JPH042889B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method and apparatus for measuring liquid level using a microwave radar, mainly for high-temperature molten metal such as converters and casting machines.

[Prior Art] FM (frequency modulation) radar using microwaves is suitable as a method for measuring the liquid level of molten metal etc. with high precision in a high temperature, dusty environment. When measuring using FM radar, if the microwave reflectance of the target is very small,
If the measurement distance is long, only weak reflected waves can be obtained. In this case, the influence of reflected waves due to antenna mismatch and reflected waves from a container holding the target object becomes large, resulting in a large measurement error.

As a method to remove the above unnecessary reflected waves from the beat wave obtained by mixed detection of the transmitted wave and reflected wave,
A common method is to use a filter to discriminate based on frequency bands. However, since the frequencies of the signal wave and the beat wave caused by the unnecessary reflected wave are close to each other, it is difficult to remove the unnecessary reflected wave to the extent that there is no problem in practical use.

Therefore, as a conventional technology, for example,
No. 82926 proposes a "method and device for measuring liquid level using microwaves" as shown in FIG. This method and apparatus are common
It features the addition of beat waveform storage and a subtraction circuit to the FM radar configuration.

In FIG. 2, 51 is a microwave sweep oscillator, 52 is a modulation signal generator, 53 is an antenna, and 5
4 is a container, 55 is a liquid, 56 is a liquid level, 57 is a mixing circuit, 58 is a beat signal measurement circuit, 59 is a wall of the container 54, 60 is a waveform recording circuit, 61 is a subtraction circuit, 62 is a recording command switch, 63 is a reproduction command switch, 64 is a delay circuit, 65 is a radio wave reflector or absorber, R is a reflected wave from the liquid surface, and Rd is an unnecessary reflected wave.

In the measurement procedure using this conventional method, first, a microwave reflector or absorber is placed on the liquid surface to prevent the reflected wave R from the liquid surface from entering the antenna. In this way, a beat signal due to the reflected wave Rd reflected from a source other than the liquid surface is recorded in advance.

During measurement, the reflected wave actually received [R+Rd]
By subtracting the recorded signal from the beat signal while synchronizing with the modulation period of the microwave, the beat wave due to the reflected wave R from only the liquid surface is extracted, and the distance to the liquid surface is calculated.

[Problem to be solved]

The above conventional method can be applied when the beat wave (hereinafter referred to as a noise component) caused by the unnecessary reflected wave Rd recorded before the start of the measurement does not change during the liquid level measurement.

However, in actual radar, (1) the noise waveform changes due to the frequency drift of the oscillator 51, especially when the target is molten gold, (2) metal adheres to the walls of the container 54, etc. (3) The noise waveform changes from moment to moment due to dust and the like adhering to the front surface of the antenna 53, making it impossible to remove noise sufficiently.

The present invention aims to solve the above-mentioned problems, and aims to provide a microwave radar liquid level measuring method and apparatus that can measure the position of the liquid level with high precision without requiring manual labor.

[Means for solving problems]

The microwave liquid level measurement method of the present invention integrates a beat time series signal obtained by mixed detection of transmitted and received waves a predetermined number of times in synchronization with the frequency modulation cycle, and divides the integrated value by the predetermined number of times. to obtain a time-averaged beat time-series signal, and subtract the time-averaged beat time-series signal from the beat time-series signal being measured in synchronization with the frequency modulation cycle. The microwave radar liquid level measuring device according to the microwave liquid level measuring method of the present invention calculates the position of a surface using a beat time series signal obtained by mixed detection of transmitted and received waves with a period of frequency modulation. an adder that adds up a predetermined number of times in synchronization with the
a divider that divides the output amplitude value of the adder by the predetermined number of times; and a subtracter that subtracts the output of the divider from the beat time series signal being measured in synchronization with the frequency modulation cycle. It is characterized by the presence of

[Effect]

In the case of industrial applications, molten metal is rarely left standing for long periods of time, and the liquid surface is constantly undulating due to the inflow and outflow of molten metal, gas blowing, etc.

The present invention was made with attention to the above fact, and if there is positional information that fluctuates within a period of time approximately equal to the liquid level vibration period, it is assumed that this is the target liquid level.
The liquid level position is measured separately from information such as contamination and deformation of the container or antenna, which does not change suddenly.

The microwave radar measurement signal is integrated many times,
On average, information on the mixing of the liquid surface with no apparent waves and surrounding containers etc. can be obtained. Next, once more radar measurement is performed and the average signal is subtracted from the data, only the wave portion of the liquid level remains in the subtracted data, so the liquid level position is measured using this data.

〔Example〕

Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram of a microwave liquid level measuring device using a microwave liquid level measuring method as an embodiment, in which 1 is a microwave sweep oscillator;
1 is a modulation signal generator that generates a modulation signal that controls the frequency of the microwave sweep oscillator 1; 3 is an antenna that transmits microwave radio waves and receives reflected waves from the liquid surface 5; 4 is a superposition of the transmitted and received waves. A detection mixer that detects the microwave signal and outputs a beat signal.
5 is the liquid level of the molten metal whose position is to be measured, and 6 is the liquid level 5.
7 is an unnecessary reflected wave from container 8 etc.,
8 is a container for molten metal; 9 is an adder for adding the beat signal by the number of times set by the addition number setting device 11;
is a divider that divides the output of the adder 9 by the number of additions set in the addition number setting container 11; 11 is an addition number setting device;
12 is a subtracter that subtracts the output of the divider 10 from the current beat signal; 13 is a liquid level calculation circuit that calculates the distance from the beat signal output from the subtracter 12 to the liquid level 5; 14 is a past average beat signal; 15 is the current instantaneous beat signal, and the above 9, 10, 11, 12
constitutes the noise correction circuit 16.

