JP4456682B2 - Non-contact flow velocity detection method and apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a non-contact flow velocity detection method and apparatus, and more particularly, to an erroneous component of the flow velocity of a conductive fluid below the free surface of a continuous metal casting facility as a function of a prediction gap between a molten metal surface and a detection coil. The present invention relates to a novel improvement for obtaining a highly accurate flow rate by removing using the obtained value.
[0002]
[Prior art]
Conventionally, as disclosed in Japanese Patent Laid-Open No. 9-33554, a non-contact flow rate detector proposed for a molten metal continuous casting facility will be described with reference to FIG.
In the conventional non-contact flow velocity detector, the excitation coil 4 for applying the low frequency magnetic field φ0 to the conductive fluid 30 to be measured is disposed in a non-contact manner with respect to the molten metal surface 18, and the excitation coil 4 and The detection coil 6 is configured to detect a magnetic field generated by the action with the conductive fluid 30.
At this time, the low frequency and high frequency from the low frequency oscillator 1 and the high frequency oscillator 2 are applied to the excitation coil 4 via the amplifier 3, and the low frequency magnetic field φ 0 from the excitation coil 4 is incident on the conductive fluid 30. An eddy current is formed in the conductive fluid 30. In addition, when the conductive fluid 30 moves at a certain speed, an induced current generated by the action of the low frequency magnetic field φ0 and the speed is formed. Therefore, the detection coil 6 arranged around the exciting coil 4 detects the velocity component magnetic flux φv generated by the induced current and the eddy current magnetic flux φs generated by the eddy current unrelated to the velocity. When these two magnetic fluxes φs and φv pass through the detection coil 6, eddy current component voltage es and velocity component voltage ev are output to the detection coil 6 as detected electromotive voltages.
Since these two components are 90 ° out of phase with each other, the speed component voltage and the eddy current are detected from the electromotive voltage 6a detected by the rectifier circuit 8 and the phase rectifier circuit 9b via the high frequency filter 7a and the low frequency filter 7b. A method of taking out the flow velocity V composed of the velocity component voltage through the gap correction circuit 10b is used.
[0003]
[Problems to be solved by the invention]
However, the above-described prior art is a method of extracting the velocity component voltage by separating it from the electromotive voltage only through the phase rectifier circuit, and this method cannot completely separate the velocity component voltage and the eddy current component voltage. The velocity component voltage was output with the eddy current component voltage remaining. The component resulting from the eddy current component voltage remaining in the velocity component voltage is simply referred to as a residual component Δes. In addition, the eddy current component voltage may fluctuate due to an inclination existing between the flow velocity detector head and the molten metal surface of the conductive fluid, or a molten metal surface shape of the conductive fluid, for example, undulation or ripple caused by flow.
This is caused by a deviation in the distance (gap) from the conductive fluid in the sensing coil surface due to inclination or undulation, and the eddy current component magnetic field penetrating the sensing coil changes accordingly, and as a result, the eddy current component voltage fluctuates. It will be. As described above, since this eddy current component voltage remains in the velocity component voltage even when phase rectified, the velocity component voltage ev (= Δes) is apparently generated even when the conductive fluid is stationary. It will be. For this reason, the residual component Δes apparently changes according to the shape of the molten metal surface regardless of the flow rate, so that the velocity component voltage ev changes, causing a decrease in the measurement accuracy of the flow velocity detection (shown in FIG. 9). It was the cause that made measurement under the surface difficult.
[0004]
The present invention has been made to solve the above-described problems. In particular, an error in the flow velocity of the conductive fluid below the free surface of the continuous casting equipment for metal is detected between the molten metal surface and the detection coil. It is an object of the present invention to provide a non-contact flow velocity detection method and apparatus capable of obtaining a highly accurate flow velocity by removing using a value obtained as a function of the prediction gap.
