Abstract: An apparatus and a method for controlling the shear rate at which an acoustic wave device measures viscosity, by utilizing an automatic level control or an automatic gain control circuit to control power input to the sensor as a function of the sensor's output power. Further improvement is provided by measuring the input power and combining the input power and output power measurements, preferably by averaging, to control the input power to the sensor. A method is also provided for characterizing the fluid under test by providing a set of viscosity measurements at various shear rates.