JP2006313079A - Level measurement device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a level measurement device which is capable of easily and precisely measuring the level of a liquid e.g. liquid level in a water tank or a weir and is also very advantageous in cost, and also to provide a flow rate measurement device using the same. <P>SOLUTION: The device is for measuring the liquid level in the tank for storing the liquid, on which a differential pressure transmitter is provided and also a pressure pipe extending from the high pressure side of the differential pressure transmitter toward the lower bottom through the inside of the tank, while keeping the pressure of the high pressure side or the low pressure side of the differential pressure transmitter negative pressure and grasping the pressure difference by the change of the liquid level in the tank by the pressure difference of the pressure difference transmitter. The liquid level on the tank is obtained based on the pressure difference, and the flow rate also can be obtained at need. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a level measuring device, and more particularly to a level measuring device suitable for measuring a fluid level in a container such as a water storage tank or measuring a water level of a drain having a weir. The present invention also relates to a flow rate measuring device that can determine the flow rate of the weir after measuring the fluid level in the weir.

  For example, it is necessary to constantly monitor and control the water level of a water storage tank such as domestic water or industrial water. Usually, such a water storage tank has a sealed structure, and therefore, the liquid level measurement is performed by installing a mechanical measuring means such as a float type level meter in the tank, and by displacing the wire connected to the float. This is done by measuring the level and detecting the result externally. However, the float type level meter frequently causes troubles such as mechanical parts failure due to deterioration over time, wire breakage, and hooking of the float, resulting in inability to measure or a decrease in measurement accuracy. The current situation is that manual monitoring is forced.

On the other hand, when industrially used water is subjected to a predetermined treatment and discharged to rivers, seas, etc., it cannot be drained without limitation, and its discharge (flow rate) is naturally limited. Usually, weirs are provided midway in the drainage channel (the weir structure has triangles, squares, full-width shapes, etc. defined by JIS), and the water level in the drainage weir is ascertained. It is necessary to obtain the flow rate, and for this purpose, a so-called weir type flow meter is installed. The weir type flow meter calculates the flow rate by measuring the head height of the weir, and in the contact type that measures by directly contacting the fluid, the capacitance type, throwing type, float type, As a non-contact type, an ultrasonic level meter is often used.
However, the contact-type level meter has problems that it becomes impossible to measure due to adhesion of dirt, water, or deposits, and measurement errors increase. On the other hand, with the non-contact type level meter, the above-mentioned problem of the contact type is solved, but because of the ultrasonic wave, special techniques are required for periodic calibration (traceability), and bubbles, steam, wind There are disadvantages such as being easily affected by such factors as poor measurement accuracy.

Furthermore, as shown in Patent Document 1 or Patent Document 2, a method of using a differential pressure detector as a liquid level measuring means in a tank has been proposed. The pressure difference is output as a differential pressure signal.
JP-A-8-219776 JP 2000-337944 A

However, the pressure of the measuring liquid input to the differential pressure detector in the level measuring apparatus of Patent Documents 1 and 2 described above is a positive pressure. It is necessary to arrange at a position below the liquid level, and a pressure guiding pipe is also attached to the bottom of the tank and led from there to the detector. For this reason, depending on the installation position of the differential pressure detector, it may be possible to dig deeper than the ground level, such as a water storage tank (particularly a tank installed in a narrow place or an inconvenient place) or a drainage ditch. It is impractical to apply such a differential pressure detector to the weir, and almost no examples of actual application were found.
An object of the present invention is to solve the problems of the prior art as described above, and it is possible to easily and accurately measure the fluid level in the water storage tank or the weir as described above, and in a narrow or inconvenient place. It is an object of the present invention to provide a level measuring device that can be easily installed even at a very low cost, and a flow rate measuring device using the level measuring device.

