JP3375899B2 - Bypass pipe level gauge - Google Patents

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 portion of a tank and measures the liquid level.

[0002]

2. Description of the Related Art There are various types of so-called tank level gauges for measuring the level of liquid in a liquid storage tank, one of which is a communication pipe as shown in FIG. There is a bypass pipe type (also called outer cylinder type) level gauge that uses the principle of.

In this system, a substantially vertical measuring pipe communicating with the tank by a joint pipe provided at the bottom of the tank and at the upper part of the tank is attached to the side of the tank, and the liquid level in the pipe is measured to measure the liquid in the tank. It is possible to remove the entire measuring pipe by closing the valve by attaching the valves to the upper and lower joint pipes as shown in Fig. 5,
Also, by squeezing the inner diameter of the joint pipe small, even if the liquid level in the tank fluctuates, the fluctuation of the liquid level in the measuring pipe is suppressed.
It has various advantages, such as the difficulty of measuring the liquid level, and is widely used in practice.

This "bypass pipe type" classification is
The same "bypass pipe type" for classification of mounting structure
However, there are various methods for measuring the liquid level in the measuring tube, and the following three methods are typical.

A so-called sight glass type in which the liquid surface is directly viewed from the outside by using a transparent measuring tube.・ A so-called bypass float system (Fig. 6) in which a float with a built-in magnet is floated in the liquid of the measuring pipe and the position (height) of the float is detected from the side of the pipe by a magnetic detection type position sensor to obtain the liquid level. .・ Apparent specific gravity (weight ÷ volume) in the liquid of the measuring tube
A so-called displacement type (Fig. 7) in which a liquid level sensitizer (displacer) having a large value is suspended and the buoyancy acting on the liquid level sensitizer 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 measuring tube, and therefore the measuring tube is inferior to the metal tube. It is limited to tanks where there is little danger even if the liquid breaks out and liquid leaks out.

[0007] The bypass float type and displacement type are excellent in safety because the pipe is made of metal and can have a completely closed structure, but it has a movable part in the measuring pipe, so it has long-term durability. There is a problem with respect to the property and maintenance when the liquid is shaken abnormally, and there is a strong demand from the users to realize a "bypass pipe type liquid level gauge" that does not have a moving part.

For a general liquid level gauge having no moving parts, (1)
There are three types, ultrasonic type, (2) radio type, and (3) optical type, but each has the following problems when applied to the bypass pipe type level gauge, and it has not been put to practical use. Absent.

That is, in the ultrasonic method (1), in principle, the propagation velocity (sonic velocity) of ultrasonic waves must be known in order to obtain the liquid level, but the velocity of sound greatly depends on the temperature and density of the propagating substance. To do.

Most of the objects to which the bypass pipe type liquid level gauge is applied are closed tanks, and since the pressure and temperature in the tank are not constant, depending on the time required for ultrasonic waves to reciprocate in the space from the tank top to the liquid level. In the conventional ultrasonic liquid level gauge measuring method for obtaining the liquid level, the accuracy is poor and practically useless unless the temperature and pressure are separately measured to accurately estimate the sound velocity in the space. Therefore, a thermometer, a pressure gauge, a sound velocity estimation calculation circuit, and the like must be added, which significantly increases the cost.

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

However, when the measuring pipe is made of metal, it is technically possible to discriminate between the direct reflected wave from the liquid surface and the indirect reflected wave passing through the inner surface of the measuring pipe in the measuring pipe having a small inner diameter and a large inner curvature. It is difficult to use, and if the measuring tube is non-metallic, radio waves may be radiated to the outside, which may interfere with other electronic devices, and the cost is higher than the ultrasonic type. There was nothing that was done.

In the optical system of (3), since the light flux can be arbitrarily adjusted by the lens system, there is no difficulty in discriminating the reflected waves as in the radio wave system, but condensation of liquid and dust of the light emitting portion and the light receiving portion can be prevented. There are many restrictions on the measurement environment, such as weak adhesion, and a slight fluctuation of the liquid surface that attenuates the reflected light.

[0014]

[Purpose] The present invention is to attach a liquid level in a substantially vertical measuring pipe (so-called bypass type measuring pipe), which is attached to the side surface of the tank through joint pipes at the top and bottom of the tank and communicates with the inside of the tank. A low-cost bypass pipe type liquid level gauge for measuring the liquid level in a tank by measuring without using a movable part is provided.

[0015]

The liquid level gauge of the present invention is constructed such that a bypass pipe is connected to the inside of a tank by bypass connection and the lower part of the measuring pipe provided on the side of the tank is connected to the inside of the measuring pipe. provided low reference chamber side pipe height than, the respective bottom of the measuring tube and the reference chamber side tube, receives the ultrasonic signal reflected by the liquid surface of the measuring tube is originated in the liquid from the bottom A signal transmission / reception element and a signal transmission / reception element for receiving the ultrasonic signal reflected on the inner surface of the upper portion of the reference chamber side tube are provided. It is assumed that the liquid level L in the tank is connected to a control arithmetic circuit which is calculated by the equation L = a · t ₂ / t ₁ from the height a which is a number.

