JPH0543973B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to a level measuring device for high-temperature molten metal in continuous furnaces and casting machines, and powder and granular materials such as raw materials in blast furnaces.

(Prior Technology) FM (frequency modulation) radar using microwaves is suitable as a method for measuring the level of molten metal and powdery raw materials with high precision in harsh environments with high temperatures and large amounts of dust. However, since the microwave reflectance of these materials is low, it is difficult to avoid the influence of reflected waves due to antenna mismatching and reflected waves from the container holding the target object, which becomes a major error factor.

A common method for removing unnecessary reflections from a beat wave obtained by mixed detection of a transmitted wave and a reflected wave is to use a filter to discriminate based on frequency bands. However, the frequency of the beat wave due to the signal wave and the unnecessary reflected wave is often close to each other, and it is difficult to remove the unnecessary reflection to a sufficient degree to achieve practical accuracy.

Therefore, in the conventional level measuring device, as shown in FIG. Beat signals caused only by unnecessary reflections reflected from other than the liquid surface 3 are recorded in advance so that they do not enter the antenna 4. When measuring the liquid level 3, from the beat signal generated by both the reflected waves from the liquid level 3 and unnecessary reflections,
By subtracting the recorded signal while synchronizing with the modulation period of the microwave, the beat signal caused by the reflected wave only from the liquid surface 3 is extracted, and then the level is determined based on the conventional FM radar signal processing method. There are some methods that calculate it (for example, JP-A-Sho
55−82926).

(Problems to be Solved by the Invention) The conventional device as described above only detects noise when the beat waves (hereinafter referred to as noise components) caused by unnecessary reflected waves recorded before the start of measurement do not change during the measurement of the liquid level 3. Applicable. However, in actual radar,
Not only does the noise waveform change due to the frequency drift of the oscillator, but especially when the target is molten metal, metal may adhere to the container wall, etc.
Dust and the like may adhere to the front surface of the antenna 4, causing the noise waveform to change from moment to moment, making it difficult to accurately measure the position of the measurement surface with conventional devices.

In view of the above-mentioned problems, the present invention is designed to accurately measure the level on a measurement surface even when the noise waveform changes from moment to moment.

(Means for Solving the Problem) The technical means of the present invention for solving this technical problem is that the transmission wave 12a of the microwave 12 and the measurement surface 16 are
A beat signal 21 is created by mixing the reflected wave 12b from the measurement surface 1.
In the level measuring device configured to calculate the position of 6, a transmitting antenna 14 for transmitting microwaves 12 having a polarized wave plane toward a measuring surface 16 is provided, and the polarization of the transmitted wave 12a is caused by diffuse reflection on the measuring surface 16. The wavelength of the transmitted wave 12a is selected to be equal to or less than the diameter of the unevenness of the measurement surface so that the wave surface is rotated, and the reception antenna 18 receives only the microwave 12b having a polarization plane rotated by diffused reflection on the measurement surface 16. The microwave 12b received by the receiving antenna 18 is mixed with the transmitted wave 12a.

(Function) The frequency-modulated transmission wave 12a from the microwave oscillator 11 is transmitted from the transmission antenna 14 via the directional coupler 13. The transmitted wave 12a
has a polarization plane in the X direction (Y direction) shown in FIG. 2, and is reflected by the liquid surface 16, the container wall 19, or the antenna protection radome 20. In this case, since the wavelength of the microwave 12 used is selected to be less than the wavelength of the ripples on the liquid surface, the plane of polarization rotates when it is diffusely reflected on the liquid surface 16, causing it to move in the Y direction (or X direction) as shown in Figure 2. components are generated. On the other hand, reflected waves 12c and 12d from the radome 20 and the container wall 19, which are considered to have mirror surfaces sufficiently for microwave wavelengths, reach the receiving antenna 18 while maintaining the plane of polarization at the time of transmission. Therefore, the receiving antenna 18 receives only the reflected wave 12b from the liquid surface 16, and does not receive the reflected waves 12c and 12d from the radome 20 and the container wall 19.

Therefore, the microwave 12 reflected by the liquid surface 16 etc.
b, 12c, and 12d, only the component having the same polarization as the receiving antenna 18 is detected as a signal, and the microwave signal received by the receiving antenna 18 is sent to the detection mixer 23 by the directional coupler 15. It is mixed with a part of the transmitted wave 12a separated at , and a beat signal 21 is output. The beat signal 21 is subjected to processing such as counting the number of beat waves in the beat signal processing circuit 23, and the distance to the liquid surface 16, that is, the level, is accurately calculated without being affected by the nozzle waveform that changes from time to time.

