阅读说明：本技术 具有介质导电率测量的磁性流量计 (Magnetic flowmeter with media conductivity measurement ) 是由 C.希奥巴努 S.威尔斯 于 2020-01-09 设计创作，主要内容包括：具有介质导电率测量的磁性流量计。一种用于测量流路径中的导电流体的速度的磁性流量计组装件。所述流量计组装件包括：线圈驱动器,其用于向线圈组装件提供驱动电流；电极,其用于测量由流过线圈组装件所产生的磁场的导电流体来产生的电信号；以及微处理器,其用于控制磁性流量计。所述微处理器基于感测的电信号而确定流体的电导率。所述微处理器然后响应于流体的电导率来修改线圈驱动器的频率,以优化流量计的采样率。流量计组装件通过如下来修改线圈驱动器频率：为高导电性流体增大驱动频率或者为不太具导电性的流体减小驱动频率。(A magnetic flowmeter having a media conductivity measurement. A magnetic flow meter assembly for measuring a velocity of a conductive fluid in a flow path. The flow meter assembly comprises: a coil driver for providing a driving current to the coil assembly; an electrode for measuring an electrical signal generated by the electrically conductive fluid flowing through the magnetic field generated by the coil assembly; and a microprocessor for controlling the magnetic flow meter. The microprocessor determines the conductivity of the fluid based on the sensed electrical signal. The microprocessor then modifies the frequency of the coil driver in response to the conductivity of the fluid to optimize the sampling rate of the flow meter. The flow meter assembly modifies the coil driver frequency by: increasing the drive frequency for highly conductive fluids or decreasing the drive frequency for less conductive fluids.)

1. A method for operating a flow meter configured to measure a velocity of a conductive fluid in a flow path, the method comprising:

driving at least one coil assembly with a drive current provided by a coil driver, the at least one coil assembly being located adjacent to the fluid flow path;

measuring an electrical property associated with a conductive fluid in the fluid flow path;

determining the conductivity of the fluid based on the measured electrical property; and

the frequency of the drive current is modified in response to the conductivity of the fluid to optimize the measurement rate of the flow meter.

2. A method as defined in claim 1, wherein driving at least one coil assembly comprises alternating a drive current to induce a magnetic field in the at least one coil assembly.

3. The method as defined in claim 1, wherein measuring the electrical property associated with the conductive fluid comprises measuring a peak voltage (U) induced in the conductive fluid in response to the magnetic field in the at least one coil assembly_EPeak value).

4. A method as defined in claim 3, wherein determining the conductivity of the fluid based on the measured electrical property comprises determining the conductivity of the fluid from a relationship between the peak voltage measurement and the conductivity of the fluid.

5. A method as defined in claim 4, wherein the relationship between the peak voltage measurement and the conductivity value is non-linear.

6. The method as defined in claim 1, wherein modifying the frequency of the drive current comprises increasing the drive current frequency for fluids of high conductivity and decreasing the drive current frequency for fluids of lesser conductivity.

7. The method as defined in claim 1, wherein modifying the frequency of the drive current comprises:

comparing the conductivity of the fluid to a minimum fluid conductivity value; and

if the conductivity of the fluid is below the minimum fluid conductivity value, no fluid velocity measurement is performed.

8. An apparatus for operating a flow meter configured to measure a velocity of an electrically conductive fluid in a flow path, the apparatus comprising:

at least one coil driver configured to provide a drive current to the coil assembly;

at least one electrode configured to measure an electrical signal generated by the electrically conductive fluid flowing through the magnetic field generated by the drive current in the coil assembly; and

a computer processor configured to:

determining the conductivity of the fluid in response to the electrical signal; and

the frequency of the drive current is modified in response to the conductivity of the fluid to optimize the measurement frequency of the flow meter.

9. The apparatus as defined in claim 8, wherein the coil driver alternates the drive current to generate the magnetic field in the coil assembly.

