GB330497A - Improvements in indicating systems - Google Patents

Abstract

330,497. Slough, F. M. Nov. 29, 1928. Elastic-diaphragm pressure gauges.- Liquid level or pressure is indicated by opposing the pressure by a force due to electrically generated heat and measuring the heating effect by including an indicator in the electric circuit. The pressure of liquid in a tank 1, e.g. the fuel tank of a motor vehicle, is exerted on one side of a diaphragm 4 through a small aperture 13 in a tube 12 which damps out rapid fluctuations of level. Two bimetallic strips 14, 20 are mounted in the casing 7 with their free ends joined together and to the centre of the diaphragm 4. The strips are so arranged that on increase of temperature they tend to curl towards one another. An electric contact screw 25 is arranged below the strips and is in the circuit including a battery 28 and relay switch 31. When the pressure due to the liquid causes the strips to contact with the screw 25, and the contacts 29 are momentarily closed, a circuit is completed through battery 28, wire 42, relay 31, wires 33, and 32. The contacts 30 are thereby closed, and are substituted in the circuit for the contacts 29, so that current flows in the heating coil 43 surrounding the strip 20. This causes an upward force against the diaphragm 4 which ultimately breaks contact at the screw 25. The current flows also through a heating coil 36 surrounding a bimetallic strip 38, and the corresponding warping of the strip actuates a pointer 27 through rack and pinion 39, 40. The strips 14, 37 are for the purpose of compensating the effect of varying atmospheric temperature. The scale 41 is calibrated to indicate quantity of liquid or pressure. The pawl 45 prevents return of the pinion 40 until released by hand. A modification is described, Fig. 2, not shown, in which the switch 29 and relay 31 are omitted, and a continuous indication is given. In another modificalaminations of equal length arranged side by side omitted and the pressure on the diaphragm to oppose the liquid pressure is secured by the heating effect of the coil in the chamber 7 upon the enclosed air, or upon the vapour of alcohol or water. The indicator operates in a similar manner.