GB2114745A - Electromagnetically driven tuning fork for determining fluid properties - Google Patents

Electromagnetically driven tuning fork for determining fluid properties Download PDF

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Publication number
GB2114745A
GB2114745A GB08303865A GB8303865A GB2114745A GB 2114745 A GB2114745 A GB 2114745A GB 08303865 A GB08303865 A GB 08303865A GB 8303865 A GB8303865 A GB 8303865A GB 2114745 A GB2114745 A GB 2114745A
Authority
GB
United Kingdom
Prior art keywords
tuning fork
yoke
fluid
coil
tines
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
GB08303865A
Other versions
GB8303865D0 (en
GB2114745B (en
Inventor
Martin Alan Hogbin
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
BESTOBELL
Original Assignee
Bestobell
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority to GB8204217 priority Critical
Application filed by Bestobell filed Critical Bestobell
Priority to GB08303865A priority patent/GB2114745B/en
Publication of GB8303865D0 publication Critical patent/GB8303865D0/en
Publication of GB2114745A publication Critical patent/GB2114745A/en
Application granted granted Critical
Publication of GB2114745B publication Critical patent/GB2114745B/en
Application status is Expired legal-status Critical

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Classifications

    • GPHYSICS
    • G01MEASURING; TESTING
    • G01NINVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N11/00Investigating flow properties of materials, e.g. viscosity, plasticity; Analysing materials by determining flow properties
    • G01N11/10Investigating flow properties of materials, e.g. viscosity, plasticity; Analysing materials by determining flow properties by moving a body within the material
    • G01N11/16Investigating flow properties of materials, e.g. viscosity, plasticity; Analysing materials by determining flow properties by moving a body within the material by measuring damping effect upon oscillatory body
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01FMEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
    • G01F23/00Indicating or measuring liquid level, or level of fluent solid material, e.g. indicating in terms of volume, indicating by means of an alarm
    • G01F23/22Indicating or measuring liquid level, or level of fluent solid material, e.g. indicating in terms of volume, indicating by means of an alarm by measurement of physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water
    • G01F23/28Indicating or measuring liquid level, or level of fluent solid material, e.g. indicating in terms of volume, indicating by means of an alarm by measurement of physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water by measuring the variations of parameters of electric or acoustic waves applied directly to the liquid or fluent solid material
    • G01F23/296Acoustic waves
    • G01F23/2966Acoustic waves making use of acoustical resonance or standing waves
    • G01F23/2967Acoustic waves making use of acoustical resonance or standing waves for discrete levels
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01HMEASUREMENT OF MECHANICAL VIBRATIONS OR ULTRASONIC, SONIC OR INFRASONIC WAVES
    • G01H13/00Measuring resonant frequency
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01NINVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N9/00Investigating density or specific gravity of materials; Analysing materials by determining density or specific gravity
    • G01N9/002Investigating density or specific gravity of materials; Analysing materials by determining density or specific gravity using variation of the resonant frequency of an element vibrating in contact with the material submitted to analysis
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01NINVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N9/00Investigating density or specific gravity of materials; Analysing materials by determining density or specific gravity
    • G01N9/002Investigating density or specific gravity of materials; Analysing materials by determining density or specific gravity using variation of the resonant frequency of an element vibrating in contact with the material submitted to analysis
    • G01N2009/006Investigating density or specific gravity of materials; Analysing materials by determining density or specific gravity using variation of the resonant frequency of an element vibrating in contact with the material submitted to analysis vibrating tube, tuning fork
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01NINVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2291/00Indexing codes associated with group G01N29/00
    • G01N2291/02Indexing codes associated with the analysed material
    • G01N2291/028Material parameters
    • G01N2291/02836Flow rate, liquid level

