JP2000162020A - Bypass pipe type liquid level gage - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a bypass pipe type liq. level gage at a low cost which measures the liq. level in an approximately vertical measuring pipe (what is called a bypass type measuring pipe) mounted on the side face of a tank through a joint pipe at the top and the bottom of the tank so as to communicate with the tank, without using any movable part in the pipe, thereby obtaining the liq. level in the tank. SOLUTION: A measuring pipe 1 is disposed at the side of a tank to bypass and communicate in the tank, a reference chamber side pipe 2 bypassing and communicating in the measuring pipe 1 is provided at the lower side of this pipe 1, and signal transmitting-receiving elements for receiving ultrasonic signals transmitted from the bottoms and reflected at the liq. level in the measuring pipe and signal transmitting-receiving elements for receiving ultrasonic signals reflected at a top reflection in the reference chamber side pipe are provided respectively at the bottoms of the measuring pipe 1 and the reference chamber side pipe 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bypass pipe type liquid level gauge which is attached to a side of a tank and measures a liquid level.

[0002]

2. Description of the Related Art There are various types of so-called tank level meters for measuring the level of a liquid in a liquid storage tank. One of them is a communication pipe as shown in FIG. There is a bypass pipe type (also called an outer cylinder type) liquid level gauge using the principle of the above.

[0003] In this method, a substantially vertical measuring pipe communicating with the tank is attached to the tank side by a joint pipe provided at the bottom of the tank and at the top of the tank, and the liquid level in the tank is measured by measuring the liquid level in the pipe. It is possible to remove the entire measurement pipe by closing the valve by attaching the valve to the upper and lower joint pipes as shown in FIG. 5,
Also, by narrowing the inner diameter of the joint pipe to a small value, even if the liquid level in the tank fluctuates, the fluctuation of the liquid level in the measurement pipe is suppressed,
It has various advantages, such as that the measurement of the liquid level does not become difficult, and is widely used in practice.

[0004] The classification "bypass pipe type"
Classification by mounting structure, same "bypass pipe type"
Even so, there are various methods for measuring the liquid level in the measuring tube, and the following three are typical.

A so-called sight glass type in which the liquid level is directly viewed from the outside using a transparent measuring tube. -A float with a built-in magnet floats in the liquid in the measuring tube, and the position (height) of the float is detected from the side of the pipe by a magnetic detection type position sensor to determine the liquid level, a so-called bypass float type (Fig. 6). .・ Apparent specific gravity (weight ÷ volume) in liquid in measuring tube
A so-called displacement formula (FIG. 7) in which a liquid level sensor (displacer) having a large value is suspended and the buoyancy acting on the liquid surface sensor is detected to determine the liquid level.

[0006] Each of these methods has advantages and disadvantages, and is selectively used according to the purpose. However, the sight glass method is inferior in strength and durability to the measurement pipe compared to the metal pipe. Is limited to tanks with low risk even if the liquid breaks out and liquid flows out.

[0007] The bypass float type and the displacement type are excellent in terms of safety because the pipe is made of metal and can have a completely sealed structure. However, since the measuring pipe has a movable part, it has a long-term durability. However, there is a problem in terms of performance and maintenance when the liquid is abnormally shaken, and there is a strong demand from users for the realization of a "bypass pipe type liquid level meter" having no moving parts.

[0008] A general liquid level gauge having no moving parts includes (1)
There are three types: ultrasonic type, (2) radio wave type, and (3) optical type. However, there are the following problems when applied to a bypass pipe type liquid level meter, and they have been put to practical use. Absent.

That is, in the ultrasonic method of (1), the propagation speed (sound speed) of the ultrasonic wave must be known in principle to determine the liquid level, but the sound speed greatly depends on the temperature and density of the propagation material. I do.

Many applications of the bypass pipe type liquid level gauge are closed tanks, and the pressure and temperature in the tank are not constant. Therefore, the time required for the ultrasonic wave to reciprocate in the space from the tank top to the liquid level depends on the time required. The measurement method of an ordinary ultrasonic liquid level meter for obtaining the liquid level is inferior in accuracy and is not practical unless the temperature and pressure are separately measured to accurately estimate the sound velocity in the space. Therefore, it is necessary to add a thermometer, a pressure gauge, a circuit for estimating and calculating the speed of sound, and the cost is greatly increased.

On the other hand, the radio wave type (2) differs from the ultrasonic type in that the propagation speed is hardly affected by temperature and density, and is practically used as a highly accurate liquid level gauge in an open space.

