JPH09101321A - Flow velocity measuring method and measuring apparatus therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a flow velocity measuring method and a measuring apparatus therefor which enables highly accurate measurement of the flow velocity by eliminating effect of a metal body in the perimeter of a magnetic sensor head. SOLUTION: An AC magnetic field is excited to a moving conductive object to be measured to detect magnetic field components thereof and the from velocity of the object to be measured is measured flow a magnetic field signal detected. In addition, a magnetic sensor head 100 is provided with exciting windings 102a and 102b and detection windings 103, 104/105 and 106 for detecting magnetic fields arranged vertically at different positions, a subtraction circuit 115 to determine a difference signal of the pair of detection windings 103 and 104, a subtraction circuit 116 to determine a difference signal of a pair of the detection windings 105 and 106, an addition circuit 117 to add output of the subtraction circuit 115 to output of the subtraction circuit 116 and a detection circuit 120 to determine the flow velocity of the object to be measured from an output of the addition circuit 117.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flow velocity measuring method and a measuring apparatus for measuring the flow velocity on the surface of a molten steel flow in a mold into which molten steel is cast in a continuous casting process.

[0002]

2. Description of the Related Art In a continuous casting line, molten steel 3 is poured from a tundish 1 through a nozzle 2 into a copper mold 4 for casting as shown in FIG. Mold 4
The molten steel 3 poured into the mold hits the wall surface of the mold and rises 7
And downflow 8. Upflow flows on the surface 9a, 9
Although b is created, if the left-right balance of the molten steel flow on the surface is lost here, a vortex 11 is generated as shown in the figure, and the powder 5 sprinkled on the molten steel surface is entrained. Further, when the molten steel flow on the surface becomes excessive, a part 10 of the powder on the molten steel surface is scraped as shown in the figure.

In any case, inclusions are trapped in the slab, causing product defects. For these reasons, stabilizing the molten steel flow in the mold has become an extremely important issue, and in particular, continuous measurement of the flow velocity near the surface of the molten steel has been strongly demanded.

The conventional measurement of the flow velocity near the surface of molten steel has mainly been a contact type measurement as described in, for example, JP-A-5-60774. In this, as shown in FIG. 10, a fine ceramic rod 12 is immersed in molten steel 14 and the pressure F received by the molten steel flow is detected by a pressure sensor 13 to measure the flow velocity. .
However, according to this method, the ceramic rod 12 is immersed in the high temperature molten steel 14, so that continuous measurement for a long time is impossible.

On the other hand, it is also known that the velocity of a fluid can be measured in a non-contact manner using magnetism. For example, there is a method of measuring the flow velocity of an object to be measured using a magnetic sensor head 200 as shown in FIG. In the figure, a magnetic sensor head 200 is a symmetrical U-shaped magnetic core 202.
On the other hand, the excitation winding 203b is wound around the center portion between the two legs which is parallel to the target surface, and the detection windings 203a and 203c are respectively attached to the leg portions which are perpendicular to the target surfaces at both ends. It is constructed by winding in the same direction. Then, the conductive measurement object 201 moving in the U-shaped magnetic core 202
Is placed on the top of the two so that the open surface of the leg faces the target surface and the two legs are aligned in parallel to the moving direction of the target surface. Since the direction of the flow velocity is often known in advance, the two legs of the U-shaped magnetic core 202 are arranged in parallel with the direction of the flow velocity.

Here, an alternating current is supplied to the central excitation winding 203b to excite a magnetic field perpendicular to the conductor surface. At this time,
When the conductor 201 is stopped, the U-shaped magnetic core 202 has a symmetrical shape, so that the exciting magnetic fields are equal in magnitude and opposite in direction at the positions of the left and right detection windings 203a and 203, The sum of the outputs of the detection windings 203a and 203c is 0. Also, when the conductor moves, the magnetic field is distorted by the eddy current generated in the conductor corresponding to the flow velocity, and the vertical component of the magnetic flux at the positions of the detection windings 203a and 203c at both ends of the U-shaped magnetic core 202 becomes different. Each detection winding 203
The sum signal of a and 203c changes. This change amount corresponds to the flow velocity of the target, and the flow velocity of the target can be measured from this change amount.

[0007]

By the way, in this type of flow velocity measurement, the magnetic sensor head 200 is placed in a mold for measurement. As shown in FIG. 12, when the magnetic sensor head 200 is placed in the mold, a metal body such as the copper mold 4 exists in the vicinity thereof. Therefore, the magnetic field is distorted due to the influence of the metal body, and the magnetic sensor head 200
Output is affected. It should be noted that FIG. 12 is a cross-sectional view of the copper mold viewed from the short side direction.

