This more recent addition to our long-established range of metrology furnaces offers an alternative for those who prefer a three zone furnace to heat pipe technology. The three zone furnace creates a controlled volume of constant temperature within the furnace, in which High-Temperature Fixed Points such as aluminum, silver and copper can be frozen and melted. Because high-temperature thermometers can be easily contaminated by metallic vapors, great care has been taken to eliminate the use of metals throughout the calibration volume. The cell holder is made of alumina.
A ceramic equalizing block is available with this thermal furnace, composed of a closed-ended tube, alumina tubes to house the sensors being compared, and alumina powder to act as an equalizing medium.
The sensor for the main controller is a mineral-insulated type N thermocouple, which has been found to be more stable than the type R thermocouple. In addition, two slave controllers compensate for any temperature gradient along the furnace by eliminating any temperature difference that they sense.
There is a cooling oil in the lid of the thermal furnace with connections to circulate tap water to keep the furnace lid cool, protecting the SPRT and reducing heat load into the lab. A flow of 0.5 to 1 liter per minute is required at temperatures above 700°C
This 3-Zone Furnace can be used for the realizations of zinc, aluminium, silver, gold and copper points, or with an optional equalizing block used for annealing or comparison calibration.