The device of this embodiment is configured as described above,
Its operation is as follows.

A detection mixer 4 performs mixed detection of the transmitted and received microwaves to obtain a beat signal. In addition to the reflected wave 6 from the liquid surface 5, this beat signal contains a noise component caused by a mismatch in the antenna 3, a reflected wave 7 from the wall of the container 8, etc.

Therefore, the beat signal is defined as time series data (Ai ₁ , Ai ₂ , ~Aim) from the start of modulation to the end of modulation,
The adder 9 converts the beat signal time series data (Ai ₁ , Ai ₂ , ~Aim) into n in synchronization with the modulation period.
times to obtain an integrated value (S ₁ , S ₂ , ~Sm). Next, by dividing according to the number of additions n in the divider 10, the time-averaged beat time series signal (A ₁ ,
A ₂ , ~Am) is obtained.

A ₁ = 1/n _o 〓 ⁱ⁼¹ Ai ₁ , A ₂ = 1/n _o 〓 ⁱ⁼¹ Ai ₂ , ..., Am=1/n _o 〓 ⁱ⁼¹ Aim The number of additions n is the number of additions n The product of the modulation period and the modulation period is set so that it is equal to or more than the waving period of the liquid surface 5. For example, if the waving period of the liquid surface 5 is 1 second and the modulation period is 1 ms, the number of additions n will be 1000 or more.

Here, the phase of the beat wave caused by reflection from the liquid surface 5 fluctuates continuously, so by taking the time average, the fluctuation is canceled out, and if a sufficiently large number of averaging times of about 1000 is set, The amplitude of the fluctuation becomes negligibly small. On the other hand, since the mismatch of the antenna 3 and the phase of the reflected wave 7 from the container 8 do not change within a short period of about 1 second, the divider 10
The output (A ₁ , A ₂ , ~Am) 14 is equal to the noise component of the beat caused only by unnecessary reflections.

Therefore, the subtracter 12 subtracts the noise component (A ₁ , A ₂ , ~Am) 14 from the newly measured beat signal (Ax ₁ , Ax ₂ , ~Axm) 15 to calculate the oscillating liquid level 5. Only the beat signal caused by the reflected wave is extracted, and the S/N ratio is greatly improved.
Thereafter, the distance to the liquid level 5 is calculated using a known method.

In this way, the device according to the microwave liquid level measuring method of the present invention can accurately measure the position of the liquid level of molten metal without requiring manual operation of a reflection plate or the like.

〔Effect of the invention〕

The microwave liquid level measurement method of the present invention integrates a beat time series signal obtained by mixed detection of transmitted and received waves a predetermined number of times in synchronization with the frequency modulation cycle, and divides the integrated value by the predetermined number of times. A time-averaged beat time-series example signal is obtained, and the position of the target liquid level is calculated from the time-averaged beat time-series signal in synchronization with the frequency modulation period from the beat time-series signal being measured. (1) In this method and device, the beat signal is time-averaged with a time constant of about several seconds and the noise waveform is dynamically detected. Accurate noise correction can be made by sufficiently following changes in the noise waveform caused by metal adhering to the container wall, antenna, etc., and high measurement accuracy can be obtained.

(2) Unlike conventional methods, there is no need to place an absorber or reflector on the object to be measured and record the noise waveform in advance, and it has the advantage of being able to perform noise correction fully automatically. .

[Brief explanation of drawings]

FIG. 1 is a block diagram of a microwave liquid level measuring device using a microwave liquid level measuring method as an embodiment, and FIG. 2 is a block diagram of a conventional microwave liquid level measuring device. 1...Microwave sweep oscillator, 2...Modulation signal generator, 3...Antenna, 4...Detection mixer, 5
...Liquid level, 6... Reflected wave from liquid level 5, 7... Unnecessary reflected wave, 8... Container, 9... Adder, 10...
Divider, 11...Addition number setter, 12...Subtractor, 13...Liquid level calculation circuit, 14...Past average beat signal, 15...Current momentary beat signal, 16...
...Noise correction circuit.

Claims (1)

[Claims] 1. In a microwave radar liquid level measurement method based on a frequency modulation method, a beat time-series signal obtained by mixed detection of transmitted and received waves is integrated a predetermined number of times in synchronization with the period of a frequency tone, and the same integration is performed. The noise obtained by dividing the value by the predetermined number of times to obtain a time-averaged beat time-series signal, and subtracting the time-averaged beat time-series signal from the beat sequence signal under measurement in synchronization with the frequency modulation period. A microwave liquid level measurement method characterized by calculating the position of a target liquid level using a corrected beat time series signal. 2. In a microwave radar level measuring device based on a frequency modulation method, an adder that integrates a beat time series signal obtained by mixed detection of transmitted and received waves a predetermined number of times in synchronization with the frequency modulation period, and an output of the adder. It is characterized by comprising a divider that divides the amplitude value by the predetermined number of times, and a subtracter that subtracts the output of the divider from the beat time series signal being measured in synchronization with the frequency modulation cycle. Microwave radar liquid level measuring device.