JPH0348448B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for detecting the position of a molten metal surface using an electromagnetic coupling effect.

As a conventional method for detecting the level of molten metal, a method using electromagnetic induction, an example of which is shown in FIG. 1, is well known. That is, in FIG. 1, M is an object to be detected (molten metal), S is powder or slag, B is a metal container (for example, a mold), 31 is a reference signal oscillator that oscillates an alternating current signal of a predetermined frequency, and 41 is a known signal. an AC bridge consisting of impedances Z ₁ , Z ₂ , Z ₃ and a variable Z ₄ with values of , where Z ₄ is in this case the detection coil 2 shown here.
1 is an impedance, and 51 is a differential amplifier.

In this configuration, after setting the distance D between the detection coil 21 and the object M to be detected to be substantially zero distance,
When an AC signal is applied from the reference signal oscillator 31 to the AC bridge 41 including the detection coil 21, the AC bridge 41 becomes balanced when the condition of Z ₁ ·Z ₃ =Z ₂ ·Z ₄ is satisfied, as is well known. Therefore, under this balanced state, the output of the AC bridge 41 is zero, and no output appears in the differential amplifier 51.

When the distance D between the detection coil 21 and the detected object M is reduced from this initial setting state, the impedance Z ₄ of the detection coil 21 corresponds to the distance D due to the change in impedance due to electromagnetic induction between the detection coil 21 and the detected object M. Obtain the output change of the AC bridge 41. Thus, it becomes possible to continuously measure the position of the detected object M from the detection coil 21.

However, in the conventional detection method described above, the measurement span is almost exclusively limited by the coil diameter, and the detection coil inevitably needs to be enlarged for objects with large positional fluctuations. In order to improve the output variation or measurement span, which is often difficult to apply, the number of turns of the detection coil 21 is increased, and the detection coil 21 is further wound around a ferromagnetic material such as a ferrite core, but such a configuration is not well known. As shown in the figure above, not only does the impedance of the detection coil change due to external temperature changes, making it impossible to obtain good accuracy, but it is also difficult to provide a heat-resistant structure on its own in a high-temperature atmosphere, and some type of cooling device is required. In addition to being disadvantageous in terms of cost, it cannot be used in lines where accidents such as cooling water leakage are particularly averse.When detecting the level or position of molten metal in a container such as a ladle or mold, detection is performed by the action of the metal container. This causes a change in the impedance of the coil,
Furthermore, the output changes depending on the type of metal in the container and its change over time, making it difficult to obtain good accuracy.

The present invention solves the problems of the conventional method and provides a device that can continuously detect the level of hot water in a container without contact in a high-temperature atmosphere without using a cooling device. is a detection unit in which a pair of non-magnetic and heat-resistant coils are arranged close to the molten metal surface at symmetrical positions with a constant interval as the axis. a detection smoothing section that applies an AC voltage to one of the pair of coils and uses the induced voltage of the other coil in the electromagnetic field generated thereby as a DC voltage signal; A correction function section is provided which stores in advance a voltage value that is determined by the action of the container and does not correspond to the distance between the detection section and the molten metal surface, and corrects the output voltage of the detection smoothing section using the stored voltage. This is a molten metal level detection device characterized by:

The device of the present invention includes a pair of detection coils each having a heat-resistant strand wound around a bobbin having heat-resistant and high insulation properties.
One is a transmitting coil and the other is a receiving coil, which are arranged side by side with a certain interval and inclination, and are fixed facing each other on the molten metal surface.

With this configuration, a high frequency constant current is passed through the transmitting coil, thereby generating an electromagnetic field. As is well known, an induced voltage due to electromagnetic induction is generated in the receiving coils arranged in parallel within this electromagnetic field. When the distance between the transmitting/receiving coil and the object to be detected is set to substantially infinity, this induced voltage becomes a constant voltage mainly determined by the excitation current of the transmitting coil and the arrangement of the transmitting/receiving coil.

When the detected object approaches the detection coil from this state, the distribution of the electromagnetic field changes due to the effect of the detected object, and the induced voltage in the receiving coil corresponds to the distance between the detection coil and the detected object. A voltage change is obtained from which distance can be measured. Furthermore, a function that self-learns the degree of influence of containers such as ladles and molds in advance compensates for the influence of the outside world and always maintains constant output characteristics with respect to distance, making highly reliable detection possible.

