Device for detecting the effective dielectric constant of a medium, particularly for determining the water content in a filled container for oil or alcohol

摘要

A device for detecting the effective dielectric constant of a medium is used, in particular, for determining the water content of an oil-water emulsion and the height of the boundary area between a water layer and oil layer in a tank. The device has a receiving electrode (7) surrounded by an insulator, which is connected to the input of an evaluating device operating frequency selectively and phase selectively. The receiving electrode (7) is associated with field-generating first and second transmitting electrodes (5, 6) to which alternating voltages with opposite phases are applied via first and second drive amplifiers (10, 11). The amplitude ratios of the alternating voltages are adjusted with the aid of a null correction circuit (21, 24) in such a manner that the currents induced in the receiving electrode (7) by the transmitting electrodes (5, 6) compensate one another. The receiving electrode (7) is shielded against the alternating electrical fields generated by the first and second transmitting electrodes (5, 6) on at least one side, a third transmitting electrode (9), which is connected to the voltage of one of the drive amplifiers (11) via a switch (13, 14), being arranged in the area thus shielded. The space existing between the third transmitting electrode (9) and the receiving electrode (7) forms a measuring space (8) for the medium to be examined. <IMAGE>