[0005]
[Means for Solving the Problems]
The non-contact flow velocity detection method according to the present invention is generated by applying two alternating currents from a low-frequency oscillator and a high-frequency oscillator to a core exciting coil arranged in a non-contact manner with respect to a conductive fluid to be measured. The eddy current component voltage es generated by the linkage of the magnetic flux generated in the direction that interferes with the low frequency magnetic field generated by the excitation coil when the low frequency magnetic field and the high frequency magnetic field are incident on the conductive fluid, and the excitation The flow velocity of the conductive fluid is measured by using a flow velocity detector head having a detection coil for detecting a low frequency magnetic field from the coil and a velocity component voltage ev generated by relative movement of the conductive fluid to be measured. In the non-contact flow velocity detection method obtained, an electromotive force (speed component voltage ev + eddy current component voltage es + gap voltage eo + error Δes) is generated by the detection coil. ) Was measured, among the electromotive voltage, eddy current component voltage es is outputted are separated Ri by the phase commutation gap portion voltage eo is removed by rectification of high-frequency magnetic field, of the eddy current component voltage es The error Δes is defined as Δes = α · es, where α is removed using a value obtained as a function of a prediction gap obtained in advance for the gap between the molten metal surface of the conductive fluid and the detection coil. Thus, the flow velocity of the conductive fluid is obtained, and the prediction gap is a method of measuring the conductive fluid in a stationary state, and the non-contact flow velocity detection device according to the present invention. Is a low-frequency magnetic field and a high-frequency magnetic field generated by applying two alternating currents from a low-frequency oscillator and a high-frequency oscillator to a core exciting coil arranged in a non-contact manner with respect to a conductive fluid to be measured. For conductive fluid The eddy current component voltage es generated when the magnetic flux generated in the direction that hinders the low-frequency magnetic field generated in the excitation coil is interlinked, and the low-frequency magnetic field from the excitation coil and the conductivity to be measured In the non-contact flow velocity detection device, wherein the flow velocity of the conductive fluid is obtained using a flow velocity detector head having a detection coil for detecting the velocity component voltage ev generated by relative movement of the conductive fluid, A phase rectification circuit for separating an eddy current component voltage and a velocity component voltage by performing phase rectification on the detection voltage from the detection coil after passing through a low frequency filter, and detected by the detection coil via a high frequency filter Based on the value of the gap signal voltage obtained in this way, the gap with the conductive fluid is obtained, and the change in the velocity component voltage and eddy current component voltage accompanying this gap change. For correcting the velocity component voltage and the eddy current component voltage extracted by the phase rectifier circuit, and an arithmetic circuit connected to the gap correction circuit, and through the gap correction circuit determined from the velocity component voltage outputted error component △ es eddy current component voltage △ es = α · es Te, the alpha got previously the spacing between the sensing coil and the molten metal surface of the conductive fluid The value obtained as a function of the prediction gap is removed, and the flow velocity of the conductive fluid is obtained from the arithmetic circuit.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of a non-contact flow velocity detection method and apparatus according to the present invention will be described with reference to the drawings. The same or equivalent parts as those in the conventional example will be described using the same reference numerals.
A reference numeral 15 in FIG. 1 indicates a flow velocity detector head including a core 5, an excitation coil 4 and a detection coil 6, and the excitation coil 4 includes a low frequency and a low frequency from the low frequency oscillator 1 and the high frequency oscillator 2. A high frequency is applied to the exciting coil 4 via the amplifier 3. The core 5 is configured to detect by changing the position 180 degrees alternately forward and reverse.
[0007]
The electromotive voltage e obtained from the detection coil 6 is applied to the first gap correction circuit 10a via the high-frequency filter 7a and the rectifier circuit 8, and the low-frequency filter 7b and the pair of phase rectifier circuits 9a and 9b. Then, it is applied to the first and second gap correction circuits 10a and 10b, and the outputs of the gap correction circuits 10a and 10b are input to the arithmetic circuit 16 to output the flow velocity V.
[0008]
Next, the operation will be described. First, an eddy current is formed in the conductive fluid 30 by the low-frequency AC magnetic field from the exciting coil 4, and accordingly magnetic fluxes φsa and φsb in a direction that cancels the low-frequency magnetic field are formed as shown in FIG.
