GB1125448A - Apparatus for measuring the force on a body due to fluid pressure - Google Patents

Abstract

1,125,448. Measuring fluid-pressure electrically. C.M.R. PALLIS. Dec. 12, 1966 [Dec. 16, 1965; March 8, 1966], Nos.53360/65 and 10002/66. Heading G1N. The component of force in a selected direction on a body due to variable fluid-pressure is measured by capacitative transducers in a bridge circuit and may be applied to the measurement of the mass of liquid or granulated material in a tank or the force on an aerofoil in a fluid stream. In one embodiment, Fig. 1, the mass of liquid in an enclosed tank 10 subject to variable acceleration (vector G) is measured by lining both the floor and the roof of the tank with a capacitor web comprising a pair of metal foil electrodes 12 and 13, spaced apart by a rubber matrix 14 and enclosed in a flexible insulating film 15. The interiors of the rubber matrices are linked together and to the interior of the tank by vent pipes 16, 17. The pipe 17 is closed by a zero-stiffness diaphragm or bladder 18. The two capacitor webs from adjacent arms of a bridge circuit, Fig. 4 (not shown), having fixed capacitors in the other two arms. The bridge is energized by an alternating voltage proportional to the reciprocal of the vertical component of the acceleration to which the tank is subjected. Acceleration is measured by an accelerometer 24 of unspecified type. It It is shown that the resultant output signal from the bridge is proportional to the mass of the liquid in the tank. Compensation for changes in flow gradient may be made by cutting holes in the foil electrodes so as to locally grade the capacitor web. Similarly, compensation for openings in the tank which cannot be lined with the capacitor web may be made by surrounding the area with an annular capacitor of increased effectivness Fig. 3 (not shown). In a first modification, applicable when the roof of the tank is not wetted, the capacitor web on the roof is replaced by either a device responsive to the external pressure acting on the liquid or by a manually pre-set signal device. In a second modification, applicable when the acceleration is due solely to gravity, the accelerometer 24 may be replaced by a device providing a signal proportional to the angle of tilt of the tank, or if the tank is fixed the accelerometer is omitted altogether. In a second embodiment, Fig. 5 (not shown), the floor of the tank is lined with strip shaped capacitors connected in parallel. Each capacitor comprises a compressible oval tube forming one electrode 2 within which is mounted an elongated, cruciform structure the horizontal arms of which form the other electrode. In another embodiment, Fig. 6 (not shown) the pressure on an aerofoil due to a stream of fluid is measured by covering the upper and lower surfaces with capacitor webs and comparing their values.