Calibration furnace is designed for calibrating thermocouples and resistance thermometers. Calibrations of those are important for most accurate temperature measurement. That is why the furnace needs to be evaluated and calibrated before use. This is the only way to be sure about it's accuracy and credibility of later calibrations.
In my thesis I evaluated calibration furnace FLUKE 9118A from the Laboratory of metrology and quality. I determined its themperature stability and homogenity. I was performing the measurements with the inserted ceramic isothermal block and without it. These measurements are essential for determining calibration uncertainties of thermometers later on.
I was performing measurements with the ceramic isothermal block at temperatures of 300 °C, 500 °C, 800 °C, 1000 °C and 1200 °C, and without isothermal block at 500 °C, 750 °C, 1000 °C and 1200 °C. I was pulling a measurement thermometer from the starting point of full immersion out by steps of 3 cm. The reference thermometer was fully immersed at all times.
While using isothermal block I was performing measurements until I reached a 15 cm offset from full immersion or to the point where the temperature difference was greater than 0,5 °C.
I performed measurements without isothermal block until reaching 9 cm offset from full immersion.
At temperatures of 300 °C and 500 °C using isothermal block I used the calibrated resistance thermometer and at higher temperatures and measurements without isothermal block I used the calibrated type S thermocouples.