Note that FIGS. 3 to 6 show the results of experiments conducted to confirm the effectiveness of the present invention. 2 in the diagram
5 is an oscilloscope photo of sweep voltage for FM,
Horizontal and vertical scales are each 2ms/div,
It is 5mv/div. 26 is a beat waveform recorded for coke with an average particle size of about 30 mm using a microwave with a wavelength of 12 mm and an antenna with the same polarization plane for transmission and reception (called a parallel polarization antenna), and the signal amplitude is about 5 mV. It has been obtained.

27 is a transmitting/receiving antenna 14 based on the present invention,
This is a beat waveform recorded by a radar set at right angles to the antenna, and a signal amplitude comparable to that of a conventional parallel polarized antenna is obtained. On the other hand, when the target is an iron plate that is regarded as a mirror surface, Figures 5 and 6
As shown in the figure, the amplitude of the beat wave 29 due to the orthogonally polarized antenna is the same as the amplitude of the beat wave 29 due to the parallel polarized antenna.
It is less than 1/10 of 8, which confirms the effectiveness of the present invention.

(Embodiment) The present invention will be explained below according to the illustrated embodiment. Reference numeral 11 represents a microwave oscillator;
is frequency modulated and output. 13 is a directional coupler which outputs a part of the microwave 12 output from the microwave oscillator 11 to the transmitting antenna 14 and sends the other part to the detection mixer 15. The transmitting antenna 14 is arranged in the Y direction (or
Of the microwaves 12 which have a polarization plane of
A wave having a polarization plane in the direction (or the Y direction) is output as a transmission wave 12a toward a liquid surface 16 of molten metal or the like that is a measurement surface.

Reference numeral 18 denotes a receiving antenna, which has a polarization plane in the Y direction (or Receives a wave having a plane of polarization in the Y direction (or X direction) shown in FIG. The detection mixer 15 is connected to the receiving antenna 18.
The microwave 12b received by the directional coupler 1
3 and a part of the transmitted wave 12a separated in step 3, and outputs a beat signal 21. A beat signal processing circuit 23 performs processing such as counting the number of beat waves to calculate the distance to the liquid level 16, that is, the level.

By frequency modulating the microwave oscillator 11, the wavelength of the microwave 12 used is selected to be less than the wavelength of the ripples on the liquid surface 16. Therefore, when the transmitted wave 12a is diffusely reflected on the liquid surface, its polarization On the other hand, the reflected waves 12c and 12d from the radome 20 and the container wall 19, which are considered to have a sufficiently mirror surface with respect to the wavelength of the microwave 12, reach the receiving antenna 18 while maintaining the polarization plane at the time of transmission. The antenna 18 receives only the reflected wave 12b from the liquid surface 16, and does not receive the reflected waves 12c and 12d.

In the above embodiment, the measurement surface is the liquid level 16 of high-temperature molten metal, etc., but the measurement surface is not limited to this. For example, the measurement surface may be the level of powdery raw material, and in this case, the microwave used The wavelength of 12 may be selected to be equal to or less than the average particle diameter of the powder or granular material.

(Effects of the Invention) According to the present invention, by making good use of the rotation of the plane of polarization due to diffuse reflection on the measurement surface, only the microwaves diffusely reflected on the measurement surface are received, and the received microwaves and the transmitted waves are mixed. Since the position of the measurement surface is calculated by using The position of the measurement surface can be measured accurately and easily using only the reflected microwaves, and the effect is significant.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing one embodiment of the present invention, and FIG.
The figure shows the polarization plane of the microwave, and FIGS. 3 to 6 are beat waveform diagrams showing the experimental results. FIG. 7 is a configuration diagram showing a conventional example. 12...Microwave, 14...Transmission antenna, 1
6...Measurement surface, 18...Receiving antenna.

Claims (1)

[Claims] 1. Transmission wave 12a of microwave 12 and measurement surface 16
A beat signal 21 is created by mixing the reflected wave 12b from the measurement surface 1.
In the level measuring device configured to calculate the position of 6, a transmitting antenna 14 for transmitting microwaves 12 having a polarized wave plane toward a measuring surface 16 is provided, and the polarization of the transmitted wave 12a is caused by diffuse reflection on the measuring surface 16. The wavelength of the transmitted wave 12a is selected to be equal to or less than the diameter of the unevenness of the measurement surface so that the wave surface is rotated, and the reception antenna 18 receives only the microwave 12 having a polarization plane rotated by diffused reflection on the measurement surface 16. established,
A level measuring device characterized in that the microwave 12 having a polarized wave plane received by the receiving antenna 18 and the transmitted wave 12a are mixed.