copper thermometer
TRANSCRIPT
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TEMPMEKO 2010Slide 1
Welcome
A NEW THERMOMETER FOR THE
COPPER POINT
John Tavener : President & Head of Laboratories
Isothermal Technology Ltd, UK(Isotech)
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TEMPMEKO 2010Slide 2
Demand
There is a significant demand for CopperCells and Apparatus for thermocouplecalibration
However the uncertainties associated withmeasuring the Copper Point are larger thanthose at the Silver Point for exampleThe major source of measurementuncertainty is the sensor
The preferred sensor at the millikelvin levelwould be a quarter ohm PlatinumResistance Thermometer.
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TEMPMEKO 2010Slide 3
A New Design
1 The Sheath Recrystalised alumina waschosen for its rigidity. Because alumina isslightly porous the inside of the senor was
kept at a slight positive pressure comparedto the outside of the sheath using oxygenrich gas
The theory being that any leakage would beoutward. Alumina has a tempco of about9ppm/C and is thermally fragile and so thesheath is designed to be easily replaceable
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TEMPMEKO 2010Slide 4
A New Design
2 The Mandrel on which thePlatinum sensor is wound is made of
synthetic sapphire because firstlysapphire is a more nobel insulatorthan either quartz or alumina, andsecondly its expansion and
contraction closely matches that ofthe Platinum
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TEMPMEKO 2010Slide 5
A New Design
3 The Bias The thermometer isbiassed to +9vDC. The reasons are
two foldFirstly biasing the thermometerincreases its insulating resistance
Secondly a positive voltage acts asan electro magnet repelling themetalic ions.
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TEMPMEKO 2010Slide 6
A New Design
4 Physically The thermometer is500mm long, 7.8mm diameter with a
100mm long handle and 2 metres oflead
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The Rest of the Apparatus
A microK 100 was used in conjunction witha Temperature Controlled 1 TinsleyResistor
The Copper Point was realised in anIsotower described elsewhere
It is however significant to mention that theCopper Cell is housed in a metalic
enclosure, including the re-entrant tube inwhich the thermometer was positionedduring measurements.
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Testing
Testing was simple, the thermometer wasused repeatedly for the melts and freezesof the Copper Cell in the Isotower
Between each sequence Rtpw and Wgawere measured
Part way through the testing the Copper
Cell was heated to 1100C under vacuumto remove oxygen
since 1ppm of oxygen in Copper can depress itstransition point by 5mK.
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Immersion Test
Because, uniquely theImmersionCompensator's
temperature can beadjusted the gradientover the bottom100mm is 2 or 3mK.(less than 1mK overthe bottom 40mm)
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History of Measurements
Rwtp & Wga Rcu
.236, 0412,2( ) M 1.092,387( )
116
Hours
F 1.092,362( )
M 1.092,350( )
F 1.092,308( )
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History of Measurements
.236, 034,0( ) 1.118120 M 1.092,310( ) 47
Hours
F 1.092,302( )
M 1.092,300( )
F 1.092,299( )
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History of Measurements
Rwtp & Wga Rcu
.236, 029,7( ) 1.118175 M 1.092,298( ) 53
Hour
s
F 1.092,294( )
.236, 040,0( ) 1.118129 M 1.092,293( ) 68
HoursF 1.092,287( )
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History of Measurements
Rwtp & Wga RcuPrevious
Value
1.092,287.236, 040,8( ) 1.118124 M* 1.092,287( )
25
HoursF* 1.092,283( )
.236, 041,0( ) 1.118133
*After Copper Cell deoxidised
All measurements use 10(mA)
The Copper Point was realised in an Isotower described elsewhere
The resistances marked M and F are the liquidus and solidus resistances
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History of Measurements
Rwtp & Wga Rcu
5 Cycles 7 x M & F -27(mK) 310 Hours
.All measurements use 10mA
The Copper Point was realised in an Isotower described elsewhere
The resistances marked M and F are the liquidus and solidusresistances
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Results
The graphs chart Rwtp and Wga and showsthat over the test period of 5 weeks thesevalues remained stable having no
significant drift or contaminationThis is amazing considering thethermometer was being repeatedly put intoand removed from a metalic re-entranttube at 1084.62C
The outside of the thermometer's sheathwas blackened by the end of the tests
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Results - Rwtp
