A viscosity measuring transducer especially useful for process control of fluids. The transducer oscillates an immersed blade sensor in the direction of the plane of the blade in order to maximize generation of shear waves and to minimize generation of compression waves. The transducer includes a bar which penetrates and is secured and peripheral sealed to an isolation plate which serves to protect the oscillation driver and pickup adjacent one end of the bar from the sensor blade to be immersed in a fluid adjacent the other end of the bar. Either the bar is relatively rigid and the isolation plate is relatively compliant, or vice versa. In the former case the isolation plate acts as an intrinsic flexible member of the oscillating system of the transducer; and in both cases the isolation plate constitutes a strong impermeable seal between the fluid and the driver/pickup mechanism. The isolation plate may be corrugated or ribbed to allow vibratory motion in the desired direction (parallel to the sensor blade major surfaces) while resisting movement in the direction perpendicular thereto.