CN1164023A - Electromagnetic flowmeter for measuring non-newtonian fluids - Google Patents

Abstract

The electromagnetic flowmeter further comprises: two coils (12, 13) positioned diametrically opposite to each other on the measuring tube which serve to produce a magnetic field when a coil current (i) flows therethrough; electrodes (14, 15) serving to pick off an induced first potential and an induced second potential, with a respective radius (14<sub>1<sub>, 15<sub>1<sub>) of the measuring tube at the point of each of the electrodes making an angle less than 90.degree. with the direction of the magnetic field; a coil-current generator (21); a double-pole switch (22) for connecting the two coils either in series aiding or in series opposition; and evaluation electronics (24) which form a velocity signal (S<sub>r<sub>) and a flow index signal (S<sub>N<sub>).

Description

Be used to measure the electromagnetic flowmeter of non-Newtonian fluid

The present invention relates to a kind of electromagnetic flowmeter, can measure the average velocity and the mobile index of the non newtonian conductive fluid that in measuring channel, flows with it.

Because the measuring channel that uses in the reality generally all is the Cylinder shape, thereby in pipeline, form the rotational symmetric mobile section figure of stable state.Particularly in viscous fluid, mobile or the laminar flow formula, thereby its speed v is the function of the radial distance r of range observation conduit axis.

v＝v(r) (1)

In laminar flow, the fluid layer of friction speed slides over each other and because the relation of friction forms a shear stress τ between each layer.The intrinsic flow characteristics of real fluid can be that velocity gradient is also referred to as shear rate V description with a relational expression between the velocity variations of shear stress and radial direction appearance:

δ is well-known nabla in V=δ v/ δ r (2) formula, and V has the dimension time ^-1

For Newtonian fluid (representing with subscript w later on), equation (2) is a linear equation:

τ _wProportionality constant ε is a dynamic viscosity in=ε V (3) formula, has dimension power time/length ²

For non-Newtonian fluid (representing with subscript n w later on), equation (2) is a nonlinear equation:

τ _nw＝f(V) (4)

The respective flow property list of non-Newtonian fluid is shown as the form that flow graph is so-called rheological diagram.Shear stress τ draws among the figure _NwRelation curve to shear rate V.According to family curve shown in Figure 1, dissimilar non-Newtonian fluids is distinguished:

A kind of Bingham plastics of family curve 1 expression;

Family curve 2 expression a kind of intrinsic viscosity type (shear weakens) fluids;

A kind of Newtonian fluid of family curve 3 expressions; And

Family curve 4 expression a kind of bloated flow pattern (shear enhancing) fluids.

In the situation of non-Newtonian fluid, the merchant of shear stress and shear rate is not a constant.Therefore, viscosity neither constant.As an alternative, defined apparent viscosity ε _sWith differential viscosity ε _d, both all depend on shear rate.

As shown in Figure 2, the apparent viscosity ε of a set point P on the family curve in the rheological diagram _sSlope for the secant of ordering from true origin to P.Differential viscosity ε _dThe tangent slope of ordering at P for family curve.

Therefore,

ε _s＝τ _nw/V (5)

ε _d＝δτ _nw/δV (6)

Use for many technology, can approach the nonlinear characteristic curve with a simple formula.Common method is to use Oswald Er De-De Waaile law of exponent (book " non-Newtonian fluid " Leipzig of being shown referring to J Wu Erbolaihete and P Mi Xika 1967 version the 26th page):

τ _Nw=K|V| ^N-1Two vertical lines are represented absolute value in V (7) formula.This absolute value sign has considered that shear rate V also can be the fact of negative value.

In equation (7), K is the viscosity of fluid, and index N is the index that flows.If N=1, fluid are Newtonian fluid, K is exactly its viscosity (constant).If N＜1, fluid are intrinsic viscosity type fluid, and if N＞1, then be dilatant fluid.

By viscosity K and mobile index N, apparent viscosity ε _sWith differential viscosity ε _dCan calculate:

ε _s＝τ _nw/V＝KV ^N-1 (8)

ε _d＝δτ _nw/δV＝KNV ^N-1 (9)

The fluid that is completed into laminar flow is set up and shown to exponential relationship formula (7) find the solution hydrodynamical differential equation, draw the following relation (referring to the 30th page in the above-mentioned quoted passage) of flow distribution figure:

V=f (r)=V _m(1+3N)/(1+N) (1-(r/R) ^(1+1N)) V in (10) formula _mBe average velocity, R is the internal diameter of measuring channel.

