The Solartron Electronic Group Limited

James W Stansfeld

A fluid density transducer with a vibrating tube 16 coupled to excitation pick-up transducers 32 utilizes an elliptical tube 16, having a small degree of ellipticity, to compensate for the variation in the natural frequency of vibration, resulting from a variation in the fluid pressure, i.e. a rise in fluid pressure tending to lower the frequency produces a more circular and hence stiffer tube cross-section tending to increase the frequency. A sealed evacuated chamber 36, formed by connecting together cylindrical nodal masses 24 and 26 using a flexible coupling 28, is used to enclose the vibrating tube 16, thus avoiding the risk of contaminating, and thereby also affecting the calibration of, the tube 16. The tube is supported at each end by a spring plate 12 fixed around its outer periphery to a collar 10 and around its inner periphery to an end-plate 25 of the nodal mass 24 or 26. This provides rigid transverse support and allows use of the transducer in any orientation while accommodating small axial movements of the tube at either end.

Fluid density transducer

A vibrating fluid density transducer 10 provides a gas density measurement D, used in conjunction with a flowmeter signal f.sub.B to meter the mass of gas fed through a pipeline. D is subject to errors dependent upon the velocity of sound C in the gas. The errors are corrected to yield Da by application of a correcting formula (block 18) in which C is introduced by calculation (block 17) from a measurement of gas pressure P by a transducer P. The value of C may alternatively be measured directly, computed from a measurement of specific gravity or in the case of a liquid, be inferred from D or be preset.

Measurement of fluid density

A transducer for sensing density, pressure or pressure difference in fluids comprises a resonantly vibratable cylinder as its sensing element. The cylinder has a mounting ring at one end, the mounting ring being clamped against a base member by means of a spring arranged to exert a substantially constant clamping force on the mounting ring. An outer cover fits over the cylinder, the cover having a flange which is directly bolted to an upstanding annular rim of the base member and a depending skirt portion in which the spring is integrally formed by machining.

Transducer for sensing a parameter of a fluid

A density transducer employs a hollow cylinder capable of vibrating in the circumferential (or hoop) mode as the density sensing element, the cylinder being open at both ends and arranged so that the fluid whose density is to be transduced can come into contact with only the internal surface of the cylinder. The opposite ends of the cylinder are each secured to a respective clamping ring, which establishes a node at its respective end of the cylinder. The clamping rings each have a piston face which faces axially away from the cylinder and is acted on by the pressure of the fluid, thereby applying a compressive axial force to the cylinder which tends to reduce the effect of variations in the pressure of the fluid on the frequency of the vibration.

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Beech, Near Alton, United Kingdom

James W Stansfeld