FAQs

A thermocouple is composed of a pair of dissimilar metal wires joined at one end, which generates a net thermoelectric voltage between the open ends, corresponding to the temperature difference between these ends.

Working Principle:

Thermocouples operate based on the Seebeck Effect, the foundation of modern thermocouple technology. When two different metals are joined at two junctions, an electromotive force (emf) is produced at these junctions. The magnitude of the emf varies depending on the combination of metals used.

• Hot Junction: The junction inserted into the process where the temperature is being measured.
• Cold Junction: The other junction, located at the endpoint of the thermocouple material, usually connected to a measuring instrument.

The emf generated between the hot and cold junctions allows for temperature measurement, with different metal combinations producing varying emf levels for accurate readings.

Industrial heaters are employed in a wide range of applications to meet various heating requirements:

1. Industrial Immersion Heaters: These heaters are designed for direct contact heating of substances such as water, oils, viscous materials, solvents, process solutions, and gases across numerous industrial heating applications.
2. In-Line Heaters: Utilized for applications including water heating, freeze protection, heat transfer oil heating, fuel oil heating, steam, air, and gas heating, among other variable uses.
3. Furnace Heaters: Commonly used in different furnace applications, such as annealing furnaces and galvanizing furnaces, to achieve specific temperature conditions.
4. Component Heaters: Applied in processes like heat staking, plastic welding, laminating, drying, heat sealing, as well as high-temperature or corrosive applications. They are also critical in nuclear applications.

This outlines the diverse roles industrial heaters play in various industrial processes, highlighting their versatility and importance.

There are many material combinations used to produce thermocouples, each with specific applications. However, a few types are commonly available and cover most temperature and environmental applications. The standard includes eight specific and widely used thermocouple types, divided into three groups: base metal, noble (rare) metal, and refractory metal thermocouples.

Base Metal Thermocouples

These are made from common, inexpensive metals like nickel, iron, and copper. The most frequently used types in this group are:

• Type E (Chromel & Constantan, Ni-Cr & Cu-Ni): -200 to 900ºC, suitable for inert and oxidizing media.
• Type J (Iron & Constantan, Fe & Cu-Ni): 0 to 750ºC, suitable for inert, oxidizing, reducing media, and vacuum.
• Type K (Chromel & Alumel, Ni-Cr & Ni-Al): -200 to 1250ºC, suitable for inert and oxidizing media.
• Type N (Nicrosil & Nisil, Ni-Cr & Ni-Si): -270 to 1300ºC, suitable for inert and oxidizing media.
• Type T (Copper & Constantan, Cu & Cu-Ni): -200 to 350ºC, suitable for inert, oxidizing, reducing media, and vacuum.

Noble Metal Thermocouples

Made with precious metals like platinum and rhodium, the main types are:

• Type R (87% Platinum/13% Rhodium & Platinum, Pt-Rh & Pt): 0 to 1450ºC, suitable for inert and oxidizing media.
• Type S (90% Platinum/10% Rhodium & Platinum, Pt-Rh & Pt): 0 to 1450ºC, suitable for inert and oxidizing media.
• Type B (70% Platinum/30% Rhodium & 94% Platinum/6% Rhodium, Pt-Rh & Pt-Rh): 0 to 1700ºC, suitable for inert and oxidizing media.

Refractory Metal Thermocouples

Made with exotic metals like tungsten and rhenium, these thermocouples are expensive and difficult to manufacture, and their wires are very brittle:

• Type C (95% Tungsten/5% Rhenium & 74% Tungsten/26% Rhenium): 0 to 2320ºC, suitable for vacuum, inert, and reducing environments.
• Type G (Tungsten & 74% Tungsten/26% Rhenium): 0 to 2320ºC, suitable for vacuum, inert, and reducing environments.
• Type D (97% Tungsten/3% Rhenium & 75% Tungsten/25% Rhenium): 0 to 2320ºC, suitable for vacuum, inert, and reducing environments.

This summarizes the main types of thermocouples, their material compositions, temperature ranges, and suitable applications.

Thermocouples are ideal for measuring a broad temperature range, up to 2300ºC. However, they are less suitable for applications requiring high accuracy in measuring small temperature differences, such as the 0-100ºC range with 0.1ºC precision. For such precision, thermistors and resistance temperature detectors are more appropriate. Thermocouples are used in various applications, including temperature measurement for kilns, gas turbine exhausts, diesel engines, and other industrial processes. Here are some specific industries where thermocouples are commonly applied:

• Steel Industry
• Cement Industry
• Pharmaceutical Industry
• Petrochemical Industry
• Nuclear Industry
• Power Industry
• Laboratories
• Furnace Industry

This highlights the wide-ranging applications of thermocouples in various industries and their suitability for high-temperature measurements.