抄録
This paper presents a circuit system functioning as a capacitance and resistance meter suitable for very-high-loss materials with a wide range of application in various fields of scientific research and industrial operation.
The system for the capacitance meter has two measuring arms; thus, it requires a pair of specimens. An apparent positive reactance variation caused by the low resistance of the specimen placed in one arm is cancelled by the apparent negative reactance variation in the other arm. Therefore, the error due to a large shunt conductance is eliminated from the capacitance measurement.
The system for the resistance meter is a resonance circuit having a very-high Q coil and a differential condenser with a series resistor which acts variable resistance at radio frequencies. The resistance variation caused by inserting the resistance of the specimen into the capacitance measuring circuit is detected as a change in the output of the amplifier circuit. This value is measured by the diferential condenser and the series resistor.
The minimum equivalent parallel resistance of the specimen to be measured reaches as low as 50Ω and the measuring range of the capacitance is about 0.1∼1200pF at 2MHz.
As an application of this circuit system, the dielectric property of wet paper, textile fibers and wood is measured. From the result of the measurement, it becomes clear that the capacitance of woods is proportioned to the moisture content in a region of free water. And the capacitance deviation due to the moisture content is proportioned to the apparent density of wet wood, but not affected by the kind of wood.