However, when the measuring tube is made of metal, in a measuring tube having a small inner diameter and a large inner surface curvature, it is technically necessary to discriminate between a directly reflected wave from the liquid surface and an indirect reflected wave passing through the inner surface of the measuring tube. Practical use because the measurement tube is non-metallic, radio waves may be radiated to the outside and damage other electronic devices, and the cost is higher than the ultrasonic type. Nothing was done.

In the optical method (3), since the light flux can be arbitrarily adjusted by a lens system, there is no difficulty in discriminating reflected waves as in the radio wave method. There are many restrictions on the measurement environment, such as weakness to adhesion and attenuated reflected light due to slight fluctuations in the liquid surface, and its application is limited.

[0014]

[Object] The present invention aims to measure the liquid level in a substantially vertical measuring pipe (a so-called bypass type measuring pipe) attached to the side of a tank via a joint pipe at the top and bottom of the tank and communicating with the inside of the tank. The present invention can provide a low-cost bypass pipe-type liquid level gauge for measuring the liquid level in a tank by measuring the liquid level without using a movable part.

[0015]

According to the liquid level gauge of the present invention, a reference chamber side pipe communicating with the inside of the measuring pipe is provided at the lower side of the measuring pipe which is connected to the tank by bypass and provided on the side of the tank. And a signal transmission / reception element for receiving an ultrasonic signal transmitted from each bottom and reflected on the liquid surface in the measurement tube, and reflected on an upper reflection surface in the reference room side tube at each bottom of the reference room side tube. It is assumed that a signal transmitting / receiving element for receiving an ultrasonic signal is provided.

More specifically, whether a pair of ultrasonic transmitting element and receiving element are provided at each bottom of the measuring pipe and the reference chamber side pipe,
Alternatively, a single piezoelectric element having transmission and reception functions is provided.

Further, the signal transmitting / receiving elements are included in the control arithmetic circuit.
This circuit connects the ultra
The sound wave signal is reflected from the liquid level in the measuring tube and the bottom part is sent and received
Time t to reach the element_Two And from the bottom of the reference chamber side tube
The transmitted ultrasonic signal is reflected by the upper reflecting surface in the reference room side tube.
The time t until the light reaches the bottom signal transmitting / receiving element ₁ 
And the signal transmission / reception element at the bottom of the reference chamber side tube
From the height a, which is a constant from the surface to the upper reflective surface, the tank
L = at_Two / T₁Control performance calculated by
It is connected to the arithmetic circuit.

[0018]

<Embodiment 1> As shown in FIG. 1, an ultrasonic wave is directed upward from the lower end of a bypass measuring pipe 1 having joint pipes 1a and 1b communicating with the inside of a tank at an upper part and a lower part. And an element 3b for detecting ultrasonic waves incident from above.

A bypass reference chamber side pipe 2 serving as a reference chamber is provided at a lower side of the measurement pipe 1, and an upper part and a lower part thereof are connected to a communication part 2.
The inside of the reference chamber side tube 2 is flush with the inner bottom surface of the measurement tube 1 by providing the inside of the measurement tube 1 at a and 2b. An element 4a that emits ultrasonic waves and an element 4b that detects incident ultrasonic waves are also provided below the reference chamber side tube 2. Note that the reference chamber side tube 2 may be provided at an arbitrary position outside the measurement tube 1.

When the liquid level in the bypass measuring pipe 1 attached to the side of the tank with the joint pipe is above, the ultrasonic wave is emitted upward from the ultrasonic emitting element 3a at the lower end of the pipe (transmitted). ), The ultrasonic wave propagates in the liquid in the measuring tube. The ultrasonic wave travels to the liquid surface, is reflected by the liquid surface, propagates down the inside of the measuring tube, returns to the lower end of the measuring tube, and transmits it to the detecting element 3.
b detects.

On the other hand, when an ultrasonic wave is emitted (transmitted) from the ultrasonic wave emitting element 4a provided at the lower end of the reference room side tube 2 toward the upper reflecting surface 2c (upper inner surface of the reference room side tube). The ultrasonic wave propagates in the liquid in the reference chamber side pipe, is reflected by the reflection surface 2c, returns to the end of the reference chamber side pipe, and is detected by the detection element 4b.

FIG. 3 shows an example of pulsed voltages applied to the ultrasonic radiation elements 3a, 4a and output voltages when the detection elements 3b, 4b receive reflected waves. As shown in the figure,
The time from when the ultrasonic wave transmitted from the bottom radiating element 4a of the reference chamber side tube 2 is reflected by the upper reflecting surface 2c of the same side tube 2 until it is received by the detecting element 4b is t ₁ , and the bottom radiating element 3 of the measuring tube 1
When the time until ultrasonic wave transmitted from a receives the detection element 3b is reflected by the liquid surface of the measurement pipe and t _2, elements of the reference chamber side tube 2 (4a, 4b) from the reflecting surface 2c (the The distance to the upper inner surface of the pipe) is constant and known,
If the distance is a, V × t ₁ = 2a V × t ₂ = 2L (V: ultrasonic wave propagation velocity, L: distance from the element to the liquid surface).

