GB695074A - Improvements in or relating to apparatus for measuring the weight of liquid - Google Patents

Abstract

695,074. Electric tests and measurements. LIQUIDOMETER CORPORATION. July 30, 1951 [Aug. 4, 1950], No. 17982/51. Class 37. Apparatus for determining the weight of liquid in a tank comprises a capacity gauge of the type described in Specification 693,600, e.g. two concentric cylinders immersed in the tank, so that the volume of liquid may be ascertained from the resultant dielectric constant of the test capacitor, and the capacitor is included in a bridge circuit wherein an electrical quantity is created representing the density of the liquid on the assumption that the relationship between density D and dielectric constant K is K=aD+b, a and b being constants, the bridge being automatically balanced by a reversible 2-phase motor fed with the unbalance voltage on one phase, driving a potentiometer to maintain balance, and also a counter mechanism which indicates weight of liquid in the tank. Fig. 1 represents the basic electrical circuit of the invention. The two halves of the secondary winding of a transformer 2 constitute two arms of a bridge, the test capacitor Ct being the third arm, and the fourth arm being a condenser Cc in parallel with a condenser Cr fed from the slider 14 of a potentiometer 12 across one half winding. The capacity of Cc is equal to that of the test capacitor Ct when empty, Co. The weight of the liquid in the tank is then proportional to the fraction m of the potentiometer 12 feeding condenser Cr, when the bridge is balanced, if Cr=<SP>K-1</SP>/ K -banCo, where n is a con- K-b stant. Expanding this term by Taylor's series, it is shown that Cr#(α+#K)nCo, where α and # are constants. In an embodiment (Fig. 3), Cr is constituted by a fixed condenser Cd (=αnCo) in parallel with a condenser Cs formed by spaced plates immersed in the tank so that Cs=#KnCo. The unbalance voltage of the bridge is fed into an amplifier 22 whose output is taken to a 2-phase motor 26 which moves the slider 14 of potentiometer 12 to balance the bridge, and also operates an indicator 42, which is made to read correctly when the tank is empty by adjusting a potentiometer 44, and when full by adjusting a variable resistor 48.