Acoustic thermometer

of an insulating disc with conductive coating on each side. Each clock pulse causes mechanical movement of the disc, and ultrasonic energy is emitted. The clock pulse simultaneously resets the 74C74 output flip-flop. The ultrasonic energy travels down the tube, bounces off the far end, and returns to the transducer, causing mechanical displacement of the transducer. This shifts the transducer capacitance, resetting the 74C74 through A2 and C1. The 74C74 output pulse represents the transit time down the tube and it varies with the temperature, according to the equation: The pulse width (time between set and reset) can be converted into desired temperature information with a monitoring processor. Linear Technology. Linear Applications Handbook 1990. p AN7-5,