JPH0367578B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to an improvement of a method and device for calibrating an electromagnetic induction type mold level meter in continuous casting. [Prior art] In continuous casting equipment, automatic control of the level of molten metal in the mold is extremely important in order to maintain the quality of cast products, especially surface quality, and in terms of automating operations and saving labor. That's true. In particular, recently, steel companies have been researching attempts to fully automate continuous casting casting operations, but this is to automate the start and end of continuous casting casting operations, and is usually referred to as auto-start and auto-stop. ing. Among these, auto-start is a technology used to pour hot water until the hot water level reaches a steady state, and along with technology to control the hot water level in an unsteady state, the selection of a hot water level meter is important. On the water level meter
There are RI type, electromagnetic induction type, thermocouple type, etc., and each type has its own features, but the electromagnetic type is superior to other types in terms of performance and safety. Table 1 shows a comparison of each method.

[Problem that the invention seeks to solve]

By the way, the level meter calibration method using this AGC method has no problems when the casting is large, but when applied to the automatic start of small-section molds such as continuous casting of pillars, the following problems arise. There is. In other words, in a small-section mold, the rising speed of the molten metal level at the start of pouring is too fast, and sufficient calibration accuracy cannot be obtained, making it impossible to apply the method to auto-start. Generally, the rate of rise of the melt level is 5 to 8 in the case of slab casting.
mm/sec, but in the case of small cross-section billets, the speed is 20 to 40 mm/sec, several times the speed in the case of slabs. The time required for AGC calibration is normally 500 m.s. Therefore, it is difficult to use the conventional technology for molds with small cross-sections.
If the AGC calibration method is applied, the hot water level will change by 10 to 20 mm during the calibration, and the function as a hot water level gauge will be lost, making it impossible to apply it to automatic starts, etc. As an electromagnetic induction level meter that can be used for small-section molds such as continuous pillar casting, an eddy current stop level meter using a differential voltage feedback method by the same applicant is known, but the relative distance between the sensor, the nozzle, and the mold The error due to changes in is large. Figure 5 shows infinite AGC for a small electromagnetic induction level meter.
However, there is an error of about 5 to 7 mm due to changes in the relative distance between the level meter and the mold side wall and nozzle, and when combined with the AGC error of 3 to 4 mm due to the circuit nozzle, it is very large. Sufficient calibration accuracy cannot be obtained. The present invention aims to provide a highly accurate and high-speed calibration method and apparatus that solves the problems of the conventional calibration methods described above. [Means for solving the problem] In the calibration circuit of the electromagnetic induction level meter,
Added an AGC switch, infinite voltage setting section, and high-speed calculation circuit. [Function] The above configuration reduces the time required for calibration compared to conventional
It can be significantly shortened from 500m.s. to 40m.s., and
It is now possible to use either 1-point AGC or infinite AGC. This situation will be explained in more detail. When the output voltage f(h) of the sensor coil 3 changes by Δf due to the influence of the mold side wall, nozzle, etc. and becomes f(h) + Δf, and the level meter output voltage e _put changes to e _put + Δe, e _put +Δe=−G ₁ e _io /1−G ₁ [f(h)+Δf] ...(3). In equation (3), when controlling so that Δe=0v, it is necessary to consider K related to the control voltage from the control circuit 9, so e _put +Δe=−G ₁ e _io /1−G ₁ (K+f(h)+Δf) This formula shows the following. The relationship between e _put and K is expressed as a hyperbola. (The x-axis is K, and the y-axis is e _put. ) The influence of the mold side wall, nozzle, etc. on the level meter output voltage is that this hyperbola moves in parallel in the x-axis direction. By adjusting K so that Δe=0, that is, K−Δf, the level meter output voltage can be restored to the original voltage e _put . From the above, the coefficient K can be set for the deviation Δe of the voltage e _put corresponding to the reference position by adjusting K so that Δe=0, that is, K−Δf.
In other words, in the past, a feedback system using PI operation was configured for nonlinear level meter output characteristics, and the presence of an integrating circuit required time for calibration. However, according to this method, the control amount required for calibration can be determined immediately, making it possible to shorten the calibration time. Furthermore, in order for this method to be realized, the following three terms are the conditions mentioned above. The relationship between Δe and Δf is defined by a fixed law. It is possible to realize a high-speed calculation circuit that calculates Δf from Δe. e _put is not saturated before calibration. The results of the study regarding whether or not the above conditions can be realized are explained below. FIG. 6 shows characteristic curves of the control voltage and level indication value measured for each case while varying the distance d between the mold side wall and the sensor, superimposed at the reference position. From this diagram, the level indication value is 90mm.
Although there are some differences in the characteristics above,
Overall, it can be considered that it remains unchanged for practical purposes. Therefore, it can be determined that the relationship between Δe and Δf is not affected by the presence or absence of disturbance. Next, consider the relationship between Δe and Δf. For ease of handling, in equation (2), Δe is expressed as y, K
By replacing x with x, equation (2) is expressed as the following equation (4). y=b/x+a...(4) However, a and b are constants. In FIG. 7, curve C shows the characteristics in the standard state, and curve D shows the characteristics after changes due to gain changes. In the standard characteristic curve C, x
When = x ₀ , y = y ₀ , and the characteristic curve D after change
Assume that when x=x ₀ , y=y ₀ . Here, y ₁ =y ₀ +Δy. Now, in curve D, if we assume that y= _y0 when x= _x1 , then the following equation (5)
holds, and x ₁ = x ₀ +Δx. By expanding and rearranging equation (5), we obtain the following equation (6). Δx＝b/y ₀ −b/y ₀ +Δy ...(6) This shows that the relationship between the deviation amount and the control output is expressed as a hyperbola. Even if it is not used, it can be calculated using a commercially available inexpensive multi-function module. Furthermore, the module is capable of analog operation and can construct a circuit without time delay. Furthermore, level meter output voltage e _put due to gain change
Regarding saturation, it is possible to keep it in a non-saturated state by using infinite AGC etc. in advance. FIG. 8 is a diagram showing an example of measuring the response time of the level meter output voltage E to a change in the control voltage F when the control coefficient K is changed in a stepwise manner. As shown in the figure, the required time is approximately 40 m.s. with conventional equipment.
It can be seen that the AGC time required can be significantly reduced compared to the previous 500 m.s. [Embodiment of the Invention] FIG. 1 is a configuration diagram of an auto-start AGC circuit showing an embodiment of the present invention. In the figure, 1 to 9 are the same parts as the conventional device. 10 is AGC switch,
11 is an infinite voltage setting section, and 12 is a high-speed calculation circuit. In the figure, by switching the AGC switch 10, it is configured so that it can be used for either 1-point AGC or infinite AGC. In other words, when a 1-point AGC command is issued, the amount of deviation between the level meter output voltage and the reference voltage setting section 7 is input to the control circuit 12, and in the case of infinite AGC, the AGC switch 10 is switched and the level meter output voltage and the infinite The amount of deviation from the large voltage setting section 11 is input to the control circuit 9. As described above, the present invention has the advantage that it can be easily modified without significantly changing the conventional circuit. Although this embodiment has been described as being applied to auto-start, the present invention is not limited to this and can be applied to devices that require high-speed calibration. [Effects of the Invention] The present invention provides an electromagnetic induction level meter for a continuous casting casting device, which includes an AGC switch in its calibration circuit,
Equipped with an infinite voltage setting section and a high-speed calculation circuit,
Both 1-point AGC and infinite AGC can be used, and the time required for AGC has been significantly shortened, making it possible to perform high-precision and quick calibration even in continuous casting of small-section castings such as billet casting. We were able to achieve the excellent effect of making auto-start possible.

