JPH0682291A - Liquid level detector - Google Patents

Abstract

PURPOSE:To obtain a level detector which can detect the height of a liquid level of a chemicals bath 1 continuously with high reliability. CONSTITUTION:A frequency-variable oscillator 24 is provided and a speaker 19 for oscillating a sound wave and a microphone 21 for receiving a sound are fitted to the upper end of a tube 18 for detecting a liquid level. An oscillation frequency and a peak frequency of the intensity of a received sound wave are detected and the height of the liquid level is known by using the resonance of an air column of a so-called one-ended tube. Only by using one tube 18 for detecting the liquid level, the height of the liquid level can be known continuously and, besides, a detector of long lifetime and high reliability can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid level detector for a chemical liquid tank of acid, alkali, etc., which is mainly used in manufacturing semiconductor devices and the like.

[0002]

2. Description of the Related Art The structure of a conventional liquid level detector will be described with reference to FIG. FIG. 5 shows a schematic configuration of an automatic chemical liquid supply type tank equipped with a conventional liquid level detector.

That is, in the conventional automatic chemical solution supply type tank shown in FIG. 5, 1 is a tank made of quartz or Teflon, 2 is a chemical solution, 3 is a liquid level, and 4, 5 and 6 are for liquid level detection. Tubes made of Teflon or quartz, 4 is a lower limit tube, 5 is an appropriate amount tube, 6 is an upper limit tube, 7, 8 and 9 are pressure switches 10, 11, 12
Is a valve for keeping the gas flow rate constant, 13 is the direction of N ₂ gas flow, 14 is a chemical solution supply valve, 15 is the direction of chemical solution flow,
Reference numeral 16 denotes a chemical liquid waste valve, and 17 denotes a flow of the chemical liquid waste liquid.

Next, the operation will be described. In the automatic chemical liquid supply type tank 1 configured as shown in FIG. 5, chemical liquids such as hydrofluoric acid, sulfuric acid, nitric acid, hydrochloric acid, phosphoric acid and alkalic acid were supplied into the tank 1 through the valve 14 and the appropriate amount was obtained. By the way, the chemical solution is stopped, and a wafer is immersed in the chemical solution tank 1 in the semiconductor field for etching or cleaning. Further, when exchanging the chemical liquid, the valve 16 is opened to drain the chemical liquid 17.

At this time, there is a liquid level detector for detecting the liquid level 3 in order to automatically supply an appropriate amount of the chemical liquid, replenish it, waste it, and detect the amount of the other chemical liquid.

In this conventional liquid level detector, N ₂
Gas (nitrogen) 13 and valve 1 for keeping this flow rate constant
0, 11, 12 and the pressure switch 7, which is connected to this
There are 8 and 9 and tubes 4, 5 and 6, and the tips of these tubes 4 to 6 are installed on the liquid surface 3 to be detected. That is, the tube 4 is for the lower limit, the tube 5 is for the appropriate amount, and the tube 6 is for the upper limit.

In principle, when N ₂ gas is flowing at a constant flow rate into the tubes 4, 5 and 6, these tubes 4
Letting Pa be the pressure inside the tube when the tip of ~ 6 is not blocked by the liquid level 3, the pressure inside the tube rises to Pa + α when the tip of the tube is blocked by the liquid level. If the pressure switches 7, 8 and 9 are set to operate only when Pa + α during this rise, the height of the liquid surface can be detected.

[0008]

The conventional liquid level detector has the following problems.
Since it is configured as described above, there is a problem in that it is necessary to provide a tube, a pressure switch and the like for the number of liquid levels to be detected, and it is not possible to continuously know the height of the liquid level. In addition, the reliability of the pressure switch and the valve that keeps the flow rate constant is lowered due to the influence of acid or the like, which causes a malfunction.

The present invention has been made to solve the above problems, and provides a highly reliable liquid level detector capable of detecting the continuous liquid level height with a single detecting tube. The purpose is to get.

[0010]

A liquid level detector according to the present invention comprises the following means. [1] A speaker that emits sound waves to the hollow of a tube whose lower end is installed in a liquid tank. [2] A microphone that receives the reflected sound waves. [3] The frequency of the sound wave emitted from the speaker is varied, the peak frequency of the strength of the sound wave received by the microphone is detected, and the resonance of the air column of the closed tube is used to increase the height of the liquid surface of the liquid tank. Level measuring means for detecting the level.

[0011]

In the liquid level detector according to the present invention, the speaker for emitting the frequency variable sound wave and the sound receiving microphone are
By detecting the oscillation frequency and the peak frequency of the intensity of the received sound wave, the so-called one-side closed air column resonance is used to know the height of the liquid surface. Therefore, the liquid level detector according to the present invention needs only one liquid level detecting tube, and the continuous liquid level can be known by utilizing the variable frequency sound wave. Further, in the case of the electronic type, it is possible to obtain a highly reliable liquid level detector.

[0012]

【Example】

Example 1. Hereinafter, the configuration of the first embodiment of the present invention will be described with reference to FIG. First Embodiment FIG. 1 is a diagram showing a first embodiment of the present invention.

In FIG. 1, a sound wave oscillating speaker 19 and a sound receiving microphone 2 are provided at the upper end of one liquid level measuring tube 18.
1 is attached. Reference numeral 23 is a liquid level measuring circuit for calculating the liquid level by calculating the natural frequency of the air column of the tube 18 from the sound wave oscillation frequency and the received sound volume, and displaying it. Further, 24 is a frequency variable oscillator, 25 is an amplifier, 26 is a sound receiving peak detector, 27 is a CPU, CRT, etc., and controls the frequency variable oscillator 24 and the sound receiving peak detector 26 to calculate the liquid level. It is a control display circuit for displaying. Reference numerals 20 and 22 denote covers of the speaker 19 and the microphone 21, which are made of Teflon film or the like to protect them from acid.

