Rf admittance apparatus and method for monitoring the contents of a pipe

Abstract

A hollow probe which is adapted to respond to the degree to which a pipe is filled with fluid includes the use of a tubular conductive probe measuring electrode and a pair of tubular conductive guard electrodes axially displaced from the probe electrode. The tubular electrodes are hollow and are adapted to form a fluid conducting portion of the fluid-carrying pipe. The probe electrode and guard electrodes are separated by solid insulation. The guard electrodes are separated from sections of the pipe on either side of the hollow probe by solid insulation. The guard electrodes are exposed to the contents of the pipe and, by driving the guard electrodes at substantially the same potential as the probe electrode, the adverse effects of a coating of fluid adhering to the probe are substantially eliminated. Also disclosed is RF admittance-responsive circuitry which responds to the electrical characteristics of the contents of the probe and pipe, and which is adapted to drive the guard electrodes at substantially the measuring potential applied to the probe measuring electrode. By capacitively coupling the admittance-responsive circuitry to the contents of the probe, a substantial improvement in the ability of the system to tolerate conductive coating of the probe is achieved.