Measurement of Very High Pressure Using The Pressure Effect on The EMF of Thermocouples.

点击翻译按钮获取中文摘要

(1) A Measurement and data processing system was composed of a high precision emf measuring instrument and a personal computer, and genarated pressure in a cubic anvil apparatus was evaluated based on the difference (known pressure effect) in apparent temperatures measured by the two kinds of thermocouples (Alumel/Chromel and Pt/Pt10%Rh) on a common hot junction in the high pressure space. The period of the pressure output could be selected as one to six seconds, which means attainment of an effectively real-time measurement. The evaluated pressure contained a random noise of an amplitude of (]SY.+-。[)0.2 GPa, which might be caused by the thermal noise in the emf measurement. The noise was, however, reduced by a smoothing technique, in which the most probable value was calculated by processing past 50-100 values with a kind of the least-square method. Thus the resolution of 0.02-0.05 GPa was attained in detection of pressure.(2) A method was devised and completed for correcting the eva … More luated pressure which should be affected by the "lost pressure effect" dependent on the temperature Tm (60 to 80ﾟC) at which the thermocouple wires are lead-in to the pressure space. The correction amounted to 10-20%, if the hot junction temperature was 600 to 700ﾟC.(3) In the present study a new method was realized for measuring the thermocouple emf through the anvils, where the top face temperature of the anvil Tm should be known precisely, and could be measured within 1ﾟC.The method allowed to use a thin wire and resulted in eliminating an error caused by a temperature gradient around the hot junction (spurious pressure effect and the main error in the conventional method of leading-in the wire). A new serious error (of around 1 GPa) was brought in from difference in Tm's of anvils. It is, however, expected to be eliminated completely by knowing Tm for each anvil.(4) At the present stage an object of relative pressure evaluation was successfully attained with a resolution of 0.02 to 0.05 GPa.(5) It was revealed that degradation of the thermocouples was avoided and very stable measurement was possible for more than 10 hours, if the hot junction temperature did not exceed 700ﾟC.(6) Absolute value of the evaluated pressure contained a systematic error of up to 1 GPa, different from experiment to experiment. For this problem, however, the cause and the solution in the next stage has been made clear. Less