An object of the present invention is to use electromagnetic flowmeter to obtain average velocity V at least _mWith mobile index N.

In order to reach this purpose, the invention provides a kind of electromagnetic flowmeter, be used for measuring the average velocity V of the conduction non-Newtonian fluid that flows at measuring channel _mWith mobile index N (position of measuring channel contacting with fluid is non-conductive), described flowmeter also comprises except that measuring channel:

Outside the measuring channel both sides or among tube wall, face toward one first coil and one second coil of placing mutually;

Described coil is used for producing a magnetic field of crossing duct wall and fluid when coil current flows through coil;

First electrode that is used to pick up by first electromotive force of magnetic field induction;

Second electrode that is used to pick up by second electromotive force of magnetic field induction;

The relevant radii of each electrode loca and magnetic direction constitute one less than 90 ° angle on the measuring channel;

A coil current generator;

A double-break switch can or connect into the series connection of help formula or connect into mutually trans series connection with it two coils; And

Calculating electronic equipment, first electric potential difference that electrode picked up when it connected into the series connection of help formula according to coil produces one and is proportional to average velocity V _mRate signal, perhaps

Second electric potential difference that electrode picks up when connecting into mutually trans series connection according to coil and first electric potential difference produce a mobile index signal that is proportional to the index N that flows.

Use improvement design of the present invention, viscosity K and/or apparent viscosity ε _sAlso can obtain.

Improve in the design at this, first pressure transducer and second pressure transducer are installed on the duct wall along a bus of measuring channel, and the signal difference that calculating electronic equipment provides according to pressure transducer produces the viscosity signal of a viscosity K who is proportional to fluid and/or is proportional to the apparent viscosity ε of fluid according to first electric potential difference and according to second electric potential difference _sThe viscosity signal.

In a preferred embodiment of the invention, the relevant radii of each electrode loca and magnetic direction constitute the angle of 60 ° or 45 ° on the measuring channel.

Two coils of electromagnetic flowmeter are alternately connected into the series connection of help formula narrated in DE2743954 in essence with mutually trans series connection, only that is for other purpose, even the electric potential difference that electrode picks up is not subjected to the influence of flow distribution figure disturbance.

By below in conjunction with the narration of accompanying drawing to the embodiment of the invention, it is more very clear that the present invention will become, and parts identical in the accompanying drawing represent with identical reference character, wherein:

Fig. 1 illustrates the qualitative features rheological diagram of various non-Newtonian fluids and Newtonian fluid;

Fig. 2 illustrates a rheological diagram that is used to define the apparent viscosity and the differential viscosity of non-Newtonian fluid;

Fig. 3 illustrates an embodiment of (form that part adopts block scheme) electromagnetic flowmeter generally;

Fig. 4 illustrates the synoptic diagram that is used for calculating magnetic field when coil connects into the series connection of help formula;

Fig. 5 illustrates the synoptic diagram that is used for calculating magnetic field when coil connects into mutually trans series connection;

Fig. 6 illustrates help formula when series connection DISTRIBUTION OF MAGNETIC FIELD that coil connects into Fig. 4;

DISTRIBUTION OF MAGNETIC FIELD when Fig. 7 illustrates coil and connects into the mutually trans series connection of Fig. 5;

Fig. 8 illustrates a kind of be used to measure viscosity K and/or apparent viscosity ε _sThe rough longitudinal profile of embodiment of improvement design; And

Fig. 9 illustrates the oscillogram of coil current and clock signal.

Fig. 3 illustrates (form that part adopts block scheme) a kind of electromagnetic flowmeter 10 generally.Its mechanical part is the nonconducting measuring channel 11 in position that flow sensor comprises the fluid that its contact is flow through.

Measuring channel 11 can be entirely with such as suitable pottery especially aluminium oxide ceramics make, perhaps make with suitable plastics, extraordinary rubberite, but also can use non-ferromagnetic metallic conduit, within it drape layer such as suitable plastics, extraordinary rubberite, soft rubber or teflon on the wall.

The outside that first coil 12 and second coil 13 are installed in measuring channel 11 both sides just in time faces toward mutually.Coil current i flows through these coils, sets up a magnetic field of crossing measuring channel wall and fluid.Hereinafter will magnetic field usually be described with a vectorial B.