As shown in FIG. 13A, when the magnetic sensor head 200 and the metal body 210 are arranged in parallel, the metal body 2 is attached to the detection windings 203a and 203c.
10 is symmetrical, and the detection windings 203a and 203c
When the outputs of the two coincide with each other and the signal processing is performed based on the difference, the influence of the metal body 210 is not exerted. However, as shown in FIG. 13B, the magnetic sensor head 200
When the magnetic sensor head 200 and the metal body 21
When 0 is no longer parallel, the detection windings 203a and 203c
The metal body 210 is asymmetrical with respect to the detection winding 203.
a and 203c are different in output, and the magnetic sensor head 20
The zero point of 0 shifts and accurate measurement cannot be performed.

The present invention has been made in order to solve such a problem, and eliminates the influence of the metal body around the magnetic sensor head and makes it possible to measure the flow velocity with high accuracy. It is an object to provide a measuring method and a measuring device therefor.

[0010]

A flow velocity measuring method according to one aspect of the present invention detects a magnetic field component by exciting an alternating magnetic field with respect to a moving conductive object to be measured. In the method of measuring the flow velocity of a measuring object based on a magnetic field signal, it is possible to measure the flow velocity of the object different in the direction perpendicular to the object surface
The magnetic field component at the location is detected, the differential signal between the two magnetic field signals in the vertical direction is determined, and the flow velocity of the measurement target is determined based on the differential signal. A flow velocity measuring method according to another aspect of the present invention is to excite an alternating magnetic field on a moving conductive measurement object, detect a magnetic field component thereof, and based on the detected magnetic field signal, the measurement object. In the method of measuring the flow velocity of, the magnetic field components at two different locations in the vertical direction with respect to the target surface are respectively detected at two locations on the target surface, and differential signals of the two magnetic field signals in the vertical direction are respectively obtained. , The difference signal is added to obtain the flow velocity of the measurement object.

A flow velocity measuring device according to another aspect of the present invention is
An alternating magnetic field is excited with respect to a moving conductive measurement object, the magnetic field component is detected, and based on the detected magnetic field signal, a device for measuring the flow velocity of the measurement object,
Exciting device, first pair of detectors for detecting magnetic fields at different positions in the vertical direction, and magnetic field at different positions in the vertical direction, arranged at positions different from the first pair of detectors And a magnetic sensor head having a second pair of detection devices, a first subtraction circuit that obtains a difference signal between the first pair of detection devices, and a difference signal between a second pair of detection devices. Second
Of the first subtraction circuit, an addition circuit for adding the output of the first subtraction circuit and the output of the second subtraction circuit, and a detection circuit for obtaining the flow velocity of the measurement object based on the output of the addition circuit.

[0012] For example, in the measurement in the mold, it is a copper mold that has a large influence, and this is symmetric in the direction perpendicular to the target surface. Therefore, as described above, even if the magnetic sensor head is tilted with respect to the copper mold, the copper mold is symmetrical with respect to the upper and lower detection points, and if the difference between the upper and lower detection devices is taken at the time of detection, the effect is Disappear.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Next, the measurement principle of the present invention will be described in terms of the basic configuration, the flow velocity detection principle, and the influence of the surrounding metal body. (A) Basic Configuration In the present invention, the magnetic sensor head 100 has the configuration shown in FIG. 2 or 3. In FIG. 2, the magnetic sensor head 100 has a U-shaped ceramic bobbin 101 having a symmetrical shape, and the detection windings 103 and 105 are arranged in the same direction on the leg portions which are perpendicular to the target surface at both ends. Further, the detection windings 104 and 106 are wound on the detection windings 103 and 105, and the excitation winding 102 is wound on the detection windings 104 and 106.
a and 102b are wound. Further, in FIG. 2, the excitation windings 102a and 102b are connected to the detection winding 104.
1 and 103 and between the detection windings 106 and 105, respectively, and the structure of the detection winding is the same as that in FIG. In the present invention, the detection winding 1
It is characterized in that the difference between 03 and 104 and the difference between the detection windings 105 and 106 are obtained.

