JP2829158B2 - Deviation position detection method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring the position of a drift flowing in a pipe. The present invention also relates to an apparatus for determining a velocity distribution of a fluid flowing in a pipe.

[0002]

2. Description of the Related Art Generally, the flow velocity of a fluid flowing in a pipe is not uniform, but has a velocity distribution.
It often includes a portion where the flow velocity is as fast as about 30%. A flow including a flow velocity different from that of the other portions is called a drift.

[0003]

The drift has a great influence on the measured value of the flow rate by the flow meter. Therefore, a system that can easily measure the position, velocity, and the like of the drift is desired.
However, there has not been a measuring device for measuring a drift position or the like which satisfies this requirement or a device for obtaining a velocity distribution of a fluid.
SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method capable of measuring a position of a drift, a flow velocity, and the like with a simple configuration. Another object of the present invention is
An object of the present invention is to provide a method capable of measuring a velocity distribution of a fluid to be measured in a pipe with a simple configuration.

[0004]

In order to achieve the above object, a drift position detecting method according to the present invention comprises a measuring pipe through which a fluid to be measured passes, and a plurality of excitation coils for applying a magnetic field to the fluid to be measured. A plurality of electrodes for detecting a voltage induced by the magnetic field in the fluid to be measured, and means for determining a flow rate of the fluid to be measured corresponding to a signal from a selected one of the plurality of electrodes; A control circuit for switching on / off of a plurality of excitation coils or a selection state of the electrodes,

[0005] By switching the excitation state of the plurality of excitation coils or the selection state of the plurality of electrodes, the flow velocity in the section area in the pipe is obtained, and the position of the drift is identified by comparing the measured flow velocities. And

The flow velocity distribution measuring apparatus according to the present invention mainly applies a magnetic field to a measurement pipe through which a fluid to be measured passes and a flow rate in a specific area in the measurement pipe according to the law of electromagnetic induction. A flow rate measuring means for outputting a corresponding signal; and a means for switching the specific area, and by measuring the flow rate by switching the specific area, the velocity distribution of the fluid to be measured in the measurement pipe can be measured. It is characterized by the following.

[0007]

In the drift position detecting method having the above-described structure, the control circuit switches between the excitation state of the plurality of excitation coils and the selection state of the plurality of electrodes, so that the flow velocity in the divided region on the cross section of the measurement tube can be accurately measured. . Even if the measurement sensitivities of the respective divided areas are different, each is multiplied by a calibration coefficient, and the result of the multiplication corresponds to the flow rate of each of the divided areas. Calibration coefficients are obtained in numerical analysis and experimental tests. As an example of the actual flow test method, using an ideal flow without drift, switching the excitation coil and multiple electrodes, collecting data, setting the main calibration coefficient, and measuring the actual flow velocity distribution with a laser Doppler velocimeter Then, a correction coefficient is determined. By measuring the flow velocity in a plurality of regions on the cross section of the measurement pipe, the flow velocity distribution in the measurement pipe can be specified.

[0008]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing a method for measuring a drift position according to an embodiment of the present invention; FIG. 1 shows a sectional structure and a circuit structure of the drift position measuring device of this embodiment.

In FIG. 1, an excitation coil 15 with a yoke for applying a magnetic field to a fluid to be measured is provided on a measurement tube 11.
a and 15b are arranged. Exciting coils 15a, 15
b can be excited independently, and applies a square-wave magnetic field to the fluid to be measured by, for example, a square-wave excitation current supplied from the excitation circuit 19. Exciting coils 15a, 1
5b is configured so that its characteristics are substantially the same. As shown, the excitation coils 15a, 1
A line connecting 5b is defined as a y-axis, and an axis orthogonal to the y-axis is defined as an x-axis.

Two pairs of measuring electrodes 13a and 13b and 13c and 13d are arranged at positions of the measuring tube 11 rotated substantially 45 degrees from the y and x axes. The measurement electrodes 13a to 13d measure the electromotive force induced in the fluid to be measured according to Faraday's law of electromagnetic induction.