Except coil is installed in the measuring channel, also can be as at the magnetic field of three phase electric machine winding, with coiler part extend in the wall of measuring channel.

In Fig. 3, three parallel arrows point out that magnetic field can be uniform magnetic field B _KThis is the general situation of available electromagnetic flowmeter on the current market, is by two coils 12,13 being connected into the series connection of help formula so that equidirectional acquisition the in magnetic field that the magnetic field of a coil generation and corresponding another coil produce.

As shown in Figure 3, first electrode 14 that contacts with flowing liquid and second electrode 15 (being the Galvanic electrode) are installed on the wall of measuring channel 11.The electrode that also can be equipped with fluid isolation is a capacitance electrode, and these electrodes (Galvanic electrode or capacitance electrode) all are used for picking up the electromotive force according to the induction of faraday's electromagnetism law of magnetic induction.

The electrode position of the available electromagnetic flowmeter that only is used for the measurement volumes flow rate is different on the position that electrode 14,15 is installed and the market, those electrode positions just in time mutually facing to place and the straight line of connection electrode with always uniform magnetic direction is vertical.The relevant radii of each electrode 14,15 loca and uniform magnetic field B on the measuring channel 11 _KDirection constitute one less than 90 °, particularly (situation is referring to following in detail) in the angle of 60 ° and 45 °.

A coil current generator 21 produces coil current i.So coil 12 is loaded with a coil current i ₁₂, coil 13 then is loaded with a coil current i ₁₃Coil current i can be the general any electric current that uses in the electromagnetic flowmeter, promptly for example says it can is direct current, interchange or pulse current.

If coil current i is a DC current, in the present invention also with the same in the electromagnetic flowmeter of routine, this electric current is the ambipolar electric current of segmentation, it is the electric current that its direction is periodically switched by coil current generator 21, for example as United States Patent (USP) 4 the applicant, in 410,926 general narration like that.

As everyone knows, do like this be for compensate form on each electrode and the induced potential that is added on electrochemical potential, erect image (such as) in applicant's United States Patent (USP) 4,382,387,4,422,337 and 4,704,908, narrated like that.

In the present invention, except coil current generator 21, also be equipped with a double-break switch 22, the direction of passing through the coil current of one of two coils 12,13 (can be the current i by coil 13 in the embodiments of figure 3 with it ₁₃Direction) switch.By this method, two coils 12,13 can or connect into help formula series connection (corresponding to the position of the switch shown in Figure 3), perhaps connect into mutually trans series connection.

Double-break switch 22 is subjected to the control of a sequence controller 23 to turn to another position from a position of the switch, and controller 23 is gone back control coil current feedback circuit 21 and switched above-mentioned coil current i ₁₃Direction.

Sequence controller 23 comprises that for example the back is with the clock generator of a frequency divider.The output signals at different levels of frequency divider are combined into each spike train with needed lasting cycle and frequency by some logic gates, can be by designing requirement control coil current feedback circuit 21 and double-break switch 22 with these spike trains.

Fig. 3 also includes calculating electronic equipment 24, is used to generate the average velocity v of the non-Newtonian fluid that first electric potential difference of being picked up by electrode 14,15 when being proportional to coil 12,13 and connecting into the series connection of help formula calculates _mRate signal S _V, perhaps generate one and be proportional to the mobile index signal S that coil 12,13 connects into the mobile index N that second electric potential difference that mutually trans when series connection picked up by electrode 14,15 and first electric potential difference calculate _N

Calculating electronic equipment 24 is subjected to the signal controlling of sequence controller 23 to form rate signal S _VOr mobile index signal S _N

With reference in a kind of improvement design of the present invention of Fig. 8 explanation, calculating electronic equipment 24 is also imported the signal that has from pressure transducer 31,32 below.

Illustrate in greater detail by Fig. 4 to 7 now and form signal S _VAnd S _NBasic law, each figure all is illustrated in the zone of coil 12,13 and the rectangular simple sectional drawing of axis of measuring channel 11.

In Figure 4 and 5, respective coil 12,13 is respectively represented with three wire turns.Wherein round spot is represented to flow out from paper plane along the direction perpendicular to paper plane at these points by the electric current of wire turn, and the cross that intersects represents that then electric current enters paper plane at these points along the direction perpendicular to paper plane.

