WO1995013523A1

WO1995013523A1 - Method and apparatus measuring mass flow

Info

Publication number: WO1995013523A1
Application number: PCT/HU1994/000050
Authority: WO
Inventors: Gábor ENDRO^'CZI; Sándor KUN
Original assignee: Flo - Met Elektronikai Fejleszto^'
Priority date: 1993-11-12
Filing date: 1994-11-11
Publication date: 1995-05-18
Also published as: AU1075095A; HUT71161A

Abstract

The invention relates to a method and an apparatus suitable for mass flow measuring wherein a sensing, elastic, element (4) moved or vibrated by an exciting force which is a prescribed function of the time, is subjected to the mass flow of flow medium and the proportional signal to the mass flow of flow medium has been determined by the relationship, which is coming from the phase relationship of measured exciting force at the driven point and the response measured at given point(s). On the other hand the embodiment of the invention is a mass-flow meter comprising: sensing, practically elastic, element(s) (4), contacted with mass-flow outside or inside or out- and inside to their surfaces, exciter(s) (5), and sensors (8), placed at suitable point(s) of the sensing element(s) (4), and data acquisition module which determine the required function and output proportional to mass-flow from the effects of the different forces (Coriolis-, inertial-, friction-, etc.) caused by the flow itself to the sensing element(s). For the measurement of the complex mechanical impedance and/or the derived function (using the angular frequency) the exciter(s) and sensor(s) are placed at the same or different points of the sensing element(s).

Description

METHOD AND APPARATUS MEASURING MASS FLOW

The invention relates to a method and an apparatus table for mass flow measuring, wherein elastic body - moved or vibrated by an exciting force which is a prescribed function of the time - is interacted by the mass flow of flow medium and we take proportionally the relationship of the driving force and response of elastic body to the mass flow.

The prior art of mass flowmeters - even their advantages ( like direct and because of that density independent mass measurin , small viscosity dependency , high accuracy etc. ) - has a meaningful disadvantage , mainly on application site. This is a size limit if the mass flow is more than 100 t/hr metering range.

However, this sizing limit is the result of their operating method . In this prior art Coriolis-type mass flow sensor a phase difference of various point of a dynamically excited elastic body gives the output signal.

That means the phase difference between the vibrations at two points spaced apart along the length of a dynamically excited elastic body is resulted by a mechanical deformation and in this meaning proportional to the mass flow.

Applying this known method of prior art of mass flowmeters at high mass flow rate and big tube diameters their sizes became too large what means a relatively high energy consumption.

Because of the possible sizes this known prior art of methods is limited on upper side on the pipe diameters as well as on the mass flowmeter point of view.

On the other hand the output signal - here obviously mass flow - is related to the mechanical sizes.

That means the sizes of this known prior art of mass flowmeters a few times more than traditional flowmeters, like turbine -, vortex shedding-, or even magnetic flowmeters. This ratio sometimes goes up to 1 : 40.

Those big sizes have not decreased the method of design of this prior art of mass flowmeters described in US. Patent Applications No. 4 660 421, 4 733 569, 4 879 910 and 4 840 071 or Hungarian Patent Applications No. 198 556, 205 657.

But it has to be decreased by the present invention .

The basic aim of the development of this invention comprises a method and an apparatus was to release the size and flow range limits of the known prior art of Coriolis-type mass flow sensor increasing the flow rate to high end or low end keeping in focus the good features of the vibrated elastic body design.

Furthermore aim to increase the accuracy of the known prior art of Coriolis-type mass flow meters as well as to decrease of the density and viscosity effect. According to the mentioned aims a perfectly new way has to be selected at this new design, namely that a special dynamycal - till now not used -parameters of a vibrated elastic body is subjected to the mass flow has to be selected as an output signal proportional to the mass flow.

According to the present invention comprises a method and apparatus are based on a relationship ( phase different) between force function of the exciting or moving and a response of a given point of the elastic body exciting by a force which is a prescribed function of the time and subjected to the mass flow effect and applying those as a starting parameters , the disadvantages of the known prior art of Coriolis-type mass flow meters, like size limits , low- and high- flow rate limits are removable simply.

