JPH10221135A - Electromagnetic flowmeter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable the measurement of a flow rate in a short time by arranging a plurality of electrodes, right and left in pairs on respective upper and lower planes at positions where the internal wall of a measuring pipe contacts planes set being separated by an equal distance above and below a reference surface containing the axis of the measuring pipe and orthogonal to a magnetic field generated. SOLUTION: Two sets of electrode pairs 103a and 103b, pairs of right and left electrodes, are installed in symmetry with each other with respect to a horizontal axis containing the axis of a measuring pipe while being deviated at different positions from each other in the direction of the axis of the pipe. The electrodes set on the one side and the electrodes set on the side as opposed thereto are arranged being overlapped therebetween as viewed from the direction of the axis of the measuring pipe. In other words, the limit of detection is basically raised by expanding parts of the electrodes as immersed in a fluid. In the determination of a flow rate from potential differences between the upper and lower electrodes, when the water is full, the volumetric flow rate and the potential difference between the electrodes are primarily determined. When the water is not full, the relationship between the two factors is not defined primarily under the influence of the installation conditions of a piping. This means that the two factors are necessary as parameters of non-water filling rate. Thus, the correction of the flow rate is accomplished based on the potential difference thereby enabling accurate measuring of the flow rate during the non-full water period.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention is applicable to the measurement of the flow rate of most conductive fluids, and is particularly suitable for controlling and controlling the flow rate in plants, water treatment facilities, etc. The present invention relates to an electromagnetic flowmeter that is optimal for measuring the flow rate when water is full.

[0002]

2. Description of the Related Art A conventional electromagnetic flow meter has a flow signal based on Fleming's law, as shown in JIS Z8764 and JIS B7554.
Several tens of μV to several meters in a direction perpendicular to the direction of the magnetic field
The voltage signal of V is generated in proportion to the velocity of the fluid flowing through the pipe. In an electromagnetic flowmeter currently used, a current is supplied from an alternating power supply to a pair of excitation coils arranged above and below a pipe as a means for generating a magnetic field. , So as to reduce zero point drift and aging.

[0003] The reason for the alternating excitation is that, in a DC magnetic field excitation, a flow signal generated in a fluid is a direct current, so that a weak current flowing in a certain direction between the fluid and the electrode causes a continuous electrochemical reaction at the fluid-electrode interface. This is because the interface state changes and the interface state changes to generate a weak electromotive force, or the interface electric resistance increases and fluctuates. These are not constant values, but change over time or change with the flow velocity, and become noise for the flow rate signal. If alternating excitation is used to solve such a problem, the flow signal is also alternating current, and the electrochemical reaction does not proceed because the forward and reverse reactions occur alternately, so that stable measurement becomes possible.

FIG. 5 shows an example of such an electromagnetic flow meter.
This includes a measuring tube 102 through which a fluid 101 flows, and a pair of electrodes 103a attached to the inner wall of the measuring tube 102.
103b, excitation coil 10 for applying magnetic flux to measurement tube 102
4, an excitation circuit 105 for flowing a current through an excitation coil 104 of the detector 100, and an electrode 103.
A differential amplifier (AMP) 106 that amplifies a potential difference (a voltage proportional to the intensity of magnetic flux and the average velocity of the fluid 101 flowing through the measuring tube 102) generated between the a and 103b. And a converter 108 comprising an arithmetic circuit 107 for processing the processed signal.

FIG. 6 is a waveform chart of each part for explaining the operation of FIG. Hereinafter, the operation of FIG. 5 will be described with reference to FIG. That is, the fluid 10 flowing through the measurement tube 102
1 is measured from the excitation circuit 105 in FIG.
The excitation signal (rectangular wave current) shown in FIG.
An alternating magnetic field as shown in FIG.
As shown in FIG. 6D, the magnetic field strength between the electrodes 103a and 103b due to the alternating magnetic field and the potential difference proportional to the average velocity of the fluid 101 are reduced while preventing the polarization potentials due to the DC components from being generated at the electrodes 103a and 103b. And amplifies it by the differential amplifier 106.