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Results Wga
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Results
The following graph charts Rcu during thetestsAfter the initial sequence where the
thermometer was stabilising; over a periodof 300 hours at or above 1085C the totaldownward shift is 30mK or around0.1mK/hourInspection of this graph shows that the
majority (25mK) of the drift occured whilethe thermometer was above the liquidustemperature
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TEMPMEKO 2010Slide 19
Results
In fact it occured during the cold rod processwhere the thermometer exits the cell at1084C and is quenched in air for a minute
while the cold rod nucleates the Copper alongits re-entrant tube the thermometerreaches 400C before it is replaced in theCopper Cell
What is still a puzzle is why, when Rcu is
slowly decreasing Rtpw and Wga remainstable
However at 0.1mK/hour the numbers arerelatively small compared to alternative
sensors
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TEMPMEKO 2010Slide 20
Results - Changes in Rcu
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TEMPMEKO 2010Slide 21
Thermometer Drift over aFreeze/Melt
Date F to M T(C) F/M (mK)
3-8 Jan 2010 5 days 1085 +28-9 Jan 2010 1 day 5 -2
9-29 Jan 2010 20 days 1085 -1
1-2 Feb 2010 3 days 1085 -1
3-6 Feb 2010 4 days 1085 0
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TEMPMEKO 2010Slide 22
Thermometer Drift During a Meltor Freeze
The change in Rcu has been identified as mainlyhappening during the cold rod process.To discover the drift during a melt or freeze it isnecessary to consider the changes in Rcu during afreeze followed by a melt (FM). The previous tableshows 5 such cycles that occured during testing.In 4 of the 5 cycles the thermometer was cooled over3 hours to 480C and then Rwtp and Wga weremeasuredTo summarise the table, independent of the number
of days between freeze and melt or whether thethermometer's temperature excursion is 5C or1085C the solidus/liquidus temperature change wasbetween 0 and 2mK.So the thermometer drift is between 0 and 1 mKfor a melt or freeze
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TEMPMEKO 2010Slide 23
A Second Copper Cell
A new high purity copper point cellwas manufactured and the new
thermometer was used to measurethe melt and freezes
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TEMPMEKO 2010Slide 24
Results in Second Cell
The table shows the resistances at liquidusand freeze initiation
Intial Rtpw 0.236,041,0 Wga 1.118133
Slopes RcuPreviously
1.092,283( )
5 Hour Melt 80% 3(mk) 1.092,285()
4 Hour Freeze 50% Flat+ 1.092,280()
Final Rtpw 0.236,041,7 Wga 1.1181343
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TEMPMEKO 2010Slide 25
Results in Second Cell
This table shows a further melt and freezemade with a second synthetic sapphiremandreled thermometer which had been
stabilised for 100 hours prior to use
Feb 28 2hr F, 50% 0mK 1.099,557
Feb 28 2.5 hr M, 80% 3mK 1.099,553
Mean Melt =3mK Mean Freeze 0mK Drift 4mK
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TEMPMEKO 2010Slide 26
Results in Second Cell
These results confirm the melt and freezemeasurements of the first thermometer and
this newer thermometer also exhibits averagedrift of less than 0.1mK / hour after 100hours of stabilisation
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The graphs clearly show the unique stabilityof the thermometer during the freezing andmelting of the very pure cell
Copper Isotower Freeze Plateau25th Feb 2010
1.092238
1.09224
1.092242
1.092244
1.092246
1.0922481.09225
1.092252
1.092254
1.092256
1.092258
1.09226
1.092262
1.092264
1.092266
1.092268
1.09227
1.092272
1.092274
1.092276
1.092278
1.09228
1.092282
1.092284
160700 164300 167900 171500 175100
Time/Secs
Res/Ohms
108642/001 Res/Ohms
1 division = 2mK Four Hour Freeze
50% Freeze 2mK
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The graphs clearly show the unique stability of thethermometer during the freezing and melting of thevery pure cell
Copper Isotower Melt Plateau24th Feb 2010
1.09227
1.092272
1.092274
1.092276
1.092278
1.09228
1.092282
1.092284
1.092286
1.092288
1.09229
1.092292
1.092294
1.092296
1.092298
1.0923
85700 89300 92900 96500 100100 103700 107300
Time/Secs
Res/Ohms
108642/001 Res/Ohms1 division = 2mK Five Hour Melt
80% Melt in 3mK
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Conclusion
The new thermometer works up to1085C with little drift (0.1mK/hour)
and no contamination(stable Rwtp and Wga)
It is therefore suitable for theintercomparison and characterisation
of Copper Cells at uncertaintiessmaller than previously achieved