It is therefore a method and an apparatus of the present invention what base the mass flow proportional response to the relationship or a selected combination of the exciting and the response, instead of the phase difference between the vibrations at two points spaced apart along the vibrated body .

That practically means the measuring of the mass flow proportional response is transferring into the circle of the measuring of the mechanical impedance or dynamic mass , using this method a completely new measuring device being established.

Applying appropriately of the relationship between exciting and response (acceleration / velocity/deflection ) for mass flow measurement also give a really interesting more advantage , that the outside disturbances will have less effect to the whole system , because it is effecting to both parameters involved into the basic relationship, on the other words, make a common mode rejection by that means make unnecessary the stiff and hard installation what was first of the conditions of an early known prior art Coriolis-type mass flow meter described in Russian Federation (foπner Soviet Union) Patent Applications No. 577 1 19, 587 764.

According to the present invention there is an apparatus used for mass flow measurement when the mass flow of flow medium is directed to the vibrated body and having an output signal which is proportional to the mass flow of flow medium.

The proportional signal to the mass flow of flow medium has been determined by a relationship which is coming from the phase- relationship of measured exciting force at the driven point and the response(s) measured at given point or point(s) of the vibrated , appropriately elastic structure.

One possible version of the method according to the present invention is when the measured signals comes from mathematical forming of the force and response.

Another possible version of the method according to the present invention is wherein the measured response is proportional to the acceleration , or velocity, or deflection.

Another version of the method according to the present invention is when the measurement of the exciting force and the response is made same or various points of the elastic structure.

Another version of the method according to the present invention is when the mass flow is leaded inside -, or outside- , or both side - of the vibrated body appropriately elastic structure.

At one possible version of the method according to the present invention is wherein we are leading the mass flow of flow medium through the measuring device 13, wherein the structure comprises a elastic body 4 , appropriately plane figure for immersion in a fluid , PCIYHI.94.00050

vibrated cross direction (perpendicularly ) to the flow whose mass flow is to be sensed : means for sensing the effect of Coriolis force on said structure to the response.

The measurement from the sensing is realised by the method of the measuring of the point impedance where the proportional output signal is determined from the phase relationship of the exciting force and response (acceleration , or velocity, or deflection.) , measured at same point but both sides of the said structure.

Alternatively applying a tube instead of the plain figure at same arrangement, the tube will be advantageous because of its well defined dynamic-mechanical features rather than good pressure - keeping features with a big wall thickness described in EPA. Patent Applications No. 270 706, 275 367.

Applying a plain figure - otherwise - using its good features on the vibration technics, a better mass flow meter is possible with measurement of point or cross impedance , than just using the effect of the Coriolis force described in EPA. Patent Applications No. 379 799.

In either case (when the whole mass flow is involved into a vibrated tube ) this metliod is also possible because this case the basic technics - applying the measurement of point or cross impedance - is really new and different from the known prior art Coriolis-type mass flow meters.

The possible realisation of the method and measuring device, according to present invention, based on mechanical impedance or dynamical mass measurements, depends on the positioning of the sensor and driver elements on the excited elements.

In the embodiments of the invention the force transducer and the acceleration sensor might be placed in the same or different points. In the first case the realised invention is based on the so called point- impedance (point-dynamical-mass, etc.) measurement. In the second case the point functions are replaced with the cross-function...

The embodiments of the invention might be classified according to the connection of measured mass-flow and sensing element too.

In an embodiment of the invention the measured mass-flow encloses the sensing elements. In other embodiments the mass-flow takes place inside the sensing element or a mixed version is used where the foπner variations are realised together.

On the other hand the embodiment of the invention is a mass-flow meter comprises: sensing, practically elastic, element(s), contacted with mass-flow outside or inside or out- and inside to their surfaces, exciter(s) and sensors placed at suitable point(s) of the sensing element(s) and data acquisition module which determine the required function and output proportional to mass-flow from the effects of the different forces (Coriolis-, inertial-, friction-, etc.) caused by the flow itself to the sensing element(s).

For the measurement of the complex mechanical impedance and/or the derived function (using the angular frequency) the exciter(s) and sensor(s) are placed at the same or different points of the sensing element(s). In the former case the exciter and the sensor form a complete exciter-sensor module.

