GB1016915A - Pressure transducers - Google Patents

Abstract

1,016,915. Pressure gauges. SOC DE PROSPECTION ELECTRIQUE SCHLUMBERGER. Nov. 29, 1962 [Jan. 6, 1962], No. 45202/62. Headings G1L and G1N. In a transducer for measuring fluid pressure comprising a hollow cylinder 18 (Fig. 1) of magnetic material, containing two coils 24, 26 with their axes at right angles, which are used to make the cylinder vibrate axially and/or radially at its natural frequency, this frequency being indicative of the magnitude of the fluid pressure on one face of the cylinder, a ring member 40 held by a bellows 30 is added, to produce compensation for variations in pressure due to changes in temperature. The inside of cylinder 18 is filled with gas at a low pressure, so that the absolute change in pressure inside the cylinder with changes in temperature are small. The chamber 42 between the outside of cylinder 18 and an external casing 10 is filled with a standard fluid, and is in communication with the bellows 30 whose free end 34 carries a rod 36 attached to the ring member 40. When the temperature of the fluid in chamber 42 rises the bellows 30 expands, accompanied by a decrease in the density of the fluid, and by a shift of the ring 40. Each of these alterations affects the oscillatory frequency of the cylinder 18, and it is shown that there are two positions of the ring 40 at which they are equal and opposite, these positions being found experimentally. The ring 40 may be provided with lobes 41 (Fig. 5). In operation the external surface of bellows 30 is subjected to a fluid pressure which is transmitted through the bellows to the external surface of the cylinder 18, and determines its natural oscillations frequency, which is measured electrically. In another embodiment (Fig. 6, not shown) the inside of cylinder 18 is also subjected to a test pressure via a bellows, and the vibrating frequency indicates the pressure difference. The fluid inside chamber 42 is preferably a mixture of decane and tetradecane whose ratio is adjusted to give a predetermined basic frequency of oscillation.