Mineral Insulated Thermocouple

Mineral Insulated Thermocouple

A Mineral Insulated (MI) thermocouple features a mineral oxide insulated sheathed cable of metal. This thermocouple comprises a thermocouple wire that is insulated with magnesium oxide, typically compacted by the process of swaging or drawing the sheath. At Therm-x, we provide MI thermocouples manufactured using the best quality MI thermocouple probes housed in an alloy sheath. Owing to their rugged and reliable construction, these thermocouples are being widely considered for harsh and rigorous conditions.

Beneficial Features of Mineral Insulated Thermocouples

Our MI thermocouples are being considered over bare wire and beaded thermocouples, owing to the following benefits that they offer.

  • The compacted and strong MgO insulation improves the ability of the sensor to “read temperature” easily owing to the quick heat transfer to the measuring junction.
  • The MgO insulation also protects the thermocouple from thermal shocks, high temperatures, and moisture in various industrial environments.
  • These thermocouples are flexible and compact. They can be easily bent into small radii, which makes it easy to measure temperatures in difficult areas. The smallest bending radius of 2X sheath diameter can be easily achieved with these thermocouples.
  • The outer alloy sheath of the thermocouple protects the MI thermocouple probe from hostile environments and oxidation.
  • The thermocouple can be easily flattened or twisted at any points, and unlike regular bare wire thermocouples, these distortions will produce no ruptures or short circuits.
  • Small sheath diameters and immense flexibility are two features that make them ideal for any space-saving applications.
  • MI thermocouples are capable of withstanding temperatures up to the melting point of the metal.
  • They can easily withstand corrosive conditions; however, their capabilities will depend on the choice of material.
  • Unlike beaded thermocouples, our mineral insulated thermocouples feature no brittle or moving parts, which contributes to their high vibration strength.
  • They are proven to withstand external pressures up to 50,000 psi.
  • We can provide MI thermocouples of types - E, J, K, N, T, B, C, and R/S. Of these, type J, K, and T are base metal thermocouples, and type R/S, and B are noble metal thermocouples. These types vary in terms of durability, temperature range, chemical resistance, vibration resistance, and application compatibility. Noble metal thermocouples are used in high-temperature applications.


We provide both standard and custom MI thermocouples. Our vast engineering capabilities combined with an understanding of the temperature control requirements across industries enable us to provide the best MI thermocouples. The following capabilities have helped us serve our clients better:

  • We can provide M.I. cables in sheath diameters from .010ʺ to .500ʺ, in ± .0015" or ± 15% of nominal wall thickness. A thickness of 10% is always considered a minimum.
  • The insulation material used is 98% (min.) magnesium oxide (MgO).
  • They can be availed in special and standard limits of error, and with multiple element cables.
  • Some applications may require certified temperature measurement devices. We have been meeting these requirements by providing MI thermocouples built to American Society for Testing and Materials (ASTM) tolerances. The thermocouple wire used in these devices conform to ASTM E230 specifications.

Applications of Mineral Insulated Thermocouples

Over the years, our experts have helped clients across the following industries to build performance-driven custom MI thermocouples for challenging industrial applications. The following are the industries that utilize our MI thermocouples:

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