Fig. 4 is the situation of unidirectional electric current by coil 12,13; The magnetic line of force of this situation distributes and is shown in Fig. 6.Fig. 5 is the situation of rightabout electric current by coil 12,13; The magnetic line of force of this situation distributes and is shown in Fig. 7.

In Fig. 6 and 7, be shown in the approximation space amplitude distribution that round spot district on the measuring channel respective external wall represents strength of current.

Fig. 4 also illustrates in order to represent two coordinate systems of above-mentioned rule, just has the common cartesian coordinate system and the common polar coordinate system that has in radius vector r and the polar angle of mutually perpendicular horizontal ordinate X and ordinate Y.The initial point of two coordinate systems is all consistent with the central point of measuring channel xsect.

Below, subscript k represents that coil 12,13 connects into the series connection of help formula, subscript g represents that then coil 12,13 connects into mutually trans series connection.

At the situation of Fig. 4, magnetic field vector B _kOnly at directions X a numerical value being arranged is B _KxComponent, and in the Y direction, its component B _KgBe zero.

At the situation of Fig. 5, magnetic field vector B _gHaving one at directions X, to have the numerical value that depends on the position be B _gThe component B of X/R _Gx, having one in the Y direction, to have the numerical value that depends on the position be B _gThe component B of Y/R _GyR is the internal diameter of measuring channel 11, B _gLocal greatest measure for magnetic field:

B _gx＝B _g·X/R (11a)

B _gy＝B _g·Y/R (11b)

In addition, the corresponding current capacity of each wire turn of supposition has been stipulated for calculating: the current capacity of Fig. 4 situation is j _k, and the current capacity of Fig. 5 situation is j _g

Following relational expression is set up:

j _k＝B _k/μ ₀(Sinφ) (12)

j _g=B _g/ μ ₀μ in (Sin2 φ) (13) formula ₀Magnetic permeability for free space.

For the like stable state rotation symmetrical expression flow graph of in equation (1), supposing, magnetic field B _k, B _gElectromotive force below on the wall of measuring channel, inducing:

U _k(φ)＝(2/R)(B _kM ₁)Sinφ (14)

U _g(φ)＝(2/R ³)(B _gM ₃)Sin2φ (15)

Become the electrode measurement electric potential difference of suitable angle by cloth, can obtain square M ₁, M ₃For these squares, following relational expression is set up (using cartesian coordinate system): ${\mathrm{<figure-callout\; id="1"\; label="M"\; filenames="A9612247600151.png,A9612247600171.png"\; state="\{\{state\}\}">M</figure-callout>}}_1=\underset{r=0}{\overset{R}{\&Integral;}}v\left(r\right)\mathrm{rdr}=(1/2\mathrm{\&pi;})\underset{r=0}{\overset{R}{\&Integral;}}\underset{\mathrm{\&phi;}=0}{\overset{2\mathrm{\&pi;}}{\&Integral;}}v\left(r\right)\mathrm{rd\&phi;dr}=$ $(1/2\mathrm{\&pi;})\underset{\mathrm{\&Omega;}}{\&Integral;\&Integral;}$ $v(X,Y)\mathrm{dxdy}---\left(16\right)$ ${\mathrm{<figure-callout\; id="3"\; label="M"\; filenames="A9612247600151.png"\; state="\{\{state\}\}">M</figure-callout>}}_3=\underset{r=0}{\overset{R}{\&Integral;}}v\left(r\right){\mathrm{<figure-callout\; id="3"\; label="r"\; filenames="A9612247600151.png"\; state="\{\{state\}\}">r</figure-callout>}}^3\mathrm{dr}=(1/2\mathrm{\&pi;})\underset{R=0}{\overset{R}{\&Integral;}}\underset{\mathrm{\&phi;}=0}{\overset{2\mathrm{\&pi;}}{\&Integral;}}v\left(r\right)r^2\mathrm{rd\&phi;dr}=$ $=(1/2\mathrm{\&pi;})\underset{\mathrm{\&Omega;}}{\&Integral;\&Integral;}v(X,y)r^2\mathrm{dxdy}---\left(17\right)$

In equation (16) and (17), the double integral of Ω is represented integration to the xsect of measuring channel.