Abstract

An instrument for sensing a characteristic of a fluid by its effect on a vibrating tuning fork exposed in the fluid comprises a non-magnetic wall (4) forming in use a boundary to the space occupied by the fluid; a W- shaped magnetic yoke the three legs (1,2) of which extend through the wall in use into contact with the liquid with the base part of the W on the outside of the wall; the end of the central leg (2) being bifurcated to form tuning fork tines (3) each spaced from, and facing in its direction of vibration, a respective adjacent one of the outer legs; and a coil (5) associated with the base part of the W and arranged to be energized with an oscillating electrical current whereby periodic magnetic flux (6) is produced in the yoke to cause the tines to be vibrated as a result of the periodic magnetic attraction between each tine and the adjacent outer leg. A piezoelectric crystal detector (7) is connected to the base of the yoke to sense oscillation of the tuning fork. Associated circuitry is connected to the coil (5) and detector (7) to derive the density, viscosity, or the presence or absence of particular fluids from the resonant frequency of vibration or the attenuation in the vibration of the tuning fork. <IMAGE>

Description

SPECIFICATION Fluid sensor There has recently been proposed an instrument for measuring the density of a liquid, the instrument comprising a tuning fork which is immersed in the fluid and the tines of which are caused to vibrate. The fluid provides a mass loading effect on the vibrating tines and the resonant frequency of vibration is dependent upon the density of the fluid. The effect is particularly marked when the tines of the tuning fork are closely spaced and wide in the transverse direction perpendicular to their direction of vibration.

The tines of one such instrument have been vibrated by means of a magnetic core which is surrounded by a coil carrying an oscillating electrical current, and which is positioned adjacent to a pole piece of magnetic material carried on the outer face of each tine. However, this involves mounting of the cores and coils within the fluid space and this is inconvenient as it requires protection for the core and coils from the fluid, a mounting within the fluid for the cores and coils, and additional sealing where the electrical connections to the coils pass through the boundary wall of the fluid space.

In accordance with the present invention, an instrument for sensing a characteristic of a fluid by its effect on a vibrating tuning fork exposed in the fluid comprises a non-magnetic wall forming in use a boundary to the space occupied by the fluid; a W-shaped magnetic yoke the three legs of which extend through the wall in use into contact with the liquid with the base part of the W on the outside of the wall; the end of the central leg being bifurcated to form tuning fork tines each spaced from, and facing in its direction of vibration, a respective adjacent one of the outer legs; and a coil associated with the base part of the W and arranged to be energised with an oscillating electrical current whereby a periodic magnetic flux is produced in the yoke to cause the tines to be vibrated as a result of the periodic magnetic attraction between each tine and the adjacent outer leg.

This construction is simple and not susceptible to failure as only the ends of the three legs of the yoke have to pass through the boundary wall to which they can readily be sealed. The coil is mounted on the dry side and the energy for vibrating the tuning fork tines passes along the yoke through the boundary wall as an oscillating magnetic flux, and not as a mechanical oscillation which might promote failure of the seals between the yoke legs and the wall. The tines are vibrated as a result of the periodic attraction between the effective pole pieces adjacent to the ends of the tines and the adjacent ends of the outer legs, thereby utilizing a maximum moment arm in the flexure of the tines. The electrical energy for promoting the vibration can thus be minimised.

The coil may be wound on one of the three legs, preferably on the central ieg, or on a web portion of the base part of the yoke extending transversely between and interconnecting the central leg with one of the outer legs.

If the instrument is to be used for measuring the density of the fluid, usually a liquid, it will be necessary to determine the resonant frequency of the tuning fork exposed in contact with the liquid.

This may be achieved by means of a piezoelectric crystal, or other detector, fitted to the base or other part of the yoke and responsive to the frequency of vibration of the tuning fork tines. The energizing frequency may then be caused to sweep through a range of frequencies and the peak response, corresponding to the resonant frequency, obtained from the detector.

Alternatively the electrical output from the detector may be fed back through a positive gain amplifier to energize the coil, so that automatic resonance is obtained, and the resonant frequency determined.

In alternative applications the instrument may be used for determining the viscosity of the fluid.

