Thermocouple Construction Materials
The most basic thermocouple construction is the wire type consisting of two dissimilar metals homogeneously joined at one end to form the measuring junction. All wire-type thermocouples have an exposed junction. While wire-type thermocouples offer good response time, ruggedness, and high temperature use, they are susceptible to environmental conditions and therefore must be
protected. Mineral insulated thermocouples overcome the disadvantages of
wire type construction by imbedding the thermocouple wires in ceramic insulation and protecting them with a metallic sheath. The mineral insulated cable (MI cable) design is based on small mass and high thermal conductivity which in turn promotes rapid heat transfer from the heat source to the measuring junction.The sheaths are impervious to most liquids and gases and withstand high external pressures. The seamless design protects against moisture or other contaminants attacking the thermocouple elements. Since the only materials used to make the MI cable are the thermocouple conductors, the mineral oxide insulation and the metallic sheath, the cables are inherently fireproof thus providing the safest temperature measuring system.
MI Cable Sheath Material The table below shows just some of the many different materials which can be used to protect the mineral insulated thermocouple. Sheath materials used vary from standard stainless alloys like 304, 310, 316, 321, 347, 446 to the slightly more exotic alloy 600 or Hasteloy®.
These sheaths are selected based on the rigors of the application with corrosion and temperature being the leading factors in sheath selection. The atmospheric environmental parameters are oxidizing, reducing, neutral, and vacuum. For example, 304 Stainless Steel can be used in each type of atmosphere with a maximum operating temperature of 1650°F.
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protected. Mineral insulated thermocouples overcome the disadvantages of
wire type construction by imbedding the thermocouple wires in ceramic insulation and protecting them with a metallic sheath. The mineral insulated cable (MI cable) design is based on small mass and high thermal conductivity which in turn promotes rapid heat transfer from the heat source to the measuring junction.The sheaths are impervious to most liquids and gases and withstand high external pressures. The seamless design protects against moisture or other contaminants attacking the thermocouple elements. Since the only materials used to make the MI cable are the thermocouple conductors, the mineral oxide insulation and the metallic sheath, the cables are inherently fireproof thus providing the safest temperature measuring system.
MI Cable Sheath Material The table below shows just some of the many different materials which can be used to protect the mineral insulated thermocouple. Sheath materials used vary from standard stainless alloys like 304, 310, 316, 321, 347, 446 to the slightly more exotic alloy 600 or Hasteloy®.
These sheaths are selected based on the rigors of the application with corrosion and temperature being the leading factors in sheath selection. The atmospheric environmental parameters are oxidizing, reducing, neutral, and vacuum. For example, 304 Stainless Steel can be used in each type of atmosphere with a maximum operating temperature of 1650°F.
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