The signal (induced electromotive force) detected by the electrode pair 13a, 13b is output to the evaluation circuit 17 via the amplifier AM1. Similarly, signals detected by the electrode pairs 13c and 13d are output to the evaluation circuit 17 via the amplifier AM2. The evaluation circuit 17 measures the flow rate of the fluid to be measured based on the supplied signal. Amplifier AMP1 and amplifier AMP
2 have substantially the same properties. The evaluation circuit 17 has the same configuration as the evaluation circuit used in an electromagnetic flow meter or the like.

For example, when the excitation current is a square wave, the evaluation circuit 17 inputs a timing signal for switching the polarity of the excitation signal from the excitation circuit 19, and outputs the signal to the amplifier AMP1 or AM.
The most stable portion (the signal level immediately before the polarity inversion) of the output signal (square wave detection signal) of P2 is sampled. The evaluation circuit 17 converts the sampled value into a flow velocity signal having a DC signal level corresponding to the flow velocity of the fluid to be measured and outputs it.

The controller 21 supplies a control signal to the excitation circuit 19 and switches the supply of the excitation current to the excitation coils 15a and 15b. That is, the controller 21 switches between a state in which both the excitation coils 15a and 15b are excited, a state in which only the excitation coil 15a is excited, a state in which only the excitation coil 15b is excited, and the like.

The controller 21 includes amplifiers AMP1 and AM
A control signal is supplied to P2, and each is operated or
Set to a non-operation state (the output is in a floating state or a ground state).

With the above configuration, for example, when the exciting coils 15a and / or 15b are excited (turned on) in a state where there is no drift, and the amplifiers AMP1 and AMP2 are both operated, the outputs of the amplifiers AMP1 and AMP2 are output. The signal levels of the signals almost coincide. The controller 21
, The measurement area on the cross section of the measurement tube 11 changes as described later using the weight function.
Next, the operation of the circuit shown in FIG. 1 will be described. The controller 21 controls the excitation circuit 19 to control the amplifiers AMP1 and AMP2 to generate the following four states in a time-sharing manner. (1) Excitation the excitation coil 15a and the excitation coil 15b
Is turned off, the amplifier AM1 is turned on, and the amplifier AM2 is turned off. (2) Excitation the excitation coil 15a and the excitation coil 15b
Is turned off, the amplifier AM1 is turned off, and the amplifier AM2 is turned on. (3) Turn off the exciting coil 15a and turn off the exciting coil 11b.
, And the amplifier AM1 is turned on and the amplifier AM2 is turned off. (4) Turn off the exciting coil 15a and turn off the exciting coil 11b.
Is excited, the amplifier AM1 is turned off, and the amplifier AM2 is turned on.

In the state (1), that is, when only the exciting coil 15a is excited and the amplifier AMP1 is on, the magnetic field distribution in the measuring tube is as shown in FIG. , Such as strong at the top of the drawing and weak at the bottom of the drawing. The electrodes for measuring the induced electromotive force are 13a and 13b. For this reason, the measuring tube 11
1 is divided into four quadrants as shown in FIG. 1, the influence of the flow velocity of the fluid flowing in the first quadrant appears strongly in the flow velocity signal output from the evaluation circuit 17. This is illustrated in FIG. 3A using a weight function. In FIG. 3A, W1 to W6 indicate the degree of the influence of the flow velocity of the fluid at that position on the output of the amplifier AMP1, and W1 sequentially decreases most greatly.

In the state (2), that is, when only the exciting coil 15a is excited and the amplifier AMP2 is turned on, FIG.
As can be understood from the distribution of the weight function, the influence of the flow velocity of the fluid flowing in the second quadrant appears strongly in the flow velocity signal.

In the state (3), that is, when only the exciting coil 15b is excited and the amplifier AMP1 is turned on, the magnetic field distribution in the measuring tube is opposite to that shown in FIG. Is strong at the bottom of the drawing and weak at the top of the drawing. Therefore, as can be understood from the distribution of the weight function in FIG. 3C, the influence of the flow velocity of the fluid flowing in the third quadrant appears strongly in the flow velocity signal.