In the present invention, the exciting windings 102a, 1a
An alternating current is supplied to 02b to generate a symmetric vertical magnetic field,
Then, as shown in FIG. 4, the conductor 15 is subjected to a uniform magnetic field.
When E moves, a velocity electromotive force of E = v × B is generated in the conductor, and this velocity electromotive force induces an eddy current Jv in the conductor, and an induced magnetic field Bv is generated on the conductor 15. The magnetic field is distorted from B to B ′ so that it is dragged in the velocity direction of the conductor.
This is called the velocity effect of the magnetic field), and the degree of this strain changes according to the velocity of the conductor. Therefore, the velocity of the target conductor can be measured by measuring the amount of strain. That is, in the present invention, this induction magnetic field is detected by the detection windings 103 to 106, and a signal having the same frequency component as the exciting magnetic field is extracted by the phase detector or the like to obtain the flow velocity. At that time, as shown in FIG. 2 or FIG. 3, four detection windings are provided on the upper, lower, left and right sides, and the difference between the upper and lower sides of each of the two pairs of right and left is obtained (103-104, 105-106),
The flow velocity is detected by eliminating the influence of the surrounding metal body and obtaining the sum of the left and right detection windings.

(B) Principle of Flow Velocity Detection The induced magnetic field Bv is derived from the induced current represented by jv = σv × B. When the distance from this induced current, that is, the distance from the target surface becomes large, As shown in 5, the induced magnetic field becomes small. Therefore, when the difference between the upper and lower detection windings is taken, the electromotive force with respect to the speed becomes larger in the detection winding closer to the object to be measured, and even if the difference is taken, the signal with respect to the speed remains. In addition, the excitation magnetic field is opposite in the left and right,
Since the magnetic fields with respect to the velocity are in the same direction, if the sum of the left and right is taken, the component of the exciting magnetic field disappears and only the signal with respect to the velocity can be accurately detected.

(C) Influence of surrounding metal body Even if the magnetic sensor head 100 is tilted so that either one of the detection windings on the left and right becomes closer to the metal body, if the difference between the upper and lower detection windings is obtained, the metal body is detected. Since the effect of proximity is equal in the upper and lower detection windings, the effect is eliminated. FIG. 6 is a diagram showing the state at that time, FIG. 6A is a diagram as seen from the side, and FIG. 6B is a diagram as seen from above. Detection windings 103, 104 on the left side and detection windings 105 on the right side,
Even if the distance is different from the metal body 210 with respect to 106, the influence on the distance l1 (= 12) is eliminated by taking the difference between the detection windings 103 and 104, and the detection windings 105 and 106 have different distances. By taking the difference, the distance l3
The effect on (= 14) is eliminated. That is, the difference between the detection windings 103 and 104 and the difference between the detection windings 105 and 106 are information excluding the factor of the distance from the metal body.

Now that the measurement principle of the present invention has been clarified, an example of the embodiment of the present invention will be described. FIG.
FIG. 1 is a block diagram showing a configuration of a flow velocity measuring device according to an example of an embodiment of the present invention. This flow velocity measuring device includes a magnetic sensor head 100, an exciting circuit 110, subtractors 115, 1
16, an adder 117, and a detection circuit 120. The excitation circuit 110 is composed of an oscillator 111 and a constant current amplifier 112, and has excitation windings 102a and 102.
An exciting current is supplied to b to excite the magnetic field on the object to be measured.
Here, a sine wave of 1 to 100 Hz is generated by the oscillator 111, and the excitation winding 1 is passed through the constant current amplifier 112.
An exciting current is supplied to 02a and 102b.

Here, if the excitation frequency is too high (about 1 kHz or more), the eddy current generated in the object to be measured becomes large, and the property of the eddy current rangefinder becomes stronger than that of the anemometer, and the undulation of the object surface is caused. The noise becomes stronger. Further, if the frequency is too low (about 1 Hz or less), the electromotive force generated in the detection windings 103 to 106 becomes weak and the detection sensitivity is lowered. Therefore, the excitation frequency is set to 14 Hz here.

Output of detection winding 103 and detection winding 104
Of the output of the detection winding 105, the difference between the output of the detection winding 105 and the output of the detection winding 106 is calculated in the subtractor 116, and the difference between the left and right detection windings is obtained. Are added in the adder 117, and the addition result is input to the detection circuit 120.
In the detection circuit 120, an unnecessary noise signal is removed from the input signal through a bandpass filter 121 having an excitation frequency as a center frequency, and a phase detector 122 detects a component having a phase shifted by −90 degrees from the excitation current. The magnitude of the signal after this detection becomes a magnetic field distortion signal corresponding to the flow velocity.