10. The apparatus as defined in claim 8, wherein the at least one electrode measures a peak voltage (U) produced by the conductive fluid flowing through the magnetic field generated by the coil assembly_EPeak value).

11. The apparatus as defined in claim 10, wherein the computer processor determines the conductivity of the fluid using a mathematical relationship between the peak voltage measurement and the conductivity of the fluid.

12. The apparatus as defined in claim 11, wherein the mathematical relationship between peak voltage and conductivity is approximately logarithmic rhythm.

13. An apparatus as defined in claim 8, wherein the computer processor modifies the frequency of the drive current by: increasing the drive current frequency for conductive fluids and decreasing the drive current frequency for less conductive fluids.

14. A non-transitory computer-readable storage medium comprising computer-executable instructions that, when executed by a computer processor, perform a method comprising:

energizing at least one coil assembly with a drive current provided by a coil driver, the at least one coil assembly being located adjacent to the fluid flow path;

measuring an electrical property of an electrically conductive fluid in the fluid flow path;

determining the conductivity of the fluid based on the measured electrical property; and

the frequency of the drive current is adjusted in response to the conductivity of the fluid to optimize the measurement frequency of the magnetic flow meter.

15. The non-transitory computer readable storage medium as defined in claim 14, wherein energizing at least one coil assembly comprises alternating a drive current to induce a magnetic field in the at least one coil assembly.

16. The non-transitory computer readable storage medium as defined in claim 14, wherein measuring the electrical property of the conductive fluid in the fluid flow path comprises measuring a peak voltage (U) induced in the conductive fluid by the magnetic field generated by the at least one coil assembly_EPeak value).

17. The non-transitory computer readable storage medium as defined in claim 14, wherein determining the conductivity of the fluid based on the measured electrical property comprises determining a conductivity value using a relationship between a peak voltage measurement and the conductivity of the fluid.

18. The non-transitory computer readable storage medium as defined in claim 17, wherein a relationship between the peak voltage measurement and the conductivity of the fluid is a non-linear relationship.

19. The non-transitory computer readable storage medium as defined in claim 18, wherein the relationship between the peak voltage measurement and the conductivity is approximately a logarithmic rhythm relationship.

20. The non-transitory computer readable storage medium as defined in claim 14, wherein adjusting the frequency of the drive current comprises increasing the frequency of the drive current for a fluid of higher conductivity and decreasing the frequency of the drive current for a fluid of lower conductivity.

Technical Field

The present invention relates generally to the operation of sensors for measuring the velocity of a fluid, and more particularly to magnetic flow meters for performing fluid flow measurements.

Background

A magnetic flowmeter measures the velocity of a conductive fluid passing through a conduit by: a magnetic field is generated and the resulting voltage is measured. These flow meters rely on faraday's law, in which the flow of an electrically conductive fluid through a magnetic field causes a voltage signal that is sensed by electrodes. The sensed voltage is proportional to the velocity of the fluid.

While these flow meters are generally effective, there are deficiencies. For example, one limitation in the case of current flow meters is: the fluid medium being measured must meet a minimum conductivity level. If the fluid medium falls below this minimum conductivity value, it cannot be accurately measured. Furthermore, for fluids with low conductivity, the sensed voltage U_EMust be given sufficient time to settle so that accurate voltage measurements can be achieved. This time delay can be significant for fluids of low conductivity and adversely affect the sampling rate of the magnetic flowmeter. In applications where the fluid velocity changes rapidly and is discontinuous, this reduced sampling rate may in turn affect the measurement accuracy.

Thus, it should be appreciated that a need exists for a magnetic flow meter assembly that addresses these concerns. The present invention fulfills these needs and others.

Disclosure of Invention

Briefly, and in general terms, the present invention provides a system and related method for measuring the conductivity of a fluid medium being measured by a magnetic flow meter.

