JP2000321114A - Molten metal level gage for molten metal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a molten metal level gage capable of accurately measuring a level of a molten metal in a mold even when an electromagnetic agitator is used. SOLUTION: A control unit 13 excites an electromagnetic agitating coil 11 in a frequency of its supply voltage, and outputs a reference signal P each time an exciting current becomes zero. A sampling signal generating circuit 14 generates a sampling signal S deviated by a phase decided according to a mounting position of a molten metal level sensor 14 from the signal P each time the signal P is received. An output of the sensor 14 is sampled according to the signal S, and hence a molten metal level can be accurately measured even when an electromagnetic agitator is used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a level gauge for molten metal, and more particularly to a level gauge of molten metal in a mold even when the molten metal injected into the mold is stirred by an electromagnetic stirrer. The present invention relates to a molten metal level gauge capable of accurately measuring a meniscus.

[0002]

2. Description of the Related Art Molten steel produced in a converter is formed into slabs, billets and the like in a continuous casting machine. In a continuous caster, molten steel in a ladle is injected into a mold via a dandysh. Due to the flow of molten steel generated in the mold by this injection, powder, which is an impurity floating on the surface of the molten steel in the mold, may be caught in the molten steel. This powder is absorbed by the molten steel remaining in the solidified steel due to uneven solidification of the molten steel and causes seizure, so that it is possible to prevent the entrainment of the powder of the molten steel. is necessary.

[0003] It is also necessary to promote the floating of the gas in order to prevent gas such as carbon monoxide (CO) generated when the molten steel solidifies from remaining in the solidified steel. To cope with this problem, an electromagnetic stirrer for generating a steady flow of molten steel in a mold along a mold wall by using a linear motor has already been proposed (for example, see JP-A-1-228645). ).

In the electromagnetic stirrer according to the above proposal,
The electromagnets installed on both sides of the mold are always excited by three-phase AC power, and the moving magnetic field generated in the molten steel stirs the molten steel, so that powder of the molten steel is prevented from being entrained and gas floating is promoted. You. However, in order to maintain product quality in a continuous casting machine, it is important to control the level of the molten metal in the mold, but to control the level of the molten metal, it is necessary to accurately measure the level of the molten metal. Becomes
Since the molten steel surface is hot,
Non-contact measurement is required, and it is common to use an eddy current type level gauge.

The eddy current level meter has a structure in which a secondary coil, a conductive ferromagnetic material, and a primary coil are laminated, and a primary magnetic flux generated by exciting the primary coil at a high frequency. As a result, an eddy current is generated on the molten steel surface. The secondary magnetic flux generated by the eddy current is detected by the secondary coil, so that the level of the molten metal is measured.

[0006]

However, since the eddy current type level gauge utilizes the electromagnetic induction phenomenon, the signal is affected by the magnetic flux generated from the electromagnetic stirrer during excitation of the electromagnetic stirrer. The deterioration of the noise ratio cannot be avoided. The present invention has been made in view of the above problems,
An object of the present invention is to provide a molten metal level gauge capable of accurately measuring the level of a molten metal in a mold even when the molten metal injected into the mold is stirred by an electromagnetic stirrer. I do.

[0007]

SUMMARY OF THE INVENTION A molten metal level gauge according to the present invention comprises: a control unit for supplying an exciting power of a predetermined frequency to an electromagnetic stirring coil for electromagnetically stirring a molten metal surface; A reference signal output unit for outputting a reference signal each time the absolute value of the output excitation current is minimized, and sampling having a predetermined phase difference from the reference signal each time the reference signal is output from the reference signal output unit A sampling signal generator for generating a signal, a level sensor for detecting the level of the level of the molten metal stored in the container, and an output of the level sensor each time a sampling signal is output from the sampling signal generator. And a sampling unit for sampling.

In the present invention, the noise induced by the electromagnetic stirrer in the level sensor fluctuates at a frequency twice the frequency of the exciting current of the electromagnetic stirring coil. By sampling the output of the level sensor at the shifted position, the level of the level with less noise is output.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a structural view of a molten metal level gauge according to the present invention. A coil 11 for electromagnetic stirring is provided on a side surface of a mold 10. Further, a nozzle 12 for injecting molten steel is arranged at the center of the mold 10. The control unit 13 supplies power of a predetermined waveform to the electromagnetic stirring coil 11 and outputs a reference signal P every time the current of a specific one phase, for example, the U phase becomes zero.

FIG. 2 is a waveform diagram of the current and the reference signal output from the control unit 13. The reference signal P is output every time the current becomes zero when the current changes from negative to positive. An eddy current sensor is arranged above the mold 10.
The eddy current sensor 14 is connected to a signal processing unit 15, and the signal processing unit 15 includes a filter 151 and a sampler 15.
2, a holder 153, and a sampling signal generation circuit 154.

