GB922569A - Improvements in or relating to apparatus for measuring or responsive to the electrical conductivity of a fluid - Google Patents

Abstract

922,569. Determining liquid level; current measuring. WAYNE KERR LABORATORIES Ltd., and R. CALVERT. Nov. 2, 1961 [Aug. 3, 1960], No. 26894/60. Class 37. A conductivity measuring head comprises a pair of plate electrodes 11, 12, Fig. 1, screened from each other by a larger plate 10, the plate 10 being insulated on both sides and the whole being encapsulated by an insulating surround 14. The outer electrodes may be deposited on the insulation 13 and the outer surface may be thinly insulated so that liquid into which it is to be inserted for, for example, liquid level measurement is capacitatively coupled to the electrodes. The current to one electrode 12, Fig. 3, from an A.C. source may be opposed by current through a standard impedance 23 and applied to a null detector 30 through a rectifier 29. In an alternative arrangement, Fig. 4, the current through electrode 12 is measured by applying a signal proportional to it, to a high-gain amplifier having a degree of feedback sufficient to give a substantially zero input, the amplifier voltage output then indicating the current. Alternatively a current indicator may be inserted in the feedback path. In a further arrangement described with reference to Fig. 5 (not shown) the current measured by the amplifier is the difference between the electrode current and a reference current, the latter being injected in the amplifier input circuit.