GB634149A - Improvements in apparatus for determining electrical properties of granular or other materials - Google Patents

Abstract

634,149. Electric tests. MARCONI INSTRUMENTS, Ltd., and BROCKELSBY, C. F. Oct. 30, 1945, No. 28773. [Class 37] In bridge arrangements for electrically determining properties of materials, compensation for temperature changes is effected by an element in heat exchange relationship with the material under test producing mechanically a variation of the test or standard arms and also of the ratio arms, the electrical adjustment thereby introduced including both arithmetic and logarithmic components. As shown, for measuring the dielectric constant and hence the moisture content of granular material DT, the material forms the dielectric of a guardring type test condenser KT arranged in a capacity bridge. The out-of-balance voltage of the bridge is applied through a transformer T to an indicator I or it may control a motor arranged to adjust the standard arm KS to maintain the bridge balanced automatically. Compensation for temperature changes of the test material is effected by an element E in heat exchange relationship therewith arranged mechanically to adjust condensers such as KR2, KR3, arranged one to vary either the test or standard arm arithmetically and the other/s to vary one or both the ratio arms logarithmically. The element E, Fig. 2, may comprise the outer casing of a known thermometer movement adapted to move a push-rod P axially with temperature changes. The rod P, through a strip S, adjusts the spring-biassed movable elements of the concentric cylinder type condensers KR2, KR3 in the corrective senses. The element E may be of any form adapted to produce a mechanical change such as a linear or rotary displacement when the temperature changes. For example, it may comprise a -vessel containing an expansible fluid such as toluene, the expansion of which adjusts the degree of immersion of the electrodes of the correcting condensers KR2 &c. in their toluene dielectric. Alternatively, the element E could be a liquid containing Bourdon tube or a bimetallic helix. The material under test. e.g. cereal grains, may flow continuously through the test condenser.