Additionally, with this configuration, the effects of changes in the physical properties of the object to be detected can be minimized, the heat-resistant detection coil has high insulation characteristics, and can be installed in high-temperature atmospheres, and the excitation current can be made constant. , by optimizing the detection coil that is less susceptible to impedance fluctuations due to temperature and the circuit constants including the detection coil and amplifier, it eliminates the need for correction information and circuitry for temperature compensation. By adding a self-correction function that corrects the influence of molten metal, highly reliable molten metal level detection can be performed.

The present invention will be explained in more detail based on illustrated embodiments.

FIG. 2 is a block diagram showing the overall configuration of an apparatus according to an embodiment of the present invention. In the figure, B is a mold, M is a molten metal, and S is a molten suspended substance (slag or powder), which in this case is a non-detectable substance.

2 is a pair of detection coils, 2T is a transmitter coil,
2R is a receiving coil. In this case, the transmitting and receiving coils 2T and 2R have the same structure, and a pair constitutes the detection coil 2.

Reference numeral 1 denotes a high-frequency power source that oscillates a predetermined high-frequency signal and supplies a constant current to the transmitting coil 2T.

3 is an amplifier for amplifying the induced voltage from the receiving coil 2R, 4 is a detection smoother for converting the high frequency signal from the amplifier 3 into a DC signal, 5-1 is a DC bias voltage setting device, and 5 is an adder. An amplifier adds and amplifies the signal from the detection smoother 4 and the voltage from the voltage setting device 5-1. 6 is an arithmetic processor, the operation of which will be described later. PB is a push button switch, and 7 is a linearizer for linearizing the DC signal from the arithmetic processor 6.

FIG. 3 is a diagram showing circuit details of the arithmetic processor 6 of FIG. 2. This circuit is related to the self-correction function described above. In FIG. 3, 6-1 is a differential amplifier. 6-2 is a digital servo module (hereinafter referred to as DISMO), which is internally composed of a composite circuit including a comparator circuit, a reversible counter, a D/A/A/D conversion circuit, etc., and is connected to the differential amplifier 6-1. By forming a closed loop with, for example, when pushbutton PB is pressed, DISMO6-
2 enters the tracking state, outputs the same voltage with the opposite phase to the input voltage at point _a , and then presses the push button.
When PB is opened, it becomes a hold state and the voltage mentioned above is memorized. Thereby, the output of the differential amplifier 6-1 is automatically adjusted to zero by opening and closing the push button PB. 6-3 is the above DISMO6-2
The output of the logarithmic amplifier 6-3 is used as a reference voltage for correction. VR is a variable resistor, 6
-4 is a multiplier, and 6-5 is a linear amplifier for amplifying the output of the multiplier 6-4 to a required voltage level. With the circuit configuration shown in Figure 3,
The degree of influence of the container B mentioned above is detected by itself, and based on the detected amount, the influence of the container B is self-corrected (compensated) through real-time calculation processing.

FIG. 4 is a characteristic diagram showing an example of the influence of the outside world, that is, the influence of the metal container B. Here we show an example of the output characteristics used as parameters for the short side dimension (indicated by MS in the figure) of the mold for continuous slab casting. As the dimension of the short side of the mold increases, the output characteristics change as shown by curves a, b, and c. curve d
is the output characteristic when the mold dimensions are set to substantially infinity, that is, when there is no influence from the mold. V _MSO is written at the tail end of curve b, and this is the output voltage when MS = 140 mm and the object to be detected is set at substantially infinity. Similarly each
Different output voltages are obtained for the MS.

FIG. 5 is a diagram showing an example of the correction effect of the arithmetic processing unit 6 on the influence of the mold. Here, we show an example where the short side dimension of the mold is MS = 140 mm.
The horizontal axis shows the voltage corresponding to curve d (MS=∞) in Fig. 4, and the vertical axis shows the voltage corresponding to curve b (MS=140 mm) in Fig. 4.
Indicates the corresponding voltage. The straight line e in the figure shows the input voltage of the arithmetic processor 6, that is, the voltage before correction, and the straight line f shows the output voltage of the arithmetic processor 6, that is, the voltage after correction. As can be seen from the figure, the voltage before correction includes a bias component and has a small tilt angle, but the voltage after correction has the effect of the mold removed.

