Method for measuring a fluid density or a fluid viscosity

Patent metadata

Field	Value
Publication number	US-9927402-B2
Application number	US-201414444561-A
Country	US
Kind code	B2
Filing date	Jul 28, 2014
Priority date	Jan 27, 2012
Publication date	Mar 27, 2018
Grant date	Mar 27, 2018

Abstract

A method and device for estimating a density value ρ m indicative of a true density ρ or for estimating a viscosity value η m indicative of a true viscosity η of a fluid is disclosed. For this, a first resonance frequency f R of a first mechanical oscillator in a reference volume and a second resonance frequency f F of a second mechanical oscillator in contact with the fluid are measured. The estimated value ρ m or η m is then derived using these resonance frequencies f R and f F . During this derivation, at least one fluid-temperature- or fluid-pressure-dependent parameter of the fluid is used. Additionally or alternatively, the first (i.e. reference) mechanical oscillator is arranged in contact with a reference fluid. Thus, fundamental errors in the derivation of the estimated value ρ m or η m are reduced and the estimated value becomes more reliable.

First claim

The invention claimed is:

1. A method for deriving an estimated value ρ m which is indicative of a density ρ of a fluid with a fluid temperature T F and a fluid pressure p F , the method comprising the steps of:
a) measuring a first resonance frequency f R of a resonant vibration of a first mechanical oscillator, wherein said first mechanical oscillator is arranged in a reference volume and wherein said first mechanical oscillator is secluded from said fluid;
b) measuring a second resonance frequency f F of a resonant vibration of a second mechanical oscillator, wherein said second mechanical oscillator is arranged in a measurement volume, wherein said measurement volume comprises said fluid, and wherein said fluid is in contact with said second mechanical oscillator;
c) deriving said estimated value ρ m using said first resonance frequency f R and said second resonance frequency f F ;
wherein in said step c) said fluid temperature T F and/or said fluid pressure p F and/or at least one parameter which is dependent on said fluid temperature T F and/or on said fluid pressure p F is/are used for deriving said estimated value ρ m ;
wherein in said step c) a fluid-temperature-dependent viscosity function η(T F ) is used for deriving said estimated value ρ m , wherein the fluid-temperature-dependent viscosity function η(T F ) is known, pre-measured or pre-modeled;
wherein said estimated value ρ m , which is indicative of said density ρ of said fluid, is derived; and
wherein in said step c) a fluid-temperature-dependent offset parameter C(T F ) is used for deriving said estimated value ρ m , wherein said fluid-temperature-dependent offset parameter C(T F ) is indicative of a temperature-dependent frequency offset between said first and said second mechanical oscillators, and/or between a first oscillator circuit connected to and used to operate said first mechanical oscillator and a second oscillator circuit connected to and used to operate said second mechanical oscillator.

2. The method of claim 1 , wherein a plurality of values of η for different fluid temperatures T F are pre-stored in a lookup-table or calculated on-the-fly.

3. The method of claim 1 , wherein in said step c) a fluid-pressure-dependent viscosity function η(p F ) is used for deriving said estimated value ρ m , wherein a plurality of values of η for different fluid pressures p F are prestored in a lookup-table or calculated on-the-fly, by fitting and/or interpolation or extrapolation algorithms.

4. The method of claim 1 ,
wherein in said step c) a fluid-pressure-dependence of the offset parameter C(T F , p F ) is also used for deriving said estimated value ρ m .

5. The method of claim 1 , wherein a reference-fluid-temperature-dependence δη/δT F of a viscosity function η(T R ) of the reference fluid is equal to or differs less than ±30% from a fluid-temperature-dependence δη/δT F of the fluid-temperature-dependent viscosity function η(T F ) of said fluid, at least for fluid temperatures T F and reference fluid temperatures T R in a range between 170 K and 400 K.

6. The method of claim 1 , wherein said estimated value ρ m is derived according to:



f
R

-

f
F



=



A
⁢

⁢

ρ
m

+

B
~

⁢

ρ
m

⁢

η
⁡

(

p
f

,

T
f

)

+

C
⁡

(

p
F

,

T
F

)



with

A
=

c
1

⁢
t

2
⁢

ρ
q

⁢
w

⁢

f
d

and

B
~

=

c
2

2
⁢

ρ
q

⁢
w

⁢

f
d

π

and with c 1 , c 2 , t, and w being oscillator-geometry-dependent constants, with ρ q being an effective density of a material of said mechanical oscillators with η(p F ,T F ) being a fluid-pressure- and/or fluid-temperature-dependent viscosity function of said fluid, with f d being a common design resonance frequency of said first and second mechanical oscillators, and with C(p F ,T F ) being a fluid-pressure- and/or fluid-temperature-dependent offset parameter which is indicative of a frequency offset between said first and said second mechanical oscillator and/or between a first oscillator circuit connected to said first mechanical oscillator and a second oscillator circuit connected to said second mechanical oscillator;
wherein said reference fluid temperature T R in Kelvin is equal to or differs less than

Assignees

• Abb Schweiz Ag

Inventors

• Kramer Axel
• Brandle Hubert
• Paul Thomas Alfred

Classifications

• G01N9/002

  using variation of the resonant frequency of an element vibrating in contact with the material submitted to analysis (G01N9/34 takes precedence) · CPC title

• G01N11/16

  by measuring damping effect upon oscillatory body · CPC title

• G01N2291/02818

  Density, viscosity · CPC title

• G01N29/036 Primary

  by measuring frequency or resonance of acoustic waves · CPC title

• G01N2291/0427

  Flexural waves, plate waves, e.g. Lamb waves, tuning fork, cantilever · CPC title