Here, when the flow velocity detector head 15 and the molten metal surface 18 of the conductive fluid 30 are smooth, the distance between the bottom surface of the flow velocity detector head 15 and the molten metal surface 18, that is, the gap 20 is the same at any point. The magnetic fluxes φsa and φsb due to the eddy currents formed on the upstream side and the downstream side of the flow 21 act in a direction that cancels each other, and the difference between the magnetic fluxes φsa and φsb is detected. Note that φo is an excitation magnetic flux, and φv is a velocity component magnetic flux.
However, when the flow velocity detector head 15 is installed, the gap between the bottom surface of the flow velocity detector head 15 and the molten metal surface 18, such as when there is an inclination with the molten metal surface 18 or when the molten metal undulates and flows due to flow. When 20 is different, the difference between the magnetic fluxes φsa and φsb increases, and the eddy current component voltage es also increases. Further, when the molten metal surface shape continuously varies, the eddy current component voltage es also varies. Conventionally, the eddy current component voltage es is subjected to signal processing for phase rectification and separation from the electromotive voltage e. However, the eddy current component voltage es is not completely separated / removed, and remains and becomes a great disturbance when detecting the flow velocity.
Therefore, in the present invention, the velocity component voltage ev is corrected from the eddy current component voltage es generated by the difference between the magnetic fluxes φsa and φsb generated by the eddy current that is the cause of the disturbance. In order to perform the correction process, the eddy current component voltage es and the velocity component voltage ev are separated from the electromotive voltage e through the phase rectifier circuits 9a and 9b, the residual component is obtained from the eddy current component voltage es, and the velocity component voltage ev Subtract processing from.
The residual component, that is, the error Δes and the eddy current component voltage es can be defined by the following equation.
△ es = α ・ es (1)
Here, α is a residual ratio, which is a coefficient obtained in advance. That is, the gap between the detection coil 6 and the molten metal surface 18 on the static molten metal surface is measured in advance as a prediction gap 20A, and a value obtained as described below is used as a function of the prediction gap 20A. Therefore, the speed component voltage ev to be obtained is expressed by the following equation from the equation (1).
ev = evt−α · es (2)
By always correcting the velocity component voltage ev by the eddy current component voltage es based on the equation (2), the flow velocity V can be detected with high accuracy even under the free surface. Note that the prediction gap 20A is possible even when the molten metal surface 18 is flowing in a stationary state.
[0009]
Next, how to determine α of the above-mentioned error α · es will be described.
When measuring the electromotive voltage e at the forward and reverse positions while rotating the core 5 180 degrees,
e (electromotive voltage) = ev (speed min) + es (eddy current component) + eo order (gap portion voltage) + △ es (error component) is generated, the sum of the velocity components of the forward and reverse removed es phase rectifier ½, and eo is removed by rectification of the high-frequency magnetic field (the same as the conventional method so far), but the error Δes is proportional to the eddy current and is removed as Δes = α · es. Thus, the flow velocity V with high accuracy is obtained.
That is, the present application corrects an error due to the inclination of the detector in addition to the above-described conventional technique, and how to determine α in the correction will be described with reference to FIGS.
First, the detector head 15 is installed in the shape of a stationary molten metal surface, and the inclination of the N / S pole of the detector head 15 is changed for each gap length (the center position of the NS pole tip of the core 5 and the stationary molten metal surface distance). The relationship between the slope and the eddy current component voltage es is plotted as shown in FIG.
Next, a certain flow velocity is given to the molten metal surface 18, and the flow velocity by both detectors is measured with a detector head 15 (α = 1) and a conventional flowmeter (for example, a contact type manufactured by well-known Sukegawa Electric Works). .
In this case, the detector head 15 of the present invention performs measurement while changing the inclination for each gap length. However, the measurement speed of the detector head 15 changes corresponding to the gap and inclination because the conventional anemometer is constant. Difference.
The difference (corresponding to the residual rate α) is converted back to a voltage by back-calculating the difference from the relationship between the detection voltage of the detector head 15 during horizontal installation and the speed of the conventional detector, and the voltage is used as a residual component. A plot of the slope and the residual component Δes as shown in FIG. 5 is created.
FIG. 6 is a graph obtained by rearranging and plotting FIG. 4 and FIG. 5 with the same gap and inclination and the eddy current component voltage es by the residual component. As can be seen from this figure, the residual component for each gap is proportional to the eddy current component voltage and can be linearly approximated for each gap, and it is clear that the slope varies depending on the gap.
