Vibration meter and method of measuring a viscosity of a fluid

A method of measuring a viscosity of a fluid flowing through a pipe using a vibration meter comprising:

• a transducer assembly
• with at least one flow tube inserted into the pipe which in operation oscillates relative to a position of rest at an adjustable excitation frequency,
• with an electromechanical excitation arrangement for producing spatial deflections of the flow tube, and
• with a sensor arrangement, responsive to lateral deflections of the flow tube, for sensing an inlet-side and an outlet-side deflection of the flow tube;
• and
• meter electronics with
• an excitation circuit which generates an excitation current feeding the excitation arrangement, and
• an evaluating circuit,
• the vibration meter providing a density value, representative of a density of the fluid, and an excitation frequency value, representative of the excitation frequency,
• said method comprising the steps of:
• generating vibrations of the flow tube at the excitation frequency to produce viscous friction in the fluid;
• sensing the excitation current feeding the excitation arrangement to generate a friction value representative of the viscous friction;
• sensing an inlet-side and/or an outlet-side deflection of the flow tube to generate an estimate representative of a velocity of a motion of the fluid, which causes the viscous friction;
• dividing the friction value by the estimate to obtain a quotient value representative of a damping of the oscillating flow tube caused by the viscous friction;
• deriving from the density value and the excitation frequency value a correction value dependent on the density of the fluid and on the excitation frequency;
• and
• deriving from the quotient value and the correction value a viscosity value representative of the viscosity of the fluid.