More specifically, a pair of ultrasonic transmitting element and receiving element are provided at the bottom of each of the measuring tube and the reference chamber side tube, or
Alternatively, one piezoelectric element having a transmission function and a piezoelectric element having a reception function is provided.

Further, the signal transmitting / receiving element is connected to a control arithmetic circuit. In this circuit, the ultrasonic signal transmitted from the bottom of the measuring tube is reflected by the liquid surface in the measuring tube and is transmitted to the transmitting / receiving element at the bottom. and the time t ₂ to reach, to detect the time t ₁ until the ultrasonic signal transmitted from the bottom of the reference chamber side pipe reaches the signal transmitting receiving device at the bottom and reflected by the upper inner surface of the reference chamber side pipe , A control calculation for obtaining the liquid level L in the tank by the calculation of L = a · t ₂ / t ₁ from the height a which is a constant from the signal transmitting / receiving element surface at the bottom of the reference chamber side tube to the upper inner surface. It is supposed to be connected to a circuit.

[0018]

<Example 1> As shown in FIG. 1, ultrasonic waves are directed upwards at the lower end of a bypass measuring pipe 1 having joint pipes 1a and 1b for communicating with the inside of a tank on the upper side and the lower side. The element 3a for radiating the light and the element 3b for detecting the ultrasonic wave incident from above are respectively provided.

A bypass reference chamber side pipe 2 serving as a reference chamber is provided on the lower side of the measuring pipe 1, and an upper portion and a lower portion of the bypass reference chamber side pipe 2 communicate with each other.
The reference chamber side tube 2 has an inner bottom surface flush with the inner bottom surface of the measuring tube 1. An element 4a for emitting an ultrasonic wave and an element 4b for detecting an incident ultrasonic wave are also provided below the reference chamber side tube 2. 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 upward, the ultrasonic wave is emitted upward from the ultrasonic wave emitting element 3a at the lower end of the pipe. ), The ultrasonic wave propagates in the liquid in the measuring tube. The ultrasonic wave propagates to the liquid surface, is reflected by the liquid surface, propagates downward in the measuring pipe, returns to the lower end of the measuring pipe, and detects the detection element 3
b detects.

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

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

Therefore, the bottom element (3
The liquid level L based on the positions 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 is changed, it is not affected, and the speed at which the ultrasonic wave propagates through the partition wall between the element and the liquid in the measuring tube is not generally the same as the sound velocity V of the liquid. If the partition wall is not extremely thick, the error due to the difference in sound velocity generated by the above calculation formula is negligible and can be ignored.

The above calculation is performed by a switching circuit as shown in the figure,
A control arithmetic circuit including a transmitting circuit, a receiving circuit, and a measuring / arithmetic circuit is used as follows. (1) A switching circuit 7b driven by a control signal from a measurement circuit connects a radiating element 4a with a transmitting circuit, and a switching circuit 7a connects a detecting circuit with a receiving circuit, and the transmitting circuit outputs a pulse to the radiating element 4a. The ultrasonic wave is emitted by applying a voltage of the form. The ultrasonic wave transmitted from the radiating element 4a into the liquid reaches the reflecting surface of the reference chamber side tube 2, is reflected here, 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 detecting element 4b. At this time, the electric signal detected by the receiving circuit is an amplified output of the detection element, and its waveform is similar to that shown in FIG. (4) The measuring circuit stops the timer at the moment when the receiving circuit receives the ultrasonic wave from the reflecting surface of the reference chamber side tube, and measures the propagation time t ₁ . (5) The radiating element 3a is connected to the transmitting circuit by the switching circuit 7b, the detecting element 3b is connected to the receiving circuit by the switching circuit 7a, and the same procedure as in (1) to (4) above is performed. 3b, the propagation time t _{2 of the} ultrasonic wave reflected from the liquid surface of the measuring tube is measured. (6) The measuring circuit substitutes t ₁ and t ₂ obtained in (4) and (5) into the above calculation formula (I) to calculate 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 pipe is always equal to the liquid level in the tank, the liquid level in the tank is obtained by the following equation (II). Liquid level of tank = L−h (II) h; Distance between element surface and liquid level 0 plane

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

As shown in the figure, 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.
Fix B closely. Although it is pressed by the spring 6 in the figure, it may be adhered.

