JPS6093316A - Eddy current type hot water level measuring method - Google Patents

Abstract

PURPOSE:To prevent a measurement error due to phase shift and the occurrence of self-oscillation causing measurement impossibility by allowing the phase of a feedback voltage, which applies an AC voltage to a primary coil, to coincide with the phase of an output voltage through a phase shifter. CONSTITUTION:An eddy current is generated on the surface of a hot melted steel in accordance with the length from a head by a magnetic flux due to the detecting head consisting of the primary coil and a pair of secondary coils on and under the primary coil, and a voltage corresponding to the level of this surface is induced in secondary coils. The AC voltage due to an oscillator 6 and the feedback voltage are applied to the primary coil from a feedback amplifier 7. The phase of the feedback voltage, which passes an adder 9 which adds the output of the amplifier 7 and the differential output of a pair of secondary coils due to a differential amplifier 8, is allowed to coincide with the phase of the output of the amplifier 7 by a phase shifter 10 having feedback resistance R3 and R4, a phase shift controlling variable resistance R5, a capacitor C, etc. Consequently, the measurement error due to phase shift of the feedback voltage, the occurrence of self-oscillation causing measurement impossibility, etc. are prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a vortex-type hot water level measurement method.

For example, when continuously casting steel, it is necessary to maintain a constant level of the molten steel in the mold in order to improve the quality of the slab, and for this purpose it is necessary to accurately measure the level of the molten steel.

Conventionally, as a method for measuring the surface level of molten steel in a mold, there has been a thermocouple method in which a plurality of thermocouples are attached in the vertical direction of the mold and the surface level of molten steel is measured based on the measurement results by the thermocouples.

Another method is to attach an RI source to one wall of the mold, install a sensor to measure the intensity of the RI radiation on the other wall of the mold, and use the change in the intensity of the FtI radiation measured by the sensor to determine the inside of the mold. R to measure the molten steel surface level
There was the I-law, etc.

However, the thermocouple method described above requires processing to install the thermocouple on the mold wall.

Moreover, since the molten steel surface level is measured through the mold wall, responsiveness is poor.

On the other hand, the above-mentioned RI method measures the molten steel surface level through the mold wall, similar to the thermocouple method, and has poor responsiveness. proposed.

This vortex type hot water level measuring method will be explained with reference to FIG. In FIG. 1, molten steel 2 is continuously injected into a mold 1 from a tube (not shown).

A detection head 3 is vertically fixed on two surfaces of molten steel. The detection head 3 has one primary coil 4 and a pair of secondary coils 5° and 5b provided above and below the primary coil 4. An oscillator 6 applies a constant frequency father current voltage e='tr to the primary coil 4 via a feedback amplifier 7. Differential amplifier 8
is the difference between the voltages induced in the pair of secondary coils 5a and 5b. Adder 9 receives output voltage e of feedback amplifier 7. is added to the output voltage of the differential amplifier 8. This added first output voltage, ie, the feedback voltage end, is fed back to the feedback amplifier 7.

When the feedback amplifier 8 is valved and an alternating current voltage e of a constant frequency is applied from the oscillator 6 to the primary coil 4, a magnetic flux is generated, and as a result, a pair of secondary coils 5. An induced voltage is generated at and 5b. On the other hand, the magnetic flux intersects with the molten steel 2 in the mold 1, and eddy currents are generated on the surface of the molten steel. As a reaction to this, the induced voltage generated in the pair of secondary coils 5α and 5b changes, but of the pair of secondary coils 5a and 5b, the secondary coil 5b that is closer to the molten steel 2 surface is farther away from the molten steel 2 surface. The change is larger than that of the secondary coil 54 that is present. A pair of secondary coils5. and the difference in voltage induced in 5b (V
S = Va-Vb ) becomes a function f CL of the distance 1 between the detection head 3 and the bath @21 river.

The differential amplifier 8 calculates the difference Vs between the voltages induced in the pair of secondary coils 54 and 5b. The adder 9 adds the difference voltage Vs and the output voltage eO' of the feedback amplifier 7. This added output voltage is applied to the feedback amplifier 7 as a feedback voltage ea
It is returned as d.

Output voltage e of feedback amplifier 7. is expressed by a linear equation.

eo--e,,A,/(1-AH(K+A2 f(
f) l -41) However, e,: Output voltage of the oscillator 6.