The fluid will tend to dampen the oscillation of the tuning fork tines and this can be sensed by the energy requirement to maintain the tuning fork oscillating resonantly. In practice this may be achieved by determining the gain necessary in the previously described automatic resonant feedback circuit to maintain oscillation.

The instrument could of course be used as a level sensor, for example for measuring the presence or absence of liquid at a level in a container at which the instrument is fitted. All that would then be necessary would be for the instrument to be able to discriminate between the resonant frequency or attenuation of the vibrating tuning fork when the tines are immersed in liquid and air.

An example of an instrument constructed in accordance with the present invention is illustrated diagrammatically in the accompanying drawings, in which: Figure 1 is a plan; Figure 2 is an end elevation on the wet side; and, Figures 3, 4 and 5 are alternative circuit diagrams.

As shown in Figures 1 and 2, the instrument comprises a W-shaped yoke made of magnetic stainless steel, outer legs 1 of which form pole pieces and a central leg 2 of which forms a tuning fork. The free ends of the pole pieces and tines 3 of the tuning fork formed by the bifurcated end of the leg 2, are, as shown in Figure 2, appreciably elongate in the direction perpendicuiar to the plane of Figure 1. The construction is symmetrical about the central plane between the tines of the tuning fork. The separation of the tines is substantially twice that of the separation of the outer face of each tine from the adjacent pole piece.

The three legs of the yoke extend through and are sealed to a non-magnetic stainless steel wall 4, which separates the wet side (above the wall in Figure 2) from the dry side, and which may be part of a container for the fluid. During assembly the base part of the yoke may be welded up after insertion of the legs through the wall, or the wall may be assembled in pieces between the legs and welded up.

A coil 5 is wound on the root of the central leg and develops in the yoke a magnetic flux 6. The flux induces opposite poles at the end of each pole piece and at the end of the adjacent tuning fork tine respectively so that the two are attracted. When the coil is energised with an oscillating current, the periodic attraction causes the vibration of the tines.

A piezoelectric crystal detector 7, from which an output is taken through leads 8, is interposed between the base of the yoke and a counterweight 9.

Figure 3 illustrates the application previously referred to for measuring the density of a fluid, particularly a liquid, by determining the resonant frequency of the tuning fork exposed in contact with the fluid. The drive coil 5 is energized by a frequency sweep generator 10 via an amplifier 11. The output of the crystal detector 7 is fed via an amplifier 12 to a frequency measurer 13 from which the necessary calculation and display is derived in a unit 14.

Figure 4 illustrates the alternative arrangement for measuring density, in which the electrical output from the crystal detector 7 is fed through a positive gain amplifier 1 5 to energize the drive coil 5 so that automatic resonance is obtained, the resonant frequency being recognised by a frequency measurer 1 6 which feeds a calculation and display unit 17.

Figure 5 shows the use of the instrument for determining the viscosity of a fluid, particularly a liquid. Thus the automatic feedback circuit of Figure 4 is modified by substituting a variable gain amplifier 18, for the positive gain amplifier 1 5 optionally with the interposition of a filter 19.

The signal amplitude is measured by the unit 20.

The resonant frequency is again measured by a unit 21 and the gain necessary to maintain oscillation is calculated and displayed by the unit 22.

Any of the illustrated circuits could be used when the instrument is adapted for use as a level sensor. As previously mentioned, it is only necessary for the calculation and display unit to discriminate between the resonant frequency or gain, which represents attenuation of the vibrating tuning fork, when the tines are immersed in different fluids, particularly liquid and air.