Average flow velocity V _mBy formula $V_m=(1/\mathrm{\&pi;}{R}^2)\&Integral;\underset{\mathrm{\&Omega;}}{\&Integral;}v(x,y)\mathrm{dxdy}---\left(18\right)$ Provide.That carries out between equation (16) and (18) comparison shows that M ₁Be proportional to v _m:

v _m＝(2/R ²)M ₁ (19)

By contrast, square M ₃Then depend on the shape of flow graph, its calculating must be used the special and De Waaile law of exponent of Oswald that according to equation (7).So, ${\mathrm{<figure-callout\; id="3"\; label="M"\; filenames="A9612247600151.png"\; state="\{\{state\}\}">M</figure-callout>}}_3=\underset{r=0}{\overset{R}{\&Integral;}}v\left(r\right){\mathrm{<figure-callout\; id="3"\; label="r"\; filenames="A9612247600151.png"\; state="\{\{state\}\}">r</figure-callout>}}^3\mathrm{dr}=\frac{1+3\mathrm{<figure-callout\; id="1"\; label="N"\; filenames="A9612247600151.png,A9612247600171.png"\; state="\{\{state\}\}">N</figure-callout>}}{1+N}{v}_m\underset{r=0}{\overset{R}{\&Integral;}}[1-{(r/R)}^{1+1/N}]{\mathrm{<figure-callout\; id="3"\; label="r"\; filenames="A9612247600151.png"\; state="\{\{state\}\}">r</figure-callout>}}^3\mathrm{dr}=$ $=\frac{1+3\mathrm{<figure-callout\; id="1"\; label="N"\; filenames="A9612247600151.png,A9612247600171.png"\; state="\{\{state\}\}">N</figure-callout>}}{1+N}{v}_m[R^4/4-\frac{R^{5+1/N}}{{(5+1/N)\mathrm{<figure-callout\; id="1"\; label="R"\; filenames="A9612247600151.png,A9612247600171.png"\; state="\{\{state\}\}">R</figure-callout>}}^{1+1/N}}]=$ $=\frac{1+3\mathrm{<figure-callout\; id="1"\; label="N"\; filenames="A9612247600151.png,A9612247600171.png"\; state="\{\{state\}\}">N</figure-callout>}}{1+N}{v}_m{R}^4[1/4-N/(1+5N)]=\frac{1+3\mathrm{<figure-callout\; id="1"\; label="N"\; filenames="A9612247600151.png,A9612247600171.png"\; state="\{\{state\}\}">N</figure-callout>}}{1+N}{v}_m{R}^4\frac{1+N}{4(1+5N)}$ ${\mathrm{<figure-callout\; id="3"\; label="M"\; filenames="A9612247600151.png"\; state="\{\{state\}\}">M</figure-callout>}}_3=\frac{1+3N}{4(1+5N)}{v}_m{R}^4---\left(20\right)$

According to equation (19), with (2/R ²) M ₁Replace V _mAnd find the solution the index N that flows, obtain $N=\frac{2M_3-R^2{\mathrm{<figure-callout\; id="1"\; label="M"\; filenames="A9612247600151.png,A9612247600171.png"\; state="\{\{state\}\}">M</figure-callout>}}_1}{3R^2{M}_1-10M_3}---\left(21\right)$

In the electromagnetic flowmeter of routine, above-mentioned electric potential difference by two electrodes mutually facing to place make φ=± pi/2 measures.So equation (14) and (19) become

U _k(π/2)-Uk(-π/2)＝(4B _kM ₁)/R (22)

v _m＝(1/2B _kR)[U _k(π/2)-U _k(-π/2)] (23)

But this is the fact of knowing already about electromagnetic flowmeter, in other words, fluid for uniform magnetic field (corresponding to subscript k) and rotation symmetry but arbitrarily, the electric potential difference of induction or voltage are proportional to average velocity v _m, thereby be proportional to volumetric flow rate.

But, said during above using just in time facing to the electrode arranged, can not obtain square M ₃, because if coil connects into mutually trans series connection, corresponding electric potential difference U _g(pi/2)-U _g(pi/2) always equals zero.

