Improvements in or relating to vacuum freeze drying processes

摘要

988,372. Automatic temperature control systems for vacuum freeze drying apparatus. LEYBOLD-ANLAGEN HOLDING A.G. Nov. 30, 1961 [Dec. 1,1960], No. 42950/61. Heading G3R. An automatic temperature control system for controlling the heating apparatus used in a vacuum freeze drying process in which the material to be dried is initially frozen into a solid state and then placed in a vacuum chamber wherein the material is dried by sublimation has the heating apparatus of the vacuum chamber controlled with the aid of temperature responsive resistors connected in a Wheatstone bridge, the temperature responsive resistor 1 being embedded in the material to be dried, the temperature responsive resistor 2 being placed adjacent the heating apparatus 7 and the resistors 3,4 being placed in a chamber the temperature of which is maintained constant, a measuring instrument 5 being placed across the diagonal of the bridge, the constants 13,14 of which instrument are operated to energize the heating apparatus 7 and a cooling apparatus 8 such that the heating of the vacuum chamber is maintained at a point to cause drying of the frozen material by sublimation thereof. In a second embodiment the two resistors 1, 2 are placed in the same arm of the bridge and the cooling apparatus 8 excluded whilst in a further embodiment the measuring instrument 5 is protected against overload by the provision of a further, relatively insensitive, measuring instrument which is operative when the bridge is severely unbalanced. A transistorised amplifying element may be included in the bridge diagonal.