RF ADMITTANCE APPARATUS AND METHOD FOR MONITORING THE CONTENTS OF A PIPE

摘要

Various electrodes of a probe which are adapted to respond to the degree to which a pipe is filled with fluid include the use of a tubular conductive probe electrode (10) and a pair of tubular conductive guard electrodes (12) axially displaced from the probe electrode. The electrodes are adapted to form a portion of the fluid-carrying pipe. The probe electrode and guard electrodes are separated by solid insulation (11). The guard electrodes are separated by solid insulation (15). 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 (t) of fluid adhering to the probe are substantially eliminated. Also disclosed is RF admittance-responsive circuitry (Fig. 9) which responds to the electrical characteristics of the contents of the pipe, and which is adapted to drive the guard electrodes at substantially the measuring potential applied to the probe. By capacitively coupling the admittance-responsive circuitry to the contents of the pipe through the probe electrode (10), a substantial improvement in the ability of the system to tolerate conductive coating of the probe is achieved.