ULTRASONIC DENSITY METER
Process control is a very important part in the chemical and food industries. Especially the accurate measurement of the density of fluids challenges the engineers. With changes in concentration of the fluid the density varies and therefore the velocity of sound. A few steps to arrive at time measurement (see animation below)!
The velocity of sound in water is 1483m/s (at 20° C). Many solutions show a change of velocity of sound depending on concentration between 1200m/s and 1800m/s. For a distance between ultrasonic transceiver and receiver of 2 cm this gives delays between 10us and 20us. With small distances of the transducers and an upper limit for velocity of sound of 10.000m/s we find delay times of only a few microseconds. The typical resolution of current available devices is about 0,1m/s - this means a resolution in time of 500ps - no problem for the TDC !