The standard thermometer is a type S element whose nominal composition consists of Platinum-10 % Rhodium (positive leg) against Platinum (negative leg) and belongs to the group of noble thermocouples. It is characterized by its high stability. The quality of the thermowell used is essential for stability at high temperatures. For this reason, the high-purity aluminum oxide ceramic C 799 is used. The type S thermocouple, besides the low aging drift, also offers the advantage of a low basic tolerance.
During measurement it must be ensured that the compensating leads from the measuring point to the cold junction consist of substitute materials which have, in a limited temperature range, the same thermoelectric properties as the materials of the thermocouple. Therefore, at this transition, there is no thermoelectric voltage. This voltage is only generated at the point where the compensating leads are connected to normal copper leads.
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