JPH10148560A - Liquid level detector - Google Patents

Abstract

(57) [Summary] The present invention relates to a liquid level detecting device for detecting a liquid level in a tank, which can be attached to an existing tank. A sound source and a sound sensor are provided in a pipe.
Is attached, the frequency of the sound is swept, the resonance frequency is detected, and the liquid 3 in the tank 10 is detected based on the resonance frequency.
Know the liquid level of 0.

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 detecting a liquid level of a liquid stored in a tank.

[0002]

2. Description of the Related Art Conventionally, many types of liquids have been used in a very wide range of fields such as chemicals, foods and semiconductors, and tanks are generally used for storing the liquids and waste liquids. It is a very important technique to detect the amount of liquid stored in a tank or the level of the liquid in the tank.

Conventionally, as a general technique for detecting the level of a liquid stored in a tank, a float (floating) floating on the liquid stored in the tank is installed in the tank, and the float is moved by the movement of the float. A float system for detecting a liquid level is known. As another conventional technique, a liquid level detection method using ultrasonic waves is known.

FIG. 3 is a schematic explanatory view of a liquid level detection system using ultrasonic waves. An ultrasonic transmitter / receiver 20 that oscillates ultrasonic waves and receives the ultrasonic waves that have returned in opposition is installed on the outer wall surface of the tank 10.
By transmitting and receiving the ultrasonic wave at and detecting the acoustic impedance change in the tank, it is detected whether the liquid level of the liquid stored in the tank 10 is higher or lower than the height of the ultrasonic transceiver 20. You.

[0005]

However, in the case of the above-mentioned float system, it is necessary to incorporate a float in the tank 10, and a tank that needs to be cleaned or an existing tank, particularly, as shown in FIG. Is closed and is not suitable for a tank having a structure in which the liquid can flow into or out of the tank only via the pipe 40.

In the case of the ultrasonic system shown in FIG. 2, since the ultrasonic system is installed outside the tank, it is relatively easy to install compared with the float system which needs to be installed in the tank, and the liquid in the tank exceeds a predetermined level. Although it has the advantage of being able to detect whether or not it is contactless, it is often used for storage of food and beer, etc.
In the case of a double-structure tank for preventing heat exchange between the liquid inside the tank and the outside, it is impossible to detect the liquid level by the ultrasonic method as shown in FIG. Also, even in the case of a tank that can employ the ultrasonic method, if you want to detect the liquid level in any number of stages,
Accordingly, it is necessary to attach a number of ultrasonic transceivers, which increases the cost.

In view of the above circumstances, the present invention is directed to a closed tank in which liquid flows into a tank via a pipe, and a tank having a double structure, the liquid level in the tank. An object of the present invention is to provide a liquid level detecting device capable of detecting a level, which can be attached to an existing tank.

[0008]

According to the present invention, there is provided a liquid level detecting apparatus for detecting a liquid level of a liquid stored in a tank to which a pipe connected to an upper part of the tank is connected. In the surface level detection device, (1) a sound source that emits sound waves of a plurality of frequencies in a pipe (2) a sound sensor that obtains a sound pressure signal by detecting a sound pressure in the pipe (3) a sound wave from the sound source into the pipe A signal that detects the acoustic resonance frequency or anti-resonance frequency inside the pipe and tank from the sound pressure signal obtained by the sound sensor in the emitted state, and detects the liquid level of the tank based on the resonance frequency or anti-resonance frequency A processing unit is provided.

Here, the liquid level detecting device of the present invention includes a valve for opening and closing the pipe at a position of the pipe farther from the tank than the mounting position of the sound source and the sound sensor. It is preferable that a sound source emits a sound wave in a state where the pipe is closed, and a sound sensor obtains a sound pressure signal. The liquid level detecting device of the present invention can be installed in the middle of the pipe leading to the tank, so that it can be easily installed in an existing tank whether it is a closed tank or a double-structure tank. be able to.

Further, the liquid level detector of the present invention detects the liquid level by acoustically measuring the total length of the pipe and the length from the tank upper part to the liquid level. In addition, it is possible to detect a liquid level by dividing a liquid level into a number of stages using a sensor for one sound source and one sound. Also,
When the above-described valve is provided in the liquid level detecting device of the present invention, the acoustic length of the pipe can be positively defined.