Claims (10)

Claims
1. An instrument for sensing a characteristic of a fluid by its effect on a vibrating tuning fork exposed in the fluid, the instrument comprising a non-magnetic wall forming in use a boundary to the space occupied by the fluid; a W-shaped magnetic yoke the three legs of which extend through the wall in use into contact with the liquid with the base part of the W on the outside of the wall; the end of the central leg being bifurcated to form tuning fork tines each spaced from, and facing in its direction of vibration, a respective adjacent one of the outer legs; and a coil associated with the base part of the W and arranged to be energised with an oscillating electrical current whereby a periodic magnetic flux is produced in the yoke to cause the tines to be vibrated as a result of the periodic magnetic attraction between each tine and the adjacent outer leg.
2. An instrument according to claim 1, in which the coil is wound on one of the legs of the yoke.
3. An instrument according to claim 1 or claim 2, in which a detector is fitted to the yoke and is arranged to be responsive to the frequency of vibration of the tuning fork tines.
4. An instrument according to claim 3, in which the detector is a piezoelectric crystal detector fitted to the base of the yoke.
5. Afluid density measuring instrument according to claim 3 or claim 4, wherein the coil is energized by a frequency sweep generator and means are coupled to the detector for determining the peak response, corresponding to the resonant frequency of the tuning fork.
6. A fluid density measuring instrument according to claim 3 or claim 4, wherein means are provided for feeding an electrical output from the detector back through a positive gain amplifier to energize the coil, so that automatic resonance is obtained, and means are provided for determining the resonant frequency.
7. A fluid viscosity measuring instrument according to claim 3 or claim 4, wherein means are provided for sensing the energy requirement to maintain the tuning fork oscillating resonantly.
8. An instrument according to claim 7, wherein means are provided for feeding an electrical output from the detector back through a variable gain amplifier to energize the coil, and means are provided for deriving the viscosity from the gain necessary for maintaining oscillation of the tuning fork.
9. A level sensing instrument according to claim 3 or claim 4, wherein means are provided for discriminating between the resonant frequency or attenuation of the vibrating tuning fork when the tines are immersed in different fluids.
10. An instrument substantially as described with reference to any one of the modifications illustrated in the accompanying drawings.
GB08303865A 1982-02-12 1983-02-11 Electromagnetically driven tuning fork for determining fluid properties Expired GB2114745B (en)

Priority Applications (2)

Application Number Priority Date Filing Date Title
GB8204217 1982-02-12
GB08303865A GB2114745B (en) 1982-02-12 1983-02-11 Electromagnetically driven tuning fork for determining fluid properties

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB08303865A GB2114745B (en) 1982-02-12 1983-02-11 Electromagnetically driven tuning fork for determining fluid properties

Publications (3)

Publication Number Publication Date
GB8303865D0 GB8303865D0 (en) 1983-03-16
GB2114745A true GB2114745A (en) 1983-08-24
GB2114745B GB2114745B (en) 1985-03-06

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Family Applications (1)

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Cited By (14)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2152665A (en) * 1984-01-03 1985-08-07 Ae Cds Autoclave Inc Liquid level detection
GB2184541A (en) * 1985-12-20 1987-06-24 Clevite Ind Inc Liquid level indicator system
WO1989012805A1 (en) * 1988-06-16 1989-12-28 Wild Leitz Gmbh An acoustic screen scan microscope for the examination of an object in the short-range field of a resonant acoustic oscillator
US5212987A (en) * 1988-06-16 1993-05-25 Hommelwerke Gmbh Acoustic screen scan microscope for the examination of an object in the short-range field of a resonant acoustic oscillator
GB2268807A (en) * 1992-07-17 1994-01-19 Xerox Corp Detection of material consumption
CH683375A5 (en) * 1991-10-01 1994-02-28 Vibro Meter Ag Detecting presence, level or condition of fluid - using evaluation circuit to register frequency of diaphragm inserted flush into wall of vessel
WO1998009139A1 (en) * 1996-08-28 1998-03-05 Videojet Systems International, Inc. Resonator sensors employing piezoelectric benders for fluid property sensing
WO2000075712A1 (en) * 1999-06-08 2000-12-14 Optiscan Pty Ltd Electrically operated tuning fork
DE10050299A1 (en) * 2000-10-10 2002-04-11 Endress Hauser Gmbh Co Medium viscosity determination and monitoring arrangement has stimulation and reception unit, which excites vibrating unit and receives vibrations of vibrating unit for viscosity determination
US6711942B2 (en) 2000-10-10 2004-03-30 Endress + Hauser Gmbh & Co. Kg Apparatus for determining and/or monitoring the viscosity of a medium in a container
WO2004036207A2 (en) * 2002-10-18 2004-04-29 Symyx Technologies, Inc. Environmental control system fluid sensing system and method comprising a sesnsor with a mechanical resonator
US20130139576A1 (en) * 2010-07-21 2013-06-06 Joseph H. Goodbread Coupled Torsional Resonators Viscometer
US8732938B2 (en) 2003-03-21 2014-05-27 MEAS France Method of packaging a sensor
EP2614353A4 (en) * 2010-09-07 2018-01-24 Rheonics GmbH Fluid properties measurement device having a symmetric resonator

