Method and measuring system for ascertaining density of a fluid

Patent metadata

Field	Value
Publication number	US-2016356686-A1
Application number	US-201615181811-A
Country	US
Kind code	A1
Filing date	Jun 14, 2016
Priority date	Dec 23, 2011
Publication date	Dec 8, 2016
Grant date	—

Abstract

A method for producing at least one oscillation measurement signal, which has vibrations of a vibratory body are registered. A temperature sensor is applied thermally attached with a non fluid contacting, second surface of the vibratory body for producing a temperature measurement signal representing a time curve of a variable temperature of the vibratory body. The temperature measurement signal can follow, however time delayed, a change of the temperature of the vibratory body from a beginning temperature value, to a new temperature value. Based on the oscillation measurement signal as well as the temperature measurement signal, density, measured values are produced representing the density, wherein, during such, discrepancies possibly occurring between the time curve of the temperature of the vibratory body and the temperature measurement signal are taken into consideration, respectively at least partially compensated.

First claim

What is claimed is:

1 . A method for ascertaining density, ρ, of a fluid contacting an oscillatably held, vibratory body, especially a metal vibratory body, which can be excited to execute vibrations, wherein the vibratory body has a specific thermal conductivity, especially one greater than 5 W K −1 m −1 , and, thus, a thereon dependent, thermal conductivity, effective for heat transfer from, on the one hand, a fluid contacting, first surface of the vibratory body, which has a fluid temperature, namely a temperature of the fluid contacting the first surface, to, on the other hand, a non fluid contacting, second surface, as well as having a heat capacity, and wherein a temperature, of the vibratory body, namely a temperature of the vibratory body dependent on the fluid temperature, is variable, the method comprises the steps of:
causing the vibratory body contacted by fluid to vibrate in such a manner that it executes, at least partially, resonant oscillations, namely mechanical oscillations with a resonant frequency, dependent on the density of the fluid contacting the first surface of the vibratory body as well as also on the temperature, of the vibratory body;
registering vibrations of the vibratory body for producing at least one oscillation measurement signal, which has at least one signal component with a signal frequency corresponding to the resonant frequency and consequently dependent on the density of the fluid;
applying a temperature sensor thermally coupled with the vibratory body via its second surface for producing a temperature measurement signal, representing a time curve of a temperature of the vibratory body, namely a temperature of the vibratory body dependent on a temperature of the fluid contacting the vibratory body on its first surface; and
producing a measured value of density, based on the oscillation measurement signal as well as the temperature measurement signal during a change of the temperature of the vibratory body, especially a change of the temperature of the vibratory body resulting from a change of the temperature of the vibratory body on its first surface, in such a manner that a discrepancy, especially a time dependent discrepancy, occurring during the producing of the measured value of density between the time curve of the temperature of the vibratory body and the temperature measurement signal, is taken into consideration, especially in such a manner that said discrepancy, is at least partially compensated, wherein:
the temperature measurement signal, especially as a result of the thermal conductance, and the heat capacity, of the vibratory body, follows a change of the temperature of the vibratory body from a beginning first temperature value, to a second temperature value, only time delayed, a change resulting especially from a change of the temperature of the fluid contacting the vibratory body on its first surface and/or from a fluid change; and
so that the temperature measurement signal, corresponds consequently to said second temperature value, only time delayed.

2 . The method as claimed in claim 1 , further comprising the step of:
applying the oscillation measurement signal for producing a measured value, of frequency representing the resonant frequency of the vibratory body contacted by the fluid; applying the temperature measurement signal for producing a measured value, of temperature representing the temperature of the vibratory body; and applying both the measured value, of frequency as well as also the measured value, of temperature for producing the measured value of density.

3 . The method as claimed in claim 1 , further comprising the step of:
producing a sampled sequence, of frequency, namely a sequence of digital frequency values ascertained at different points in time based on the at least one oscillation measurement signal, wherein the sampled sequence, approximates a time curve of the resonant frequency of the vibratory body.

4 . The method as claimed in claim 2 , further comprising the step of:
applying the sampled sequence of frequency for producing the frequency measured value.

5 . The method as claimed in claim 3 , further comprising the step of:
applying the sampled sequence of frequency for producing a delayed sampled sequence, of frequency, namely a sequence of digital frequency values ascertained at different points in time based on the sampled sequence of frequency, in order to approximate the time curve of the resonant frequency of the vibratory body, in such a manner that said delayed sampled sequence of frequency more slowly approaches a time curve of the resonant frequency following on a change of the resonant frequency, especially a jump-like change of the resonant frequency, than the sampled sequence of frequency.

6 . The method as claimed in claim 5 , further comprising the step of:
applying the delayed sampled sequence of frequency for producing the frequency measured value.

7 . The method as claimed in claim 1 , further comprising the step of:
producing a sampling sequence, of surface temperature namely a sequence of digital temperature values ascertained at different points in time based on the at least one temperature measurement signal, in order to approximate a time curve of the temperature on the second surface of the vibratory body.

8 . The method as claimed in claim 1 , further comprising the step of:
producing an estimated sequence of temperature of the vibratory body, namely a sequence of digital temperature values ascertained at different points in time based on the at least one temperature measurement signal, in order to approximate a time curve of the temperature of the vibratory body, in such a manner that said estimated sequence of temperature of the vibratory body more quickly approaches a time curve of the temperature of the vibratory body following on a change of the temperature on the second surface of the vibratory body, especially a jump-like change and/or a change resulting from a change of the fluid temperature, than the temperature measurement signal.

9 . The method as claimed in claim 7 , further comprising the step of:
applying the sampling sequence of surface temperature for producing the estimated sequence of temperature of the vibratory body, in such a manner that the estimated sequence of temperature of the vibratory body more quickly approaches a time curve of the temperature of the vibratory body following on a change of the temperature on the second surface of the vibratory body, especially a jump-like change and/or a change resulting from a change of the fluid temperature, than the sampling sequence of surface temperature.

10 . The method as claimed in claim 8 , further comprising the step of:
applying the estimated sequence of temperature of the vibratory body for producing the measured value of temperature.

11 . The method as claimed in claim 7 , further comprising the step of:
applying the sampling sequence of surface temperature for producing the measured value of temperature.

12 . The method as claimed in claim 7 , further comprising the step of:
applying both the sampling sequence of surface temperature as well as also the estimated sequence of temperature of the vibratory body for producing the measured value of temperature.

13 . The method as claimed in claim 7 , further comprising the step of:
applying a digital filter differentiating the sampling sequence of surface temperature, in order to produce the estimated sequence of temperature of the vibratory body, especially a digital filter designed as a high pass digital filter of first or higher order and/or a digital filter embodied as a FIR f

Assignees

• Endress & Hauser Flowtec Ag

Inventors

• Van Dijk Coen
• Momente Omar
• Hagenmeyer Heinerich

Classifications

• G01N9/002 Primary

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

• G01F1/8472

  having curved measuring conduits, i.e. whereby the measuring conduits' curved center line lies within a plane (G01F1/8481 takes precedence) · CPC title

• G01N2009/006

  vibrating tube, tuning fork · CPC title

• G01F1/8436

  signal processing · CPC title

• G01F1/8477

  with multiple measuring conduits · CPC title