CAPACITANCE MEASUREMENTS OF THE VOLUME FRACTION AND VELOCITY OF DIELECTRIC SOLIDS NEAR A GROUNDED WALL

We describe capacitance probes that infer the volume fraction of solid s near a grounded wall from a measurement of the effective dielectric constant of the suspension. The probes consist of three conductors, na mely the sensor, guard, and ground surfaces. The instrument records ca pacitance between the sensor and ground by supplying an oscillating cu rrent of constant amplitude to the sensor. A control circuit maintains the guard and sensor voltages equal without affecting the sensor circ uit. Because it surrounds the sensor conductor everywhere except at th e probe surface, the guard eliminates stray and cable capacitances. By locating the ground at the periphery of the probe, this configuration renders the new instrument particularly useful in metallic vessels. C ross-correlation of the signals from two adjacent capacitance probes a lso permits measurements of the velocity of dielectric solids. (C) 199 6 American Institute of Physics.