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ITS-90 Isothermal Towers Iss.07 – 05/14
USING YOUR ISOTOWER
Congratulations, you have just purchased the most advanced fixed point calibration cell and apparatus ever invented!
Before you power up your Isotower it is worth spending a little time to get to understand its operation.
Isotowers work by using the amazing thermal properties of heat siphons. Once the fluid inside a heat siphon reaches
its boiling temperature, it transfers heat by evaporation and condensation creating a thermal conductance up to 200
times better than copper. The ITS-90 cell inside the heat siphon therefore warms quickly and uniformly.
Due to thermal losses, a thermometer under test will conduct heat out of the cell causing a thermal gradient. To
balance this loss a heated collar is included above the cell called an Immersion Compensator; this collar has its own
controller and follows the main controllers’ temperature.
The main controller and the top controller are factory set prior to despatch. The settings can be found on the melt
and freeze that accompanies the Isotower.
Safe Operation of an Isotower
Always ensure that the ceramic cap is in place before connecting the power supply to the Isotower.
DON’T operate the equipment without the ceramic cap in place.
To Prevent Irreparable Damage the top of the thermometer pocket MUST not be allowed to become cooler than the
bottom of the thermometer pocket
Inside the Isotower is a graphite crucible that contains metal, Indium, Tin, Zinc or Aluminium. These metals expand as
they melt and contract as they freeze.
The crucible has sufficient volume to contain the metal when it is fully molten. As the metal freezes it contracts
therefore occupying a smaller area of the crucible.