In a preferred embodiment of the invention the exciter consist of an inductive coil, a permanent magnet, a piezoelectric force-transducer and a piezoelectric accelerometer on the opposite side of the sensing element.

For the increasing of the accuracy of the measurements in a further preferred embodiment of the invention not single but several accelerometers are placed at predefined points of sensing element(s).

The invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Fig.l . demonstrates schematically the cross-section of a typical embodiment of the invention

Fig.2. illustrates an other cross-section of the embodiment from the view-point perpendicular to Fig.l .

Fig.3. illustrates the exciter-sensor unit of an embodiment

Fig.4. demonstrates a typical version of exciter-force-transducer unit of an embodiment

Fig.5. illustrates a typical embodiment of the invention.

A typical embodiment of the invention, shown in Fig.l .-4., consists of a housing 1, elastic or flexible sensing element 4, which is in this case a flat plate. The sensing element 4 is fixed at the inlet section to a console 2. At a predefined point the exciter-sensor unit 3 (similar to Fig.3.) or at predefined points the exciter-sensor-unit 3 or exciter-force- transducer 5 , ( see. Fig.4.) and piezoelectric accelerometers 3ab are integrated to the sensing element 4.

Fig.3. shows that the exciter-sensor 3 unit consist a mass-element 3a and a piezoelectric crystal 3b (piezoelectric accelerometer), and on the opposite side of the sensing element 4 a piezoelectric crystal 3b, permanent magnet 3c (piezoelectric force-transducer), moreover an inductive driver-coil 3d.

On the upper side of the sensing element (see. Fig.3.) the mass- element 3a and the piezoelectric crystal 3b form together the piezoelectric accelerometer 3ab.

Fig.4. shows that the main parts of the exciter-force-transducer 5 on the lower side of the sensing element 4 are the follows: piezoelectric crystal 3b, permanent magnet 3c and inductive drive-coil 3d.

Fig.5. illustrates a typical embodiment of the invention which consists a housing 1 , a sensing element 4 (in this case a plate element) fixed at the inlet to the console 2. The exciter-sensor unit 3 is integrated to the sensing element 4 at a predefined point. At the driving-point 9 a drive- rod 10 connects the exciter-force-transducer 5 , in detail the piezoelectric crystal 3b, the permanent magnet 3 c and the inductive drive-coil 3d, to the sensing element 4. On the other side of the sensing element 4 a similar drive rod 10 makes connection to the piezoelectric accelerometer 3 ab, which consists a piezoelectric crystal 3b and a mass element 3a. The accelerometer are covered by an electromagnetic shielding 1 1. Both the accelerometer 3ab and the force transducer 3bc are integrated into the pressurised room of the instrument thus these elements are hermetically isolated from the outer space. The inductive drive-coil 3d is placed outside the pressure-proof cover 12 of the force transducer 3bc.

The functioning of the embodiment of the invention will be shown according to Fig.5.

The measured mass is streaming in the housing 1 in the direction, signed by 6. The mass-flow encloses the sensing element 4 which is excited perpendicularly to the flow-direction 6 at the driving-point 9. On the force-transducer side of sensing element 4 the alternate current in the driving-coil 3d creates alternate magnetic field around the permanent magnet 3d. As a result of the interaction of magnetic field and permanent magnet 3d alternate force appears on the piezo crystal 3b, on the drive-rod 10 and on the sensing element 4 too. Thus these element excites the sensing element 4 and the electric charges produced by the piezo crystal 3b are proportional to the excitation force. In the embodiment of invention the outputs proportional to the charges produced by the piezoelectric force-transducer 3bc and accelerometer 3ab are the basic data for further processing.

The mass-flow modifies the dynamical behaviour of the sensing element 4 so that the phase shifts of the complex force and acceleration or the complex mechanical impedance - ratio of acceleration and force - varies proportional to the mass-flow.

The output signal of the embodiment of invention - proportional to mass-flow - is the phase difference between the output of force- transducer 3bc and the accelerometer 3ab. Thus the basic data of further acquisition process is the phase difference. The embodiments of the present invention make possible the accomplishment of the mass-flow and size limit restrictions of prior Coriolis-type mass-flow meters and extend the upper and lo er mass- flow velocity ranges.

