Noble metal thermocouples, types B, R and S, based on platinum or platinum\/platinum rhodium thermocouples share similar properties.<\/p>\n\n
Diffusion<\/strong><\/p>\n\n The diffusion of metal vapour at high temperatures can change the calibration of the platinum wires; therefore they should only be used inside a non-metallic sheath e.g made from high purity ceramic. An exception to this rule is a platinum sheath, but that is an expensive option. <\/p>\n\n Stability<\/strong><\/p>\n\n Thermocouples based on platinum are by far the most stable of all. The type S is so stable that it is used as a standard for calibrating the temperature between the solidification point of antimony (630.74\u00b0C) and that of gold (1064.43\u00b0C). <\/p>\n\n Type B<\/strong><\/p>\n\n The type B thermocouple is the only common thermocouple which shows a double evaluation ambiguity.<\/p>\n\n Non-precious metal thermocouples<\/strong><\/p>\n\n In contrast to noble metal thermocouples, non-precious metal thermocouples do not have a precise chemical composition. It is possible to use any combination of metals which give temperature curve results within standard error limits. This results in a number of rather interesting combinations. For example, as we saw above, constantan does not have defined proportions, but is a generic name for copper-nickel alloys. <\/p>\n\n Type E<\/strong><\/p>\n\n The type E thermocouple is suitable for low temperature measurements due to its high Seebeck coefficient (58 \u00b5V\/\u00b0C), low conductivity and corrosion resistance. The Seebeck coefficient for the type E is the highest of all standard thermocouples, which makes it useful for detecting small changes in temperature. <\/p>\n\n Type J<\/strong><\/p>\n\n Iron, the positive element in a type J thermocouple is an inexpensive metal, but one which is rarely very pure. The properties of type J thermocouples may vary due to impurities in the iron. Nevertheless, type J thermocouples are popular due to their high Seebeck coefficient and low cost. A type J thermocouple should never be used above 760\u00b0C because of sudden magnetic transformation which can cause decalibration even on return to lower temperatures. <\/p>\n\n Type T<\/strong><\/p>\n\n The type T has a copper wire, a significant advantage in the monitoring of temperature differences in that enables two type T thermocouples to be installed in series thus eliminating the need for cold junction compensation. <\/p>\n\n Types K and N<\/strong><\/p>\n\n Type K thermocouples have always been widely used. They are suitable for measuring high temperatures due to their resistance to oxidation. The type N is becoming increasingly popular as a replacement for the type K. The result is slightly below that of the type K (lower Seebeck coefficient), but its resistance to oxidation is even greater. The yield curve of the type N thermocouple depends on the wire gauge and there are two distinct characteristic Nicrosil-Nisil curves depending on the wire gauge. <\/p>\n","protected":false},"featured_media":0,"template":"","format":"standard","class_list":["post-3245","faq","type-faq","status-publish","format-standard","hentry"],"acf":[],"aioseo_notices":[],"yoast_head":"\n![\"image\"](\"https:\/\/thermibel.be\/app\/uploads\/2023\/05\/faq-18.png\")
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