| 摘要 |
1,121,098. Vibrating string measuring instruments. WIRTH, GALLO & CO. Oct. 7, 1965 [Nov. 27, 1964], No. 42614/65. Heading G1N. In a vibrating string measuring instrument, to suppress parasitic vibrations it is arranged that the resonant frequency of vibration in a desired transverse plane should differ by a wide margin from the resonant frequencies of other possible vibrations when the string tension has a given value or is within a given measuring range. Parasitic vibrations result from deviations from circularity of the string cross-section, clamping means &c. The invention relates to a stiff string, that is one in which the resonant frequency of the desired vibration at zero tension is at least 1% of that under maximum tension. The stiffness depends on the configuration of the string crosssection, or more precisely on the radii of gyration of its cross-section. For a completely circular cross-section the ellipse of gyration would be a circle. If for example the string cross-section is rectangular the radii of gyration are unequal and the string stiffness across the breadth exceeds that across its width. The frequency of vibration in planes containing these two different axes will be different irrespective of the tension. According to the invention it is arranged that when the string is set into transverse vibration, the ratio of the two axes of the mean ellipse of gyration of the string cross-section, is suitably chosen so that the two resonant frequencies of like mode which develop in the planes of the axes differ by more than one or the other of their respective resonance band widths though remaining between the resonant frequencies of neighbouring modes. To provide the desired frequency spacing it is arranged that the string has a uniform cross-section along its length of a configuration as shown in Figs. 4a, 4b, 5, 6 or 7, which permit correct orientation of the string with reference to the plane of excitation, the string being excited by electrical means, along its x axis. Alternatively the string may have non- uniform cross-section, Figs.8 to 14 (not shown). The permissable limit of the intentional difference between the radii of gyration of non-circular sections may be calculated or determined by experiment.
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