The Isotech Low Temperature Fixed Point Furnace is designed specifically to realize and maintain the freeze plateaus of Isotech Indium, Tin and Zinc Fixed-Point Cells, for calibration of thermometers on the International Temperature Scale of 1990.
The Low Temperature Furnace is a single-zone furnace.
The recommended procedure for establishing a freeze plateau requires operator attention until the plateau is realized. Following that, the Model 17701 Furnace will maintain the indium or the tin plateau, essentially automatically, for a period of 10 to 12 hours, and the zinc plateau for 6 to 8 hours.
1. The furnace core, into which the freeze-point cell is inserted, is of aluminium alloy, which provides a very low thermal gradient along the core length. The main furnace heater is of the parallel-tube design used at NIST. A pre-warming tube is provided.
2. An advanced proportioning electronic control system regulates furnace temperature, using a platinum resistance thermometer as the sensing element. The controller may be calibrated in-situ using Freeze Point Cells as references.
Two entirely independent over-temperature safety devices are included. A dedicated (on-off) over-temperature control circuit provides active safety. A fusible link in the main power circuit provides passive safety.
3. The Low Temperature Furnace is completely self-contained, mounted on caster wheels, and requires no external supplies (except power).