GB675157A - Improvements in and relating to measuring or observing changes in the electrical conductivity of liquids - Google Patents

Abstract

675,157. Electro-chemical analysis; measuring resistance. NATIONAL RESEARCH DEVELOPMENT CORPORATION. Oct. 5, 1950, No. 24332/50. Class 37. In apparatus for measuring changes in the conductivity of liquids for determining, e.g. its brine content, in which a cell with a sample of the liquid has two electrodes whereby the cell is capacitatively coupled across the tuned circuit of an oscillator valve, and the resulting change in anode current is indicative of the electrolyte conductivity the measuring circuit also includes a temperature-sensitive element acted on by the test fluid to compensate for changes in temperature. The cell may comprise a glass tube S1 (Fig. 5) having electrodes S2 at the ends, and S3 at the centre, or a flat box X (Figs. 6, 7, not shown), with flat electrodes H, or, in a form for immersion in the liquid, may consist of concentric glass tubes M, W (Figs. 8, 9), containing metal electrodes J, V, respectively. The electrodes are connected by coaxial cable to a plug P (Fig. 1) across the tuned circuit L, C1 of an oscillator valve, the change in anode current being determined in a bridge circuit R1-R10, shown by a meter across the diagonal of the bridge. The oscillator frequency is normally adjusted to give a'linear relationship between resistance and anode current, or may be adjusted to give maximum current for a particular value of conductivity, thereby energizing an alarm circuit. Temperature compensation is introduced by using a temperature-sensitive resistance R3 in one arm of the bridge, assembled on the cell, as shown in two parts T1, T2 (Fig. 5). The apparatus may be adjusted and checked by operating a control switch SW to positions 2 and 3.