[Brief explanation of drawings]

Figure 1 is a configuration diagram of an electromagnetic induction level meter showing an embodiment of the present invention, Figure 2 is a configuration diagram of a conventional electromagnetic induction level meter, and Figure 3 is the relationship between the hot water level and the level meter output voltage. Figure 4 is a diagram showing the configuration of conventional continuous casting, Figure 5 is a diagram showing changes in the level meter reading according to changes in the distance between the level meter sensor and the mold, and Figure 6 is the diagram showing the level meter. A diagram showing changes in the control voltage-level indication value characteristic curve depending on the distance between the meter sensor and the mold side wall, Figure 7 is a diagram showing the control voltage-level indication value characteristic curve, and Figure 8 shows changes in the control voltage. FIG. 3 is a diagram showing the response characteristics of the level meter output voltage when the output voltage is increased. In the figure, 1 is an oscillator, 2 is an amplifier, 3 is a sensor coil, 4 is an adder, 7 is a reference voltage setting section, 8 is a switch circuit, 9 is a control circuit, 10 is an AGC switch,
11 is an infinite voltage setting section, and 12 is a high-speed calculation circuit.

Claims (1)

[Claims] 1. A positive feedback circuit calibrated by a sensor coil to which an alternating current voltage is applied and a feedback amplifier, and a control voltage for zeroing the deviation between the output of the positive feedback circuit and a reference value as described above. a control circuit for feeding back to a feedback amplifier, and detects the level of hot water in the mold by detecting a change in the impedance of the sensor coil; A casting mold water level gauge characterized in that it is equipped with a high-speed arithmetic circuit that calculates a control voltage of the second control voltage and feeds back the second control voltage to the feedback amplifier. 2 The feedback amplifier connects the AGC circuit, whose gain is adjusted so that the output of the hot water level gauge is constant when there is no hot water in the mold, to the hot water level gauge when there is hot water at a predetermined level in the mold. 2. The casting mold level gauge according to claim 1, further comprising an AGC circuit whose gain is adjusted so that the output of the level gauge is constant, and these circuits are switchably connected.