| 摘要 |
1,092,532. Ultrasonic liquid-level sensing; ultrasonic probes. BRITISH PETROLEUM CO. Ltd. July 23, 1965 [July 31, 1964], No. 30280/64. Headings H4D and H4J. A multi-stage probe for liquid-level sensing comprises a solid body (e.g. of aluminium or aluminium alloy) having (a) a head portion 20 including a piezoelectric transducer 23, (b) an integral frusto-conical member 21 comprising a first-stage portion between head portion 20 and a semicircular cut-out 24, and a second stage portion between cut-out 24 and a diametrically opposed semicircular cut-out 28, (c) a first ultrasonic wave reflector-plate 26 between cut-out 24 and a further cut-out 25, and (d) a second reflector plate 33 defined by cut-out 28 and the lower end of member 21. In a second embodiment (Fig. 1) the first-stage and second-stage portions are defined by two frusto-conical sections (2, 3) of a solid body and the reflector plates comprise a non-integral annulus (7) and a non-integral disc (10) spaced from the lower ends of sections (2) and (3) respectively by spacers (9). In a liquid-level control system which is a development of that described in Specification 1,092,531, transducer 23 acts as both transmitter and receiver for pulses of 5 Mc/s. waves with a pulse repetition frequency of 200 c/s. For liquid levels below reflector plate 33, strong echoes are received at transducer 23 only from the lower faces 30, 31 of the first-stage and second-stage portions. As the liquid level rises to successively fill cutouts 28, 25, 24, so echoes are received from the upper surfaces 29, 27 of the reflector plates 33; 26 respectively, the thickness of the reflector plates being an odd number of quarter-wavelengths to give strong reflections. To ensure that echoes are received from surfaces 30, 27, 31, 29 in that sequence, and do not overlap in time at transducer 23, the ratio of the distance d 1 between surfaces 30, 27 to the distance d 3 between surfaces 30, 31 is made less than the ratio of the velocity of sound in the liquid to the velocity in the material of the probe, and the distances between transducer 23 and surfaces 30, 31 are made integral multiples of the length of the head portion 20. Echoes from reflector plates 26, 33 are detected by gating circuits (45, 46) (Fig. 4) in a development of the control and monitoring system of Specification 1,092,531. The signal from reflector plate 33 may be employed to partially shut off a liquid feed, and the signal from reflector plate 26 may cause complete shut-off of the feed. The control system may be adapted for use with four probes, selectively switched into circuit, each probe being associated with a different liquid flow.
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