Method for the measurement of the amount of cementitious material in a concrete mixing truck using a resonant electroacoustic transducer

A method for measuring an amount of cementitious material in a concrete mixing truck, comprising:

• (A) placing into contact with the cementitious material at least one electroacoustic transducer comprising a radiating surface that contacts the cementitious material and transmits an acoustic wave as the electroacoustic transducer is supplied an electrical signal, said electroacoustic transducer having a resonant frequency fr and an antiresonant frequency fa, said electroacoustic transducer being connected to an electronic circuit configured to measure the magnitude of driving point impedance of the electroacoustic transducer at its resonance frequency fr and its antiresonant frequency fa and calculate activity of the electroacoustic transducer;
• (B) rotating a drum of the concrete mixing truck so that said radiating surface of said electroacoustic transducer submerges in and then emerges from said cementitious material while measuring with said electronic circuit the driving point impedance magnitude of fr and fa, and calculating the activity of said electroacoustic transducer a plurality of times as said drum rotates;
• and
• (C) using the calculated activities and the corresponding rotational angles, time values or both to determine a volume of cementitious material in the concrete mixing truck.