Control circuitry for viscosity sensors

US5054313A · kind A · utility

Assignee

• National Metal Refining Company · US

Inventors

• John V. Fitzgerald · Metuchen, US
• Teresa M. Walsh · Lawrenceville, US
• Frank J. Matusik · Piscataway, US
• John R. Stone · Greenfield, US
• Edmond J. Dougherty · Wayne, US
• John L. Batton · New York, US

Key dates

• Filing date: Jul 17, 1990
• Grant date: Oct 8, 1991
• Expiry date: Jul 17, 2010

Classification

• Technology area (CPC G): Physics
• CPC primary: G01N2011/0006
• WIPO field: Measurement
• WIPO sector: Instruments

Abstract

Electronic control circuitry for obtaining precise inline process control data as to viscosity of fluids over a wide viscosity range, with high tolerance of ambient noise and vibration. An electromechanical transducer with an oscillating sensor is immersed in a flowing liquid, with the power required to sustain predetermined oscillation parameters being a measure of viscosity-density product. The gain of a variable gain amplifier which provides positive feedback to sustain oscillation is controlled in response to the integrated error signal output of a comparator which compares a DC value corresponding to the RMS amplitude of mechanical oscillation with a DC reference value. The monitoring of RMS amplitude rather than peak amplitude (as is done by a phase-sensitive sample-and-hold arrangement in the prior art), coupled integration of the error signal, results in a great improvement in immunity to ambient noise and vibration. Other features includes automatic calibration and temperature compensation whereby viscosity at a desired temperature can be determined even though the measurement is made at different temperature.