The piezoelectric elements 5A and 5B are connected to a control arithmetic circuit composed of a switching circuit, a transmitting circuit and a receiving circuit, and a measurement / arithmetic circuit. The piezoelectric elements 5A and 5B are switched to transmit or receive ultrasonic waves. Then, the liquid level is measured by the control arithmetic circuit as follows. (1) An oscillation circuit is connected to the piezoelectric element 5B by switching circuits 7a and 7b driven by a control signal from the measurement circuit, and a pulse voltage is applied to the piezoelectric element 5B to emit 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 chamber side tube 2 and is reflected by the piezoelectric element is received, and the propagation time t ₁
To measure. (3) As in (1) and (2) above, the piezoelectric element 5A is used as an oscillator circuit,
The propagation time t ₂ is measured by sequentially connecting to the receiving circuit. (4) The measurement circuit uses 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 calculation formula (I),
Further, the liquid level in the tank is obtained by the above formula (II).

[0029]

EFFECTS OF THE INVENTION Since the present invention has no moving parts, there is almost no problem in terms of long-term durability and maintenance in the case where liquid is shaken abnormally. A "bypass pipe type liquid level gauge" can be provided.

Most of the objects to which the bypass pipe type liquid level gauge is applied are closed tanks, and since the pressure and temperature in the tank are not constant, it depends on the time required for the ultrasonic waves to reciprocate in the space from the tank top to the liquid level. The conventional ultrasonic liquid level measurement method for determining the liquid level is inaccurate unless the temperature and pressure are separately measured and the sound velocity in the space is accurately estimated. Therefore, a thermometer, a pressure gauge, a sound velocity estimation calculation circuit, etc. However, in the present invention, the detection signal is only a propagation signal in the liquid, and the ultrasonic wave reciprocates in the space from the tank top to the liquid surface depending on the time required for the liquid to flow. Since it is not required to calculate the unit, it is not necessary to add a thermometer, a pressure gauge, a sound velocity estimation calculation circuit, etc., and the manufacturing cost can be greatly reduced.

Further, since the ultrasonic wave propagation speed 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 temperature, concentration (in the case of chemical liquid) of the liquid in the tank, and the propagation speed V. Also has the additional advantage that it can be obtained at the same time.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view showing a state in which a liquid level gauge according to the present invention is attached to a tank.

FIG. 2 is a vertical cross-sectional view showing a state in which a liquid level gauge according to another embodiment of the present invention is attached to 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 vertical sectional view showing an example of a conventional bypass pipe type liquid level gauge.

FIG. 5 is a vertical cross-sectional view showing another example of a conventional bypass pipe type liquid level gauge.

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

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

[Explanation of symbols]

1 Measuring tube 2 Reference chamber side tube 3a Ultrasonic radiating element 3b Ultrasonic detecting element 4a ultrasonic radiating element 4b ultrasonic detecting element 5A, 5B Piezoelectric element 6 Spring 7a, 7b switching circuit

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shigemi Kato 1-13-309 Aioicho, Itabashi-ku, Tokyo (56) References JP-A-51-75557 (JP, A) JP-A-8-145763 (JP, A) Japanese Patent Publication Sho 35-4380 (JP, B1) (58) Fields investigated (Int.Cl. ⁷ , DB name) G01F 23 / 00-25 / 00

Claims (2)

(57) [Claims] 1. A reference chamber side, which communicates with the inside of the measuring pipe and is lower in height than the measuring pipe, which is connected to the inside of the measuring pipe by bypass connection to the inside of the tank and is provided on the side of the tank. A pipe is provided to each of the bottoms of the measurement pipe and the reference chamber side pipe, and a signal transmission / reception element that receives the ultrasonic signal transmitted from the bottom into the liquid and reflected by the liquid surface in the measurement pipe, and the reference chamber. A bypass pipe type level gauge provided with signal transmitting / receiving elements for receiving ultrasonic signals reflected by the upper inner surface of the side pipe. 2. A reference chamber side, which communicates with the inside of the measuring pipe and is lower in height than the measuring pipe, is connected to the lower side of the measuring pipe which is provided on the side of the tank by bypass communication with the inside of the tank. A pipe is provided to each of the bottoms of the measurement pipe and the reference chamber side pipe, and a signal transmission / reception element that receives the ultrasonic signal transmitted from the bottom into the liquid and reflected by the liquid surface in the measurement pipe, and the reference chamber. Each of the signal transmitting / receiving elements for receiving the ultrasonic signal reflected by the inner surface of the upper portion of the side tube is provided, and these signal transmitting / receiving elements are
Time t ₂ from the signal transmitting / receiving element at the bottom of the measuring tube to the signal transmitting / receiving element at the bottom of the measuring tube after the ultrasonic signal generated in the liquid in the measuring tube is reflected by the liquid surface in the measuring tube Until the ultrasonic signal emitted from the signal sending / receiving element at the bottom of the chamber side tube into the liquid in the reference chamber side tube is reflected by the upper inner surface of the tube inside the reference chamber side and reaches the signal sending / receiving element at the bottom of the reference chamber side tube. Time t ₁
And a height a which is a constant from the signal transmitting / receiving element surface in the reference chamber side pipe to the upper inner surface, a control calculation circuit for calculating the liquid level L in the tank by calculation of L = a · t ₂ / t _1. Bypass pipe type level gauge connected to.