JPH0781898B2 - Molten metal level detector - Google Patents

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to the top level of molten metal.
To a device for detecting .

[0002]

2. Description of the Related Art Japanese Unexamined Patent Publication (Kokai) No. 3-105219 discloses a transmitter coil, a receiver coil, and a means for applying an alternating voltage to the transmitter coil, which are arranged so as to be sandwiched from the left and right sides or the front and rear sides outside a container or the like in which molten metal exists. And means for detecting the induced voltage in the receiver coil induced by the alternating flux generated by the transmitter coil and transmitted through the container and the molten metal.

The method disclosed in Japanese Patent Laid-Open No. 3-105219 will be described below with reference to FIG. By applying an alternating voltage from the AC power supply 5a to the transmission coil 4a wound on the laminated steel plates, the transmission coil 4a generates an alternating magnetic flux. Part of the alternating voltage is distributed directly above and below the transmitter coil, and part of the alternating voltage enters the inside of the mold 2 made of a water-cooled steel plate and passes through the mold 2 in the upward and downward directions. To do. Further, although the magnetic flux density is small, a part of the magnetic flux passes through the mold 2 and flows into the molten steel 1 or the space (this may be in the molten steel 1 or in the air 6 or in FIG. 3 depending on the level position of the molten steel at that time). (Which is one of the intermediate positions as shown in FIG. 2) to reach the mold 3.

A part of the magnetic flux reaching the mold 3 enters the mold 3 and passes upward and downward of the mold 3. Then, a small part of the magnetic flux passes through the mold 3 and reaches the receiving coil 7a, which induces an electromagnetic induction voltage in the receiving coil 7a. In the induced voltage of the receiving coil 7a, the alternating magnetic flux reaching the receiving coil 7a has a low level (for example, the AC power source 5a
Is about 1/4000 of the generated voltage, and is easily affected by noise. In order to reduce the influence of noise and accurately extract the induced voltage, a bandpass filter 8a that connects only the frequency band of the alternating voltage of the AC power supply 5a and blocks the other is connected to the receiving coil 7a. In order to cut the noise component of the band, the output of the bandpass filter 8a is converted by the synchronous rectifier 9a into only direct current signals synchronized with the alternating voltage of the alternating power source 5a. The asynchronous AC noise component is output from the synchronous rectifier 9a as an AC component, and this noise component is used as the DC voltage SVa of the level corresponding to the magnetic flux amount of the alternating magnetic flux generated by the transmission coil 4a and received by the coil 7a, as the low-pass filter 10a. Appears in the output of.

When the molten metal 1 is filled between the transmitting coil 4a and the receiving coil 7a, when a part of the alternating magnetic flux passing through the mold 2 passes through the molten metal 1, the magnetic flux causes a vortex to the molten metal 1. A current is generated, which reduces the transmitted magnetic flux energy, reduces the amount of alternating magnetic flux reaching the receiving coil 7a, and reduces the induced voltage S of the receiving coil 7a.
Va becomes low. However, when the upper surface of the molten metal 1 exists at the height of the transmission / reception coils 4a-7a, the induced voltage SVa of the reception coil 7a is relatively high because the amount of decrease of the alternating magnetic flux passing therethrough is small. Therefore, the induced voltage SVa of the receiving coil 7a is low when it is high and high when it is low, corresponding to the molten metal level between the transmitting coil 4a and the receiving coil 7a. That is, the molten metal level can be measured from this SVa. Figure 2
In addition, the output voltage SV of the low-pass filter 10a, which is proportional to the molten metal level (horizontal axis) and the induced voltage of the receiving coil 7a.
The relationship with a is shown.

[0006]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
The method for detecting the level of molten metal according to Japanese Patent Laid-Open No. 9 is disclosed in the case where the container or the like in which the molten metal is placed is a nonmetal, or even if it is a metal, its thickness is constant and the electrical property values (conductivity, relative permeability) are constant. ) Is constant, the level of molten metal can be measured with high accuracy. However, if the container or mold is made of metal, eddy current flows in it, and most of the magnetic flux is blocked by this. Therefore, the effective magnetic flux that reaches the receiving coil is very small, such as several thousandths of the magnetic flux that is emitted from the transmitting coil, and the ratio of the amount of magnetic flux that is blocked by the container or the mold is higher than the magnetic flux that reaches the receiving coil. Is very large.

