definition, thermocouple theory and functionality, Component selection for ultra high temperature thermocouples, material used, characteristics advantages and applications. categorized in refractory thermocouples in which precious metals are used. these thermocouples mainly used for high temperature applications.

1. Ultra High Temperature Thermocouples

2. Contents
• Definition of Ultra high temperature thermocouples
• Thermocouple Theory
• Thermocouple Functionality
• Component Selection
• Material used
• Characteristics
• Advantages
• Applications

3. What is Ultra High
Temperature Thermocouple?
• Thermocouples are pairs of dissimilar metal wire joint at one end, which generate a
net thermoelectric voltage between the open pair according to temperature
difference between the ends.
• Ultra high temperature thermocouples are used for high temperatures up to
2300°C for highly corrosive and/or reducing atmospheres.
• These thermocouples are used in inert, oxidizing, reducing or vacuum conditions,
depending upon the sheath material selected.
• The maximum temperature is based on the lowest max. temperature of the
element, insulation and sheath material.

4. Thermocouple Theory
• A thermocouple consists of two wires of dissimilar metals joined together at one
end, called the measurement (“hot”) junction. The other end, where the wires are
not joined, is called the reference (“cold”) junction.
• The voltage produced at the reference junction depends on the temperatures at
both the measurement junction and the reference junction.
• Since the thermocouple is a differential device rather than an absolute temperature
measurement device, the reference junction temperature must be known to get an
accurate absolute temperature reading. This process is known as reference junction
compensation (cold junction compensation).

5. Measuring
tip
Thermocouple
Cu-Wires
Cool Joint Comp.
Ice – Water
Mixture @ 0 °C
Traditional arrangement of a cool joint compensation . Still at present often used in
calibration labs for precise measurements.

7. Components of Ultra high
Temperature Thermocouple
• Thermocouple element.
• Thermocouple Junction.
• Sheath Materials.
• Insulation Material.

8. Material Used
Thermocouple Type
• Type R, S, & B thermocouples are made in Platinum/Rhodium element.
• Type C, D & G thermocouples are made in Tungsten/Rhenium element.
High Temperature Sheath material type
• Inconel-600
• Platinum Alloy
• Tantalum
• Ceramic
• Molybdenum
Insulation material type
• Magnesia (MgO)
• Alumina Oxide (Al2O3 )
• Hafnium Oxide (HfO2)
• Beryllium Oxide (BeO)

9. Characteristics of Thermocouples
Thermocouple
Combination
Calibration Type Standard limits of error Recommended
Temperature Range
Tungsten 5% Rhenium (+) Vs
Tungsten 26% Rhenium (-)
C ±4.4°C or ±1% 0-2200°C
Tungsten 3% Rhenium(+) Vs
Tungsten 25% Rhenium (-)
D ±4.4°C or ±1% 0-2200°C
Tungsten (+) Vs. Tungsten
26% Rhenium (-)
G ±4.4°C or ±1% 0 to 2200°C
Platinum 13% Rhodium (+)
Vs Platinum (-)
R ±1.5°C or .25% ** 0-1450°C
Platinum 10% Rhodium (+)
Vs. Platinum (-)
S ±1.5°C or .25% ** 0-1450°C
Platinum 30% Rhodium (+)
Vs. Platinum 6% Rhodium
(-)
B ±0.5% 800-1700°C
High Temperature wire types

10. Sheath type Max. Temp Melting Temp Allowable
environment
STD SHEATH
DIA (mm)
MIN. BEND
RADIUS
Inconel 600 1175°C 1345°C Inert, Vacuum,
Oxidizing
1.016, 1.57, 3.17,
4.77,6.35
5 X Sheath
Diameter
Platinum Alloy 1550°C 1850°C Inert, Oxidizing 1.016, 1.57, 3.17 5 X Sheath
Diameter
Tantalum 2200°C 2995°C Inert, Vacuum 1.016, 1.57, 3.17 10 X Sheath
Diameter
Molybdenum 2000°C 2620°C Inert, Vacuum,
Reducing
1.57, 3.17, 4.77,
6.35
Do not Bend
Ceramic 1900°C 2030°C Oxidizing,
Reducing,
Vacuum
4, 6, 8, 12 Do not Bend
High temperature Sheath Material

11. Insulation Type Max. Operating
Temp.
Approx. Melting
Temp.
Comments
Magnesia (MgO) 1700°C 2800°C Very hygroscopic. Used mostly in compacted
Sheaths.
Alumina
Oxide(Al2O3)
1550°C 2040°C Excellent with Platinum alloys
Hafnium Oxide
(HfO2)
2200°C 2790°C Comparable to Beryllium Oxide and safe to
handle
Beryllium Oxide 2200°C 2650°C Excellent High Temperature thermal
conductivity and resistivity
High Temperature Insulators

12. Advantages
• Suitable for high temperature up to 2300˚C.
• ŸSuitable for oxidizing, reducing, neutral atmospheres and vacuum.
• Transition elements variable within a wide range.
• Calibration at high temperature in Inert or vacuum atmosphere.

13. Applications
These thermocouples are mainly used in very high temperature applications like:
• Aeronautics
• Research Laboratories
• Nano technology.
• Quartz Industry.
• Vacuum Furnaces.
• Solar power generation.
• Graphite Furnaces
• Brick and Ceramic Kilns
• Hot Isotactic Presses
• Metal Treatment

14. THANK YOU!
Tempsens Instruments (I) Pvt. Ltd.
B-188 A, Road No. 5, MIA, Madri
Udaipur - 313 003 (Rajasthan) INDIA
Phone : +91-294-3057700
Fax : +91-294-3057750
E-mail : info@tempsens.com
Website : www.tempsens.com
Temperature Sensing, Heating & Cables