In parallel with the above operation, every time the square wave current of FIG. 6C is stabilized, the sampling circuit as shown in FIG. 6B output from the excitation circuit 105 causes the arithmetic circuit 107 to perform a sampling operation. 6 (e), a flow signal output from the differential amplifier 106 is taken in, and a predetermined operation is performed based on each flow signal taken in the sampling operation, thereby obtaining a signal cable 109 and a detector. FIG. 6 is a diagram in which noise caused by a change in magnetic flux traversing a loop circuit constituted by the loop circuit 100 and noise having a period longer than the period of the square wave current are removed.
A flow signal as shown in (f) is generated and displayed, or a digital signal such as a 4-20 mA current signal is transmitted.

[0007] By the way, in such an electromagnetic flowmeter, when it is installed, as shown in FIG. Since the pair of electrodes 103 is provided, the non-full state of the fluid 101 flowing through the measuring tube 102, for example, the water level in the measuring tube 102 is barely equal to the water level of the full state.
It has been pointed out that when at an arbitrary position 111 in the middle of the water level contacting with No. 3, a flow rate error occurs according to the water level. In general, the electromagnetic flow meter is based on the premise that a flow in a full state is flowing, and measures the actual flow by appropriately converting signals obtained from a pair of electrodes. Therefore, assuming that the flow rate error of the flow meter output when the water is actually full is zero, at a certain arbitrary water level, the positive flow rate of about (gap area / total flow path cross-sectional area) in the cross-sectional area of the measuring pipe flow path An error occurs. As means for solving this problem, for example, one disclosed in Japanese Patent Application Laid-Open No. 5-223605 has been proposed (also referred to as a proposed device).

[0008] The principle of measuring the non-full water flow rate in the above proposed device is as follows. (1) The known flow rate Q is determined by different magnetic flux density distributions BA and BB.
Let Va, Vb be the outputs measured in advance. (2) an unknown flow rate Q ^N, different magnetic flux density distributions BA and B
The outputs measured at B are defined as Va ^N and Vb ^N. (3) The ratio Vb ^N / Va ^N between Va ^N and Vb ^N is obtained, and V
The flow rate Qβ at which the ratio Vb / Va of a and Vb is equal to Vb ^N / Va ^N is obtained from the data of the above item (1), and from the value Vαβ of the item (1) at the flow rate Qβ, (1) The sensitivity Vαβ / Qβ under the condition of the flow rate Qβ in the term is calculated. (4) From the Va ^N measured in the above item (2) and the sensitivity Vαβ / Qβ obtained in the item (3), the unknown flow rate Q ^N is obtained from the following equation. ^{Q N = Va N · Qβ /} Vαβ

[0009]

However, according to the above-described method, different magnetic flux density distributions BA and BB are used.
In order to measure the electromotive force between the electrodes corresponding to the individual magnetic flux distributions, it takes twice as long to measure the data required for calculating the flow rate as a conventional electromagnetic flow meter. There is a problem that the response at the time of change becomes slow. Therefore, an object of the present invention is to make it possible to calculate the flow rate in a short time and not to reduce the responsiveness when the flow rate changes.

[0010]

In order to solve such a problem, according to the first aspect of the present invention, a pair is symmetrically mounted on one side and the other side sandwiching a vertical axis passing through the center of the measuring tube. An electromagnetic flowmeter comprising at least two pairs of electrodes and capable of measuring a volume flow rate when water is not full, wherein each electrode of the pair of electrodes has a pin shape, and each of the pair of electrodes is positioned at the center of a measurement tube. It is installed at the side position that is symmetrical with respect to the passing horizontal axis. According to the second aspect of the present invention, at least two pairs of electrodes are symmetrically mounted on one side and the other side of the vertical axis passing through the center of the measurement tube, respectively, so that the volume flow measurement when the water is not full can be measured. A possible electromagnetic flowmeter, wherein each electrode of the electrode pair is formed in a strip shape, and the measuring tube is arranged in a circumferential direction of the measuring tube from a position at a predetermined distance from an intersection with a vertical axis including the center of the measuring tube. Extending to a position beyond the point of intersection with the horizontal axis including the center of the measurement tube, each of the electrode pairs is positioned at a side position that is symmetrical with respect to the horizontal axis passing through the center of the measurement tube, and in the longitudinal direction, It is designed to be installed at different positions.

