Patent GB-378020-A (GB)
Title: Improvements in and relating to pressure measuring devices
IPC: G01L9/00
Filed: 1931-04-30
Abstract: 378,020. Weighing-apparatus. BRITISH THOMSON-HOUSTON CO., Ltd., Crown House, Aldwych, London.-(Assignees of Payne, J. H. ; 79, West Street, Ballston Spa, New York, U.S.A.) April 30, 1931, No. 12772. Convention date, April 30, 1930. [Class 143.] A carbon pile resistance in an electric circuit is acted upon by a force and also by the opposing pull of an electromagnet in the circuit the current passing being a measure of the force which may be a weight, a head of liquid, or a fluid pressure, which in turn may be derived from a fluid pressure meter or an anemometer, or the device may be used as a regulating device to secure a constant current in the circuit. The device with the exception of the battery and ammeter is enclosed as a unit in a casing which in the form shown in Fig. 3 is secured to the bottom 20 of a tank containing fluid the pressure of which is to be measured. The casing comprises two parts 21, 22 between which a diaphragm 25 is clamped. To the lower end of the part 22 is secured a chamber 24 made of insulating material. The diaphragm is supported on a platform 26 to which is secured a cup-shaped armature 27 enclosing a carbon pile rheostat on which it rests. The pile comprises a stack of carbon washers 28 threaded loosely over an insulating sleeve 31 attached to a rod 30 screwed into the part 29. A light adjustable spring 32 surrounds the lower end of the road which is free. The magnetic circuit of the solenoid is nearly closed and is formed by the casing 22 with its bottom part 36, a cylindrical upward extension 37 and a plate 38 of magnetic material which makes close connection with the casing at its outer edge and extends over the upper edge of the armature 27. The device is connected up in circuit with a battery 15 and ammeter 16 one end of the outer circuit being connected to the part 21 of the casing while the other end is connected to the binding post 41 which connects to one end of the coil 13. The other end of the coil is connected to a binding post 42 which is connected through a metal strap 43 to the metal part 35 which is connected through the metal plug 33 to the carbon pile. In use, the pressure fluid enters the chamber 21 above the diaphragm through a loose plug 45 which damps oscillations, and acting on the diaphragm presses together the carbon washers causing the initial small current to increase and the solenoid to exert a counteracting balancing pull which is measured by the current. The area. of the diaphragm supported by the platform 26 may be changed by changing the size of the platform and different ranges obtained. In a modified construction the carbon rheostat is arranged parallel with but not coaxial with the coil admitting of the employment of a smaller coil. In measuring the depth of liquid in the fuel tanks of an aeroplane, each tank is fitted with a unit and the electric connections are such that one ammeter provided with a number of scales may be connected to any of the tank devices. In another form, the device is fitted to a wind vane which keeps the diaphragm head on to the wind and the pressure due to wind velocity is measured in the same way. In this form the spindle attached to the diaphragm is provided with a viscous liquid damping device, and the electrical circuit includes an oscillograph. When used as a flow meter the up and down stream pipes are connected each side of the diaphragm. Specification 317,764, [Class 143, Weighing-apparatus], is referred to.