Cited By (20)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2152665A (en) * 1984-01-03 1985-08-07 Ae Cds Autoclave Inc Liquid level detection
GB2184541A (en) * 1985-12-20 1987-06-24 Clevite Ind Inc Liquid level indicator system
WO1989012805A1 (en) * 1988-06-16 1989-12-28 Wild Leitz Gmbh An acoustic screen scan microscope for the examination of an object in the short-range field of a resonant acoustic oscillator
US5212987A (en) * 1988-06-16 1993-05-25 Hommelwerke Gmbh Acoustic screen scan microscope for the examination of an object in the short-range field of a resonant acoustic oscillator
CH683375A5 (en) * 1991-10-01 1994-02-28 Vibro Meter Ag Detecting presence, level or condition of fluid - using evaluation circuit to register frequency of diaphragm inserted flush into wall of vessel
GB2268807B (en) * 1992-07-17 1996-09-18 Xerox Corp Detection of material consumption
GB2268807A (en) * 1992-07-17 1994-01-19 Xerox Corp Detection of material consumption
WO1998009139A1 (en) * 1996-08-28 1998-03-05 Videojet Systems International, Inc. Resonator sensors employing piezoelectric benders for fluid property sensing
US6044694A (en) * 1996-08-28 2000-04-04 Videojet Systems International, Inc. Resonator sensors employing piezoelectric benders for fluid property sensing
US7010978B1 (en) 1999-06-08 2006-03-14 Optiscan Pty Ltd. Electrically operated tuning fork
WO2000075712A1 (en) * 1999-06-08 2000-12-14 Optiscan Pty Ltd Electrically operated tuning fork
US6711942B2 (en) 2000-10-10 2004-03-30 Endress + Hauser Gmbh & Co. Kg Apparatus for determining and/or monitoring the viscosity of a medium in a container
DE10050299A1 (en) * 2000-10-10 2002-04-11 Endress Hauser Gmbh Co Medium viscosity determination and monitoring arrangement has stimulation and reception unit, which excites vibrating unit and receives vibrations of vibrating unit for viscosity determination
WO2004036207A3 (en) * 2002-10-18 2004-09-02 John Feland Environmental control system fluid sensing system and method comprising a sesnsor with a mechanical resonator
WO2004036207A2 (en) * 2002-10-18 2004-04-29 Symyx Technologies, Inc. Environmental control system fluid sensing system and method comprising a sesnsor with a mechanical resonator
US8732938B2 (en) 2003-03-21 2014-05-27 MEAS France Method of packaging a sensor
US20130139576A1 (en) * 2010-07-21 2013-06-06 Joseph H. Goodbread Coupled Torsional Resonators Viscometer
US9518906B2 (en) * 2010-07-21 2016-12-13 Baker Hughes Incorporated Coupled torsional resonators viscometer
EP2596328A4 (en) * 2010-07-21 2017-01-11 Baker Hughes Incorporated Coupled torsional resonators viscometer
EP2614353A4 (en) * 2010-09-07 2018-01-24 Rheonics GmbH Fluid properties measurement device having a symmetric resonator

Also Published As

Publication number Publication date
GB2114745B (en) 1985-03-06
GB8303865D0 (en) 1983-03-16

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PCNP Patent ceased through non-payment of renewal fee