The output of the eddy current sensor 14 is a filter 151
Supplied to The filter 151 has a high-frequency cutoff characteristic that cuts off a component of the voltage supplied from the control unit 13 included in the output of the eddy current sensor 14 to the electromagnetic stirring coil 11 that is higher than the frequency f. The output of the filter 151 is the sampler 15
2 and the sampled signal is, for example, held in the zero order by the holder 153 and output as a temporally continuous signal.

The sampler 152 is driven by a sampling signal generated by a sampling signal generation circuit 154, and the sampling signal is generated at the following timing. That is, when the voltage frequency of the AC power supplied to the electromagnetic stirring coil 11 is f, the magnetic flux B _c that coil 11 is generated is expressed by the following equation.

B _c = B _c0 sin (2πft) (1) Further, the magnetic flux B at an arbitrary point (x, y, z) near the coil 11 is represented by the following equation. B = B ₀ sin (2πft + φ) (2) where B ₀ and φ are functions of the position coordinates (x, y, z) of the point.

Assuming that the eddy current sensor 14 is installed at the point (x, y, z), the eddy current sensor 1
Since the voltage v induced in the secondary coil No. 4 is proportional to the square of the magnetic flux B, the following equation holds. _{^{v α B 2 = (B 0}} /2) × {1-cos (4πft + 2φ)} (3) That is, when exciting the electromagnetic stirring coil 11 with three-phase alternating current with a frequency f, the output of the eddy current sensor 14 Noise fluctuating at the frequency 2f is generated.

This noise is theoretically the reference signal P
Is output, and becomes zero at a position shifted by 2φ after P is output. Therefore, if the sampling signal is output at a position shifted by 2φ after the output of P from the sampling signal generation circuit 154 and the output of the filter 151 is sampled, the eddy current sensor which minimizes the influence of the electromagnetic stirring device is provided. Fourteen outputs can be obtained.

Since B ₀ and φ are functions of the installation position of the eddy current sensor 14, if the installation position of the eddy current sensor 14 is determined, B ₀ and φ become known numbers. FIG. 3 is a circuit diagram of an example of the sampling signal generating circuit. The latch circuit 31 latches the reference signal P, the clock generating circuit 32 generates a clock pulse, and the output of the latch circuit 31 is "H". A counter circuit 33 counts a predetermined number of clock pulses output from the inter-clock generation circuit 32 and outputs a sampling signal S when the clock pulse reaches a predetermined number. Are reset by the sampling signal S.

Here, the predetermined number counted by the clock generation circuit 32 is set to a value corresponding to the phase difference 2φ. FIG. 4 is a circuit diagram of an example of a sampler and a holder.
The sampler 152 is connected to a first filter directly connected to the filter 151.
, A buffer 41 and an analog switch 42,
The holder 153 includes the capacitor 43 and the second buffer 44.
Consists of

That is, each time the sampling signal S is output from the sampling signal generation circuit 154, the analog switch 42 is turned on, and the output of the first buffer 41 is sampled. Then, the signal is held by the capacitor 43 until the next sampling is performed, and is output as a level signal via the second buffer 44. FIG. 5 is a waveform diagram of each part, and represents a reference signal P, a sampling signal S, and a level signal in order from the top. In addition, in the hot water signal,
The solid line is the actual level of the bath, and the dashed line is the filter 151.
And the broken line is the output of the holder 153.

That is, the swell of the frequency 2f is superimposed on the actual level of the molten metal due to the effect of the magnetic flux radiated from the electromagnetic stirring device on the output of the filter 151. The output of the filter 151 on which the undulation is superimposed is the reference signal P.
By sampling 2φ after it becomes ^ H ", it becomes possible to output a level signal which minimizes the influence of the magnetic flux radiated from the electromagnetic stirrer.

[0020]

The molten metal level gauge according to the present invention is used in combination with the electromagnetic stirrer because the output of the level sensor is sampled at a position where the noise caused by the electromagnetic stirrer is small. This also makes it possible to accurately measure the level of the molten metal.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a molten metal level gauge according to the present invention.

FIG. 2 is a waveform diagram of a current and a reference signal.

FIG. 3 is a circuit diagram of an example of a sampling signal generation circuit.

FIG. 4 is a circuit diagram of an example of a sampler and a holder.

FIG. 5 is a waveform diagram.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Mold 11 ... Electromagnetic stirring coil 12 ... Nozzle 13 ... Control part 14 ... Hot water level sensor 15 ... Processing part 151 ... Filter 152 ... Sampler 153 ... Holder 154 ... Sampling signal generation circuit

Claims (1)

[Claims] 1. A control unit for supplying an exciting power of a predetermined frequency to an electromagnetic stirring coil for electromagnetically stirring a molten metal surface, and each time an absolute value of an exciting current output from the control unit is minimized. A reference signal output unit that outputs a reference signal, a sampling signal generation unit that generates a sampling signal having a predetermined phase difference from the reference signal each time the reference signal is output from the reference signal output unit, A molten metal sensor comprising: a molten metal level sensor for detecting a level of a molten metal level to be stored; and a sampling unit for sampling an output of the molten metal level sensor every time a sampling signal is output from the sampling signal generating unit. Water gauge.