Accession Number : ADP010217

Title :   A New Electronic Viscometer Based on Rayleigh Wave Mechanics


Personal Author(s) : Kauzlarich, James J. ; Ross, Robert A. ; Abdallah, D. S.

PDF Url : ADP010217

Report Date : APR 1996

Pagination or Media Count : 10

Abstract : The operation of a new viscometer is shown to be based on Rayleigh wave mechanics, where a thin walled tube of 5 mm diameter is immersed to a fixed depth of 60 mm in a fluid and is caused to undergo axial vibrations due to a vibrating piezoelectric plate which supports the tube. The motion of the tube is damped by the fluid, and the piezoelectric crystal feedback circuit gives a voltage inversely proportional to the square root of the viscosity x density product. The design and performance characteristics of the viscometer are described. The device is under patent application. The instrument is portable and gives a measurement of viscosity x density within 1 minute over a wide range, and can be modified to permit continuous measurements as a function of time. The results are accurate for a Newtonian fluid and give an apparent viscosity x density for other fluids. A probe measures the fluid temperature during the test. Only a small amount of fluid is necessary for measurement. The Rayleigh theory is shown to be obeyed by the instrument. The electronic circuit uses a phase-locked loop to drive the thin walled tube at resonance, about 1.5 kHz. The processed feedback signal is large, varying from 2 volts down to about 0.5 volts DC when measuring SAE 10 to 60 weight motor oils. There is an onboard computer to process the data. The computer gives a prediction of viscosity at 40 deg C, or can be modified to predict viscosity at any reference temperature, for a paraffinic lubricating oil. For a particular fluid it is possible to build in data reduction in the computer. For example, equations for density as a function of temperature can be stored in the computer to reduce the viscosity x density product to viscosity and to density.


Subject Categories : Lubricants and Hydraulic Fluids
      Magnetic & Electric Fld Detection & Detectors
      Fluid Mechanics

Distribution Statement : APPROVED FOR PUBLIC RELEASE