In the state (4), that is, when only the exciting coil 15b is excited and the amplifier AMP2 is turned on, FIG.
As can be understood from the distribution of the weight function, the influence of the flow velocity of the fluid flowing in the fourth quadrant appears strongly in the flow velocity signal.

Therefore, the flow velocity distribution and the position of the drift can be specified by measuring the above four patterns for the actual fluid to be measured and comparing the measurement results. For example, when only the flow velocity in the first quadrant is measured quickly, it can be seen that there is a drift in the first quadrant. Also, for example, when the flow velocity in the first and second quadrants is faster than the flow velocity in the third and fourth quadrants, it can be seen that there is a drift between the first and second quadrants. In this way, the position of the flow velocity distribution and the drift can be specified. From the comparison of the flow velocities, an approximate value of the drift velocity can be known.

In the above description, the states (1) to (4) are individually generated. However, for example, each of the amplifiers AMP1 and AMP2 may be provided with an evaluation circuit,
7 can be operated in a time-sharing manner, if both the amplifiers AMP1 and AMP2 are turned on while the exciting coil 15a is energized, the flow velocity signal at the time of (1) and the flow velocity at the time of (2) Signals can be obtained simultaneously. Similarly, while the excitation coil 15b is being excited, the amplifiers AMP1 and AM
If both P2 are turned on, the flow velocity signal at the time of (3) and the flow velocity signal at the time of (4) can be obtained simultaneously.

In order to more accurately measure the position of the drift, the exciting coils 15a and 15b are simultaneously excited, and the flow velocity (ie, the flow rate determined by the outputs of the electrode pairs 13a and 13b) is obtained.
The flow rate determined by the output of the amplifier AMP1 and the flow rate determined by the output of the electrode pairs 13c and 13d (ie,
The flow rate determined by the output of the amplifier AMP2) may be compared. Exciting the exciting coils 15a and 15b simultaneously,
FIG. 4A shows the distribution of the weight function when the induced electromotive force is measured by the electrode pairs 13a and 13b. In addition, the exciting coils 15a and 15b are simultaneously excited, and the electrode pairs 13c and 1c are excited.
FIG. 4B shows the distribution of the weight function when the induced electromotive force is measured by 3d.

For example, if there is a drift in the first quadrant, the flow velocity determined by the outputs of the electrode pairs 13a and 13b increases, and the flow velocity determined by the outputs of the electrode pairs 13c and 13d decreases. On the other hand, when there is a drift on the X axis or the Y axis, there is no large difference between the two flow velocity signals.

In the above description, an example in which a square-wave current is used as the exciting current has been described. However, even when a sine-wave-like exciting current is used, if the configuration of the evaluation circuit is changed accordingly, it is left as it is. Can be applied. The configuration of the evaluation circuit itself is well known in the field of electromagnetic current meters and the like.
Here, further description is omitted. Next, a second embodiment of the present invention will be described with reference to FIG. In FIG. 4, the same portions as those in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted. In the second embodiment, as shown in FIG. 5, an example is shown in which an electromagnetic flowmeter using three pairs of electrodes 23a to 23f is used as it is as a drift position measuring device. In FIG.
The main electrode pairs 23a and 23b are arranged on the X axis, and the auxiliary electrode pairs 23c and 23d and 23e and 23f are arranged at positions shifted from the X axis by an angle ψ.

The signals detected by the main electrode pairs 23a and 23b are supplied to a flow measurement circuit 25 via an amplifier AM1.
The signal detected by the auxiliary electrode pair 23c and 23d is the amplifier A
The signal supplied to the flow measurement circuit 25 via M2 and the signals detected by the auxiliary electrode pairs 23e and 23f are supplied to the flow measurement circuit 25 via the amplifier AM3. Amplifiers AM1 to AM
The amplification factor of No. 3 is adjusted so that the levels of the respective output signals match in a state where there is no drift.

The signals detected by the auxiliary electrodes 23c and 23f are supplied to an evaluation circuit 27 via an amplifier AM4, and the signals detected by the auxiliary electrode pairs 23d and 23e are supplied to an amplifier AM5.
Is supplied to the evaluation circuit 27 via Amplifier AM4 and A
The amplification factor of M5 is adjusted so that the signal level of the output signal matches when there is no drift.