The system comprises: a coil driver for providing a driving current to the coil assembly; an electrode for measuring an electrical signal generated by the electrically conductive fluid flowing through the magnetic field generated by the coil assembly; and a microprocessor for controlling the magnetic flow meter. The microprocessor determines the conductivity of the fluid in response to the sensed electrical signal. The microprocessor then modifies the frequency of the coil driver in response to the conductivity of the fluid in order to optimize the sampling rate of the flow meter. Specifically, the flow meter modifies the coil driver frequency by: increasing the drive frequency for highly conductive fluids or decreasing the drive frequency for less conductive fluids.

For the purpose of summarizing the invention and the advantages achieved over the prior art, certain advantages of the invention have been described herein. It is to be understood that: not necessarily all such advantages may be achieved in accordance with any particular embodiment of the invention. Thus, for example, those skilled in the art will recognize that the invention may be embodied or carried out in the following manner: the described approaches achieve or optimize one advantage or a set of advantages as taught herein without necessarily achieving other advantages as may be taught or suggested herein.

All of these embodiments are intended to be within the scope of the invention disclosed herein. These and other embodiments of the present invention will become readily apparent to those skilled in the art from the following detailed description of the preferred embodiments having reference to the attached figures, the invention not being limited to any particular preferred embodiment disclosed.

Drawings

Embodiments of the invention will now be described, by way of example only, with reference to the following drawings:

fig. 1 is a simplified perspective view of a magnetic flow meter assembly according to the present invention.

FIG. 2 illustrates a time-varying voltage (U) generated by a conductive fluid traveling through a flow path of a magnetic flow meter_E）。

FIG. 3 illustrates the measured peak voltage U_EPeak (mV) and conductivity of the fluid (m) The relationship between them.

Fig. 4 is a simplified diagram of a magnetic flow meter system for measuring the conductivity of a fluid and optimizing its operation.

Fig. 5 illustrates a time-varying drive voltage (V) applied to a coil assembly.

Fig. 6 illustrates the time-varying drive current (I) propagating through the coil assembly.

Fig. 7 illustrates a time-varying magnetic field (B) generated by the coil assembly within the fluid flow path.

FIG. 8 illustrates a time-varying voltage signal (U) induced in a conductive fluid and detected by an electrode_E）。

FIG. 9 depicts an unoptimized voltage signal (U)_E) Illustrating the time delay T_DTime of steady state T_SAnd total measurement time T_T。

FIG. 10 depicts an optimized time-varying voltage signal (U)_E) Wherein the steady state time T has been reduced by increasing the frequency of the drive current (I)_S。

Fig. 11 illustrates how the drive current frequency is optimized based on the conductivity of the fluid medium.

FIG. 12 depicts a method for modifying the frequency of the drive current (I) according to one embodiment of the invention.

Fig. 13 is a simplified perspective view of a magnetic flow meter assembly according to the present invention including a support coupled to a pair of coils forming a magnetic circuit circumscribing a conduit.

Fig. 14 is a simplified perspective view of the magnetic flow meter assembly of fig. 13 further including a shield case and an electronics assembly.

Incorporation by reference

In certain embodiments of the present invention, the magnetic flow meter assembly may be configured as described and claimed in the applicant's co-pending patent application U.S. application No. 16/146,090 entitled "FU LL BOREMAGNETIC F L METOWER ASSEMB L Y," filed on 28.9.2018, which is hereby incorporated by reference for all purposes.

Detailed Description

The electrical conductivity of a fluid is its ability to conduct electrical current. The conductivity of a fluid is typically measured in siemens per meter (S/m). The conductivity of a fluid is generally a function of the Total Dissolved Solids (TDS) in the fluid. For example, pure deionized water has a purity of approximately 5.5While seawater with dissolved salts and other impurities has a conductivity of approximately 5S/m (i.e., seawater conductivity is one million times that of deionized water).