Therefore, the method disclosed in Japanese Patent Laid-Open No. 3-105219 is not limited to the case where the container or mold in which the molten metal is placed is made of metal and there is a change in its thickness or a change in temperature of the container. For example, the electrical property values, that is, the electric conductivity, the magnetic permeability, and the like fluctuate, and as a result, an error in the molten steel surface level measurement occurs.

Hereinafter, based on FIG. 3, Japanese Unexamined Patent Publication No. 3-10521
The problem of Japanese Patent No. 9 will be described in detail. The outer side of the metal container made of 2, 3 in which the molten metal 1 is present is arranged so as to sandwich the transmission coil 4a and the reception coil 5a from the left and right, and an alternating voltage is applied to the transmission coil 4a from 5a,
The alternating magnetic flux generated thereby is transmitted through the molten metal 1 and the containers 2 and 3, and the output voltage SVa of the low-pass filter 10a in the molten metal level detecting method in which the alternating voltage induced in the receiving coil 5a by the transmitted magnetic flux is observed. Varies depending on the level of the molten steel 1, but the output voltage SVa is affected by the electrical properties of the molds 2, 3, the conductivity σ and the permeability μ. That is, in the molten metal level detecting method according to Japanese Patent Laid-Open No. 3-105219, if the containers (molds 2, 3) in which the molten metal resides are made of metal, most of the magnetic flux is blocked by this, so reception The magnetic flux reaching the coil 4a is extremely small, such as several thousandths. Therefore, the ratio of the amount of magnetic flux blocked by the container (molds 2, 3) or the like is much larger than the magnetic flux reaching the receiving coil 4a. Therefore, the electrical properties of this container are conductivity σ and permeability μ
If even a slight change occurs, the output voltage SVa of the low-pass filter 10a changes greatly, causing a molten steel level detection error. That is, when the conductivity σ of the molds 2 and 3 is slightly high, the transmission of the magnetic flux is hindered, the output voltage SVa of the low pass filter 10a decreases, the molten steel level detection value is output high, and vice versa. Become. Further, when the magnetic permeability μ of the molds 2 and 3 is slightly high, the transmission of magnetic flux is hindered, the output of the low-pass filter 10a decreases, the molten steel level detection value is output high, and vice versa. As described above, the method disclosed in Japanese Patent Application Laid-Open No. 3-105219 is strongly influenced by the electrical property value of the container in which the molten metal is immersed, and causes a measurement error of the molten metal level.

According to the present invention, when the mold or the like is made of metal and the thickness of the mold or the temperature of the container changes, the electrical property values, that is, the electric conductivity, the magnetic permeability, etc., change. The resulting molten steel level measurement error
The purpose is to reduce .

[0010]

The molten metal level detecting apparatus of the present invention is a container (2, 3) in which a molten metal (1) is present.
Placed outside of the container, facing each other with the container (2, 3) in between
Transmitted coil (4a / 4b) and received coil (7a /
7b) as one set, from below the upper surface of the molten metal (1)
A plurality of sets of detection coils distributed upward (4a, 7a / 4
b, 7b); each transmitting coil (4
a / 4b) AC power supply (5a, 5a) that applies alternating voltage
b); each receiving coil (7a /
The alternating voltage induced in 7b) (SVa, SVb) detection
Voltage detection means (8a to 10a / 8b to 10b);
And the voltage detecting means (8a to 10a / 8b to 10b)
Detected above the upper surface of the molten metal (1)
Receiving carp unaffected by level fluctuations on the top surface of the molten metal
The level SVb of the alternating voltage induced in the rule (7b).
Of the upper surface, which is below the receiving coil (7b).
Of the alternating voltage induced in the nearby receiving coil (7a)
The ratio (Eo) of the level SVa represents the level of the upper surface.
Computation means (11, 12) for converting into an electric signal;
It In addition, in order to facilitate understanding, the figure in parentheses
For reference, refer to the symbols of the corresponding elements of the examples shown on the surface and described later.
Was added to .

