JPH09101320A - Flow velocity measuring method and measuring apparatus therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To cancel effect of changes in distance and waving by a method wherein a magnetic field with more than one frequency signals overlapped is excited to a moving conductive object to be measured and magnetic field components corresponding to the respective frequency components are detected to measure the flow velocity of the object to be measured based on a signal thereof. SOLUTION: At an exciting circuit 110, signals involving two frequencies f1 and f2 from oscillators 111 and 112 are overlapped each other by an adder 113 and supplied as exciting current to an exciting winding 102 of a magnetic sensor head 100 through a power amplifier 114. A detection circuit 120 finds a flow velocity signal through a bandpass filter 121 and a phase detector 122 from a differential signal of outputs of two detection windings 103 and 104. A waving correction circuit 125 multiplies a high frequency difference signal, obtained through a bandpass filter 126 and a phase detector 127 from a differential signal of outputs of the detection windings 103 and 104, by a coefficient with an amplifier 128 to find a waving correction signal and the results are subtracted from a flow rate signal detected by the detection circuit 120 by an arithmetic device 129 to cancel.

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 poured inside hits the wall surface of the mold and is divided into an upflow 7 and a downflow 8. Upflow flows on the surface 9a, 9b
However, if the left-right balance of the molten steel flow on the surface is lost, a vortex 11 is generated as shown in the drawing, 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. 9, 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, in this method, since the ceramic rod 12 is immersed in high temperature molten steel, 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. This is shown in FIG.
When the conductor 15 moves in a uniform magnetic field as shown in FIG. 1, 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, so that the conductor 1
An induced magnetic field Bv is generated on the magnetic field 5, and the original magnetic field is distorted from B to B ′ so as to be dragged in the velocity direction of the conductor.
The effect of the magnetic field being distorted by the motion of the conductor (hereinafter referred to as the velocity effect of the magnetic field) is used. The degree of this distortion changes according to the speed of the conductor. Can be measured.

[0006] As an apparatus for non-contact measurement of velocity using such magnetism, there is one described in Japanese Patent Application Laid-Open No. 2-311766. As shown in FIG. 11 (a), an alternating current is supplied to a primary coil 19 arranged in parallel with the flow of molten steel 18 to apply an alternating magnetic field 17 parallel to the molten steel surface to the molten steel surface. Two secondary coils 20a and 20b are arranged on both sides in the horizontal direction. The secondary coils 20a and 20b detect a magnetic field parallel to the target surface.

The detection operation by the secondary coils 20a and 20b is as shown in FIG. 11 when the conductor is stationary.
As shown in (a), the magnetic field is a target across the primary coil 19, and there is no difference in electromotive force between the two secondary coils 20a and 20b, and the output is zero. When the conductor is moving, the magnetic field is distorted in the velocity direction of the conductor due to the velocity effect of the magnetic field, as shown in FIG.
Since there is no symmetry with 9 in between, two secondary coils 20
a, a difference in the electromotive force generated in 20b, the amount of distortion of the magnetic field,
That is, a signal corresponding to the speed is obtained as the difference between the output voltages of the two secondary coils. Then, the secondary coil 20a,
The speed of the conductor is calculated based on the difference in the output voltage of 20b.

Further, in the non-contact method of measuring velocity using magnetism, the velocity sensitivity changes depending on the distance between the device and the object to be measured. For example, in Japanese Patent Laid-Open No. 4-89573, the device and object to be measured are measured. The distance between and was measured by the output voltage of one of the secondary coils for detecting the magnetic field parallel to the target surface, and correction was performed.

