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HTSPRT Model 96178 Iss.06 – 03/11
STABILITY EVALUATION
INTRODUCTION
The 96178 is one of a new generation of thermometers designed at Isotech. It is a high temperature thermometer
working up to 1000 C and being 0.25 ohms at 0 C.
Its main radical and new features are:
1.
The 96178 can be supplied pre-sealed with an inert gas containing 10% oxygen or with a valve built into the
handle so the user can allow the thermometer to breath.
2.
The quartz used is a new and more pure material.
3.
The internal construction is made of many small parts to eliminate stem conduction.
4.
The internal structure contains a platinum light scattering disc to reflect radiant energy.
In this report the first production unit was cycled to the silver point to test the reproducibility of the W value at silver,
and to check the stability of R
TPW
.
METHOD
The 96178 thermometer, like all high temperature thermometers will change its characteristics if subjected to step
changes of temperature. The way in which the thermometer is temperature cycled is therefore very important.
In this series of tests the following strategy was adopted:-
The thermometer was placed in a pre-warming/annealing furnace at 400 C. The furnace temperature was then
slowly raised to 850 C (The apparatus used was the Isotech Dual Furnace which has been pre-programmed with
ramp-rates suitable for pre-warming the High Temperature Thermometers). From this furnace, the thermometer
was transferred to a heat pipe furnace in which was placed a silver cell. The silver had previously been melted and
partially frozen.
After 30 minutes in the cell, during which time and after stabilisation 4 to 6 readings were recorded, the thermometer
was transferred back to the annealing furnace, still at 850 C.
The annealing furnace was then cooled to 425 C overnight and R
TPW
measured the next morning.
Other thermometers of proven good stability were cycled with the 96178 to add further confidence that the method
gave stable results.