The conductance (C) of a fluid solution depends on the strength and concentration of the electrolyte in the solution. Strong electrolytes typically include strong acids (e.g., HCI, H)₂SO₄、HNO₃) Strong bases (e.g. L iOH, NaOH, KOH) and/or salts (e.g. NaC L, KNO)₃、MgCl₂). These electrolytes are fully ionized or separated in solution, and the suspended ions are good electrical conductors. In contrast, weak electrolytes never completely separate in solution (i.e., form a mixture of ions and molecules in equilibrium). The weak electrolyte typically includes a weak acid (e.g., acetic acid, CH)₃COOH and phosphoric acid (H)₃PO₄) And/or a weak base (e.g. NH)₃). In weak electrolyte solutions, the concentration of ions is less than the concentration of the electrolyte itself.

The conductance (C) of the solution was determined by: measuring the fixed distance using a conductivity meter () Resistance (R) of the solution between the two electrodes separated.

R ==

Wherein:

r = resistance

C = conductance

= distance between electrodes

Specific resistance of fluid

A = cross-sectional area of test specimen.

Empirically, the minimum conductivity of a fluid measured with a magnetic flow meter is 5 micro S/cm. Solutions with lower conductivity generally have a voltage signal (U) that is challenging to detect and difficult to measure accurately_E). Alternatively, a fluid with high conductivity has a voltage signal (U) that is consistent over time_E) Have well defined voltage signals and can be measured accurately.

Magnetic flowmeters rely on faraday's law of electromagnetic induction to measure the velocity of a conductive fluid in a flow path. Specifically, faraday's law states that: the voltage induced across any conductor moving at right angles through a magnetic field is proportional to the velocity of the conductor.

Wherein:

U_E= induced voltage (i.e. signal voltage)

V = mean velocity of conductive fluid

B = magnetic field strength

L = the length of the conductor (i.e. the distance between the electrodes).

Alternatively, the velocity of the fluid。

The flow of the conductive liquid through the magnetic field B generates a voltage signal U_EThe voltage signal U_EIs sensed by the measuring electrode pairs and can in turn be used to calculate the average velocity V of the fluid. Magnetic flowmeters are typically very accurate (e.g., < 1% measurement error).

Average fluid velocity V and induced voltage U as illustrated by the Faraday equation_EDirectly proportional. We will see shortly: induced peak voltage (U)_EPeak) is a function of the conductivity C of the fluid. At induced peak voltage U_EThis relationship between the peak value and the fluid conductivity C enables the conductivity of the fluid to be determinedAnd enables optimization of magnetic flowmeter operation based on the conductivity of the fluid medium.

Referring now to the drawings and in particular to fig. 1, there is shown a magnetic flow meter assembly 10 having a novel fluid conductivity measurement system. The magnetic flow meter assembly 10 has a tubular body 12 (e.g., a pipe), the tubular body 12 having two opposing ends 14 and 16, the two opposing ends 14 and 16 being along a horizontal axis (a)_x) Aligned with and defining a fluid flow path 18 for conveying the electrically conductive fluid. The magnetic flow meter assembly 10 includes a pair of coil assemblies (20, 22), the coil assemblies (20, 22) being coupled to a middle region of the flow meter 10 and configured to pass current received from a pair of coil drivers (24, 26). The coil assembly (20, 22) generates a magnetic field 28 within the fluid flow path 18 of the tubular body 12 via electrical current passing therethrough. A pair of measurement electrodes (30, 32) attached to the body 12 is configured to detect a voltage induced by the conductive fluid passing through the magnetic field 28. The detected voltage signal is processed by a signal processor 34, which signal processor 34 provides a digital signal to a microprocessor 36, which microprocessor 36 processes the signal data and determines the conductivity C of the fluid medium.

