JPH0481733B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for measuring and controlling the level of heated liquid in a container, and more particularly to a method for measuring and controlling the level of molten metal in a container, such as a continuous casting mold.

BACKGROUND OF THE INVENTION Measuring the level of molten steel in continuous casting molds typically utilizes a plurality of thermocouple devices evenly spaced on the mold wall. These thermocouples output voltage signals corresponding to the heat distribution along the mold caused by the liquid steel in the mold. Traditional devices that determine liquid level from thermocouple signals are
Disclosed in US Pat. Nos. 3,204,460 and 3,399,566. The systems described in these patents have been popular for many years as desirable systems. However, recent changes in casting operations requiring tighter control of the casting process have necessitated modifications to such conventional equipment. Changes in casting flux and the formation of flux on the mold walls, combined with flooded tube pouring practices, have increased the problems associated with determining the level of molten steel in the mold. Additionally, sudden changes in mold level and casting speed can sometimes cause false level indications. Perhaps the most common problem is erroneous vibration and sluggish response of the recording device due to improper amplifier gain adjustment. Serious problems occur if the thermocouple device is not making contact or is shot.

In order to solve the above-mentioned problems, a method has recently been proposed in which the signal of a thermocouple detection device is digitally analyzed to determine the liquid level. This method is described in the application invented by Wilson and Reikatsuk. The digital method disclosed in this application is susceptible to jumps in the indication level each time the indication level passes the location of the detection device. This jump in indicated level will, of course, occur more frequently when the desired level in the mold is located at one detector rather than occasionally between two detectors. The present invention is an improvement on the conventional digital method and aims at solving the above-mentioned problems.

SUMMARY OF THE INVENTION The method of the present invention comprises the steps of converting voltage signals from a plurality of temperature sensing means mounted at equal vertical intervals on the container wall above and below the expected liquid level in the container into digital values. Contains. The conversion signal is periodically scanned in a vertical direction, preferably from the top to the bottom of the container. The position of the uppermost detection means n having a conversion signal value Sn of sufficient strength corresponding to the temperature below the liquid level is then determined. Preferably,
This is at least one of the highest converted signal values, more preferably the average value m of the three highest converted signal values.
This is achieved by taking . This average value is then multiplied by the fraction p to obtain the converted signal value Se where the liquid level would normally be expected to be. The fraction p is determined based on observation and experience. After the position n has been determined, the position at which the measured liquid level lies is calculated at a fraction F of the spacing between the temperature sensing means n and the temperature sensing means one above it n-1. The fraction F is
It is calculated from the functions of the converted signal values Sn-1, Se and So. Preferably, the fraction F is defined by the formula: F=(Sn-1)-So/Se-So. where Sn-1 is the converted signal value of temperature sensing means n-1 and Se is the expected liquid level in each scan based on the average value m of at least one of the largest converted signal values. So is the converted signal value at the location, and So is the converted signal value sufficient to make the numerator of the fraction F zero or near zero immediately before the position of the temperature sensing means n changes. Preferably, So is also calculated as a function of the average value m of the at least one highest converted signal value in each scan.

In the preferred embodiment, So initially So=
Defined as c×m. Here c is 0 to about 0.50
selected from within the range. In the next scan,
When Sn falls within a range from Se to a predetermined % larger than Se, So is reset to So=Sn-1, and Sn-1 determined by each scan falls within a range from Se to a predetermined % smaller than Se. When it becomes, So = So=
It is reset at Sn-2. These values remain in that state until reset again due to the conditions described above. These adjustments are made to ensure smooth movement of the indicated level as the actual liquid level in the mold is falling or rising.

The measured liquid level in the container is then determined from n and F. This is obtained by the relation L=[n-F-1](SF)+PD. Here, L is the measurement level, SF is the distance between the temperature sensing means, and PD is the distance from the top of the container to the uppermost temperature sensing means.

DESCRIPTION OF PREFERRED EMBODIMENTS The present invention will be described below based on embodiments thereof with reference to the drawings.

