An ultrasonic density probe

An ultrasonic density probe for liquids using a single transducer is developed, as a first step in the design of an ultrasonic mass flowmeter. The probe is based on the reflection of sound at the probe´s interface with the fluid. The amplitude of the echo from that interface indicates the characteristic acoustic impedance of the liquid. The liquid´s density is the ratio of its acoustic impedance to the speed of sound through it. The latter is obtained by measuring the time necessary for the transmitted sound pulse to be echoed back from a reflector located at a known distance in the fluid. The probe consists of two buffer rods in series behind which sits a transducer. This arrangement removes any dependence on the amplitude of the initial pulse. The effects of temperature on the buffer rods´ characteristics are numerically compensated for by the dependence of the measured speeds of sound on the temperature of the traveled media. Results show an accuracy of better than 1% with a 95% confidence level for water at temperatures ranging from 2 to 40°C