[0009]

However, the conventional non-contact velocity measuring method using magnetism has the following problems. 1) In the method of measuring the output voltage of one side of the secondary coil that detects the magnetic field parallel to the surface to be measured and correcting the speed sensitivity change depending on the distance, the distance detection sensitivity is not sufficient and the corrected flow velocity detection The accuracy is also poor. That is, it is necessary to increase the frequency in order to increase the distance detection accuracy, but it is necessary to decrease the frequency in order to increase the flow velocity signal. 2) Further, in the AC excitation, an eddy current of −dB / dt is generated on the surface to be measured, and the magnetic field due to the eddy current is also detected by the detection winding. As shown in FIG. 12A, when the surfaces to be measured are parallel to each other, the electromotive forces of the two detection windings are equal to each other, and the electromotive force becomes 0 by taking the difference. However, FIG.
As shown in 2 (b), if there is a wave on the surface to be measured,
Since there is a difference in the distance from the measurement target surface between the two detection windings,
Even if the difference is taken, it does not become 0, and the signal changes.

The present invention has been made in order to solve such a problem, and it is possible to accurately measure the flow velocity of a measuring object even if the distance changes or there is a wave. An object of the present invention is to provide a method and a measuring device therefor.

[0011]

A flow velocity measuring method according to one aspect of the present invention includes a step of exciting a magnetic field in which two or more frequency signals are superimposed on a moving conductive object to be measured, and Of detecting the magnetic field component corresponding to the frequency component of, and measuring the flow velocity of the measurement object based on the detected signal of each magnetic field component. A flow velocity measuring method according to another aspect of the present invention includes a step of exciting a magnetic field in which two frequency signals composed of a low frequency and a high frequency are superimposed on a moving conductive measurement target object,
The step of detecting the magnetic field component corresponding to each frequency component, the step of measuring the flow velocity of the measuring object based on the signal of the magnetic field component corresponding to the low frequency signal, and the signal of the magnetic field component corresponding to the high frequency signal The step of obtaining the ripple correction signal based on, and subtracting the ripple correction signal from the flow velocity of the measurement target to obtain the flow velocity after the ripple correction, and the distance to the measurement target based on the signal of the magnetic field component corresponding to the high frequency signal. And a step of correcting the flow velocity after ripple correction by the distance and obtaining the flow velocity after correction by the distance.

A flow velocity measuring device according to another aspect of the present invention is
A magnetic sensor head that has an exciting device and a pair of detecting devices and is arranged to face a moving conductive object to be measured, and an exciting current that overlaps two frequency signals of a low frequency and a high frequency. An exciting circuit for supplying to the exciting winding, a detecting circuit for detecting a flow velocity by extracting a signal of a magnetic field component corresponding to a low frequency signal from a difference signal of the pair of detecting windings, and a pair of detecting windings. A ripple correction circuit that extracts the signal of the magnetic field component corresponding to a high frequency signal from the line difference signals to obtain a ripple correction signal, and subtracts the ripple correction signal from the flow velocity of the detection circuit to obtain the ripple corrected flow velocity. From the sum signal of the pair of detection windings, the signal of the magnetic field component corresponding to the high frequency signal is extracted to obtain the distance to the measurement object, the flow velocity after waviness correction is corrected by the distance, and after correction by the distance Distance to find the flow velocity of And a variation correction circuit.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the measurement principle of the present invention will be described by dividing it into the sections of flow velocity detection principle, distance detection principle, correction principle of sensitivity change due to distance change, and correction principle of signal change due to ripple. To do. (A) Flow Rate Detection Principle In the present invention, as shown in FIG. 2, the magnetic sensor head 100 includes an excitation winding 102 wound around the center of a U-shaped magnetic core 101 and two legs. Two detection windings 103 and 104 each wound are provided. The detection windings 103 and 104 are wound so as to detect a magnetic field in the opposite direction. On the conductive measurement object 200 that moves the magnetic sensor head 100, the central axes of the detection windings 103 and 104 are perpendicular to the target surface, and the detection windings 103 and 104 are arranged in the moving direction of the conductor. Place it so that it is parallel to.