FIG. 7 is a characteristic diagram showing the results of measuring the flow velocity of the low melting point alloy. It can be seen that the output signal (velocity signal) is detected with high accuracy as shown in (b) of the figure with respect to the actual flow velocity of (a) of the figure. It should be noted that the characteristic shown in FIG. 7B is the characteristic in the state where no metal body is present around the magnetic sensor head 100.

FIG. 8A shows a state in which the magnetic sensor head 100 is inclined with respect to the copper plate 130 by an inclination angle θ, and FIG. 8B shows a change in the inclination angle θ and the output signal at that time. It is a characteristic view showing the relationship of. In this characteristic diagram, since the conventional type and the present system have different sensitivities to the flow velocity, the values converted into the flow velocity with respect to the low melting point alloy are shown instead of the output voltage. As is clear from FIG. 7B, according to this method, even if the inclination angle θ changes greatly, the output signal changes little.

In the above description, an example in which the air-core U-shaped (U-shaped) magnetic sensor head is used has been described, but the air-core E-shaped magnetic head may be used in the present invention.

[0023]

As described above, according to the present invention, the magnetic field components at two different positions in the vertical direction with respect to the target surface are respectively detected, and the differential signals of the two magnetic field signals in the vertical direction are obtained, Since the flow velocity of the measurement object is obtained based on the difference signal, even if the relative position to the surrounding metal body changes, the flow velocity can be measured accurately without being affected by the change.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a circuit configuration of a flow velocity measuring device according to an example of an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a configuration of an example of a magnetic sensor head of the present invention.

FIG. 3 is an explanatory diagram showing another configuration of the magnetic sensor head of the present invention.

FIG. 4 is an explanatory diagram for explaining a velocity effect of a magnetic field in the present invention.

FIG. 5 is an explanatory diagram showing a relationship between an induction magnetic field and a detection position in a vertical direction.

FIG. 6 is an explanatory diagram of relative positions of a magnetic sensor head of the present invention and a surrounding metal body.

FIG. 7 is a characteristic diagram showing the results of measuring the flow velocity of a low melting point alloy.

FIG. 8 is a characteristic diagram showing a state when the magnetic sensor head is tilted with respect to the copper plate, and a relationship between a tilt angle θ and a change in an output signal at that time.

FIG. 9 is an explanatory diagram for explaining continuous casting.

FIG. 10 is an explanatory diagram for explaining a conventional contact-type flow velocity measuring method for high-temperature liquid metal.

FIG. 11 is an explanatory view for explaining a conventional non-contact type high-temperature liquid metal flow velocity measuring method.

FIG. 12 is an explanation without showing a state in which the magnetic sensor head is arranged in a copper mold.

FIG. 13 is an explanatory diagram of a relative position between a conventional magnetic sensor head and a surrounding metal body.

Claims (3)

[Claims] 1. A method of exciting an alternating magnetic field to a moving conductive measurement object, detecting the magnetic field component, and measuring the flow velocity of the measurement object based on the detected magnetic field signal, Characteristic of detecting magnetic field components at two different locations in the vertical direction with respect to the target surface, obtaining the difference signal between the two magnetic field signals in the vertical direction, and obtaining the flow velocity of the measurement object based on the difference signal Measuring method of flow velocity. 2. A method of exciting an alternating magnetic field to a moving conductive measurement object, detecting the magnetic field component, and measuring the flow velocity of the measurement object based on the detected magnetic field signal, At two locations on the target surface, the magnetic field components at two different locations in the vertical direction with respect to the target surface are respectively detected, the difference signals of the two magnetic field signals in the vertical direction are respectively obtained, and the difference signals are added. A flow velocity measuring method, characterized in that the flow velocity of an object to be measured is obtained by. 3. An apparatus for exciting a moving conductive measurement object with an alternating magnetic field, detecting the magnetic field component, and measuring the flow velocity of the measurement object based on the detected magnetic field signal, Exciting device, first pair of detecting devices for detecting magnetic fields at different positions in the vertical direction, and magnetic field at different positions in the vertical direction, which are arranged at different positions from the first pair of detecting devices. Of a magnetic sensor head having a second pair of detection devices for detecting a difference, a first subtraction circuit for obtaining a difference signal between the first pair of detection devices, and a second pair of detection devices A second subtraction circuit that obtains a difference signal, an addition circuit that adds the output of the first subtraction circuit and the output of the second subtraction circuit, and the flow velocity of the measurement object based on the output of the addition circuit. A flow velocity measuring device, comprising: a detection circuit required.