Therefore, the bottom element (3) in the measuring tube 1
The liquid level L based on the position of a, 3b) is obtained by the calculation of L = a × t ₂ / t ₁ (I).

However, even if the propagation speed of the ultrasonic wave changes, it is not affected by the change, and the speed at which the ultrasonic wave propagates through the partition wall between the element and the liquid in the measuring tube is generally not the same as the sound speed V of the liquid. If the partition is not very thick, the error due to the difference in sound speed caused by the above formula is negligible.

The above operation is performed, for example, by a switching circuit as shown in FIG.
The operation is performed as follows in a control operation circuit including a transmission circuit, a reception circuit, and a measurement / operation circuit. (1) A transmitting circuit is connected to the radiating element 4a by a switching circuit 7b driven by a control signal from the measuring circuit, and a receiving circuit is connected to the detecting element 4b by the switching circuit 7a, and the radiating element 4a is pulsed by the transmitting circuit. An ultrasonic wave is transmitted by applying a voltage in the form of an arrow. The ultrasonic wave transmitted into the liquid from the radiating element 4a reaches the reflecting surface of the reference chamber side tube 2, where it is reflected and propagates downward. (2) The measuring circuit starts the timer at the moment when the transmitting circuit applies the pulsed voltage to the radiating element 4a. (3) The ultrasonic wave propagating downward is received by the detection element 4b. At this time, the electric signal detected by the receiving circuit is obtained by amplifying the output of the detecting element, and its waveform is similar to that of FIG. (4) measurement circuit, a timer to stop the the moment the receiving circuit receives the ultrasonic wave from the reflecting surface of the reference chamber side pipe, measures the propagation time t _1. (5) The radiating element 3a is connected to the transmitting circuit by the switching circuit 7b, and the detecting element 3b is connected to the receiving circuit by the switching circuit 7a. The procedure similar to the above (1) to (4) is performed. and performed on 3b, measuring the ultrasound propagation time reflected from the liquid surface of the measurement pipe t _2. (6) The measuring circuit substitutes t ₁ and t ₂ obtained in (4) and (5) into the above-mentioned equation (I) to determine the distance L from the radiating element and the detecting element to the liquid level in the measuring tube. Ask. Since the liquid level in the measuring tube is always equal to the liquid level in the tank, the liquid level in the tank is obtained by the following equation (II). Tank level = L-h (II) h; distance between element surface and level 0 plane

<Embodiment 2> In the case of a piezoelectric element, it has both a function of emitting ultrasonic waves by applying a pulse voltage and a function of detecting incident ultrasonic waves. If one of the receiving circuits is connected to the element, both functions can be realized by one piezoelectric element, and an embodiment thereof is shown in FIG.

As shown in the figure, the piezoelectric elements 5A and 5A are provided at the lower end of the bypass measuring pipe 1 and the lower end of the reference chamber side pipe 2, respectively.
B is adhered and fixed. Although it is pressed by the spring 6 in the figure, it may be bonded.

The piezoelectric elements 5A and 5B are connected to a control operation circuit including a switching circuit, a transmission circuit and a reception circuit, and a measurement / operation circuit. The piezoelectric elements 5A and 5B are switched to transmit or receive ultrasonic waves. The liquid level measurement is performed by the control arithmetic circuit as follows. (1) A transmitting circuit is connected to the piezoelectric element 5B by switching circuits 7a and 7b driven by a control signal from the measuring circuit, and a pulse-like voltage is applied to the piezoelectric element 5B to transmit ultrasonic waves. (2) The circuit connected to the piezoelectric element 5B is switched to the receiving circuit by the switching circuit 7b, and the ultrasonic wave that reaches the reflecting surface of the reference tube 2 and is reflected by the piezoelectric element is received by the piezoelectric element, and the propagation time t ₁
Is measured. (3) Similar to the above (1) and (2), the piezoelectric element 5A is connected to an oscillation circuit,
Sequentially connected to the receiving circuit, measures the propagation time t _2. (4) The measurement circuit calculates the propagation times t ₁ and t ₂ obtained in (1) to (3).
From the above, the distance L to the liquid surface is obtained by the above-mentioned calculation formula (I),
Further, the liquid level of the tank is obtained by the above formula (II).