An alternating current is supplied to the excitation winding 102 to create a magnetic field perpendicular to the target surface. At this time, FIG.
If the conductor 200 is stopped as shown in (a), since the magnetic sensor head 100 has a bilaterally symmetrical shape, the exciting magnetic fields are equal in magnitude and opposite in direction at the left and right detection winding positions. The difference between the outputs of the detection windings is “0”. Then, when the conductor moves, the magnetic field is distorted by the eddy current generated in the conductor corresponding to the flow velocity as shown in FIG. 2B, and a difference occurs in the vertical component of the magnetic flux at each detection winding position, The difference signal of each detection winding changes. This change amount corresponds to the flow velocity of the measurement target, and the flow velocity of the measurement target can be measured from this change amount. At this time, the distortion amount of the magnetic flux due to the velocity effect has the same sign in the detection windings on the downstream side and the upstream side of the flow, and the direct magnetic field from the magnetic sensor head 100 is
The two detection windings 10 have the same size but opposite signs.
By taking the difference between the outputs of 3 and 104, it is possible to exclude only the extra signal, and it is possible to detect only the distortion amount corresponding to the flow velocity with good S / N.

(B) Distance Detection Principle-The induced magnetic field generated by the eddy current composed of dB / dt changes depending on the distance. Therefore, the distance can be detected by detecting the induced magnetic field. The distance 1 between the magnetic sensor head 100 and the measurement object 200 and the output of the detection winding 103 have characteristics as shown in FIG. Here, the frequency f of the alternating current supplied to the excitation winding 102 is 6
It is 14 Hz. By the way, since the magnetic field distortion signal corresponding to the flow velocity is Bv = K1 × v × B (K1: proportional constant), if the frequency is high, the magnetic field in the measurement object is weakened by the eddy current, so that the frequency is high. Weaken. FIG. 5 (a)
Speed signal (V _v · f ₀ / for the frequency f of the exciting current)
It is a characteristic diagram showing the magnitude of f), and it can be seen that the velocity signal sharply decreases as the frequency increases. In FIG. 5A, V _v is the detection windings 103 and 10
4 is the differential voltage, and f ₀ is the reference frequency. Here, the reference frequency f ₀ is normalized to 14 Hz.

The magnetic field due to the eddy current is Be = -K2
-It is expressed by dB / dt (K2: proportional constant) and increases in proportion to frequency. FIG. 5B is a characteristic diagram showing the magnitude of the distance signal (V _e · f ₀ / f) with respect to the frequency f of the exciting current, and it can be seen that the distance signal increases in proportion to the frequency. Therefore, the higher the excitation current frequency, the smaller the flow velocity signal and the greater the distance signal.
The property as a rangefinder becomes stronger, and only distance can be detected.

In the present invention, the flow velocity signal and the distance signal are detected by setting the phases as follows. Regarding the flow velocity signal, if the frequency is low, it is assumed that the magnetic field, that is, the component of the phase that is deviated by -90 degrees from the excitation current is detected (the magnetic field signal is 0 degrees, but is detected by the coil, so it is deviated by -90 degrees). ), At high frequencies, the excitation magnetic field phase in the object to be measured changes due to eddy currents, so adjustment is made each time. For the distance signal, if the frequency is low, the exciting magnetic field, that is, the exciting current and 0
The phase component of the degree is detected, and the exciting magnetic field phase in the object to be measured changes at a high frequency because the eddy current changes it.

(C) Principle of Correction of Sensitivity Change Due to Distance Change When the distance between the magnetic sensor head 100 and the measurement object 200 changes, the sensitivity to the flow velocity changes as shown in FIG. 4 (b). Note that FIG. 4B shows the sensitivity to a flow velocity of 1 m / sec. Therefore, the distance is calculated from the characteristics of FIG. 4A from the high frequency signal (the sum of the output voltages of the left and right detection windings is used in order to calculate the average distance between the left and right detection windings). It can be seen that the flow velocity is detected with a low frequency signal and the distance signal detected with a high frequency signal is applied to the calibration curve of FIG. 4B to correct the sensitivity.

(D) Principle of Correcting Signal Change Due to Rippling When there is a wave on the measurement target surface, the two detection windings have a difference in distance from the measurement target surface. Therefore, there is a difference in the eddy current magnetic field related to the distance generated in each detection winding, which causes noise. In addition, since the eddy current increases as the frequency increases, the signal difference generated in each detection winding increases even with the same wave.

