GB855650A - Improvements in or relating to flowmeters - Google Patents

Abstract

855,650. Ultrasonic fluid-flow meters. NATIONAL RESEARCH DEVELOPMENT CORPORATION. June 2, 1959 [June 10, 1958], No. 18473/58. Class 40(7). An ultrasonic fluid flow meter comprises at least one pair of electro-acoustic transmitting and receiving transducers together with associated coupling blocks for transmitting ultrasonic waves by upstream and downstream paths across the pipe carrying the fluid, compressional waves being generated in the fluid by shear waves generated in the coupling blocks. In one embodiment Fig. 4 the 5 mc/s. C.W. outputs from receiving piezo-electric crystals 7,27 are heterodyned with 4À9 mc/s. oscillations, the relative phases of the 100 kc/s. outputs from mixers 31, 41 being proportional to the mean velocity v of the fluid in pipe 1. After squaring and differentiation of the 100 kc/s. oscillations they trigger bistable multivibrator 50 whose output mark/ space ratio is correspondingly proportional to v. The multivibrator output is smoothed by filter 51 to provide a D.C. signal to meter 52 calibrated in fluid velocity. In a second embodiment a pair of transducers are alternately used for simultaneous transmission and reception accomplished by a switching pulse generator, the phase difference (i.e. fluid velocity) measurement being accomplished as before, Fig. 6 (not shown). It is demonstrated that for a beam angle in the fluid of 45 degrees to the pipe axis there is partial inherent compensation for error due to ultrasonic propagation velocity change with e.g. fluid temperature. To avoid sludge-retaining cavities in the pipe wall due to transducer coupling block insertion the pipe is fitted with a plastic liner, the liner and coupling blocks having flat faces, Figs. 1 - 3 (not shown). The coupling blocks may be of tin, polystyrene, silver, or lead glass and be protected from corrosion by the fluid with a shim of stainless steel; or an anti-corrosion coating of platinum, gold or plastic material may be used. In one form the coupling block is associated with X-cut quartz crystal 5 Fig. 5 which generates a compressional wave travelling in a beam to face 19 from which shear wave beam 14 is produced and subsequently converted into a compressional wave travelling through the fluid to coupling block 6.