Apparatus for measuring electric impedances in order to make separate measurements of conductivity, dielectric constant and moisture content in a material divided into samples

摘要

The invention concerns an apparatus for measuring electric impedances so as to make separate measurements of conductivity, dielectric constant and moisture content in a material divided into samples. A bridge circuit (18) connected to a sample box (10), which contains a sample of the said divided material, emits a bridge output signal, which is related to the sample's electrical admittance. After compensating (in 32,34,36,22; 38,40,42,28) for variations in temperature and average density, the bridge output signal is passed to the first and second controlled diodes (26,30) so that conductivity and dielectric constant signal samples are obtained. The conductivity signal is passed to one input of a differential amplifier (46) into whose other input is passed a threshold value signal, which represents a predetermined conductivity value. When the measured conductivity exceeds this predetermined value, the differential amplifier (46) transmits a signal, which corresponds to the difference between the said values. This signal is then modified by a signal shaper (48) to a signal, which represents a corresponding percentage value. A multiplication circuit (50) multiplies the dielectric constant signal by this percentage value giving a moisture correction signal, which is subtracted (in 51) from the dielectric constant signal, thereby producing a signal related to the measured moisture content.IMAGE