[0011] In the first or second aspect of the present invention,
When the potential difference generated between the two electrode pairs is substantially the same, the state is filled with water. In that case, the flow rate is determined based on the potential difference generated between any one of the electrode pairs, and when the potential difference generated between the two electrode pairs is different, a non-filled state is set. In the full state, the non-full rate is calculated based on the ratio of the potential difference generated between the two electrode pairs, and the correction value of the meter constant is calculated based on the non-full rate, and the potential difference generated between the two electrode pairs is determined. The volume flow rate can be determined using the meter constant to which the correction value is applied to the average value of at least one or both potential differences (invention of claim 3), or generated at the two electrode pairs. When the potential difference is substantially the same, the state is filled with water. In that case, the flow rate is calculated based on the potential difference generated in one of the electrode pairs.
If the potential difference generated between the two electrode pairs is different, it is set to a non-full state, and in that case, a correction value of a meter constant that has been calibrated in advance based on the ratio of the potential difference generated between the two electrode pairs is obtained,
The volume flow rate can be determined using a meter constant to which the correction value is applied with respect to at least one of the potential differences generated between the two electrode pairs or an average value of both potential differences (the invention of claim 4).

According to the present invention, a pair of left and right electrode pairs A and B are provided at a position where a plane at an equal distance above and below a reference plane including the measurement tube axis and perpendicular to a magnetic field and an inner wall of the measurement tube is in contact with each other. ,
The feature is that it is provided on each of the upper and lower surfaces. That is, the weight function for each electrode of this electrode pair (contribution ratio of electromotive force to each electrode: see JIS B7554) is shown in FIG.
As shown in FIG. This means the following when the flow is an axisymmetric flow. In addition, the code | symbol E of FIG. 8 shows an electrode. (A) Full state: In the full state, the entire area defined by the weight function is valid, and the potential difference generated between the electrode pairs A and B is the same. (B) Non-full state: In the non-full state, the upper part of the definition of the weight function becomes invalid, and the potential difference generated in the electrode pair A, B corresponds to the area difference of the invalid part of the weight function of the electrode pair A, B. Are different. Therefore, in the present invention, the non-full flow rate is determined by measuring the difference in the potential difference between the two electrode pairs A and B. FIGS. 8B and 8C show weight function distributions when the position of the electrode (E) is shifted upward and downward from the horizontal axis position including the measurement tube axis, respectively.

[0013]

FIG. 1 is a schematic diagram showing a first embodiment of the present invention. Here, the measuring pipe 10 and the upper and lower faces which are separated from each other by a certain distance vertically with respect to a horizontal plane passing through the pipe axis.
2, a pair of upper electrodes 10 each having a pin-like electrode shape.
3a and a pair of lower electrodes 103b are provided. That is, the pair of the upper electrode 103a and the lower electrode 103
The pair b is installed at substantially the same distance (symmetric) with respect to a horizontal axis (see a dashed line) including the center of the measuring tube 102.

FIG. 2 is a schematic diagram showing a second embodiment of the present invention. In the case of FIG. 1, the non-full flow rate can be measured only up to the position of the upper electrode 103a. Therefore, as shown in FIG. 2, the electrode shape is a rectangular shape having a predetermined size in the vertical and horizontal directions. Extending to a position beyond the intersection with the horizontal axis including the center of the tube (see the dashed line) (see the arrow in FIG. 2A), each electrode pair is moved with respect to the horizontal axis passing through the center of the measurement tube. As shown in FIG. 2 (b), they are placed at different side positions in a symmetrical side position and displaced in different positions in the longitudinal direction.

