Patent ID: 7181957

Claim:
A method for measuring viscosity of a fluid at a desired shear rate, utilizing an acoustic wave device having an input transducer and an output transducer, and having a known relationship between input power, output power, and an acoustic wave amplitude at a selected region between the input and output transducer, the acoustic wave device being coupled to the measured fluid, the method comprising the steps of: i. selecting a desired shear rate, and an initial input power level as an estimated power level; ii. applying a harmonic signal having the estimated power level to the input transducer to impart an acoustic wave of pre-selected amplitude at the selected region; iii. using the acoustic wave device, measuring viscosity of the fluid to obtain a measured viscosity at the selected region; iv. calculating an actual shear rate of the fluid at the selected region by using the viscosity measurements and the acoustic wave amplitude; v. calculating the difference between the actual shear rate and the desired shear rate to produce a shear rate error; vi. adjusting the estimated input power level to compensate for the shear rate error; and vii. using the adjusted estimated power level, repeating steps iii through vi until the shear rate error is within acceptable tolerance from the desired shear rate.