In a normal operation state, both the exciting coils 15a and 15b are excited, and the flow rate measuring circuit 25 outputs a flow rate (flow rate) signal based on the output signals of the three pairs of electrodes 23a to 23f. On the other hand, when measuring the position of the drift or the flow velocity distribution, one of the exciting coils 15a and 15b is excited, the outputs of the amplifiers AM4 and AM5 are compared, and the position of the drift is measured as in the first embodiment. Alternatively, the flow velocity distribution is measured.

In the first and second embodiments, two exciting coils are used.
The exciting coils may be individually excited using the above exciting coils, and the position of the drift may be specified from the detected value of the electrode pair at that time. In addition, the present invention can be similarly implemented when using capacitance type electrodes 33a to 33d as shown in FIG.

As the measuring tube 11, a non-magnetic and electrically insulating pipe, for example, a pipe made of ceramics, reinforced plastics or the like may be used, or a non-magnetic conductive pipe, for example, SUS316 stainless steel pipe A pipe whose inner surface is lined with an electrically insulating substance such as plastic or rubber may be used.

[0030]

As described above, according to the present invention, the presence or absence of a drift and the position of the drift can be easily measured based on the principle of electromagnetic induction.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a drift position measuring device according to a first embodiment of the present invention.

FIG. 2 is a diagram showing an example of a magnetic flux distribution when only one of the exciting coils of the drift position measuring device shown in FIG. 1 is excited.

FIG. 3 is a diagram showing a distribution of a weight function when one excitation coil is excited.

FIG. 4 is a diagram showing a distribution of weighting functions when two exciting coils are excited.

FIG. 5 is a configuration diagram for explaining an example in which an electromagnetic flowmeter using three electrode pairs is used with a drift position measuring device.

FIG. 6 is a configuration diagram for explaining an embodiment using an electrostatic electrode.

[Explanation of symbols]

11: measuring tube, 13a to 13d: electrode, 15a, 15b
... Exciting coil, 17, 27 ... Evaluation circuit, 19 ... Exciting circuit, 21 ... Controller, AMP1, AMP2, AM1
ＡＭAM5: amplifier, 25: flow measurement circuit.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G01F 1/58

Claims (4)

(57) [Claims] 1. A measurement tube through which a fluid to be measured passes, a plurality of excitation coils for applying a magnetic field to the fluid to be measured, and a plurality of electrodes for detecting a voltage induced in the fluid to be measured by the magnetic field. Means for determining a flow rate of the fluid to be measured corresponding to a signal from a selected one of the plurality of electrodes, and a control circuit for switching on / off the plurality of excitation coils or selecting a state of the electrodes, A drift position detection method characterized in that a flow velocity is obtained by switching an excitation state of the plurality of excitation coils or a selection state of the plurality of electrodes, and a position of the drift is identified by comparing the measured plurality of flow rates. 2. The control circuit according to claim 1, wherein the control circuit switches between an excitation state of the excitation coil and a selection state of the electrodes so that a signal corresponding to a flow velocity of a fluid flowing in an arbitrary region on a cross section of the measurement tube becomes strong. The drift position detection method according to claim 1, wherein 3. A measuring pipe through which a fluid to be measured passes, and a flow velocity measuring means for applying a magnetic field to the fluid to be measured and outputting a signal mainly corresponding to a flow velocity in a specific area in the measuring pipe in accordance with the law of electromagnetic induction. And a means for switching the specific area, wherein a velocity distribution of the fluid to be measured in the measurement pipe can be measured by measuring the flow velocity by switching the specific area. . 4. A velocity distribution measuring device comprising: a plurality of excitation coils for applying a magnetic field to a fluid to be measured; a plurality of electrodes for detecting a voltage induced in the fluid to be measured by the magnetic field; A circuit for determining a flow rate corresponding to a signal from the electrode, wherein the switching means switches an excitation state of the excitation coil or selection of the electrode so as to change sensitivity to a flow rate on a cross section of the measurement tube. The velocity distribution measuring device according to claim 3, further comprising: