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Abstract

On-line measurement of viscosity of process liquids at process temperature is difficult though industrially very important. A viscometer is designed which can do this up to about 300 °C almost on-line within about 1-8% accuracy except for very viscous liquids like glucose. It uses a ferromagnetic probe designed to mechanically vibrate in the ultrasonic frequency range. An excitation coil sends repeated excitation current pulses to induce mechanical vibration in the probe tip. When placed in a process fluid, the vibration amplitude is damped due to the viscosity of the fluid, and the damped vibration is sensed by Faraday's principle by a sensing coil. The number of pulses per second needed to keep the probe vibrating above a threshold level is directly proportional to the viscosity of the fluid. Necessary calibration was done and the performance tested using several pure liquids as references with known viscosities in the range 0.1 - 2,000 cp at temperatures between -80 and +300°C.

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