High Temperature Thermocouple

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ARi High Temperature Thermocouple is used in applications where base metal thermocouples cannot be used because of excessive temperatures or severe atmosphere.  ARi can provide a wide variety of wire combinations and sheath materials to meet the harshest demands.  By selecting certain materials, temperature measurements up to 2300°C can be achieved.

ARi manufactures it's own mineral insulated cable and many of our high temperature thermocouple are available in bendable sheath and longer lengths.  This in-house capability enables us to manufacture a variety of custom material combinations.  Applications include;

  • Process control of vacuum furnaces
  • Gas furnaces
  • High temperature ovens
  • Reaction furnaces

Processes include sintering, annealing and carburizing.  While many process variables affect service life, there are two (2) important considerations for selecting the proper thermocouple for a particular application.

  1. What is the temperature range you will need to measure?
  2. What is the atmosphere the thermocouple will be exposed to during operation?

With this information, it is possible to use these tables to select a suitable wire, sheath and insulation combination.  The physical requirements of the thermocouple (sheath diameter, junction type and termination style) can then be selected to complete the design.  Of course, you can always contact our ARi sales staff for help in selecting the proper high temperature thermocouple.


Material Specifications


Sheath Materials

Sheath Type ARi Symbol Maximum Temp (°C) Melting Temp (°C) Allowable Environment Standard Sheath Diameter (inches) Minimum Bend Radius
Inconel 600 B 1175 1345 Inert, Vacuum, Oxidizing 0.040, 0.062, 0.125, 0.188, 0.250 5X Sheath Diameter
Platinum 10% Rhodium AH 1550 1850 Inert, Oxidizing 0.040, 0.062, 0.125 5X Sheath Diameter
Tantalum N 2200 2995 Inert, Vacuum 0.040, 0.062, 0.125 10X Sheath Diameter
Niobium 1% Zirconium AV 2200 2495 Inert, Vacuum 0.062, 0.125 10X Sheath Diameter
Molybdenum O 2000 2620 Inert, Vacuum, Reducing 0.062, 0.125, 0.188, 0.250 Do Not Bend
Coated Molybdenum OCR 1600 2000 Inert, Oxidizing 0.125, 0.250 Do Not Bend


Wire Types

Thermocouple Combinations Calibration Type ARi Symbol Standard Limits Of Error Recommended Temperature Range
Platinum 30% Rhodium (+) Vs. Platinum 6% Rhodium (-) B B ± 0.5% 870 - 1700 °C
Tungsten 5% Rhenium (+) Vs. Tungsten 26% Rhenium (-) C AE ± 4.4 °C (0 - 426 °C)* 0 - 2200 °C
± 1% (426 - 2315 °C)*
Tungsten 3% Rhenium (+) Vs. Tungsten 25% Rhenium (-) D AO ± 4.4 °C (0 - 426 °C)* 0 - 2200 °C
± 1% (426 - 2315 °C)*
Platinum 13% Rhodium (+) Vs. Platinum R  ± 1.5 °C or 0.25% **  0 - 1450 °C
Platinum 10% Rhodium (+) Vs. Platinum ± 1.5 °C or 0.25% **    0 - 1450 °C

*Per ASTM E-988

**Per ASTM E-230


Insulation Materials

Insulation Type ARi Symbol Maximum Operating Temp (°C) Approximate Melting Temp (°C) Comments
Magnesia (MgO) N 1700 2800 Very hydroscopic.  Used mostly in compacted sheaths.
 Alumina Oxide (Al²O³) A 1550 2040 Excellent with Platinum alloys.
Hafnium Oxide (HfO²) H 2200 2790 Comparable to Beryllium Oxide and safe to handle.
Beryllium Oxide (BeO)*** B 2200 2650 Excellent High Temperature thermal conductivity and resistivity.