FIG. 1 shows the voltage signal profile of thermocouple detection devices equidistantly placed in a continuous casting mold.
The detection device is of the type described in US Pat. No. 3,797,310 and US Pat. Nos. 3,204,460 and
Installed in a continuous casting mold as shown in No. 3399566. For more information on these, please refer to the above-mentioned US patents. US Patent No.
As described in No. 3,797,310, the signal of the detection device is converted into a digital value and periodically scanned in the vertical direction from the top to the bottom of the mold. In the method of the invention, a slightly different method is used for determining the position of the uppermost sensing device or temperature sensing means n, which has a conversion signal value Sn that corresponds sufficiently to the temperature that indicates the position below the molten steel level in the mold. be done. In a preferred embodiment of the invention, an average value of at least one highest converted signal value is calculated in each scan. This average value is denoted by m,
Preferably m is calculated as the arithmetic average of the three largest signal values of each scan. From this average value m, two other values are calculated which will be used as described later in this specification. First, Se is the relational expression
Calculated from Se=p×m. where P is a constant determined by experience and observation to obtain a value corresponding to the actual molten steel level in the mold. value p
is generally within the range of about 0.50 to about 0.90. In this example, p was set to 0.70. The uppermost detection means with a converted signal value greater than Se is n
It is indicated by.

First, for the first scan, the other value So is
Calculated from So=c×m. Here, c is a constant whose value is smaller than p, and is in the range of 0 to about 0.50. In our system, c is initially 0.3
It was set to . In the next scan, the value of So is
Immediately before the position of the temperature sensing means n is changed, the conversion signal value is adjusted to be sufficient to bring the numerator of the fraction F to zero or near zero.

After the position of the detection means n has been determined, a fraction F is calculated which together with n determines the position of the measured liquid steel level L in the mold. Preferably, F is determined from the relation: F=(Sn-1)-So/Se-So. Here, Sn-1 is the converted signal value of the temperature detection means immediately above n. In actual operation, the converted signal values are adjusted as shown in FIG. The adjustment values Se and So are shown as squares in many positions of the measuring device. All measuring devices with converted signal values greater than Se are set to Se, and all measuring devices with converted signal values less than So are set to So. This simplifies the calculation of the measurement level from the scan profile. It is clear that F takes on a negative value each time Sn-1 becomes less than or equal to So. This occurs when Sn approaches Se. That is, each time the level of liquid steel in the mold falls, for example from a level between measuring devices 3 and 4 to a level between measuring devices 4 and 5. This is indicated in the drawing by an open circle, indicating the value during a change in level, in this case a descending level. In FIG. 1, the detection device 4 detects the new value Sn=2.94
It is shown to have . The value Se calculated from the other white circles is 2.83, and m is 4.04.
So is 1.21. Thus, F takes on a negative value, which causes the measured level to jump at the measuring device 4. To correct this, a new value of So is calculated each time Sn approaches within a predetermined percentage of Se. So is the relational expression,
Determined by So=Sn-1. In the above relational expression, by replacing So with a new value, the possibility that F takes a negative value is removed. this
The approximation of Sn to Se, which requires an iterative calculation of So, is determined empirically and is of course related to the accuracy with which Se is estimated. In the system we have implemented, we have found that recalculation of So is only necessary when Sn falls within the range of Se to 1.03Se. A similar adjustment of the value of So occurs at rising liquid levels, i.e. Sn−1
is required each time approaches the value of Sn. In this way, So is reset to avoid the denominator of the fraction F becoming negative. This is Sn−
1 approaches within a predetermined % range of the value of Sn, So
This is achieved by adjusting So=Sn-2.
The measurement level L is then calculated by the relation: L=[n-F-1](SF)+PD. where SF is the spacing between measuring devices and PD is the distance from the top of the mold to the top measuring device attached to the mold.

Finally, the rate at which liquid steel is added to the mold and the rate at which steel is withdrawn from the mold is controlled based on the measured level of liquid steel in the mold. For example, this is achieved by the method of US Pat. No. 3,300,820. Second
The figure shows a preferred system for adjusting the rate of pouring steel into a mold and the rate of withdrawing steel from a mold, which is a system invented and currently pending by the inventor of the present invention. According to this method,
It is desirable to control the casting speed only when the mold level exceeds a predetermined level. Measurements of the liquid steel level in the mold can be obtained by the digital method described above. An error signal is generated as the difference between a voltage proportional to the measured level and a voltage proportional to the set level. The error signal has a polarity change indicating the direction of change between the two. If the measured level is determined to be within predetermined limits, the system continues in flow regulation mode to maintain a constant casting speed. In this mode, the flow control algorithm calculates output based on the sum of proportional, integral, and derivative functions of the error signal over time and a value proportional to the inverse of the square root of the change in liquid level in the tundish. used for. This combined control signal is used to control the flow rate by changing the position of the slide gate valve in the tundish. The slide gate valve is positioned by a hydraulic cylinder that is controlled either by a hydraulic servo valve or by a pulse example that steps through a number of positions on the cylinder.