FIGS. 6a and 6b are a front view (partially sectional view) and a plan view showing a structural example of a detection coil and a holder used in the present invention. In the figure, 2-1 is a coil bobbin made of heat-resistant and highly insulating ceramic and has grooves on its outer circumferential surface. This is made of a material with good insulation properties, such as high-purity alumina, and is baked and molded. 2-2 is a coil in which a non-magnetic heat-resistant wire such as platinum or chromel wire is wound 20 to 30 times around the outer circumferential surface of the coil bobbin 2-1. It is designed to prevent short circuits between phases. Furthermore, the bobbin 2-1 is adhesively fixed to the pedestal 2-3 of the coil storage container main body 2-4 with heat-resistant cement or the like.

The coil storage container body 2-4 is made of the same material as the coil bobbin, but the base 2-3 may be made of non-magnetic metal such as stainless steel or copper. The fitting portion of the pedestal 2-3 with the container body is threaded so that they can be attached to and detached from each other. 2-3a, 2-3b are holes for passing the lead wires at both ends of the coil, 2-5a, 2-5b
The lead wire is covered with a ceramic tube and is of the same quality as the coil wire. 2-6 is a support rod made of heat-resistant ceramic or stainless steel.

The functions of the device of the present invention will be explained in detail below with reference to the drawings of the embodiments.

As shown in FIG. 2, the detection coil is composed of a transmitting coil 2T and a receiving coil 2R with a constant interval La and an inclination θ.

A constant current high frequency signal is supplied from the high frequency power source 1 to the transmitting coil 2T. As a result, a high frequency magnetic field is generated around the transmitting coil 2T. On the other hand, since the receiving coil 2R is provided close to the transmitting coil 2T and symmetrically with respect to the perpendicular to the hot water surface,
An induced voltage is generated in the receiving coil 2R due to electromagnetic induction. This induced voltage is amplified by an amplifier 3 and converted into a DC signal by a detection smoother 4 at the next stage.

When the distance between the detection coil 2, the molten metal M, and the mold B is substantially infinite, the DC signal is mainly generated by the energizing current of the transmitting coil 2T, the distance between the transmitting and receiving coils La, and the inclination angle θ. The minimum DC signal determined by is output.

This DC signal is input to the summing amplifier 5 having a predetermined amplification degree, but at this time, in order to satisfy the initial setting conditions of the next stage arithmetic processor 6, the DC bias voltage setting device 5-1 is operated. Adjustment is made so that the output of the summing amplifier 5 becomes zero.

Next, the detection coil 2 is installed and fixed at a predetermined position above the mold B. The output of the summing amplifier 5 when there is no molten metal in the mold B is input to the arithmetic processor 6. The output of this summing amplifier 5 is, for example, the fourth
The voltage corresponding to V _MSO is shown at the tail end of curve b in the figure.
That is, the voltage corresponds to the influence of the mold. When pushbutton PB is closed, DISMO6-2 enters the tracking state, and as a result, DISMO6-2
A voltage equivalent to V _MSO is outputted from the output terminal and simultaneously inputted to one input terminal of the differential amplifier 6-1. Next, when the push button PB is opened, the DISMO 6-2 goes into a hold state, the voltage corresponding to V _MSO is stored, and the output of the differential AMP 6-1 becomes zero.
Further, the voltage stored in the DISMO 6-2 is input to a logarithmic amplifier 6-3 and subjected to nonlinear conversion, and its output is divided by a variable resistor VR and input to a multiplier 6-4. That is, this corresponds to the voltage that corrects the influence of the mold. The other input voltage of the multiplier 6-4 is the output of the differential amplifier 6-1, that is, zero voltage, so the output of the multiplier 6-4 is zero.
That is, when there is no molten metal in the mold B, the output of the processor 6 is zero. This completes the initial operation.

Next, in actual measurement, as the level of the molten metal M in the mold B rises, for example, curve b in FIG.
However, by the initial operation described above, the voltage obtained by subtracting the bias component, that is, V _MSO , from curve b is input to the multiplier 6-4, and the mold influence, which is the other input of the multiplier 6-4, is input to the multiplier 6-4. The product with the correction voltage is output, amplified by a linear amplifier 6-5, and output. In other words, by appropriately setting the voltage division ratio of the variable resistor VR, that is, the correction coefficient, the curve d in Fig. 4 can be adjusted.
You can get output equivalent to . The present inventors have also confirmed that output curves equivalent to curve d can be obtained for curves a and c. The above-mentioned correction method can be expressed as the following formula.

