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Dual Furnace Models M17705, N17706 & 17707 Iss.09 – 12/14
ELIMINATING CONTAMINATION DURING THE CALIBRATION OF HIGH
TEMPERATURE THERMOMETERS
It is quite feasible to heat a high temperature thermometer to 1000°C and return it to ambient temperature without
altering the water triple point resistance value by more than 0.5mK equivalent.
Instructions in the Isotech 962 and 96178 thermometer manuals explain how to handle and keep clean the
thermometers. It is imperative that procedures are followed because contaminants can penetrate and pass through
physically-intact quartz sheaths at temperatures above 800°C.
To prevent this happening, a secondary containment has been provided, in kit form that can be fitted to dual furnace
Models 17705 and 17706.
The completed assembly is depicted below:
ANNEALING COMPONENT OF THE DUAL FURNACE SHOWING AIR FLOW
Air percolates through the quartz wool, oxidising any pollutants and rendering them harmless and unable to
penetrate the quartz sheath of the thermometer.
The combination of air-flow and positioning ensures that thermometers will not become contaminated at high
temperature.
The dual furnace also has a pre-calibration tube made of silicon carbide, which justifies its high cost by remaining
impervious to all gases that would poison the high temperature thermometer. The pre-calibration tube can be used
not only to store each thermometer immediately prior to calibration but also to house the standard thermometer
used to monitor the cell's plateau at various stages in a calibration schedule.
