| 摘要 |
1508686 Vibrating string meters UNITED STATES DEPARTMENT OF COMMERCE 6 Aug 1975 [7 Aug 1974] 32889/75 Heading G1G The frequency or time for 100 cycles of vibration of a wire in a vibrating wire meter is displayed on a counter using LED's when the frequency of a voltage controlled oscillator in a phase locked loop 21, initially set manually by control 22 to within 2% of the resonant frequency of the wire, is automatically tracked on to that resonant frequency. In the particular embodiment described, the time taken for 100 oscillations of a wire 15 under tension uses a driver 18 for a first (sounding) period, phase locked loops 21, 24 operating on vibrations induced in the sensor 16 above a threshold level in a second (listen) period. Phase locked loop 24 discriminates against harmonics. The wire meter may be used to measure pressure, weights, displacements and tilt.
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