Vc=(Vi-V _MSO )・K(log k V _MSO )...(1) However, Vc: Detection output after correction Vi: Detection output before correction obtained from the hot water level position V _MSO : The actual hot water level position Detection output K when the distance is at infinity, k: correction constant Note that a microcomputer can also be used as the above-mentioned calculation means.

The output processed by the arithmetic processor 6 is input to the next stage linearizer 7, and is used as a linearized output for monitoring the hot water level or as a signal for controlling the hot water level.

In the case of conventional electromagnetic method of hot water level detection, measures such as preparing compensation tape for each container in advance and forcibly cooling the detection coil to prevent temperature noise are used to compensate for the influence of the outside world. Ta.

However, it does not respond quickly to external factors, such as changes in the container over time, problems with the installation repeatability of the detection coil, or changes in ambient temperature. Therefore, in order to increase reliability, frequent calibration or There were drawbacks such as the need to modify the correction table. On the other hand, according to the present invention, a highly reliable device is realized by detecting the degree of influence of changes in the outside world each time and in a short time on the detector itself and performing self-correction. I was able to do that.

Furthermore, the following points can be mentioned as other features of the present invention.

(1) Since the number of turns of the detection coil is several tens of turns and it is made of non-magnetic material, the impedance change of the detection coil due to temperature fluctuation is extremely small.
Does not require temperature compensation of the detection signal.

(2) We have created a detection coil that is small, lightweight, and has heat resistance and high insulation properties.

Regarding (1) above, the excitation power source for the transmitter coil uses a constant current source to keep the strength of the surrounding magnetic field generated by the transmitter coil constant, and furthermore, A circuit configuration is used in which widely different excitation frequencies are used, or the harmonic index Q (=ωL/R) is made as small as possible.

In addition, the receiving coil also takes the same considerations as the transmitting coil, such as reducing its tuning index Q, and furthermore, a high-frequency amplifier 3 with low input impedance characteristics is used.
This is achieved by using .

Regarding (2) above, the detection coil has heat resistance and high insulation characteristics, so there is no need for forced cooling even in high temperature atmospheres of around 1000℃, and the structure is electrically and mechanically stable, so it is close to the molten metal surface. It can be installed by Furthermore, since the detection part is small and lightweight, it can be easily applied to detecting the level of molten metal in molds with small cross-sections.

Furthermore, since the device of the present invention has no moving parts, it is easy to adjust and maintain. In addition to detecting the level of molten metal in ladles and molds, the device of the present invention can also be applied to containers such as torpedo cars and tundishes, since it can be applied in adverse environments with high temperature atmospheres as described above. It is an effective device that can be widely applied to non-ferrous metals such as zinc and tin in addition to iron.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an example of a conventional hot water level detection device. FIG. 2 is a block diagram showing the configuration of an embodiment of the device of the present invention, FIG. 3 is a block diagram showing details of the arithmetic processor in FIG. 2, and FIG. 4 is an output characteristic diagram showing an example of the influence of the container. FIG. 5 is a diagram showing an example of the correction effect of the detection output in the embodiment of the present invention,
Figures 6a and 6b are a front view and a plan view showing the configuration of a detection coil in an embodiment of the present invention. M... Molten metal, B... Container (mold), 1... High frequency constant current power supply, 2... Detection coil, 2T... Transmitting coil, 2R... Receiving coil, 3... High frequency amplifier, 4...
Detection smoother, 5... Addition amplifier, 6... Arithmetic processor,
7...Linearizer.

Claims (1)

[Claims] 1. A detection unit in which a pair of non-magnetic and heat-resistant coils are arranged in parallel on the molten metal surface at symmetrical positions with a constant interval as the axis. , a detection smoothing section that applies an AC voltage to one of the pair of coils and uses the induced voltage of the other coil in the electromagnetic field generated thereby as a DC voltage signal; and a container for the molten metal. and a correction function section that corrects the output voltage of the detection smoothing section using the stored voltage. Molten metal level detection device.