[0029]

Since the present invention has no moving parts, there is almost no problem with respect to long-term durability and maintenance when the liquid is abnormally shaken, and there is no moving part strongly demanded by users. "Bypass pipe level gauge" can be provided.

Most of the applications of the bypass pipe type liquid level meter are closed tanks, and since the pressure and temperature in the tank are not constant, the time required for the ultrasonic wave to reciprocate in the space from the tank top to the liquid level depends on the time required. In the conventional ultrasonic liquid level measurement method for determining the liquid level, the accuracy is poor unless the temperature and pressure are separately measured to accurately estimate the sound velocity in the space.Therefore, the thermometer, pressure gauge, sound speed estimation calculation circuit, etc. However, in the present invention, the detection signal is only a propagation signal in the liquid, and the liquid is determined by the time required for the ultrasonic wave to reciprocate in the space from the tank top to the liquid surface. Since the position is not determined, there is no need to add a thermometer, a pressure gauge, a circuit for estimating the speed of sound, and the like, so that the manufacturing cost can be greatly reduced.

Further, since the ultrasonic wave propagation velocity V of the liquid in the tank can be known from the propagation time t ₁ , the physical quantity of the liquid in the tank depends on the propagation velocity V, such as the temperature and concentration of the liquid in the tank (for a chemical liquid). There is an additional advantage that can be obtained at the same time.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing a state in which a liquid level gauge according to the present invention is mounted on a tank.

FIG. 2 is a longitudinal sectional view showing a state where a liquid level gauge according to another embodiment of the present invention is mounted on a tank.

FIG. 3 is a graph showing an example of an applied voltage to an element and an output voltage of the element due to reception.

FIG. 4 is a longitudinal sectional view showing an example of a conventional bypass pipe type liquid level meter.

FIG. 5 is a longitudinal sectional view showing another example of a conventional bypass pipe type liquid level meter.

FIG. 6 is a longitudinal sectional view showing an example of a conventional bypass pipe type (bypass float type) liquid level gauge.

FIG. 7 is a longitudinal sectional view showing an example of a conventional bypass pipe type (displacement type) liquid level gauge.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Measurement tube 2 Reference room side tube 3a Ultrasonic radiation element 3b Ultrasonic detection element 4a Ultrasonic radiation element 4b Ultrasonic detection element 5A, 5B Piezoelectric element 6 Spring 7a, 7b Switching circuit

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Mitsuru Tamai 2-2-6-202 Kaitori, Tama-shi, Tokyo (72) Inventor Shigemi Kato 1-13-309 Aioicho, Itabashi-ku, Tokyo F-term (reference) 2F014 AA17 AB04 FB01

Claims (2)

[Claims] 1. A reference chamber side pipe communicating with the inside of a measuring pipe is provided at a lower side of a measuring pipe provided on the side of the tank by bypass communication into the tank, and provided at each bottom of the measuring pipe and the reference chamber side pipe. A signal transmitting / receiving element for receiving an ultrasonic signal transmitted from each bottom and reflected on the liquid surface in the measuring tube, and a signal transmitting / receiving element for receiving an ultrasonic signal reflected on the upper reflecting surface in the reference chamber side tube. A bypass pipe-type liquid level gauge that is provided with each receiving element. 2. A reference chamber side pipe which is communicated with the inside of a measuring pipe provided at a lower side of a measuring pipe provided on the side of the tank by bypass communication into the tank, and is provided at each bottom of the measuring pipe and the reference chamber side pipe. A signal transmitting / receiving element for receiving an ultrasonic signal transmitted from each bottom and reflected on the liquid surface in the measuring tube, and a signal transmitting / receiving element for receiving an ultrasonic signal reflected on the upper reflecting surface in the reference chamber side tube. Each receiving element is provided, and these signal transmitting / receiving elements are measured by the ultrasonic signal emitted from the signal transmitting / receiving element at the bottom of the measuring pipe into the liquid in the measuring pipe reflected by the liquid level in the measuring pipe. The time t ₂ until the signal reaches the signal transmitting / receiving element at the bottom of the tube, and the ultrasonic signal emitted from the signal transmitting / receiving element at the bottom of the reference room side tube into the liquid of the reference room side tube is reflected at the upper part in the reference room side tube. The time t ₁ from the reflection on the surface to the signal transmitting / receiving element at the bottom of the tube on the reference room side, and the time on the reference room side From the height a, which is a constant from the signal transmitting / receiving element surface to the upper reflecting surface of the pipe, is connected to a control operation circuit for obtaining the liquid level L in the tank by the calculation of L = at ₂ / t _1. By-pass pipe level gauge.