With continued reference to fig. 1, in an alternative embodiment, the coil assembly (20, 22) may be externally coupled to the tubular body 12 and along the vertical axis (a)_z) Is aligned with the vertical axis (A)_z) With the longitudinal axis (A)_x) And a horizontal axis (A)_Y) Are orthogonal. The magnetic flow meter assembly 10 can further include a plurality of auxiliary electrodes 19 (a, b, c), the plurality of auxiliary electrodes 19 (a, b, c) including a first auxiliary electrode 19 (a) and a second auxiliary electrode 19 (b) disposed upstream of the pair of measurement electrodes (30, 32). The first and second auxiliary electrodes (19 a,19 b) are aligned with the vertical axis (Az) on opposite sides of the duct, such that the axis (Ay) and the axis (Az) are coplanar. The third auxiliary electrode 19 (c) is arranged downstream of the pair of measuring electrodes (30, 32). The measuring electrode and the auxiliary electrode are each fitted to a corresponding hole formed in the wall of the pipe 12.

FIG. 2 is a time-varying voltage signal U sensed by the pair of electrodes (30, 32)_ETo illustrate (a). Generating a time-varying voltage signal U when the conductive fluid 18 flows through the magnetic field (B) 28 generated by the pair of coil assemblies (20, 22)_E. Note that U is used whenever the magnetic field B crosses zero (i.e., the magnitude of the magnetic field goes to zero), U_EThere is a spike. Referring to view A-A, the inventors have discovered U_EAmplitude of the peak (i.e. at steady state U)_EHeight above the value) is proportional to the conductivity of the fluid medium. Thus, the geometry based on the magnetic flow meter may be based on U_EThe amplitude of the peak is used to accurately determine the conductivity of the fluid medium.

It has also been found that: time delay (T)_D) For induced voltage U_EThe time necessary for the measurement to settle and reach a plateau (i.e. reach a steady state) -is greater for fluids of low conductivity than for fluids of high conductivity. Steady state time (T)_S) Is the time during which accurate flow measurements can be performed. As illustrated in fig. 2, the time delay T_DCan take into account the total measurement time T_TA significant portion of (a). Thus, when measuring the velocity of a fluid of high conductivity, the total measurement time can be reduced (i.e. the measurement frequency is increased) and when measuring a fluid of low conductivity, the total measurement time can be increased (i.e. the measurement frequency is decreased). The ability to tailor the measurement frequency based on the conductivity of the fluid is a significant advantage over existing fluid measurement systems. Especially when measuring fluids in an unstable state (i.e. fluids with widely varying flow velocities) or fluids with widely varying conductivity (i.e. different batches of fluid medium or different fluid compositions).

FIG. 3 illustrates conductivity as a fluid: () U of function (a)_EThe relationship between the amplitude of the peaks (mV). It can be seen that: u shape_EThe amplitude of the peaks increases approximately logarithmically in rhythm with the fluid conductivity. Due to the fact thatThis, a highly conductive fluid has high, well defined signal peaks, and a low conductivity fluid has much smaller defined signal peaks, which can be much more challenging to detect and measure. By using this relationship, we can be based on "U_EThe amplitude of the peak "determines the conductivity of the fluid medium. It should be appreciated that although we graphically illustrate at U_EThe relationship between the peak value and the fluid conductivity C, but the relationship may also be recorded with a look-up table, a mathematical relationship, or other mathematical means that can be stored in a computer memory and processed or accessed by a microprocessor.

Fig. 4 is a simplified diagram of a magnetic flow meter system 40 for measuring the conductivity of a fluid medium and optimizing its operation. The system includes a tubular body 12, the tubular body 12 forming a fluid conduit for transporting an electrically conductive fluid 18. The system further comprises two coil assemblies (20, 22), the coil assemblies (20, 22) being energized by a pair of coil drivers (24, 26), the pair of coil drivers (24, 26) generating a time-varying magnetic field 28 that is trans-conductance through the fluid 18.