FIG. 7 is a plot of the slope for each gap (corresponding to the residual rate α). From this plot, it can be seen that the residual rate α is expressed by a quadratic approximate expression of the gap, and α can be determined regardless of the inclination of the detector head 15 according to the installation position of the detector head 15 and the accuracy can be improved. Can do. That is, α is a value obtained as a function of the prediction gap 20A obtained in advance from the distance between the molten metal surface 18 of the conductive fluid 30 and the detection coil 6.
[0010]
【Example】
The flow velocity detector head 15 was placed in a non-contact manner with respect to the molten metal surface (melting point = 70 ° C.) molten metal 100 ° C. 18 to be measured, and the flow velocity was measured. The hot water surface 18 is a free surface. Two alternating magnetic fields were applied to the exciting coil 4 from the low frequency oscillator 1 of 100 Hz and the high frequency oscillator 2 of 20 kHz. At this time, the electromotive voltage e from the detection coil 6 is discriminated into a high-frequency component signal and a low-frequency component signal according to the difference in frequency. The low frequency component signal is separated into the speed component voltage ev and the eddy current component voltage es by the phase rectifier circuits 9a and 9b, and output fluctuation due to a gap change by the gap signal obtained through the high frequency filter 7a and the rectifier circuit 8. The corrected speed component voltage ev and eddy current component voltage es obtained by correcting the gap voltage eo are output. That is, each of the gap correction circuits 10a and 10b obtains a gap from the conductive fluid 30 based on the value of the gap voltage eo detected by the detection coil 6 and obtained through the high frequency filter 7a. In order to correct the accompanying changes in the velocity component voltage ev and the eddy current component voltage es, the velocity component voltage ev and the eddy current component voltage es extracted by the phase rectifier circuits 9a and 9b are corrected. Further, the velocity component voltage ev is removed from the disturbance component due to the eddy current component based on the value of the eddy current component voltage es by the arithmetic circuit 16. In the arithmetic circuit 16, the net velocity component is obtained by subtracting the residual component Δes obtained from the eddy current component voltage es from the velocity component voltage evt after gap correction as shown in the equations (1) and (2). The voltage ev is output as a speed signal.
FIG. 9 (conventional method) shows the result of converting the velocity component voltage (evt) into the flow velocity when only the gap correction is performed, and FIG. 3 shows the result when the residual component is corrected by the eddy current component. Method). In the figure, the measured value of the immersion type anemometer (simultaneously indicated by a dotted line) is also shown as a reference. As shown in FIGS. 9 and 3, it is apparent that the accuracy of the non-contact velocimeter is remarkably improved by correcting the residual component. It should be noted that the contents of the signal are represented by equations in each part of FIG.
[0011]
【The invention's effect】
Since the non-contact flow velocity detection method and apparatus according to the present invention are configured as described above, the following effects can be obtained. That is, the eddy current component voltage (es) in the electromotive voltage (e) is removed by phase rectification, the gap voltage (eo) is removed by rectification of the high-frequency magnetic field, and the error (Δes) is Δes = By using α · es and removing α using a value obtained as a function of the prediction gap (20A), a highly accurate flow velocity (V) can be obtained.
[Brief description of the drawings]
FIG. 1 is a configuration diagram showing an apparatus to which a non-contact detection method according to the present invention is applied.
FIG. 2 is an explanatory diagram showing the operation of FIG. 1;
FIG. 3 is a flow velocity / time characteristic diagram according to the method of FIG. 1;
FIG. 4 is an eddy current voltage component detection characteristic diagram according to the present invention.
FIG. 5 is an influence characteristic diagram of the inclination between the flow velocity detector head and the molten metal surface according to the present invention.
FIG. 6 is a relationship characteristic diagram between an eddy current component voltage and a residual component according to the present invention.
FIG. 7 is a relationship characteristic diagram between a residual rate and a prediction gap according to the present invention.
FIG. 8 is a configuration diagram showing an apparatus to which a conventional method is applied.