FIGS. 6 (b) and 6 (c) are characteristic diagrams showing an output example when there is a ripple. As shown in FIG. 6B, in the case of a low frequency, the velocity signal is large and the ripple noise is small. Then, as shown in FIG. 6C, in the case of a high frequency, the velocity signal is small and the ripple noise is large. However, the pattern of ripples on both sides is the same. The phase at this time is set to a phase in which the flow velocity signal becomes maximum at a low frequency, and at a high frequency, a phase in which a signal change pattern due to ripples matches a signal at a low frequency is selected. Since the wave pattern is the same as described above, noise can be canceled by multiplying signals of two frequencies by appropriate coefficients and subtracting the signals.

Now that the measurement principle of the present invention has been clarified, an example of an 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 excitation circuit 110, a detection circuit 120,
It is composed of a ripple correction circuit 125 and a distance variation correction circuit 130. The excitation circuit 110 includes an oscillator 111 that generates a signal of a low frequency f1, an oscillator 112 that generates a signal of a high frequency f2, an output of the oscillator 111 and an oscillator 112.
And an output of the exciting coil 10 of the magnetic sensor head 100 for amplifying the addition result.
2 is composed of a power amplifier 114 which supplies the exciting current to the second amplifier 2. The detection circuit 120 includes the detection winding 103 of the magnetic sensor head 100, which is subtracted by the subtractor 115,
Of the difference signal of the output of 104, a bandpass filter 121 that passes a component of frequency f1 and a phase detector 122 that phase-detects the output of the bandpass filter 121 with a signal of frequency f1 of an oscillator 111. There is.

The crest correction circuit 125 phase-detects the output of the band-pass filter 126 and the output of the band-pass filter 126 of the output of the subtractor 115 with the frequency f2 component by the signal of the frequency f2 of the oscillator 112. And an amplifier 128 for multiplying the output of the phase detector 127 by a predetermined coefficient to output a ripple correction signal, and a subtracter 129 for subtracting the output of the amplifier 128 (ripple correction signal) from the output of the detector 120. ing. Further, the distance variation correction circuit 130 includes the detection windings 103 of the magnetic sensor head 100 added by the adder 116,
Of the output of 104, a bandpass filter 131 that passes a component of frequency f2, a phase detector 132 that phase-detects the output of the bandpass filter 131 with a signal of frequency f2 of the oscillator 112, and the output and phase of the ripple correction circuit 125. A / D converter 133 for converting the output of the wave detector 132 into a digital signal, and a predetermined arithmetic processing is applied to the signals input through the A / D converter 133 to obtain the flow velocity of the measurement object. It is composed of a computer 134.

In the flow velocity measuring apparatus of FIG. 1, in the excitation circuit 110, the signals related to the two frequencies f1 and f2 from the oscillators 111 and 112 are superposed by the adder 113, and the signals are passed through the power amplifier 114 to the magnetic sensor. It is supplied to the exciting winding 102 of the head 100 as an exciting current. Then, the detection circuit 120 has two detection windings 103,
From the difference signal of the output of 104, the flow velocity signal is obtained via the bandpass filter 121 and the phase detector 122. The ripple correction circuit 125 amplifies the high frequency difference signal obtained from the difference signal between the outputs of the two detection windings 103 and 104 via the band pass filter 126 and the phase detector 127 into the amplifier 128.
Thus, the ripple correction signal appropriately multiplied by the coefficient is obtained, and the ripple correction signal is subtracted from the flow velocity signal detected by the detection circuit 120 by the subtractor 129 to cancel the influence of the ripple. The distance variation correction circuit 130 A / D-converts the flow velocity signal and the high-frequency sum signal after the ripple correction by the A / D converter 133 and fetches them into the computer 134 to perform a correction calculation. That is, the characteristic of FIG. 4A is applied to the high frequency sum signal to calculate the average distance, and the characteristic of FIG. 4B is applied to the flow velocity signal after the ripple correction to correct the sensitivity change due to the distance.