The embodiments of the invention increase the accuracy of the mass- flow measurements because of the reduced density and viscosity dependence and has an excellent low sensitivity for outer disturbances because of the common mode noise reduction of the method.

MEANING OF DRAWING'S NUMBERS.

1 _= housing

2 = console

3 — exciter-sensor module

3a = metering mass element

3b = piezoelectric crystal

3ab = piezoelectric accelerometer

3c = permanent magnet

3bc = piezoelectric force transducer

3d = inductive (drive) coil

4 = sensing (elastic ) element

5 = exciter - force transducer

6 = flow direction

7 = brace (fix) end of elastic element

8 = sensor module (elastic element + transducers)

9 = driving point

10 = drive rod

11 = electromagnetic shielding

12 = pressure proof cover

13 = mass flowmeter

Claims

1. A mass flow sensor 13, comprising : an excited sensing element 4, effected by the measured mass flow where the mass flow is to be sensed; means for that the signal proportional to the mass flow determined from the relationship of the excited force at the driven point 9, and response(s) of excited element 4, at given point(s).

2. A mass flow sensor 13, as claimed in claim 1 , wherein the measured signals are derivatived from the force- and acceleration signals.

3. A mass flow sensor 13, as claimed in claiml . and in claim 2., wherein the measured response proportional to acceleration.

4. A mass flow sensor 13, as claimed in claim 1. and claim 2. wherein the measured response proportional to velocity.

5. A mass flow sensor 13, as claimed in claim 1. and claim 2., wherein the measured response proportional to displacement.

6. A mass flow sensor 13, as claimed in claims 1.-5. wherein the excitation and the , measured response are connected to the same point of the sensing element 4.

7. A mass flow sensor 13, as claimed in claims 1.-5., wherein the excitation and the measured response(s) are connected to different points of the sensing element(4).

8. A mass flow sensor 13, as claimed in claims 1 .-5., wherein optional amount or number excitation and measuring points are used and integrated on the sensing element 4.

9. A mass flow sensor 13, as claimed in claims 1.-8., wherein the measured mass flow encloses the sensing element 4. or the sensing element 4. is immersed into the measured medium.

10. A mass flow sensor 13, as claimed in claims 1 .-5. and claims 7.- 8., wherein the measured mass-flow is directed into the sensing element 4.

11. A mass flow sensor 13, as claimed in claims 1.-5. and claims 1.- 8., wherein the measured mass flow is enclosing and streaming inside the sensing element 4, where the sensing element 4 has arbitrary cross- section and shape.

12. A mass-flow sensor 13,as claimed in claims 1.-1 1., which comprising: an excited sensing, practically an elastic, element 4, effected by the mass flow at their outside, inside and/or out- and inside walls, on the sensing element 4 an exciter-force-transducer unit 5 and sensor unit 8 furthermore a data acquisition module, which determines the signal proportional to mass flow from the effects of different forces (Coriolis-, inertial-,friction-, etc.) caused by the flow itself on the sensing element 4 so that the complex mechanical impedance and/or similar dynamic parameters are measured by the exciter-force-transducer 5 and sensor unit 8 placed at the same and/or different points on the sensing element 4.

13. A mass flow sensor 13, as claimed in claim 12. which includes an exciter-force-transducer unit 5 , that comprising: an inductive drive coil 3d, a permanent magnet 3c , a piezoelectric force transducer 3bc, a sensing (practically elastic) element 4 and a piezoelectric accelerometer 3ba.

14. A mass flow sensor as claims in claim 12., wherein the sensor unit 8, is arbitrary construction, for example piezoelectric, inductive or capacitive type.

15. A mass flow sensor as claimed in claim 12., wherein the exciter- force-transducer 5, consists arbitrary type exciter element, for example piezo crystal driver.

16. A mass flow sensor as claimed in claim 12. comprising arbitrary amount of exciter-force-transducer(s) 5 and sensor unit(s) 8 for the increased accuracy of measurements.

17. A mass flow sensor as claimed in claims 12.-16., wherein the sensing element 4 has attached parts or appendages for the increased accuracy of measurements.