The two coil drivers (24, 26) are energy management ICs that provide an active power pulse output. The coil driver may be embodied as an H-bridge driver configured with a very low resistance and thus a low voltage drop. As such, the coil driver is able to alternate the direction of the current through each coil assembly and thereby affect the direction of the magnetic field emitted from each coil. Alternating the direction of the current, and thus the magnetic field, is achieved in order to avoid the electrochemical phenomenon of electrode migration. Coil driver with integrated on-chip voltage reference, ultra-low temperature drift (< 15 ppm/C)^o) And is highly reliable.

A pair of electrodes (30, 32) measures a voltage signal U induced in the conductive fluid 18 by the magnetic field 28_E. The voltage signal operates through a pair of diodes (42, 44), signal conditioners (46, 48) and an instrumentation amplifier (50), the instrumentation amplifier (50) measuring an induced voltage (U) across the fluid_E1,U_E2). Instrumented amplificationThe amplifier (50) amplifies the signal and maintains the input current (I)₁,I₂) And the output voltage (V)_E1,V_E2) A linear relationship therebetween. An A-to-D converter (ADC) (52) receives the analog output from the instrumentation amplifier (50) and converts it to a digital signal. A microprocessor (36) receives the digital signals, processes the data using instructions stored in a memory, and determines the conductivity of the fluid medium based on the digital signals. The microprocessor then determines the optimum frequency of the drive current (I) based on the conductivity measurement. The two coil drivers (24, 26) then use the optimal drive frequency to energize the two coil assemblies (20, 22) as illustrated in fig. 6. This results in an optimized time-varying voltage (U) as illustrated in fig. 10_E）。

Referring to fig. 5, 6, 7, 8, 9 and 10, we will explain: once the conductivity of the fluid medium has been determined, the control system optimizes the frequency of the drive current (I).

Referring to fig. 5, fig. 5 is a graph having a magnitude (V) provided to a coil assembly₁,V₂) And period of timeDepiction of the alternating drive voltage V. When the coil assembly is driven by an alternating voltage V, an alternating current I is generated in the coil, having a magnitude (I) as illustrated by fig. 6₁,I₂) And period of timeNote that depending on the circuit R/L ratio, it takes time (t) for the current I to achieve a constant value.

Wherein:

v = applied drive voltage

R = coil resistance

L = coil inductance

t = time.

An illustrative time-varying magnetic field B generated within the flow field is shown in fig. 7. A magnetic field B is generated by a current I flowing in alternating directions through each coil assembly. B (B)₁,B₂) Is proportional to the drive current I and the number of coil turns.

Wherein:

i = applied drive current

R = number of coil turns.

Referring to FIG. 8, FIG. 8 is a sensed voltage U generated by a time-varying magnetic field B_EThe time-varying magnetic field B flows perpendicular to the fluid flow line V and is detected by the pair of electrodes. Note that U crosses zero when the time-varying magnetic field B crosses zero (see zero crossing in FIG. 7)_EThere is a spike. U shape_EHas a peak at the zero crossing and then a short time delay (T)_D) Then stabilized to a steady state value U_E1And U_E2. It is at this short time delay T_DThen, U_EA steady state value (i.e., U) is achieved_E1Steady state) and at that time accurate flow velocity measurements can be performed.

Referring to FIG. 9, FIG. 9 is a graph of voltage U generated using a non-optimal coil drive frequency_EAnd (4) drawing a curve. Note that the total measurement time T_TIncluding a delay time T_DAnd steady state time T_SBoth of which are described below.

T_T= T_D+ T_S

Delay time T_DStrongly depends on the conductivity of the fluid medium, since it follows a conventional capacitor discharge curve. We see earlier: the resistivity R of the fluid is a function of the number of charge carriers. Thus, the lower the resistivity R, the shorter the discharge time (e.g., if R is high in an RC circuit, the higher the time constant T). Thus, the greater the conductivity of the fluidDelay time T_DThe shorter the length. Steady state time T_SIs during which U is_ETime at steady state value and voltage measurement is performed. This time can also be optimized to achieve a greater measurement frequency.

