Noble Metal Thermocouples

The most widely used noble metal thermocouple is Type “S” or Platinum vs Platinum-10% rhodium. Well known for its high accuracy over a broad temperature range, it is in common use for controlling the processing of steel, glass, and many refractory materials. It has excellent mechanical and chemical properties, low electrical resistivity and is readily obtainable in uniform quality. Platinum vs platinum-13% rhodium, Type “R”, is very similar to Type “S” in function and performance with a slightly higher EMF. Both Type “S” and Type “R” are recommended for continuous temperatures to 2700°F (1500°C) and with care, may be used intermittently to 3100°F (1700°C). Platinum-5% Rhodium vs Platinum-30% Rhodium, Type “B” can be used to 3100°F (1700°C) continuously with less drift, less grain growth and better mechanical strength.

When selecting the proper thermocouple type, consideration must be given to length of service, temperature, atmosphere, response time and cost. Also, be sure to the thermocouple type that is chosen is compatible with the instrumentation and equipment being used for the process. Industry standards may further limit the choice of thermocouple types, number of uses or limits of error. CEL’s sales and applications staff has decades of experience in the manufacture and use of thermocouples to aid in the choice and design of the correct thermocouple. CEL expertise in manufacturing and extensive inventory allows for built-to-order assemblies while simultaneously maintaining industry-best lead times.
Insulator materials, protection tube varieties, secondary coatings (tungsten) straight and bent assemblies, termination options (plugs, jacks, blocks, heads, soft wire leads, extension wire), process fittings, SAT Port, Single or Dual Junctions, wire diameters with other options upon request. Available in all standard ANSI configurations

Platinum-rhodium vs platinum thermocouples are especially well suited for use in an oxidizing atmosphere. Thermocouples can be used bare in clean, oxidizing atmospheres where no forced airflow is present. However, in areas where contaminants and a high rate of air flow are present, service life can be increased using insulators and protection tube. High-purity alumina tubes are recommended. Thermocouples are susceptible to contamination by metallic vapors or other volatile substances such as lead and zinc. The problems of contamination are increased in a reducing atmosphere, especially when silicon or sulfur is present.

Insulators and protection tubes are available in a multitude of materials and configurations. Most commonly Alumina and Mullite. Mullite has good resistance to thermal shock yet poor resistance to mechanical shock and should only be mounted in a vertical orientation. Alumina has fair resistance to both thermal and mechanical shock. It is impervious to gases up to 3200F. Inconel, and exotic protection tubes are also available including, Halsic, Hastelloy, Hexoloy, Silicon Carbide, Metal Ceramic (LT1), Sialon, Tercod, Fused Quartz, Molybdenum, Zirconia, Tantalum, Cast Iron and many others.