Practical ultrasonic spectrometric measurement of solution concentrations by a tracking technique

A practical technique for solution concentration measurement, based on a resonator with enclosed piezoceramics, which can operate at a resonant frequency mode around 500 kHz is designed and evaluated. The resonance can be tracked automatically by means of a phase-locked loop. Measurements made on water-methanol mixtures showing that concentration can be expressed as a function of temperature and resonance frequency, where a multiple regression technique is used to relate them, are reported. It was possible to evaluate the concentration with a repeatability of about 0.06%, which depends essentially on the temperature measurement. Various milk mixtures have also been tested to check if the evaluation of both butterfat and protein concentrations could be achieved from measurements at two different temperatures. It was found that calculations based on two measurements cannot be used when the composition varies too widely.