[0011]

[Function] There is no change in the electrical properties of the container (2, 3)
(Depending only on the level of molten metal (1))
Level of alternating voltage induced in the receiving coil (7a) during operation
Let Ea be the molten metal (1) and the detection coil (4a, 7)
When it is not in the position of a), the electrical property value of the container (2, 3)
The voltage value when it changes and the reference voltage value (melting
When the metal (1) is not in the position of the detection coil (4a, 7a)
Changes due to fluctuations in the electrical properties of the container (2,3)
It is desirable to take the average value of the voltage values
Then, the alternating voltage induced in the receiving coil (7a)
The level SVa is expressed by the following equation (1). SVa = Ea.ε (V) (1) On the other hand, the level of the alternating voltage induced in the receiving coil (7b)
Le SVb does not change the electrical properties of the container (2, 3).
Assuming that the level is Eb, the following equation (2)
Can be expressed as SVb = Eb · ε (V) (2) Here, in Eb, the detection coils (4b, 7b) are made of molten metal.
The position is not affected by the level fluctuation on the top surface of the
It is a fixed value. Therefore, when K ₁ is a constant of proportionality, SVb
Can be made dimensionless and expressed as the following expression (3). Exchange
In other words, SVb is the electrical property value of the container (2,3).
It changes only by fluctuations. SVb ′ = K ₁ · ε (3) Here, the ratio of SVa and SVb, that is, the equation (1)
The ratio E ₀ of the equation (3) is expressed by the following equation (4). E ₀ = SVa / SVb ′ (V) = (Ea · ε) / (K ₁ · ε) = K ₂ · Ea (4) (where K ₂ : proportional constant) Therefore, the ratio E ₀ is the container (2, 3) Changes in electrical property values
Is not affected by ε, and is proportional to the molten steel level Ea. Performance
The calculation means (11, 12) is above the upper surface of the molten metal (1).
Is not affected by level fluctuations on the upper surface of the molten metal.
Level SV of the alternating voltage induced in the receiving coil (7b)
b below and below the receiving coil (7b)
Interchange induced in the receiving coil (7a) near the upper surface.
Voltage level SVa ratio (E ₀ ) to the molten metal upper surface level
Is converted into an electric signal representing
The error due to the fluctuation of the electrical property values of the vessel (2, 3) is substantially
The above is not included. That is, the thickness of the container (2,3)
Even if there is a change in temperature or the temperature of the container
However, the level measurement error due to these is virtually eliminated.
Other objects and features of the present invention will be described below with reference to the drawings.
It will be clear from the explanation of the example.

[0012]

FIG. 1 shows an embodiment of the present invention . In the figure, the transmitting coil 4a and the receiving coil 7a are arranged near the molten steel 1 where the molten steel 1 does not reach, and the bandpass filter 8b, the synchronous rectifier 9b, and the low-pass filter 10b are placed, The alternating voltage of the AC power supply 5b is applied to the coil 4b. A part of the magnetic flux emitted from the transmission coil 4b passes through the molds 2 and 3 and reaches the reception coil 7b. The induced voltage of the receiving coil 7b is signal-processed through the bandpass filter 8b, the synchronous rectifier 9b, and the lowpass filter 10b, and becomes the DC voltage SVb.

Molten steel 1 is a transmitter coil 4a-a receiver coil 7a.
When it is not in the position, the output voltage value SVa of the low-pass filter 10a has a high value.
The amount of fluctuation due to the change in the electrical property value of is large, and conversely, when the molten steel 1 is filled between the transmitting coil 4a and the receiving coil 7a, the output voltage value SVa of the low pass filter 10a takes a low value. At this time, the variation amount due to the change in the electrical property values of the molds 2 and 3 is small, and further, the output voltage value of the low pass filter 10a when the molten steel 1 is at the intermediate position between the transmitting coil 4a and the receiving coil 7a. SV
a indicates an intermediate value, and at this time, the variation amount due to the change in the electrical property values of the molds 2 and 3 also assumes an intermediate value.

Therefore, the output voltage value of the low-pass filter 10a is Ea when there is no change in the electrical properties of the molds 2 and 3 (it changes only by the molten steel level).
Then, when the molten steel 1 is not at the positions of the transmitting and receiving coils 4a and 7a, the voltage value and the reference voltage value when the molten steel 1 changes due to the change of the electrical property values of the molds 2 and 3 (the position of the transmitting and receiving coils 4b to 7b of the molten steel 1) It is desirable to take an average value of the voltage values that change due to fluctuations in the electrical property values of the molds 2 and 3 when it is not). Let ε be the ratio of the output voltage value SVa
Is expressed by the following equation (1).

