High precision wide dynamic range viscous loss measuring apparatus

Claim 1

Apparatus for controlling the viscosity of a fluid, comprising: a vibratory member which may be immersed in said fluid; driving means including a variable gain amplifier having input and output terminals for supplying power to maintain said member in mechanical oscillation, the gain of said amplifier being controllable in response to an amplitude correction signal; a transducer for detecting said oscillation; an amplitude monitoring circuit coupled to said transducer for providing a first signal having a value manifesting the amplitude of said oscillation; means for providing an amplitude reference signal having a value corresponding to a desired amplitude of mechanical oscillation; a comparator for providing said amplitude correction signal, the value of the amplitude correction signal provided by said comparator having a value determined by the difference between the value of said first signal and the value of said amplitude reference signal; means for applying said amplitude correction signal to said driving means, so that said driving means supplies sufficient power to said member to overcome the viscous loss resulting from immersion of said member in said fluid and maintain said member in mechanical oscillation at said desired amplitude; means for providing an output signal having a value which is a measure of the power supplied to said member by said driving means; means for providing a viscosity reference signal having a value corresponding to a desired viscosity of said fluid; a second comparator for providing a viscosity correction signal having a value determined by the difference between the value of said output signal and the value of said viscosity reference signal; and viscosity control means responsive to said viscosity correction signal for modifying the viscosity of said fluid so as to approach said desired viscosity.