Phase boundary detector for small fluid channels

摘要

The fluid flows in a non-electrically conductive channel. At least two electrically conducting mutually isolated surface segments (3,4) are arranged round the flow channel (1) to form a first capacitor (2) whose capacitance is defined by the dielectric characteristics of the fluid flowing in the channel. The surface segments are connected to an evaluation circuit (6) which determines the phase boundary based on the capacitance or changes in the capacitance, and delivers a signal accordingly. The capacitor constitutes part of an oscillator circuit (7) and the phase boundary is determined from the frequency or changes in the frequency of the circuit.