SVa = Ea · ε (V) (1) On the other hand, the output voltage value SV of the low-pass filter 10b of the correction device composed of 4b, 5b, 7b, 8b, 9b, and 10b.
b is the output voltage value of the low-pass filter 10b, assuming that there is no change in the electrical properties of the molds 2 and 3.
If it is b, it can be expressed by the following equation (2).

SVb = Ebε (V) (2) Here, Eb is a constant value because the transmitting / receiving coils 5b and 7b are at positions where they are not affected by the fluctuation of the molten metal level. Therefore, when K ₁ is a constant of proportionality, SVb may be made dimensionless and expressed as the following equation (3). In other words, 4
The output voltage value SVb of the low-pass filter 10b of the correction device composed of b, 5b, 7b, 8b, 9b and 10b is
It changes only by the fluctuation of the electrical property values of the molds 2 and 3.

SVb ′ = K ₁ · ε (3) Here, the divider 12 outputs the ratio of SVa and SVb, that is, the output of the divider 11 which is the ratio of the equations (1) and (3).
₀ is represented by the following equation (4).

E ₀ = SVa / SVb ′ (V) = (Ea · ε) / (K ₁ · ε) = K ₂ · Ea (4) (where K ₂ : proportional constant) Therefore, the output of the divider 11 The value E ₀ is not affected by the variation ε of the electrical property values of the molds 2 and 3, and changes only by the molten steel level change Ea. Then, the melt level converter 12 converts the output voltage value E ₀ of the divider 11 into a molten steel melt level value.

[0019]

As described above, according to the present invention, the level of the molten steel molten metal level does not fluctuate due to the variation of the electrical property value of the mold or the like, which causes a measurement error, and the molten metal level can be accurately measured. It becomes possible to measure.

Further, the correction devices 4b to 10b have the same structure as the molten metal level measuring devices 4a to 10a, and not only the fluctuation of the electrical property values of the mold etc., but also other power source voltage of the molten metal level measuring device, for example. Even if there is a fluctuation in output due to fluctuations or the like, since the ratio of the molten metal level measuring device and the compensating device is adopted, it is not affected by this and stable molten metal level measurement is possible.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention .

FIG. 2 is a graph showing the relationship between the molten metal level of molten steel 1 shown in FIG. 1 and the output voltage values of low-pass filters 10a and 10b.

FIG. 3 is a block diagram showing a conventional molten metal level detecting device.

[Explanation of symbols]

1: Molten steel 2, 3: Metal container (mold etc.) 4a, 4b: Transmission coil 5a, 5b: AC power supply 6: Space 7a, 7b: Reception coil 8a, 8b: Bandpass filter 9a, 9b: Synchronous rectifier 10a, 10b : Low pass filter 11: Divider 12: Level controller

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Kei Hanaka Hachiro 20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel Stock Company Technical Development Division (56) Reference JP-A-3-105219 (JP, A) ) JP-A-48-43367 (JP, A) JP-A-61-233323 (JP, A) Jitsukaihei 2-17631 (JP, U)

Claims (1)

[Claims] 1. A container is provided outside the container containing the molten metal.
With a transmitter coil and a receiver coil that are placed opposite to each other.
A set of il, and the upper part of the molten metal is divided from the upper part to the upper part.
Multiple sets of detection coils to be applied; alternating voltage is applied to each transmission coil of the multiple sets of detection coils
An alternating current power supply; a voltage detecting means for detecting an alternating voltage induced in each receiving coil of the plurality of detecting coils ; and an upper surface of the molten metal detected by the voltage detecting means.
Is not affected by level fluctuations on the upper surface of the molten metal.
For the level SVb of the alternating voltage induced in the receiving coil
Below the receiving coil and near the top surface.
Ratio of alternating voltage level SVa induced in receiving coil
Operator for converting the above into an electric signal representing the level of the upper surface
Stage; molten metal level detecting apparatus comprising a.