MASS MEASUREMENT INTO A FREEZE-DRYER

A. Carullo, M. Parvis, A. Vallan

Abstract

This paper deals with two scales that are conceived to operate inside a freeze-dryer, where the environmental conditions (temperature down to -80 ºC and pressure down to 0.5 Pa) prevent traditional mass transducers to be employed. One scale is based on a parallel-electrode capacitor, whose capacity depends on the position of a moving electrode that, in turn, depends on the unknown mass. The capacity change is converted into a frequency change by means of an oscillator circuit. The second scale, which is still under development, is based on electrostatic levitation. A fixed metallic plate is divided into four sectors connected to a high voltage generator. The resulting electric field is used to levitate a moving metallic plate which carries the unknown mass. A prototype of the capacitor-based scale has shown an uncertainty of a few tenths of grams in the range of 0 g to 250 g.

Keywords

mass measurement, capacitance transducers, lyophilisation systems

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IMEKO-WC-2000-TC3-P062.pdf

DOI

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IMEKO TC

TC3 - Measurement of Force, Mass, Torque, and Gravity

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