[0011]

Embodiments of the present invention will be described below. FIG. 1 is a schematic diagram of a tank in which an embodiment of a liquid level detecting device according to the present invention is incorporated. Tank 1
A pipe 40 is connected to the upper part of the
A valve 50 for closing the pipe 10 so as to be openable and closable is provided in the middle of 0. A sound source 101 and a sound sensor (microphone) 102 constituting the liquid level detecting device 100 are attached to a position of the pipe 40 closer to the tank 10 than the valve 50. This sound source 101
Can sequentially sweep sounds of different frequencies, and the sound emitted from the sound source 101 is transmitted into the pipe 40. The sound sensor 102 detects a sound pressure in the pipe 40 and sends a sound pressure signal to a signal processing unit 103 included in the liquid level detection device 100.

When sound is sent from the sound source 101 into the pipe 40 with the valve 50 closed, when the inner diameter D of the tank 10 satisfies D <(λ / 8) with respect to the wavelength λ of the sound, When the frequency of the sound matches the resonance frequency determined by the length L of the length of the pipe 40 between the upper surface of the tank 10 and the valve 50 and the distance between the upper surface of the tank 10 and the liquid surface, The sound pressure detected by the sound sensor 102 shows a maximum peak, and when the frequency of the sound matches the anti-resonance frequency determined by the length L, the sound pressure detected by the sound sensor 102 shows a minimum peak. That is, a maximum peak is shown when L = (λ / 4) × odd number is satisfied, and a minimum peak is shown when L = (λ / 4) × even number is satisfied.

When D ≧ (λ / 8), the resonance frequency and the anti-resonance frequency deviate from the theoretical resonance frequency and the anti-resonance frequency determined by the length L. The liquid level can be detected by associating the relationship between the height and the resonance frequency in advance. D <(λ
/ 8), it is possible to obtain a more accurate liquid level by measuring the resonance frequency and the like in advance when the tank 10 is empty, when the tank 10 is full, and at several other levels. Can be detected.

FIG. 2 is a graph showing data of an experiment conducted by attaching a sound source and a sound sensor as shown in FIG. Here, an experiment was performed using small equipment in which the volume of the tank 10 was 1000 milliliters, the inner diameter of the pipe 40 was 30 mm, and the length of the pipe 40 was about 600 mm.

As shown in FIG. 2, there are some irregularities associated with the movement of the liquid level in the tank 10, but the resonance frequency changes according to the liquid level. The anti-resonance frequency was buried in the noise level and was not observed with a sufficient S / N.

[0016]

As described above, according to the liquid level detecting apparatus of the present invention, it can be installed in an existing tank, and even if the tank has a double structure, the liquid level can be detected. Can be detected.

[Brief description of the drawings]

FIG. 1 is a schematic view of a tank in which an embodiment of a liquid level detecting device according to the present invention is incorporated.

FIG. 2 is a graph showing data of an experiment conducted by attaching a sound source and a sound sensor as shown in FIG.

FIG. 3 is a schematic explanatory view of a liquid level detection method using ultrasonic waves.

[Explanation of symbols]

 Reference Signs List 10 tank 30 liquid 40 pipe 50 valve 100 liquid level detecting device 101 sound source 102 sound sensor 103 signal processing unit

Claims (2)

[Claims] 1. A liquid level detecting device for detecting a liquid level of a liquid stored in a tank to which a pipe communicating with an upper part of the tank is connected, comprising: a sound source emitting sound waves of a plurality of frequencies in the pipe; A sound sensor that obtains a sound pressure signal by detecting a sound pressure in the pipe; and a pipe and the tank from a sound pressure signal obtained by the sound sensor in a state where a sound source emits a sound wave into the pipe. A signal processing unit for detecting an internal acoustic resonance frequency or an anti-resonance frequency and detecting a liquid level of the tank based on the resonance frequency or the anti-resonance frequency. . 2. A valve for closing the pipe so that the pipe is openable and closable at a position of the pipe farther from the tank than the mounting position of the sound source and the sound sensor, wherein the valve closes the pipe. A liquid level detecting device, wherein a sound liquid is emitted from the sound source and a sound pressure signal is obtained by the sound sensor.