GB871553A - Improvements in vibrating wire accelerometers - Google Patents

Abstract

871,553. Vibrating wire accelerometer. ROE & CO. Ltd., A. V. May 19, 1959 [May 27, 1958], No. 16822/58. Class 40 (1). A linear accelerometer comprises a frame 1 in which two vibrating wires 6 and 7 are aligned under a common tension provided by a magnetic force between two seismic weights 2 and 3 carried on adjacent ends of the wires, Fig. 1 (part longitudinal section). The wires vibrate between magnetic systems 8 and 9 providing output signals of frequency corresponding to the wire tension. Any acceleration causes one frequency to be increased and the other to be reduced and the difference frequency varies linearly with acceleration provided that the sum of the frequencies remain constant. To ensure this, such sum is compared with a fixed frequency and any error is used to vary the current in coil 15. As shown in Fig. 2, the other poles 10 and 11 of the magnets 4 and 5 are attached to the weights 2 and 3 and are supported by hinges 12 and a magnetic return path is provided by the surrounding members 13 and the frame member 14 which is made of iron or other " soft " magnetic material. The gaps between 13 and 10 and 13 and 11 are made large compared with that between weights 2 and 3. The tension in the wires may be adjusted initially by varying the m.m.f. in 14 by means of coil 15, or by insertions of a permanent magnet or a predetermined amount of saturation in the return path. In an alternative embodiment, Fig. 3 (not shown), a variable air gap is used to vary the flux in the return path. An acceleration sensitive weight on the frame member varies the air gap in the latter as the acceleration changes.