In other words, the pair of two electrode pairs 103a and 103b, which are one pair on the left and right, are symmetrical with respect to the horizontal axis including the tube axis of the measuring tube (at a certain distance),
The tubes are respectively displaced at different positions in the tube axis direction, and are disposed on one side surface (electrodes indicated by dotted lines in FIG. 2B). The electrodes installed on the electrodes (see electrodes in FIG. 2) are arranged so as to overlap each other when viewed from the axial direction of the measuring tube (see FIG. 2A).
In other words, basically, the detection limit is raised by enlarging the part of the electrode that is immersed in the fluid.

A method for obtaining an unknown flow rate from each potential difference between the upper and lower electrodes will be described with reference to FIG. That is,
When the water is full, the volume flow rate and the potential difference between the electrodes are uniquely determined. On the other hand, when the water volume is not full, the volume flow rate and the potential difference between the electrodes are unambiguously affected by the installation conditions (such as inclination) of the piping. Regardless of the relationship, the non-full rate is also required as a parameter. That is, in order to obtain the non-full flow rate, two parameters are required: the potential difference at each electrode and the ratio of the potential difference at each electrode. FIG. 3A shows the relationship between the potential difference Va, Vb at each electrode and the volume flow rate at a specific non-fullness rate, and FIG. The relationship between the potential difference Va and Vb in the case of a change, that is, the relationship between a constant corresponding to the non-full rate and a correction coefficient of the meter constant is shown.

Next, the potential difference between each pair of electrodes measured at an unknown volume flow rate is defined as Va ^N , Vb ^{N. In} FIG. 3C, the potential difference Vb / Va is the same as the ratio Vb ^N / Va ^{N of the} potential difference. Find the correction coefficient for the meter constant. Next, based on the potential difference Va ^N , a non-corrected volume flow rate of the meter constant is obtained in FIG.
Further, the final volume flow rate is obtained by applying the correction coefficient of the meter constant depending on the non-full level. At this time, obtains the non-full level ratio from the ratio Vb ^N / Va ^N of the potential difference each electrode pair, furthermore, may be obtained a correction coefficient of the meter constant.

FIG. 4 shows a configuration example of a conversion unit to which the present invention is applied. The timing generation circuit 112 divides the frequency of the commercial frequency signal from the power supply and sends out an excitation command signal. The excitation circuit 105 supplies a square wave current to the excitation coil 104 to excite the measurement tube 102. An electric charge is generated in a direction orthogonal to the magnetic field vector and the flow velocity vector of the fluid due to the excitation, and the electrode pair B (103)
A potential difference corresponding to the weight function, flow velocity distribution, and magnetic field distribution of each electrode pair corresponding to the water level is generated between the left and right electrodes in b). The potential difference signal between these electrodes is subjected to the following processing in the pre-processing circuit 120 at the next stage.

First, a potential difference signal between the electrodes is converted to a differential amplifier 1.
06a, 106b and a high-pass filter (HP
F) The low-frequency fluctuation component generated at the electrode interface is removed by the circuits 113a and 113b, and the analog / digital (A
/ D) The gains are switched by the gain setting circuits 114a and 114b so that the inputs of the converters 115a and 115b are at appropriate levels. This is subjected to A / D conversion at a frequency which is n times the excitation frequency from the timing generation circuit 112, and is input to a volume flow rate calculation circuit 121 comprising a processing unit at the next stage. In volumetric flow rate calculation circuit 121 calculates the ratio Vb ^N / Va ^N potentiometric both electrodes pairs electrode potential difference ratio calculating circuit 116, by referring to a correction coefficient meter constant by the correction factor reference circuit 117, also, the meter constant reference circuit The flow rate calculation circuit 119 calculates the volume flow rate with reference to the meter constant at 118.