Therefore, according to the present invention, electrode 14,15 is not to place to such an extent that just in time face toward mutually, but presss from both sides one less than 180 ° angle.Two preferred numerical value are 120 ° and 90 °.Therefore, be that angle between the direction of the relevant radii of each electrode 14,15 loca and uniform magnetic field is corresponding to the angle φ of preferred value:

φ ₁＝±60°＝±π/3

φ ₂＝±45°＝±π/4

Like this, hereinafter, subscript 1 is relevant with ± 60 °, and subscript 2 is then relevant with ± 45 °.

Thereby, first electric potential difference or the voltage U that record with electrode 14,15 _K1, U _K2With second electric potential difference or voltage U _G1, U _G2For: U _K1=U _k(π/3)-U _k(π/3)=(23 ^1/2B _kM ₁)/R (24) U _G1=U _g(π/3)-U _g(π/3)=(23 ^1/2B _gM ₃)/R ³(25) U _K2=U _k(π/4)-U _k(π/4)=(22 ^1/2B _kM ₁)/R (26) U _G2=U _g(π/4)-U _g(π/4)=(4B _gM ₃)/R ³(27)

With equation (19) substitution equation (24) and (25) and with equation (20) substitution equation (26) and (27), thereby provide average velocity V _M1And V _M2And mobile index N ₁And N ₂Following equation of condition (introduce merchant b=B _g/ B _kBe in order to simplify mark):

V _m1＝U _k1/(3 ^1/2B _kR) (28)

V _m2＝U _k2/(2 ^1/2B _kR) (29)

N ₁＝(2U _g1-bU _k1)/(3bU _k1-10U _g1 (30)

N ₂＝(2 ^1/2U _g2-bU _k2)/(3bU _k2-5·2 ^1/2U _g2) (31)

So, just can prove by top equation, in the present invention, the average velocity v of non-Newtonian fluid _mCan pass through the first and second electric potential difference U with mobile index _kAnd U _gMeasure.

Fig. 8 illustrates the simple longitudinal section that the present invention improves an embodiment of design, and present embodiment makes increases viscosity K and/or the apparent viscosity ε that measures non-Newtonian fluid _sBecome possibility.

In order to reach this point, a bus along pipeline on the wall of measuring channel 11 is installed one first pressure transducer 31 and one second pressure transducer 32 that is spaced from each other a segment distance.Distance between two pressure transducers is represented with L.

The signal difference D that calculating electronic equipment 24 provides according to pressure transducer 31,32 is according to the first electric potential difference U _K1Or U _K2And according to the second electric potential difference U _G1Or U _G2Produce a viscosity signal S who is proportional to the viscosity of fluid _kAnd/or apparent viscosity ε who is proportional to fluid _sViscosity signal S _ε

The rule that constitutes this phenomenon basis is that shear stress equals

τ _nw＝D·r/2L (32)

Unite this formula and equation (2), (5) and (10), draw shear rate V at the wall place of measuring channel (r=R) _RAbsolute value | V _R|:

|V _R|＝|V _m(1+3N)/R(1+N)[-(R/R) ^1/N](1+1/N)|＝

＝V _m(1+3N)/(RN)

In addition, for the shear stress τ at the wall place of measuring channel _NwR=DR/2L has

ε _s＝τ _nwr/|V _R|＝(DNR ²)/〔2VmL(1+3N)〕?(34)

K＝τ _nwR/|V _R| ^N＝[D·R/(2L)]·{RN/〔Vm(1+3N)} ^N

(35)

Because each all contains Vm and N equation (34) and (35), and according to equation (28) to (31), this two number again can be by measuring the first electric potential difference U _K1Or U _K2With the second electric potential difference U _G1Or U _G2Draw, thereby this electromagnetic flowmeter also can be used to measure viscosity K and/or apparent viscosity ε _s

By the corresponding mathematic(al) structure of the above-mentioned separate equation that only comprises the elementary arithmetic computing as seen, be used to produce rate signal S _v, index signal S flows _N, viscosity signal S _kAnd viscosity signal S _εCalculating electronic equipment 24 should be equipped with and carry out the required platform of each arithmetical operation, such as totalizer, subtracter, multiplier, division four and exponent arithmetic platform.

If come the signal (simulating signal) of self- electrode 14,15 and pressure transducer 31,32 to handle with analog form entirely, then these calculate platforms will all be analog platforms.

Particularly advantageously be to come all a fed A/D converter thereby all be digitized of the simulating signal of self- electrode 14,15 and pressure transducer 31,32.Under this situation, calculating electronic equipment 24 will be a digital signal processor, the microprocessor of for example saying so.

