The DENSITRAK® Model D625 liquid density measuring instrument utilizes the spring mass principle for measuring the fluid density. A portion of the "u" tube is energized to vibrate at its natural resonant frequency by using an electrical feedback driving system. A change in the vibrating mass, (as a result of change in the fluid density) shifts the resonant frequency. A CSI SPUD signal processing unit for density uses temperature, pressure and the shift in frequency to determine the density of the measured fluid.