Referring to FIG. 10, FIG. 10 is a sensed voltage U generated using an optimal coil drive frequency_ETo illustrate (a). In this example, the fluid medium is highly conductive and the coil drive frequency has been increased to take advantage of the induced voltage U_EShort delay time T before achieving steady state values_D. In this example, the total measurement time T for the optimized process_TOThan the total measurement time T for the unoptimized process_TIs significantly shorter.

FIG. 11 illustrates a technique for optimizing the drive current frequency (i.e., approximately 1 to 10 Hz) based on the conductivity of the fluid medium. Magnetic flowmeter using initial drive current frequency (F)_Init) (i.e. 4 Hz) to start operation, the initial drive current frequency (F)_Init) Once the conductivity of the fluid has been determined, the conductivity value is compared to a lower conductivity limit (C L). The lower conductivity limit C L is a value below which the induced voltage U cannot be accurately and repeatably measured_EIf the fluid conductivity value is above the conductivity lower limit C L, but at the initial frequency F_InitBelow the corresponding conductivity value, the drive frequency is then typically lowered based on the relationship between the drive current frequency and the fluid conductivity. This has the following effect: providing additional time for the sensed voltage signal U_ESettling and establishing a steady state value, resulting in a more accurate speed measurement. If the fluid conductivity is measured at the initial frequency F_InitAbove the corresponding conductivity value, the drive frequency is typically increased based on the relationship between the drive current frequency and the fluid conductivity. Higher coil drive frequency increases data sampling rate without affecting U_EThe quality of the signal. When the composition of the fluid mediumAnd/or the flow rate is changing rapidly, this higher sampling rate may provide significant advantages. It should be noted that: although the relationship between drive current frequency and fluid conductivity is graphically shown, the relationship may also be recorded using a look-up table, a mathematical equation, a computer subroutine, or any other method for recording a relationship between variables.

Referring to fig. 12, a method for operating a magnetic flow meter in accordance with the present invention is depicted. The method starts by: providing a drive current (I) to two coil assemblies using first and second coil drivers₁,I₂) (step 102). As illustrated in FIG. 6, the drive current I has a magnitude I₁And I₂And period of time. The drive current energizes the coil assembly, which generates a time-varying magnetic field B across the fluid flow path, as shown in fig. 7.

Two-electrode sensing voltage U_ESaid voltage U_EGenerated by a conductive fluid flowing perpendicular to the time-varying magnetic field B, as depicted in fig. 8 (step 104). Voltage U_EHaving a peak value (U) indicating the conductivity of the fluid medium_{Peak value of E1}，U_{Peak value of E2}). The voltage signal also has a steady state value (U)_{E1 stabilization}，U_{E2 stabilization}) And a time delay T for the signal to achieve a steady state value_D。

The voltage signal from one or both electrodes passes through a diode and a signal conditioner, and is then converted from analog to digital using an a/D converter. The digital signal is received by a microprocessor that compares a peak voltage value (U)_{Peak value of E1}，U_{Peak value of E2}) With respect to the relationship between peak voltage and fluid conductivity (see fig. 3). As noted earlier, the relationship may be in the form of a graphical representation, a look-up table, a mathematical equation, or other recording means. From this relationship, the microprocessor determines the conductivity of the fluid (step 106).

The microprocessor then modifies the drive current frequency based on the conductivity of the fluid medium (step 108). The conductivity of the fluid is first compared to a minimum conductivity for accurate fluid velocity measurement (step 110). If the conductivity of the fluid is below the threshold, operation of the magnetic flow meter is typically suspended and an error signal is displayed (step 112). Alternatively, if the conductivity of the fluid is above the threshold, the processor then determines whether the conductivity of the fluid is high enough to warrant increasing the frequency of the drive current (step 114). For example, if the fluid has a viscosity at 50The above conductivity increases the drive current frequency to 5 Hz.

