| 摘要 |
1,011,775. Electric selective signalling. LITTON INDUSTRIES Inc. July 13, 1962 [July 14, 1961], No. 26978/62. Heading G4H. [Also in Divisions G1 and H3] In a transducer, a pair of elongated, bifurcated, rigid vibratory elements are oscillated about their longitudinal axes at or near their natural frequencies, and a force to be measured is applied to the elements in the sense to reduce the oscillation frequency of one element while increasing that of the other, and the changes of oscillation frequency are measured. As shown, Fig. 4, two piezo-crystal elements, 11a, 11b, are connected in the frequency-determining circuits of oscillators 31a, 31b, which may be transistorized Meacham bridge stabilized oscillators. Elements 11a, 11b are subjected to a common force, e.g. an acceleration, so that 11a is compressed and 11b experiences a tensile load, the frequencies of oscillation of oscillators 31a, 31b then being w 1 , w 2 respectively. The outputs of the oscillators are fed to a mixer 36, the output of which has a frequency (w 2 -w 1 ) and is applied to a counter 38, which is periodically reset by a reset circuit 40, to produce a digital signal representing the applied force. It is shown in the Specification that (w 2 -w 1 ) = 2KS/(w 2 + w 1 ), where S is the magnitude of the applied force and K is a constant; therefore, if (w 2 +w 1 ) is kept constant, e.g. at twice the unloaded frequency of one element (preferably the elements have equal natural frequencies when unloaded), (w 2 -w 1 ) is directly proportional to S. This is achieved by adding w 1 and w 2 at 33 and comparing the sum with a reference frequency, generated at 42, in a comparator 35 whose output, which represents the frequency difference #w, is amplified at 37 and used to apply such compressive or tensile forces to elements 11a, 11b, as to reduce #w substantially to zero. If counter 38 is not periodically reset it will indicate velocity. Transducer construction.-Fig. 1 shows an accelerometer in which accelerations of a frame 10 along three mutually orthogonal axes, X, Y, Z, differentially load the elements of pairs of high-Q quartz elements 13a, 13b and 11a, 11b and 15a, 15b respectively. Each element is fixed between frame 10 and a mass 17 or 19, and comprises two parallel bars 21, 23, Fig. 2a, joined at their ends. Conductive coatings 25, 27, 29 enable each element to be connected in the circuit of an oscillator 31. Alternatively, the elements may be made from a plurality of pieces of quartz &c. cemented together. Fig. 5 shows a modified accelerometer comprising only one mass 17. Analogue-to-digital converter. Fig. 7.-An analogue signal fed to coil 55 exerts a force on a magnetic mass 53, differentially loading elements 51a, 51b which are connected in a circuit such as that shown in Fig. 4.
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