GB820245A - Capacitor for conductive liquids - Google Patents

Abstract

820,245. Electric measuring systems. ENGINEERING RESEARCH CORPORATION Ltd. June 21, 1957 [June 26, 1956], No. 19604/57. Class 37. In a condenser of the type used for measuring the depth or volume of a conducting liquid in a container and having two electrodes which are surrounded by insulating material, at least one of the electrodes comprises a metallic coating at the interface of two closely fitting concentric tubular elements of insulating material. In one embodiment having electrode structures 102, 104, two main electrodes are formed by metallic coatings at the interfaces of insulating tubes 106, 108 and 144, 146. Inner structure 102 may comprise two separate spiral coatings, Fig. 3 (not shown), one of which acts as the electrode and the other as an electrostatic shield, exterior connections being made by ears 116, 114. The coatings may be profiled to match irregularities in the shape of the liquid container in which the condenser is housed. Structures 102, 104 are rigidly spaced and are sealed so that none of the liquid which enters the space therebetween can penetrate to the electrode surfaces. The condenser may further comprise a third electrode, formed by a series of vertical wires 128 supported by studs 126 on rings 122, 124, which is connected to ear 144 by a metal strap 140. In operation the wires 128 are maintained at earth potential and the capacity of the condenser is a maximum when the condenser is empty and decreases as the level of the liquid rises inside because the liquid forms a screen between the electrodes. The condenser 10, Fig. 1, with main electrodes 12, 14 and third electrode 16, may be included in a bridge circuit which is automatically balanced to indicate the liquid level. With condenser 10 empty, and slider 48 at the top of rebalancing potentiometer 44 (as viewed in Fig. 1), slider 62 of potentiometer 54 is adjusted to balance the bridge. With condenser 10 full of the liquid to be gauged and slider 48 at the bottom of potentiometer 44, the bridge is again balanced by means of potentiometer 38, thus fixing the empty and full limits for the liquid container. Intermediate indications of the liquid level may be obtained by applying the unbalanced output of the bridge at point 52 to an amplifier 66 and motor 68 which is coupled to drive slider 48 so that the bridge is again balanced.