GB1419517A - Systems for measuring the resonant frequency of a body - Google Patents

Abstract

1419517 Acoustic measurement of physical properties UNITED KINGDOM ATOMIC ENERGY AUTHORITY 4 Dec 1973 [26 Sept 1972] 44377/72 Heading H4D In a system for monitoring the vibration frequency of a body (the resonant frequency of which may depend on temperature or some other environmental factor) a transducer arrangement transmits a vibration to the body and receives an echo from it, and a measure of the phase difference between the vibration incident on the body and the echo signal, which difference depends on the closeness of the vibration frequency to the resonant frequency, is obtained by counting the oscillations of a clock signal in the interval between the occurrences of first and second predetermined parts of the echo signal. The Fig. 6 thermometer includes a magnetostrictive transducer 2 linked by a waveguide 6 and coupler 8 to a temperature-responsive resonator 10. The composite echo pulse from the coupler and resonator is shown in Fig. 4 and includes a null region C associated with a phasechange dependent on the closeness to resonance. The time interval between two predetermined points such as zero cross-overs P and Q in the echo signal is thus a phase measure and is determined by a counter 23 receiving clock pulses from oscillator 14. Logic circuit assembly 17 identifies P as being the first (or other) zero-crossing occurring after a threshold amplitude L has been exceeded, and identifies Q as being the zero-crossing occurring n cycles of the vibration frequency later. The clock frequency is divided by 100 at 15 to provide the vibration frequency signal (Fig. 5) which is fed to logic 17 and is gated at 53 to form bursts for energizing transducer 2. Counter 23 can be arranged to read zero when the measured phase corresponds to the resonant vibration condition, decoded readings other than zero being used to energize lamps 25b indicating "non-resonance" and to control at 26 the oscillator 14 frequency such that the vibration frequency is slowly adjusted to resonance. The oscillator 14 frequency is monitored or recorded at 46, 48. The echo signal is monitored on an oscilloscope connected at 69.