Platinum-rhodium thermocouple tables

The main source of uncertainty was the absolute temperature measurement, which was made with a platinum, platinum-rhodium thermocouple, calibrated by the National Bureau of Standards to i but thought to be accurate to 1 ° G. AZ/q was obtained l y substituting the experimentally determined equilibrium constants and the spectroscopically derived free energy functions into equation 3.1.6. The results obtained are shown in Table 3.2.1. 

The Type R thermocouple (Table 11.61) was developed primarily to match a previous platinum-10% rhodium British wire which was later found to have 0.34% iron impurity in the rhodium. Comments on Type S also apply to Type R. 

The experiments were carried out in a Netzsch STA 409 C (Simultaneous Thermal Analysis - STA) in the TGA/DSC configuration. The STA has a vertical san le carrier with a reference and a sample crucible, and in order to account for buoyancy effects, a correction curve with empty crucibles was first conducted and then subtracted from the actual experiments. Platinum/Rhodium crucibles were used in order to get the best possible heat transfer. The thermocouple for each crucible was positioned Just below and in contact with the crucible. The ten rerature obtained from the measurement is the temperature in the reference side. This temperature is converted to the temperature in the sample side by using the DSC-signal in pV and a temperature-voltage table for the thermocouple. The product gases were swept away by lOO Nml/inin nitrogen which exited the top of the STA, The STA was calibrated for temperature and sensitivity (DSC) with metal standards at each heating rate. 

TABLE 11.56 Type B Thermocouples Platinum-30% Rhodium Alloy vs. Platinum-6% Rhodium Alloy... 

TABLE 11.61 Type R Thermocouples Platinum-13% Rhodium Alloy vs. Platinum... 

Table 11.62 Type S Thermocouples Platinum-10% Rhodium Alloy vs. Platinum 11.148...

A platinum-10% rhodium to platinum thermocouple was operated with hot and cold junctions, respectively, in the alloy and condensed cadmium regions. Reference tables (16) were used to convert e.m.f. to absolute temperature. However, in the tables, temperatures are rounded to the nearest 0.1° C., which is too rough for our temperature differences. The tables are based on earlier work (13) with the values adjusted to the 1948 international temperature scale. To evaluate the difference between alloy and cadmium condensate temperatures, we have used without adjustment two equations from the earlier work... 

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