Patent ID: 8893544

Claim:
A viscosity measuring method, using a viscosity measuring device comprising: an oscillating body put in a fluid to be measured; an actuator for making the oscillating body oscillate self-excitedly; an oscillating velocity detector for detecting an oscillating velocity of the oscillating body; and a controller that generates positive feedback of the oscillating velocity detected by the oscillating velocity detector so as to activate the actuator according to a feedback control signal Fs represented by an equation: Fs=Cc ·( dx/dt ), where Fs denotes a feedback control signal, Cc denotes a linear velocity feedback gain, and dx/dt denotes the oscillating velocity of the oscillating body; wherein the viscosity measuring method comprises the steps of: changing the linear velocity feedback gain for feedback control; using the linear velocity feedback gain at a time when the oscillating body changes between a non-oscillation mode and an oscillating mode as an oscillation limit gain; and detecting the oscillation limit gain as a viscosity equivalent value representing viscosity of the fluid.