***Beryllium is considered a toxic material and can cause health problems if particles are inhaled.


Options / Modifications



In applications where cold end termination will see temperatures in excess of 200ºC, standard epoxy seals may breakdown causing failure. In this case ARi can supply a ceramic cement seal which can withstand temperatures up to 450ºC.
To specify this option, add the prefix HI- in front of the part number selected.
Example: HI-T-107N-12DAE(9.5)N

Most high temperature thermocouple combinations with an outside sheath diameter of 1/8" or larger are available in duplex element construction (2 separate measuring circuits in 1 sheath).

To specify this option, add the suffix .4 after the style number and "repeat the junction code a second time and add parentheses".
Example: T-91.4N-12FR(9.9)B or T-91.4B-18DAE(9.3)(9.3)O

If required with any of our male plug type thermocouples (T-91, T-191, and HI-T-91), we can supply the appropriate mating jack with the assembly.

To specify this modification, add (MOD) after the part number and specify "Supplied With Mating Jack" .

In order to minimize the effects of any residual oxidation remaining inside non-compacted sheath designs, ARi can evacuate and backfill the sheath with inert Argon gas prior to sealing the cold end.

To specify this modification, add (MOD) after the part number and specify "With Argon Backfill" in the description.

High temperature Thermocouple with R, S & B calibrations made with mineral insulated construction can be supplied with special limits of error tolerances per ASTM E-230 or Class 1 per IEC-584 subject to availability of material from stock.

To specify this modification, add (MOD) after the part number and specify "Per Special Limits of Error" or "Per Class 1 Tolerance" in the description.

For designs where extension wire attachment is required, we can supply moisture resistant Teflon insulated extension wire in place of our standard fiberglass. Other insulation types can be supplied subject to availability.
To specify this modification, add (MOD) after the part number and specify "With Teflon Insulated Leads" in the description.


Ordering Information


ARi Part Numbering Symbols/Codes

Wire Type Symbol Sheath Type Symbol Insulation Type Symbol Sheath Diameter (inches) Code
S S Inconel 600 B Magnesia (MgO) N 0.040 A
R R Platinum 10% Rhodium AH Alumina Oxide (Al²O³) A 0.060 (.060)*
B B Tantalum N Hafnia Oxide (HfO²) H 0.062 B
C AE Molybdenum O Beryllia Oxide (BeO) B 0.118 (.118)*
D AO Niobium 1% Zirconium AV     0.125 D
    Coated Molybdenum OCR     0.177 (.177)*
            0.188 E
            0.236 (.236)*
            0.250 F

 *Non-standard/ metric size.


Junction Number Codes

Sheath Type Wire Type Letter Code Insulation Type Letter Code GROUNDED - Junction Code UNGROUNDED - Junction Code
Inconel 600 R, S, B N (8.1) 9
Platinum 10% Rhodium R, S, B N 8 9
Coated Molybdenum  AE, AO A N/A (9.4)
AE, AO N, H, B N/A (9.3)
Tantalum     R, S, B A (8.1) (9.4)
R, S, B N, H, B (8.1) (9.5)
AE, AO H, A (8.1) (9.3)
AE, AO N, B (8.1) (9.5) OR (9.3)*
Molybdenum   R, S, B A N/A (9.4)
R, S, B N, H, B N/A 9
AE, AO N, H, B, A N/A (9.3)

* Assembly style.



High Temperature Thermocouple


Example part number of a high temperature thermocouple:  T-77N-24DAE(9.3)O-16

  • Style Number:  T-77
  • Insulation Material:  N - 99.4% min MgO purity
  • Sheath Length "L" in inches:  24 inches
  • Sheath Diameter:  D - 0.125 inch
  • Wire Calibration:  AE - Type C wire
  • Hot Junction:  (9.3) - Ungrounded
  • Sheath Material:  O - Molybdenum
  • Extension Wire Length "A" in inches:  16 inches


High Temperature Thermocouple 2

High Temperature Thermocouple 3

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