[0020]

According to the present invention, two electrode pairs are provided, and the flow rate is corrected based on the difference in the potential difference generated between these electrode pairs. The measurement can be performed, and the measurement can be repeated at the same frequency as the conventional flow meter for filling with water. In addition, there is an advantage that the measurement can be performed with the same accuracy as the conventional one even in a full state.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a first embodiment of the present invention.

FIG. 2 is a sectional view showing a second embodiment of the present invention.

FIG. 3 is an explanatory diagram of a method of calculating a non-full water flow rate from a potential difference from an electrode.

FIG. 4 is a block diagram illustrating a configuration of a conversion unit to which the present invention is applied;

FIG. 5 is a block diagram showing a conventional example.

FIG. 6 is an operation explanatory diagram of FIG. 5;

FIG. 7 is an explanatory diagram of a non-full state.

FIG. 8 is an explanatory diagram of a weight function according to an electrode position.

[Description of References] 102: measuring tube, 103, 103a, 103b: electrode,
104: excitation coil, 105: excitation circuit, 106, 10
6a, 106b: Difference amplifier circuit, 112: Timing generation circuit, 113a, 113b: High-pass filter (HP
F) Circuit, 114a, 114b ... gain setting circuit, 11
5a, 115b: A / D conversion circuit, 116: electrode potential difference ratio calculation circuit, 117: correction coefficient reference circuit, 118: meter constant reference circuit, 119: flow rate calculation circuit, 120: preprocessing circuit, 121: volume flow rate calculation circuit .

Claims (4)

[Claims] At least two pairs of electrodes are symmetrically mounted on one side and the other side sandwiching a vertical axis passing through the center of a measuring tube, and are capable of measuring a volume flow when water is not full. An electromagnetic flowmeter, wherein each electrode shape of the electrode pair is a pin shape, and each of the electrode pairs is provided at a side position symmetrical with respect to a horizontal axis passing through the center of the measurement tube. Electromagnetic flow meter. 2. At least two pairs of electrodes are symmetrically mounted on one side and the other side of the vertical axis passing through the center of the measuring tube, and can measure the volume flow rate when water is not full. An electromagnetic flow meter, wherein each electrode shape of the electrode pair is a strip shape, and the center of the measurement tube is located at a predetermined distance from an intersection with a vertical axis including the center of the measurement tube in the circumferential direction of the measurement tube. Each electrode pair is extended to a position beyond the position of the intersection with the horizontal axis, and each electrode pair is located at a side position symmetrical with respect to the horizontal axis passing through the center of the measurement tube, and at positions different from each other in the length direction. An electromagnetic flowmeter characterized in that it is deviated from the center. 3. When the potential difference generated between the two electrode pairs is substantially the same, the state is filled with water. In that case, the flow rate is determined based on the potential difference generated at one of the electrode pairs, and the flow rate is generated at the two electrode pairs. When the potential difference is different, the non-full state is set. In this case, the non-full rate is calculated based on the ratio of the potential difference generated between the two electrode pairs, and the correction value of the meter constant is calculated based on the non-full rate. The volume flow rate is obtained using a meter constant to which the correction value is applied with respect to at least one of the potential differences generated in one electrode pair or an average value of both potential differences. Electromagnetic flowmeter as described. 4. When the potential difference generated between the two electrode pairs is substantially the same, the state is filled with water. In that case, the flow rate is determined based on the potential difference generated on one of the electrode pairs, and the flow is generated between the two electrode pairs. When the potential difference is different, it is set to a non-full state. In this case, a correction value of a meter constant that has been calibrated in advance is obtained based on the ratio of the potential difference generated between the two electrode pairs,
The volume flow rate is obtained using a meter constant to which the correction value is applied with respect to at least one of the potential differences generated in one electrode pair or an average value of both potential differences. Electromagnetic flowmeter as described.