| 摘要 |
1,194,694. Locating liquid/fluid interfaces. NATIONAL SONICS CORP. 18 July, 1967 [18 July, 1966], No. 32898/67. Headings H4D and H4J. The location of a liquid/fluid interface in a medium located in a vessel is determined by analysing the amplitude of an ultrasonic signal of at least 500 kHz received after transmission through the medium. In embodiments described, a transmitting and a receiving transducer are mounted inside or outside the vessel and are coupled to the output and input, respectively, of an amplifier to provide acoustic feedback. An oscillator, or background noise picked up by the receiving transducer, energizes the transmitting transducer. The amplifier gain is adjusted so that the loop gain is less than unity when the acoustic propagation path is via the liquid and greater than unity when via the fluid, or vice versa. The change in loop gain is sensed by a Schmitt trigger at the amplifier output. Indications of physical characteristics (e.g. composition, temperature, density, pressure) of the fluid may also be obtained, by comparing the amplifier gain required to give unity loop gain with charted values ascertained by independent physical or chemical analysis. Circuit details are given. Transducer details (Fig. 3) .-The transducers are piezoelectric wafers 36, 38 (comprising, e.g. barium titanate, lead zirconate, lead metaniobate) mounted in chambers 32, 34 of a housing 30 of metal, plastics, ceramic or glass, behind "windows" 42 of a plastic, ceramic or glass material which will not transmit the radial mode of the wafers and thus acoustically isolates the two transducers. Further isolation is provided by seating the wafers on rubber feet, by surrounding the transmitting wafer with lead or coupling it to the housing through a gold or silver foil, or by making the housing in two sections joined by a welded or threaded part providing a tortuous propagation path. The window thicknesses are preferably integral halfwavelengths. |
