©2010 Fluke Corporation Argon Triple Point Cell 1 The 5960A Triple Point of Argon System

©2010 Fluke Corporation Argon Triple Point Cell 2 Why Introduce an Argon Cell? Important ITS-90 Fixed-Point Much better uncertainty than Liquid Nitrogen (-196C) comparator Effective measurement, time longer than other systems

©2010 Fluke Corporation Argon Triple Point Cell 3 ITS-90 Defining PointsKelvin°C He, H 2, Ne, O 2 ~ 3……54 ~ -270… Triple point of argonargon − Triple point of mercurymercury − Triple point of water 1water Melting point Melting point 2 of galliumgallium Freezing point Freezing point 2 of indiumindium Freezing point 2 of tintin Freezing point 2 of zinczinc Freezing point 2 of aluminum aluminum Freezing point 2 of silversilver Freezing point 2 of goldgold Freezing point 2 of coppercopper Why Introduce an Argon Cell?

©2010 Fluke Corporation Argon Triple Point Cell 4 What is it?  C fixed-point cell (Triple-Point)  For calibrating SPRTs in the ITS-90 sub-ranges below 0°C  A sealed cell with high purity Argon, chilled to - 189C with liquid Nitrogen to form a triple-point

©2010 Fluke Corporation Argon Triple Point Cell 5 Why Introduce an Argon Cell? ITS-90 Absolute Zero (-273C) TPW (0.01C ) Argon (-189C) Mercury (-38C)

©2010 Fluke Corporation Argon Triple Point Cell 6 What is it? Easily make connections to the required Vacuum pump, Liquid Nitrogen source, and Helium gas (Not included with the 5960A). (Top view)

©2010 Fluke Corporation Argon Triple Point Cell 7 1.Prepare: Insert SPRTs, vacuum the re-entrant well, and fill helium to specific pressure. 2.Freeze: Add LN2 to the system to Freeze the Argon gas (takes a few hours to condense and freeze) 3.Stabilize: stabilize solid Ar temperature just below the Triple Point temperature (Set the controller temperature to -190°C, and stabilize the system for 2 hours). 4.Realize: Set the controller temperature to 1.5°C above TP of Ar for 1 hour to initialize the plateau (melt some of the Argon to liquid) 5.Maintain: Set the controller temperature to 20 mK - 50 mK above TP of Ar ( °C) to maintain the plateau. Simple Steps for Realization

©2010 Fluke Corporation Argon Triple Point Cell 8 Schematic drawing of Ar cell Ar Cylinder Liquid N 2 Port for filling liquid N 2 To vacuum pump Four wells To controller Precision PRT Heater Triple- phase Ar To vacuum pump and He filling port Super insulation layer Heatershield Passive shield Sample cell shield Ar Cyliner Vacuum can

©2010 Fluke Corporation Argon Triple Point Cell 9 Main design parameters for Ar cell % Argon Four re-entrant wells with ID of 8.0 mm. Immersion depth (the bottom of re-entrant well to the surface of the cell): mm Total immersion depth: 480mm Pure Argon in the system: approximately mol and g Pressure in cell and cylinders at room temperature: not too high, safe for regular shipping

©2010 Fluke Corporation Argon Triple Point Cell 10 Up to four SPRTs can be inserted into the re-entrant wells After the first batch of SPRTs are measured, more SPRTs can be calibrated with the same plateau. Helium is used during the SPRT exchange to prevent moisture from freezing inside the re-entrant wells. Exchanging SPRTs

©2010 Fluke Corporation Argon Triple Point Cell 11 Gas Flow Ar Cylinder # 1 He Ar Cell He Ar Ar Cylinder # 2 Triple-phase Ar Liquid nitrogen Vacuum

©2010 Fluke Corporation Argon Triple Point Cell 12 Plateau of the TP of Argon Plateau with the maintenance temperature 20 mK above the triple point More than 4 days of plateau!

©2010 Fluke Corporation Argon Triple Point Cell 13 Immersion Profile (Demonstrates Axial Uniformity)

©2010 Fluke Corporation Argon Triple Point Cell 14 Temperature differences between re-entrant wells Re-entrant well #1 Re-entrant well #2 Re-entrant well #3 SPRT 1614 (W(Ar)) SPRT 4223 (W(Ar)) SPRT 4227 (W(Ar)) Average (W(Ar)) Difference (W(Ar)) E E-08 Difference (mK) (also called Radial Uniformity)

©2010 Fluke Corporation Argon Triple Point Cell 15 Specifications ItemSpecifications Assigned Value °C Ar gas purity % Uncertainty (k=2)0.25mK Length of plateau (0.1 mK)>30 hours Immersion depth *160 mm Number of re-entrant well4 Temperature differences among 4 re- entrant wells 0.05mK Total depth of re-entrant well480 mm Re-entrant well ID8.0 mm Number of Ar gas cylinders2 Liquid nitrogen cylinder size300.0 mm (ID) x 610 mm (length) Voltage110 – 220 volts Power 230 VAC (  10%), 50/60 Hz, 6A Controller display resolution0.001 °C Controller set-point accuracy0.1 °C (adjustable) * From the bottom of the re-entrant well to the surface of Ar sample