If the mold level error signal is greater than the limit value, the system begins controlling the casting speed while holding the tundish slide gate device in its final position. A warning device alerts the operator that speed control mode has been entered. The system will not return to flow control mode until the operator clears the problem in the system and resets the flow control system. Preferably, the system also has the ability to control the liquid level in the tundish through a hydraulic ladle gate system and suitable liquid level sensing in the tundish. An example of the latter is EMLI in Stadvitsk.
It is a system.

FIG. 2 shows a mold 10, a tundish 12 and a ladle 15. A plurality of thermocouple measuring devices 16 are attached to the mold,
These thermocouple measuring devices input voltage signals to the microcomputer 17. Furthermore, from the tundish slide gate control device 20 and the tundish liquid level measuring device 22,
The computer accepts input of the actual gate position. Similarly, the computer receives actual gate position input from the ladle slide gate control 24 through the tundish level indication control 26. A number of desirable settings or targets include a mold level setting of 28 and a tundish liquid level setting of 30.
and speed setting value 32 are entered manually. Actual speed 34 is also input into the computer. These signals are used to control the liquid level in the mold based on calculated measurement levels and a number of system settings. When liquid level control cannot be achieved by moving to the ladle gate and tundish gate, speed control is initiated to maintain a suitable liquid level.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing plots of the voltage signals of a number of temperature sensing means improved in accordance with the present invention, and FIG. 2 is a schematic diagram of a preferred flow and speed control system used in the method of the present invention. There is. 10...Mold, 12...Tandatetsu, 15
...RAIDLE, 16...Thermocouple detection device, 17...
...microcomputer.

Claims (1)

Claims: 1. A method for measuring and controlling the level of a heated liquid in a container, the method comprising the following steps: (a) measuring and controlling the level of heated liquid in a container, the method comprising: converting into digital values the voltage signals from a plurality of temperature sensing means mounted spaced apart in the direction, said voltage signals being indicative of the temperature distribution on the container wall for the liquid in the container; (b ) periodically scanning the converted digital signal values successively in the vertical direction; (c) having a converted signal value Sn of an intensity indicative of the temperature below the liquid level in the container from the scanning signal values; determining the position of the uppermost temperature sensing means n; (d) the temperature sensing means n between which the measured liquid level is located and the one temperature sensing means n- above;
1, the fraction F is the converted signal value Sn of the temperature detection means n-1.
-1, a converted signal value Se at the position where the liquid level is expected to exist, and a converted signal value So sufficient to bring the value of the fraction F to zero or near zero just before the position of the temperature sensing means n changes. and Se is further calculated as a function of the at least one highest converted signal value in each scan; (e) calculating the measured liquid level in the container from said n and F; (f) controlling the injection of liquid into and the discharge of liquid from the container based on the measured liquid level; 2. The method of claim 1, wherein Se is determined from the relation Se=p×m, where m is the average of at least one largest converted signal value in each scan, and p is an empirical is a fraction determined by , where n is the converted signal value Sn larger than Se
The method wherein the uppermost temperature sensing means has: 3 Se is determined by our relational expression Se=p×m, and each time the value Sn becomes a value within a predetermined range that is larger or smaller than Se in each scan, the value of So is determined according to the result of the converted signal value. , where So is Sn within a predetermined range from Se.
Every time So reaches a value larger than Se by a predetermined percentage, So becomes Sn−1.
is reset, and furthermore, So is reset when Sn is within the specified range.
Whenever Se enters a value smaller than Se by a predetermined %, So
3. A method according to claim 2, characterized in that is reset at Sn-2. 4. Method according to claim 1, characterized in that F is determined by the formula: F=(Sn-1)-So/Se-So. 5 The measured liquid level L is determined by the relation L=[n-F-1](SF)+PD, where SF is the spacing between the temperature sensing means and PD is the distance between the first temperature sensing means from the top of the container. A method according to claim 1, characterized in that the distance to the means is the distance to the means.