A1: Amplification degree of feedback amplifier 7.

A2: Amplification degree of differential amplifier 8.

f(L): A function depending on the distance between the detection head 3 and the two molten steel surfaces.

K: Constant.

As is clear from equation (1), the output voltage e of the feedback amplifier 7. changes depending on the level of the two sides of the bathtub, so the pressure e at the output section. Although it is superior to the method in mold 1 when measuring , it has the following problems.

If a phase shift occurs in the positive feedback network, the operation becomes unstable/stiff, self-oscillation is induced, and accurate measurements cannot be obtained. There are first-order causes of phase shifts that occur within the feedback network. Namely, ■ Phase delay of the arithmetic unit itself that constitutes the feedback circuit.

■ Phase delay JL due to distributed capacitance of feedback circuit wiring.

■ The influence of the distributed capacity of the coaxial cable that connects the detection head 3 and the water level gauge body.

■ The influence of the mold wall when the distance between the detection head 3 and the mold side wall becomes close.

FIG. 2 shows the characteristics of the output voltage of the feedback amplifier with and without phase shift in the feedback network.

As shown in Figure 8t42, if there is a phase shift,
Output voltage e. An error occurs in the output voltage e. When the value exceeds a certain value, self-oscillation occurs and measurement becomes impossible.

This invention was made to solve the above-mentioned problems.

An AC voltage is applied from a feedback amplifier to the primary coil No. 111 of the detection head, which is composed of a primary coil and a pair of secondary coils, and the difference in the induced voltages generated in the pair of secondary coils is In the eddy current type hot water level measurement method, which comprises calculating the difference voltage by a differential amplifier, adding the difference voltage and the output voltage of the feedback amplifier by a 7-adder, and feeding the added voltage back to the feedback amplifier.

The phase of the feedback voltage fed back to the feedback amplifier.

The present invention is characterized in that the phase of the output voltage of the feedback amplifier is matched with the phase of the output voltage of the feedback amplifier by a phase shifter.

One embodiment of this invention will be described with reference to the drawings.

FIG. 3 IJ is a schematic configuration diagram of an embodiment of the present invention.

In FIG. 3, an oscillator 6 applies an alternating voltage of constant frequency to a primary coil (not shown) of the detection head via a feedback amplifier 7. A differential amplifier 8 is connected to the detector head.
The difference in induced voltages from a pair of secondary coils (not shown) is calculated. Adder 9 receives output voltage e of feedback amplifier 7. and the output voltage of the differential amplifier. The adder 9 has a resistor R, -
Resistor R2 and resistor HN f. Phase shifter 10 compensates for the phase shift of the feedback voltage from adder 9 +3ad. The phase shifter 10 has a negative feedback resistor 83. ) (4, ηr = resistor R3 and capacitor C are excluded.

The output voltage of the adder 9, that is, the output voltage of the differential amplifier 8 and the output voltage e from the feedback amplifier 7. The feedback voltage ead, which is the sum of the above, is expressed by a linear equation.

However, eo: Output voltage of feedback amplifier 7.

A2: Amplification degree of the differential amplifier 8, r(z): A function depending on the distance between the detection head 3 and the molten steel 2 surface.

Feedback voltage eod from adder 9 is applied to phase shifter 1o. The phase shifter 10 compensates for the phase shift of the feedback voltage ead, so that the output voltage e of the feedback amplifier 7 is adjusted. A feedback voltage e matching the phase of is fed back to the feedback amplifier 7.

The operation of phase shifter 10 will be explained. The previous day r from phase shifter 1o
2 feedback voltage is expressed by the following equation.

zl + Z2 zl” Z2 If -83=R4 is set in equation (3).

However, Bp: Feedback voltage of phase shifter 10, ead: Output voltage of adder 9.

Z: Impedance of variable resistor R5, Z2: Impedance of capacitor C.

As is clear from equation (4), the phase of the feedback voltage ep from the phase shifter IO is determined by changing the value of the variable resistor R6 since the amplification degree (R4/R3) of the phase shifter 10 is 1. It can be arbitrarily set to 1+1 by by this,
Output voltage e of feedback amplifier 9. It is possible to completely match the phase of the feedback voltage ead from the adder 9.

