Development and Validation of an Argon Triple Point Apparatus with a Novel Automatic Pressure Control System

Area of Science:

• Metrology
• Thermodynamics
• Cryogenics

Background:

• Accurate realization of thermodynamic fixed points is crucial for temperature scale calibration.
• Existing methods for controlling cryostat pressure can be complex and less precise.
• The International Temperature Scale of 1990 (ITS-90) requires reliable reference points.

Purpose of the Study:

• To develop and validate a novel apparatus for realizing the triple point of argon.
• To implement and test an automatic pressure control system for a liquid nitrogen cryostat.
• To compare temperature measurements with a designated metrology institute.

Main Methods:

• Development of an automatic pressure controller and custom software for a cryostat.
• Performance testing and characterization of the pressure control system.
• Bilateral hybrid comparison using a standard platinum resistance thermometer as a transfer standard.

Main Results:

• The automatic pressure controller demonstrated suitability for precise and reliable gauge pressure control.
• Comparison of resistance ratio (W) values between two laboratories showed deviations.
• Deviations were observed within the determined combined uncertainty of the comparison.

Conclusions:

• The developed apparatus and control system are suitable for realizing the triple point of argon.
• The study highlights the importance of inter-laboratory comparisons for validating metrological capabilities.
• Further investigation into the observed deviations in resistance ratio values may be warranted.