FIG. 6 is a timing chart showing a state in which the influence of ripples is eliminated in the measuring apparatus of FIG. 1, and it can be seen from the characteristics of the figure that the influence of ripples is eliminated. In FIG. 6, (a) is the actual speed,
(B) shows the output of the phase detector 122, (c) shows the output of the phase detector 127, and (d) shows the output of the subtractor 129, respectively.

FIG. 7 is a timing chart showing the measurement results when the distance changes. It can be seen that the distance correction eliminates the influence of the distance from the flow velocity signal.

[0026]

As described above, according to the present invention, a magnetic field in which two or more frequency signals are superposed is excited, the magnetic field components corresponding to the respective frequency components are detected, and the signals of the detected magnetic field components are detected. Based on the above, since the flow velocity of the measurement object is measured, magnetic field component signals corresponding to different frequency signals can be obtained, and therefore, even if the distance changes or a wave occurs, it can be corrected. The flow velocity can be measured accurately.

[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 a magnetic sensor head of the present invention.

FIG. 3 is an explanatory diagram for explaining the principle of flow velocity measurement according to the present invention.

FIG. 4 is a characteristic diagram (calibration diagram) showing the relationship between the distance between the magnetic sensor head and the measurement object, the output voltage of the detection winding, and the flow velocity sensitivity.

FIG. 5 is a characteristic diagram showing a relationship between a frequency, a speed signal, and a distance signal.

FIG. 6 is a timing chart showing operation waveforms in the measuring apparatus of FIG. 1 when there is a wave.

7 is a timing chart showing operation waveforms in the measuring apparatus of FIG. 1 when there is a distance change.

FIG. 8 is an explanatory diagram for explaining continuous casting.

FIG. 9 is an explanatory diagram for explaining a conventional contact-type high-temperature liquid metal flow velocity measuring method.

FIG. 10 is an explanatory diagram for explaining a velocity effect of a magnetic field.

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 explanatory diagram illustrating an operation when there is a ripple.

Claims (3)

[Claims] 1. For a moving conductive object to be measured,
A step of exciting a magnetic field in which two or more frequency signals are superimposed, a step of detecting a magnetic field component corresponding to each frequency component, and a flow velocity of a measurement target is measured based on the detected signal of each magnetic field component. A method of measuring flow velocity, comprising: 2. With respect to a moving conductive object to be measured,
A step of exciting a magnetic field in which two frequency signals composed of a low frequency and a high frequency are superposed, a step of detecting a magnetic field component corresponding to each frequency component, and a signal of the magnetic field component corresponding to the low frequency signal Then, the step of obtaining the flow velocity of the measurement object, and obtaining the ripple correction signal based on the signal of the magnetic field component corresponding to the high frequency signal, after the ripple correction signal is subtracted from the flow velocity of the measurement object The step of obtaining the flow velocity of, the step of obtaining the distance to the measurement object based on the signal of the magnetic field component corresponding to the high frequency signal, the flow velocity after the waviness correction is corrected by the distance, And a step of obtaining a flow velocity, the flow velocity measuring method. 3. A magnetic sensor head, which has an exciting device and a pair of detecting devices and is arranged to face a moving conductive object to be measured, and two frequency signals consisting of a low frequency and a high frequency. An exciting circuit for supplying an overlapping exciting current to the exciting winding, and a detecting circuit for detecting a flow velocity by extracting a signal of a magnetic field component corresponding to the low frequency signal from the difference signal of the pair of detecting windings. Of the difference signals of the pair of detection windings, the signal of the magnetic field component corresponding to the high frequency signal is extracted to obtain the ripple correction signal, and the ripple correction signal is subtracted from the flow velocity of the detection circuit. A wave correction circuit that obtains a flow velocity after wave correction, and a signal of a magnetic field component corresponding to the high frequency signal is extracted from the sum signal of the pair of detection windings to obtain a distance to a measurement object, and The flow velocity after waviness correction Corrected by serial distance, velocity measuring apparatus characterized by having a length variation correction circuit for obtaining a flow rate corrected by distance.