The ijJ resistance resistance R5 of the phase shifter 10 is set to the output voltage e of the feedback amplifier 9. and the feedback voltage from adder 9 end
To adjust the phase to match.

Do as follows. For example, feedback amplifier 7 is one oscillator 6
output box, pressure e. phase and the output voltage e of the feedback amplifier 7.

The output voltages e and e operate most efficiently when they are 180 degrees out of phase with the output voltages e and e.

are each measured using a phase meter, for example.

The value of the variable resistor R3 is manually adjusted so that the phase difference between them is 180 degrees.

Next, other embodiments of the invention will be described with reference to the drawings.

This embodiment differs from the previously described embodiment in that one-phase compensation is automatically performed.

FIG. 4 is a schematic diagram of another embodiment of the present invention.

In FIG. 4, the one-phase detector 11 detects the output voltage e of the oscillator 6 and the output voltage e of the feedback amplifier 7. A DC control voltage Eci corresponding to the phase difference between Eci and Eci is supplied to one input terminal X of the phase controller 12. The phase controller 12 includes a multiplier 13 and a capacitor C connected between the other input terminal Y of the multiplier 13 and the output terminal 2. Input terminal Y of phase shift controller 12
One input voltage e of the phase shifter 10 is applied to the input terminal X, and the control voltage Ec from the phase detector 11 is applied to the input terminal i.
do.

Multiplier”. 3's output 'b, pressure eM is.

-e-EC...(5) However, since the constant of -3 (multiplier) changes, when the value of control voltage EC changes, the voltage difference (e-eu) between both terminals of capacitor C changes. Change.

This causes the value of the current flowing through capacitor C to change.

Therefore, the capacitance of the capacitor C changes isometrically in response to changes in the pressure Ec.

For example, if we take the constant KQl/10 for Q, multiplication 11 units''3.

Control 4.11 < Etc. of capacitor C against pressure EC 111
1i? , F amount C8t"2. The characteristics are as shown in FIG.

In this way, if the capacitance of the capacitor C changes according to the control voltage EC, as is clear from equation (4).

The phase shifter 10 automatically compensates the phase of the feedback voltage end of the adder 9 to adjust the output voltage e of the feedback amplifier 7. A feedback voltage epi that matches the phase of is fed back to the feedback amplifier 7.

FIG. 6 shows the output characteristics of the feedback amplifier when the phase shift in the feedback network is compensated for according to the invention described above.

As is clear from FIG. 6, according to the present invention, even if a phase shift occurs in the feedback network, it is possible to obtain an output characteristic similar to the output characteristic when there is no phase shift.

As explained above, according to the present invention, even if a phase shift of the feedback voltage occurs in the feedback circuit, the entire level of the first surface of the bath can be measured, which is an extremely useful effect.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of the conventional Uzu-9 type hot water level splitting system. Figure 2 shows the distance between the molten steel surface level and the detection head and the output voltage e. 3 is a schematic block diagram of one embodiment of the present invention, FIG. 4 is a schematic block diagram of another embodiment of the present invention, and FIG. 5 is a graph showing the relationship between control voltage EC and c.
Graph showing the relationship with e/C. FIG. 6 shows the distance between the molten steel surface level and the detection head and the output voltage e. It is a graph showing the relationship between In the drawing. 1... Mold 2... Molten steel 3... Detection head 4... Primary coil 5, . 5b・
・ Secondary coil 6... Oscillator 7... Feedback amplifier
Total... Differential amplifier 9... Adder 10... Phase shifter 1... Phase detector 12... Phase controller 13...
・Multiplier applicant Natsuo Shioya, representative of Nippon Kokan Co., Ltd. (and 2 others)

Claims (1)

[Claims]] An alternating current voltage is applied from a feedback amplifier to the primary coil in front of the detection head, which is composed of a primary coil and a pair of secondary coils, thereby generating voltage in the pair of secondary coils. The eddy current type hot water surface comprises calculating the difference between each of the induced voltages using a differential amplifier, adding the difference voltage and the output voltage of the feedback amplifier using an adder, and feeding back the added voltage to the feedback amplifier. In level measurement methods. The phase of the feedback voltage fed back to the feedback amplifier. An eddy current type hot water level measuring method characterized in that the phase of the output voltage of the feedback amplifier is matched with the phase of the feedback amplifier using a phase shifter.