Viscometer

Abstract

The viscometer provides a viscosity value (X η ) which represents the viscosity of a fluid flowing in a pipe connected thereto. It comprises a vibratory transducer with at least one flow tube for conducting the fluid, which communicates with the pipe. Driven by an excitation assembly, the flow tube is vibrated so that friction forces are produced in the fluid. The viscometer further includes meter electronics which feed an excitation current (i exc ) into the excitation assembly. By means of the meter electronics, a first internal intermediate value (X 1 ) is formed, which corresponds with the excitation current (i exc ) and thus represents the friction forces acting in the fluid. According to the invention, a second internal intermediate value (X 2 ), representing inhomogeneities in the fluid, is generated in the meter electronics, which then determine the viscosity value (X η ) using the two intermediate values (X 1 , X 2 ). The first internal intermediate value (X 1 ) is preferably normalized by means of an amplitude control signal (y AM ) for the excitation current (i exc ), the amplitude control signal corresponding with the vibrations of the flow tube. As a result, the viscosity value (X η ) provided by the viscometer is highly accurate and robust, particularly independently of the position of installation of the flow tube.

1 - 12 . (canceled) 
     
     
         13 . A digital flowmeter, comprising:
 a vibratable conduit with a mixture of a liquid and a gas flowing therethrough;   a driver connected to the conduit and operable to impart motion to the conduit;   a sensor connected to the conduit and operable to sense the motion of the conduit; and   a digital transmitter connected to the conduit, said digital transmitter having a void fraction determination system configured to determine a gas void fraction of the mixture, and a viscosity determination system configured to determine a viscosity of the liquid in the mixture; and a flow parameter correction system operable to determine a flow parameter associated with the flowing mixture, based on the gas void fraction and the viscosity.   
     
     
         14 . The digital flowmeter of  claim 13 , wherein:
 said viscosity determination system comprises an in-line viscometer.   
     
     
         15 . The digital flowmeter of  claim 13 , wherein:
 said viscosity determination system is operable to determine a viscosity correction factor for use by said flow parameter correction system in determining the flow parameter.   
     
     
         16 . The digital flowmeter of  claim 13 , wherein:
 said digital transmitter comprises a self-contained modular unit.   
     
     
         17 . The digital flowmeter of  claim 13 , wherein:
 said digital transmitter is operable to communicate with external devices and systems.   
     
     
         18 . The digital flowmeter of  claim 17 , wherein:
 said digital transmitter is operable to communicate with a central control system.   
     
     
         19 . A digital transmitter, comprising:
 a transceiver configured to send signals to, and receive signals from, sensors monitoring a vibrating flowtube and a liquid-gas mixture flowing therein;   an apparent flow parameter determination system to generate apparent flow parameter values of the mixture from the signals; and   a flow parameter correction system operable to correct the apparent flow parameter values, based on a viscosity of the liquid within the liquid-gas mixture.   
     
     
         20 . The transmitter of  claim 19 , further comprising:
 a viscosity determination system that is operable to determine the viscosity, and further operable to determine a viscosity correction factor based on the viscosity for use by the flow parameter correction system.   
     
     
         21 . The transmitter of  claim 19  further comprising:
 a void fraction determination system that is operable to determine a void fraction of the gas within the liquid-gas flow, wherein: 
 said flow parameter correction system is operable to correct the apparent flow parameter values, based on the void fraction. 
 
     
     
         22 . A method, comprising the steps of:
 determining an apparent flow parameter of a gas-liquid mixture flowing through a vibrating flowtube;   determining a viscosity of the liquid; determining a viscosity correction factor; and   determining an error in the apparent flow parameter, based upon the viscosity correction factor; and correcting the error in the apparent flow parameter.   
     
     
         23 . The method of  claim 22 , wherein:
 determining the apparent flow parameter comprises determining an apparent density or mass flowrate of the mixture by observing a deflection of the vibrating flowtube.   
     
     
         24 . The method of  claim 23 , wherein:
 determining the viscosity of the liquid comprises exposing an in-line viscometer to the liquid.   
     
     
         25 . The method of  claim 23 , wherein:
 determining the viscosity of the liquid comprises providing a sample of the liquid to a viscometer.   
     
     
         26 . The method of  claim 23 , wherein:
 determining a viscosity correction factor comprises calculating a correction factor using a bubble model that assumes that the gas within the liquid-gas mixture is contained as bubbled within the mixture.