HIGH TEMPERATURE
FURNACE HANDBOOK
ISSUE 8 - 05/05
Page 33 of 37
NOTE ON THERMOMETER USE AT HIGH TEMPERATURE
A thermometer of the Standard Platinum Resistance Thermometer type, such as ITL Model
909 or 962, should never be completely withdrawn into ambient temperature when its
temperature is above 500°C. Mechanical forces may be introduced which will cause strains
(these can probably be annealed out) or quenched-in vacancies in the platinum lattice (these
can generally not be removed by heat treatment) and consequent shifts in calibration.
Thermometers can be withdrawn in 1cm length intervals, over a period of perhaps 5 minutes,
until the thermometer temperature is known to be below 500°C and they may then be
withdrawn rapidly. The same precaution applies to re-insertion of thermometers.
For accurate work the monitoring thermometer should be annealed at 480°C for 4 hours after
each such use and its water triple point resistance measured. This is the actual water triple
point measurement that should be used in calculating ratios for the determination of
temperature.
APPENDIX 3
NOTE ON HEAT-PIPE OPERATION