FIG. 9 is a flow velocity / time characteristic diagram of the conventional method of FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Low frequency oscillator 2 High frequency oscillator 3 Amplifier 4 Excitation coil 5 Core 6 Detection coil 7a High frequency filter 7b Low frequency filter 8 Rectifier circuit 9a, 9b Phase rectifier circuit 10a, 10b Gap correction circuit 30 Conductive fluid φo Excitation magnetic flux φs Eddy current magnetic flux φv velocity component magnetic flux 15 flow velocity detector head 16 arithmetic circuit 18 molten metal surface 20 gap 20A prediction gap 21 flow of molten metal

Claims (3)

Two alternating currents from the low-frequency oscillator (1) and the high-frequency oscillator (2) are applied to the exciting coil (4) of the core (5) placed in non-contact with the conductive fluid to be measured. The low-frequency magnetic field and the high-frequency magnetic field generated in step 1 are incident on the conductive fluid (30), and the vortex generated by the linkage of the magnetic flux generated in the direction that interferes with the low-frequency magnetic field generated in the excitation coil (4). Current component voltage (es) and velocity component voltage (ev) generated by relative movement of the low-frequency magnetic field from the excitation coil (4) and the conductive fluid (30) to be measured are detected. In the non-contact flow velocity detection method in which the flow velocity (V) of the conductive fluid (30) is obtained using a flow velocity detector head (15) having a detection coil (6), an electromotive voltage is generated by the detection coil (6). e (consisting of velocity component voltage ev + eddy current component voltage es + gap voltage eo + error Δes) Constant and, among the induced voltage (e), an eddy current component voltage (es) is outputted are separated Ri by the phase commutation gap portion voltage (eo) is removed in the rectification of the high frequency magnetic field, the eddy current components The error (Δes) of the voltage (es) is defined as Δes = α · es, where α is between the molten metal surface (18) of the conductive fluid (30) and the detection coil (6). Non-contact flow velocity characterized in that the flow velocity (V) of the conductive fluid (30) is obtained by removing the gap (20) using a value obtained as a function of the prediction gap (20A) obtained in advance. Detection method.   The non-contact flow velocity detection method according to claim 1, wherein the prediction gap (20A) is measured in a state where the conductive fluid (30) is stationary. Two AC currents from the low-frequency oscillator (1) and high-frequency oscillator (2) are applied to the exciting coil (4) of the core (5) arranged in a non-contact manner with respect to the conductive fluid (30) to be measured. The low-frequency magnetic field and the high-frequency magnetic field generated as a result of being incident on the conductive fluid (30), the magnetic flux generated in the direction that interferes with the low-frequency magnetic field generated in the excitation coil (4) is interlinked. Detects the eddy current component voltage (es) generated and the velocity component voltage (ev) generated by the relative movement of the low-frequency magnetic field from the excitation coil (4) and the conductive fluid (30) to be measured. In the non-contact flow velocity detection device that obtains the flow velocity (V) of the conductive fluid (30) using the flow velocity detector head (15) having the detection coil (6) for the detection coil (6) The eddy current component voltage and velocity are generated by phase rectification after passing through the low-frequency filter (7b) for the detected voltage from The phase rectifier circuit (9a, 9b) for separating the voltage and the conductivity based on the value of the gap voltage (eo) detected by the detection coil (6) and obtained through the high frequency filter (7a) The velocity component extracted by the phase rectifier circuit (9a, 9b) in order to obtain the gap with the fluid (30) and correct the change in the velocity component voltage (ev) and the eddy current component voltage (es) due to the gap change. A gap correction circuit (10a, 10b) for correcting the voltage (ev) and the eddy current component voltage (es), and an arithmetic circuit (16) connected to the gap correction circuit (10a, 10b), gap correction circuit (10a, 10b) the error of △ es of velocity component voltage output through the (ev) from the eddy current component voltage (es), defined as △ es = α · es, the alpha is the conductivity The distance between the hot water surface (18) of the ionic fluid (30) and the detection coil (6) is removed using a value obtained as a function of the prediction gap (20A) obtained in advance, from the arithmetic circuit (16). A non-contact flow velocity detection device configured to obtain a flow velocity (V) of the conductive fluid (30).

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