A new resonant thermometer for nuclear reactor applications

An ultrasonic thermometer using the temperature dependence of ultrasonic velocity as the transducing mechanism has been developed for high temperature measurement. Essentially it is a long, thin probe consisting of a magnetostrictive launcher producing longitudinal vibrations in an acoustic line. A resonator which terminates the line constitutes the sensor. By measuring its natural resonant frequency as a function of temperature a calibration of the probe is obtained. A pulse excitation technique is used to drive the resonator after which the oscillations decay exponentially (the decrement) at the natural frequency of the resonator. The control compares this frequency with that of a signal generator to produce an error signal. This is used to make the signal frequency track that of the sensor. Digital aperiodic techniques are used throughout giving a smooth operation over the full range of the instrument. The setting-up procedure for changing a probe is minimal.