| 摘要 |
A bridge circuit, interconnected with a sample box containing a sample of particulate material, is energized by a test signal and provides a bridge output signal whose phase, relative to the phase of the test signal, and whose amplitude are related to the electrical admittance of the sample. After compensation for variations in temperature and bulk density of the sample, the bridge output signal is applied to a first controlled rectifier which is also provided with a reference signal whose frequency is identical to that of the test signal and whose phase is shifted by a predetermined amount from that of the test signal. The first controlled rectifier passes only that component of the bridge output signal in-phase with the test signal to provide a first DC signal related to the measured conductivity of the sample. The bridge output signal is also applied to a second controlled rectifier which is also provided with the reference signal, as coupled through a 90 DEG phase shift circuit. The second controlled rectifier passes only that component of the bridge output signal which is 90 DEG out-of-phase with that of the test signal to provide a second DC signal related to the measured dielectric coefficient of the sample. In order to obtain a signal which is related to the moisture content of the sample, the first DC signal is applied to one input of a differential amplifier whose other input is provided with a threshold signal representing a predetermined conductivity value. When the measured conductivity exceeds the predetermined value, the differential amplifier provides an output signal equal to the difference between the measured conductivity and the predetermined value. This output signal is modified by a signal shaper into a signal representing a corresponding percentage. A multiplier circuit multiplies the second DC signal by the percentage represented by the output signal from the signal shaper to obtain a moisture correction signal which is subtracted from the second DC signal to obtain an output signal related to measured moisture content. An alarm indication is also provided when the measured conductivity goes above a value representing an excess conductivity condition in the sample.
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