Next, if the conductivity of the fluid is above the threshold, but too low to increase the drive current frequency, then a determination is made as to whether a lower drive current frequency is warranted (step 118). In which a voltage U is induced_EIn instances where additional time is required to achieve a steady state value, the frequency of the drive current I is reduced. This results in a steady state time T_SAnd more accurate and repeatable voltage measurement (step 120). For example, if the fluid conductivity is at 15Thereafter, the driving current frequency is reduced to 3 Hz. Fluid media previously subjected to large fluid velocity measurement errors can now be accurately measured.

Once the drive frequency has been optimized for the current fluid medium, the novel method may repeat at step 124 or end at step 126 (step 122). There are many reasons for continuing to perform the optimization process, including, to name a few: batch-to-batch variations in fluid conductivity, regular changes in the fluid medium being measured, or to ensure very fast and accurate fluid velocity measurements.

This is done with our discussion of magnetic flowmeters and methods for measuring the conductivity of a fluid medium. We will now turn our attention to commercial implementations of the flow meter.

Referring now to fig. 13, magnetic flow meter assembly 10 includes a pair of coil assemblies (18, 20), the coil assemblies (18, 20) being coupled to pipe 12 in a middle region of pipe 12. The coil assembly is mounted to the exterior of the pipe, along an axis (A)_z) And (6) aligning. More specifically, each coil is held in place by a bracket 21, which bracket 21 constrains the tube 12. The magnetic pole 25 is arranged between the coil 18 and the pipe. The poles are formed of an electrically conductive material, such as the same metal as the magnetic support, soft magnetic carbon steel with Fe% > 99.4, and are shaped to conform about the conduit. Non-conductive (air gap) spacers 27 are arranged on opposite ends of the coil. In the case of each coil, a first airgap pad 27 is sandwiched between the coil and the corresponding pole 25, and a second airgap pad 27 is sandwiched between the coil and the support 21. In each coil there is a magnetic core made of a material with good magnetic properties. These cores carry flux lines from the coils to the pole pieces and magnetic supports.

The support 21 further serves as a magnetic circuit for the magnetic field generated by the coils 18, 20. The support has a generally octagonal shape which is beneficial for assembly and operation of the assembly 10. More specifically, the bracket 21 is formed of two, generally c-shaped members 29, which two, generally c-shaped members 29 slidably mate with each other with respect to the conduit to couple to each other. In this way, the bracket 21 can be used on pipes having different diameters. An attachment (e.g., a bolt) couples the coil to the bracket along the axis (Az).

The assembly 10 is configured to generate a strong alternating magnetic field (flux) B that is distributed evenly over the cross-section of the pipe. The alternating magnetic field is used to avoid the migration of the electrode material. The configuration of the support 21, for example, including the shape and material, promotes a resulting magnetic field (flux) B within the pipe 12. In the exemplary embodiment, the support 21 is formed of a "soft" magnetic material, which refers to a relative magnetic permeability, meaning that it has no residual magnetization when switched off.

Referring now to fig. 14, magnetic flow meter assembly 10 further includes a housing 35, the housing 35 configured to protect the magnetic field generator (which includes coils 18,20 and support 21) from environmental exposure. The assembly 10 further includes an electronic assembly 62, the electronic assembly 62 being attached to the housing of the assembly. The electronic assembly 62 is in electrical communication with the electrodes (19, 26) and coils (18, 20) of the assembly to operate the assembly. In an exemplary embodiment, the electronic assembly may house components such as, among others: drivers (32, 34), operational amplifiers (40, 42), A-to-D converters (ADC) (44, 46), a microprocessor 48, and a Pulse Width Modulator (PWM) 50.

The present invention has been described above in terms of a presently preferred embodiment so that an understanding of the invention may be conveyed. However, there are other embodiments to which the invention may be applied that are not specifically described herein. Accordingly, the invention is not to be considered as being limited to the forms shown, which are to be regarded as illustrative rather than restrictive.