitters compensate for the unwanted thermoelectric contributions.

ASTM Thermocouple Alloy Combinations by Letter Type

Thermocouples are classified into different types based on the metals used in their wires, capacity, and calibration. Base metals are used in Types E, J, K, N, and T thermocouples, while noble metals are used in Types C, R, and S. The calibration of a thermocouple is established based on the combination of the metal used, the desired temperature range, and the influence of external environmental factors. Wires with larger diameters are more effective in utilizing the optimal temperature range. In selecting a thermocouple, it is essential to consider its temperature range and its resistance to chemicals, vibration, and abrasion.

Type J - Iron (+) Constantan (-)

Type J, Iron (+) Constantan (-) is the most commonly used calibration.  It is suitable for vacuum, inert, oxidizing, or reducing atmospheres. If unprotected, ammonia, nitrogen, and hydrogen atmospheres may attack the iron wire. Iron & Constantan wires can generate galvanic EMF between the two wires and should not be used in applications where they might get wet. The positive leg is magnetic.

Type T - Copper (+) Constantan (-)

Type T - Copper (+) Constantan (-) is commonly used for subzero to 700°F temperatures and preferred to Type J for subzero applications because of copper’s higher moisture resistance than iron.  It will still function in a vacuum, inert, oxidizing or reducing atmospheres if unprotected.  Copper-Constantan thermocouples are susceptible to conduction error due to the high thermal conductivity of the copper. Neither leg is magnetic.

Type K - Nickel-Chromium (+) vs.  Nickel-Aluminum (-)

Type K- Nickel-Chromium (+) vs.  Nickel-Aluminum (-) is generally used to measure high temperatures to 2300°F (1261°C). It should not be used for accurate temperature measurements below 900°F (482°C) or after prolonged exposure above 1,400°F (760°C).  It can be used only in inert or oxidizing atmospheres if left unprotected. It has a short life in alternately oxidizing and reducing atmospheres, particularly in the 1,500°F (816°C) to 1850°F (1010°C) range. The negative leg is magnetic.

Type E - Nickel-Chromium (+) vs. Constantan (-)

Type E- Nickel-Chromium (+) vs. Constantan (-) has the highest EMF output of any standardized metallic thermocouple.  If used unprotected, type E wire is not subject to corrosion at subzero temperatures.  Type E can be used in inert, oxidizing or reducing atmospheres.  Because they cover a wide range with a single calibration curve, type E thermocouples are preferred for computer applications.

Type N - Nicrosil (+) vs. Nisil (-)

Type N- Nicrosil (+) vs. Nisil (-) Superior oxidation resistance over type K due to the combination of a higher level of chromium and silicon in the N (+) (Nicrosil alloy) conductor. Similarly, a higher level of both silicon and magnesium forms a diffusion barrier to protect the N (-) (Nisil alloy). Because of increased stability, it is recommended in nuclear applications.

Type R - Platinum -13% Rhodium (+) vs. 100% Platinum (-)

Type R - Platinum - 13% Rhodium (+) vs. 100 % Platinum (-), These thermo elements should always be protected from contamination by reducing oxides, metallic vapors, or other oxides at high temperatures.  Insulation should be silica free to prevent contamination. Type S is frequently used for calibration standards. Type R is slightly more sensitive and commonly used in industrial applications.

Type B - Platinum - 30% Rhodium (+) vs.Platinum - 6% Rhodium (-)

Type B- Platinum - 30% Rhodium (+) vs.Platinum - 6% Rhodium (-). For use between 1000° and 3,175°F. It is intended to prevent the problems experienced with types S and R, such as (1) weakening of the pure platinum leg due to excessive grain growth and (2) calibration shift due to the pure platinum wire picking up rhodium volatilized from the alloy wire at 2,732°F. The flatness of the temperature-millivolt curve at normal reference junction ambient temperature permits the use of copper extension wire.

Type C - Tungsten - 5% Rhenium (+) vs. Tungsten - 26% Rhenium - (-)

Type C - Tungsten - 5% Rhenium (+) vs. Tungsten - 26% Rhenium - (-) thermo elements have excellent stability in the 3,000 to 4,000°F range. A protective atmosphere must be used at high temperatures, such as hydrogen, inert gas, or vacuum. They are susceptible to mechanical damage and should be handled carefully to prevent breakage.

A Trusted Manufacturer of Thermocouples for Industrial Applications

Located north of Seattle in Lynnwood, Washington, EUSTIS/Pyrocom has manufactured high-quality thermocouples since 1962. Our expertise as a custom RTD and thermocouple manufacturer allows us to offer a diverse range of products for industrial applications, including thermocouple fittings and specialized connectors. Our accredited temperature calibration laboratory provides calibration services for RTDs and thermocouples. At EUSTIS/Pyrocom, we are committed to ensuring the highest quality standards in all our thermocouple products and services.

Contact Us for Premium Flexible Thermocouples, Fittings, & Connectors

Contact us to learn more about the thermocouples we distribute. You can also request a quote for additional pricing information on our wire thermocouples, mineral-insulated thermocouples, and industrial thermocouples. EUSTIS/Pyrocom is your trusted source for reliable thermocouples for industrial applications.
*Teflon is a trademark of E. I. du Pont de Nemours and Company or its affiliates