The quartz tank or Teflon tank 1, the chemical liquid supply valve 14, and the chemical liquid waste valve 16 are the same as those of the conventional example.

FIG. 2 illustrates the relationship between the wavelength λ and the frequency N when resonating with the length L of the air column. As shown in FIG. 6 (a), resonates at lambda _1/4 in the air column of length L by the frequency N ₁ emanating from the speaker 19.

Further, as shown in FIG. (B), it resonates the air column of length L by the frequency N ₂ emanating from the speaker 19 _{(λ 2/4) × 3} .

Furthermore, as shown in FIG. _{(C), (λ 3/} 4) in the air column of length L by a frequency N ₃ emanating from the speaker 19 to resonate at × 5.

Equations 1, 2, and 3 shown below represent these relationships.

[0019] _{L = λ 1/4 L =} (λ 2/4) × 3 L = (λ 3/4) × 5 L = (λn / 4) × (2n-1) (n = 1,2,3 ,…)… Equation 1

Λ ₁ = V / N ₁ λ ₂ = V / N ₂ λ ₃ = V / N ₃ λn = V / Nn (n = 1, 2, 3, ...) Equation 2

L = V / 4N ₁ L = 3V / 4N ₂ L = 5V / 4N ₃ L = (2n−1) V / 4Nn Equation 3

Further, the following equations 4 and 5 indicate that L can be obtained from two resonance frequencies that are adjacent to each other.

L = V / 2 (N ₂ −N ₁ ) Equation 4

L = V / 2 (N _{n + 1} −N _n ) Equation 5

FIG. 3 shows the sound volume S in the air column tube when the frequency of the speaker is changed. It can be seen that the sound volume peaks at the resonance frequency, and that there is a cycle for every λ / 2. I also understand.

FIG. 4 shows the relationship R between the two adjacent resonance frequency differences (N _{n + 1} −N _n ) and the air column height in the tube. Here, V represents the speed of sound in air, and is generally 342 m / sec at 25 ° C. and 1 atmospheric pressure.

Next, the operation of the above-described first embodiment will be described. As shown in FIGS. 2, 3 and 4, the tube 1
When a speaker 19 is installed at the upper end of 8 and the frequency is increased from 0, it resonates with an air column having a length L at some places. Equations 1, 2 and 3 represent these relationships, and the relationship between the air column length L and the resonance frequency N _n is summarized in Equation 3.

Further, the difference in resonance frequency (N)
The relationship between ( _{n + 1−} N _n ) and the air column length L is given by Equation 5 by solving Equation 3.

The configuration shown in FIG. 1 is intended to detect the liquid level in the chemical liquid tank by applying the principle of the equation (3). In this figure, the speaker 19 resonates when a sound wave having a continuously changed frequency is emitted from the upper end of the liquid level detection tube 18, and the microphone 21 receives a large sound when it resonates as the volume returned from the air column is measured. To be done. Frequency N at this time
_{If n} and the frequency N _{n + 1} of the resonance that occurs by increasing the frequency are detected, they are substituted into the above-mentioned equation 5 and the air column length L
Understand. The height L ₁ of the liquid surface is the total length L _{0 of the} tube 18.
You can understand it by subtracting the air column length L from.

If these operations for obtaining the liquid level height L ₁ are configured by the liquid level measuring circuit 23, L ₁ can be automatically obtained. In addition, in order to protect the speaker 19 and the microphone 21 from acid and the like, covers 20 and 22 made of Teflon film.
If you cover with, the reliability will be higher.

[0031]

As described above, according to the present invention, since the liquid level detector utilizing the variable frequency sound wave and the closed tube air column resonance is attached to the automatic chemical liquid supply tank, one liquid level detection tube is used. It is possible to know the height of the continuous liquid surface only by itself, and there is no need to use a valve or pressure switch for constant gas flow rate, which is weak against acid and has low reliability.

[Brief description of drawings]

FIG. 1 is a diagram showing a first embodiment of the present invention.

FIG. 2 is a diagram showing the relationship between the wavelength λ and the frequency N when resonating with the length L of the air column in the first embodiment of the present invention.

FIG. 3 is a diagram showing the vibration volume in the air column tube when the frequency of the speaker is changed in Example 1 of the present invention.

FIG. 4 is a diagram showing a relationship between a difference (N _{n + 1} −N _n ) between two resonance frequencies and a height of an air column in a tube according to the _first embodiment of the present invention.

FIG. 5 is a diagram showing a configuration of an automatic chemical liquid supply type tank provided with a conventional liquid level detector.

[Explanation of symbols]

 1 Tank 2 Chemical liquid 3 Liquid level 14 Chemical liquid supply valve 15 Chemical liquid flow direction 16 Chemical liquid waste liquid valve 17 Chemical liquid waste liquid flow direction 18 Liquid level measuring tube 19 Speaker 20 Teflon cover 21 Microphone 22 Teflon cover 23 Liquid level measuring circuit 24 Frequency variable oscillator 25 Amplifier 26 Received sound volume peak detector 27 Control display circuit

Claims (1)

[Claims] 1. A speaker that emits a sound wave to the hollow of a tube whose lower end is installed in a liquid tank, a microphone that receives a reflected sound wave, and a frequency of a sound wave that is emitted from the speaker, and the microphone is changed. A liquid level measuring means for detecting the peak frequency of the intensity of the sound wave received by the one side and detecting the height of the liquid level in the liquid tank by utilizing the resonance of the air column of the closed tube. Liquid level detector.