Fig. 9 illustrates coil current i ₁₂And i ₁₃Waveform, adopt such electric current can save double-break switch 22.These coil currents can be produced by coil current generator 23.Because when using the bipolarity DC current to make coil current, its direction must periodically be switched said as top, thus with coil 12,13 connect into the series connection of help formula or mutually trans series connection can with this current reversal in conjunction with realization.

For example, replace as shown in Figure 3 pass through a double-break switch with single circuit to two coil supply of current, can adopt to replace as shown in Figure 9 and respectively these two coils be powered with equidirectional and the mobile electric current of reverse direction.

In Fig. 9 a and 9b, coil current i ₁₂And i ₁₃Be expressed as the function of time variable t respectively.Coil current i ₁₂Be the pulse current with four isometric minute cycle E, F, G, H, its total cycle equals four branch cycle sums:

T＝4·T _t

Pulse current for just, is negative during a minute cycle, G, H during minute cycle E, F.Coil current i ₁₃Have and current i ₁₂Same waveform, only phase place is with respect to i ₁₂Moved T _t

So electric current is right+i ₁₂,-i ₁₃Belonging to branch cycle E, electric current is right+i ₁₂,+i ₁₃Belonging to branch cycle F, electric current is right-i ₁₂,+i ₁₃Belong to branch cycle G, and electric current right-i ₁₂-i ₁₃Then belong to the branch cycle H.Therefore, coil 12,13 connects into help formula series connection during F and H, connects into mutually trans series connection during E and G.In addition, can see foregoing bipolarity: H is anti-phase for cycle F relative cycle, and G is anti-phase for cycle E relative cycle.

Be shown in the clock signal T of Fig. 9 c, 9d, 9e and 9f as the function of time variable t ₁, T ₂, T ₃And T ₄Provided by sequence controller 23, each clock all has the total cycle the same with the coil current of Fig. 9 a and 9b.Clock signal T ₁, T ₂, T ₃And T ₄Between phase relation make high level similar each divide the cycle corresponding last 1/3rd during appearance.

In corresponding high period, the electromotive force that then appears at electrode 14,15 is added to calculating electronic equipment 24.Between low period, there is not signal to be added to calculating electronic equipment 24.

Claims (4)

1. one kind is used to measure the average velocity Vm of conduction non-Newtonian fluid and the electromagnetic flowmeter of mobile index N, and fluid flows in measuring channel, and the position that measuring channel contacts with fluid is non-conductive, and described flowmeter also comprises except that measuring channel:

Just in time mutually facing to being placed on the outside of measuring channel both sides or one first coil and one second coil in the measuring channel wall;

Described coil is used for producing a magnetic field of crossing measuring channel wall and fluid when coil current flows through coil;

First electrode that is used to pick up by first electromotive force of magnetic field induction;

Second electrode that is used to pick up by second electromotive force of magnetic field induction;

The relevant radii of each described electrode loca and magnetic direction constitute one less than 90 ° angle on the measuring channel;

A coil current generator;

A double-break switch is used for two coils or connects into help formula series connection or connect into mutually trans series connection; And

Calculating electronic equipment is used for producing:

A rate signal, it is proportional to coil and connects into the average velocity Vm that first electric potential difference that help formula when series connection picked up by electrode is calculated;

A mobile index signal, this signal are proportional to coil and connect into the mobile index N that second electric potential difference that mutually trans when series connection picked up by electrode and first electric potential difference are calculated.

2. the electromagnetic flowmeter that proposes in the claim 1, wherein

On the wall of measuring channel, one first pressure transducer and one second pressure transducer that is spaced from each other a segment distance is installed along a bus; And

The signal difference that provides according to pressure transducer of calculating electronic equipment wherein is according to first electric potential difference with produce one according to second electric potential difference and be proportional to the viscosity signal of fluid viscosity K and/or produce an apparent viscosity ε who is proportional to fluid _sThe viscosity signal.

3. the electromagnetic flowmeter that proposes in the claim 1, wherein 60 ° of angles of the direction in the relevant radii of each described electrode loca and magnetic field formation on the measuring channel.

4. the electromagnetic flowmeter that requires in the claim 1, wherein 45 of the direction in the relevant radii of each described electrode loca and magnetic field formation on the measuring channel.

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