Rotor Temperature Measurement and Control in the Ultracentrifuge

Abstract

Moving rotor temperatures may be measured with a precision of ±0.03°C and an accuracy of 0.1°C in a vacuum centrifuge. The method does not use physical contact with the rotor but utilizes the infrared radiation from the rotor. A reference temperature is maintained in a mass of metal (reference block) placed near and shielding the base of the rotor. A copper disk, shielded also by the reference block, assumes a temperature between rotor and reference block temperatures through radiation exchange. The various temperatures and temperature differentials are determined by copper‐constantan thermocouples. Heat conduction through thermojunction leads and copper disk supports, and radiation exchange between copper disk and reference block have been minimized, the copper disk maintaining a temperature 0.72 of that between reference block and rotor. On acceleration the rotor cools, the opposite effect occurring during deceleration. Such changes are shown to be due to the adiabatic changes concomitant with the production or release of stress in the rotor. At 60,000 rpm a change of −0.9°C is observed on acceleration. On correction for kinetic heating this becomes −1.0°C. Such changes have not generally been taken into account. By installing a chamber heating coil in addition to refrigeration, the moving rotor temperature may be kept to within ±0.05°C of a chosen temperature for indefinite periods.