A level measuring device according to the present invention for solving the above-mentioned problems is a device for measuring a liquid level in a tank containing a liquid, wherein a differential pressure transmitter is installed on the upper side of the liquid, and the differential pressure is measured. A pressure guiding pipe extending from the high pressure side of the transmitter toward the bottom bottom is provided in the tank, and the high pressure side or the low pressure side of the differential pressure transmitter is maintained at a negative pressure by filling the pressure guiding pipe with the liquid in the tank. The pressure change due to the change in the internal liquid level is grasped as the differential pressure change in the differential pressure transmitter, and the liquid level in the tank is obtained based on this differential pressure.
In the present invention, the tank containing the liquid is a sealed or open water storage tank for storing domestic water or industrial water, and the water level in the water storage tank can be measured by a differential pressure transmitter and a pressure guiding tube. is there.
Furthermore, the weir flow rate measuring device according to the present invention is a device for measuring the flow rate of a weir provided in a water channel, a reservoir, or a water tank, and a differential pressure transmitter is installed above the upstream side of the weir and the difference is measured. A pressure guiding pipe extending from the high pressure side of the pressure transmitter through the water in the weir and exceeding the lowest limit of the weir is arranged, and by filling the liquid in the weir to the pressure guiding pipe, the high pressure side or the low pressure side of the differential pressure transmitter Is maintained at negative pressure, the pressure change due to the water level change in the weir is grasped as the differential pressure change in the differential pressure transmitter, the head upstream of the weir is obtained based on this differential pressure, and automatically based on the obtained water head The flow rate of the weir is calculated.
The weir flow measuring device is best applied in such cases, especially when the wastewater discharged from the factory is discharged into rivers and seas because the amount of discharge is strictly regulated. It is. Typical weir structures include a triangular weir, a square weir, and a full width weir.

  According to the level measurement device of the present invention, the general-purpose differential pressure level meter is devised in terms of arrangement and operation without requiring special means by converting the pressure of the detection unit from positive pressure to negative pressure. Thus, the liquid level can be measured easily and with high accuracy, and the flow rate of the weir can be similarly determined with high accuracy based on this measurement level. In addition, the device according to the present invention is low in cost and has excellent durability because it is not affected by steam, bubbles, wind, etc., and can be installed and used even in severe installation space conditions. There is also an advantage that the installation work is simple. Moreover, the calibration does not require any advanced technology, and anyone can easily calibrate.

Hereinafter, the present invention will be described based on embodiments shown in the drawings.
For example, as shown in FIG. 2, a widely used differential pressure type liquid level gauge has a liquid 3 in the tank on the high pressure side of a differential pressure transmitter 2 installed at a position lower than the lowest liquid level in the open type tank 1. Is guided through the pressure guiding pipe 4 and the low pressure side is opened to the atmosphere. The differential pressure between the high pressure side pressure and the low pressure side pressure of the differential pressure transmitter 2 is obtained by the following equation.
P _H −P _L = ρg (H + h)
Where P _H : High pressure side pressure of differential pressure transmitter (Pa)
P _L : Low pressure side pressure of differential pressure transmitter (Pa)
ρ = density of the liquid (kg / m ³ )
g = gravity acceleration (m / s ² )
H = Vertical distance from the lowest liquid level to the liquid level (m)
h = Vertical distance (m) from the position of the pressure receiving element of the differential pressure transmitter to the lowest liquid level
The differential pressure type liquid level meter in FIG. 2 is a positive pressure detector, and it is essential that the differential pressure transmitter 2 be installed at a position below the lowest liquid level. It is impossible to install a pressure transmitter. For this reason, conventionally, an expensive level meter such as an ultrasonic detector has to be used.

Therefore, in the present invention, as a result of examining to use a differential pressure transmitter that is advantageous in terms of cost for water tank and weir level detection, if the differential pressure transmitter is used as a negative pressure detector instead of a positive pressure, it is described above. It has been found that the problem can be solved, and the present invention has been completed.
That is, FIG. 1 shows an example in which the present invention is applied to liquid level measurement in a water storage tank. In the figure, 10 is a tank body, 11 is life or security water stored in the tank 10, and 12 is a tank. 10 is a water ring type differential pressure level meter installed at the top of 10. The differential pressure level meter 12 includes a differential pressure transmitter 13 composed of a high pressure side and a low pressure side, a suction device 15 provided above the differential pressure transmitter 13 via a stop valve 14, and a high pressure of the differential pressure transmitter 13. And a pressure guiding tube 16 extending from the side downward to a position where the tip is almost in the vicinity of the bottom of the tank. The differential pressure level meter 12 may be fixed to the lid portion or the side wall portion of the tank body via an appropriate bracket. Further, it is desirable that the pressure guiding tube 16 be made of stainless steel or the like having excellent corrosion resistance.

In the actual level measurement operation, first, the stop valve 14 is opened, the suction device 15 is operated, the pressure guiding tube 16 is brought into a vacuum state, water is sucked to fill the water in a low water level state, and at a predetermined vacuum level. The suction is stopped, and then the stop valve 14 is closed to maintain the vacuum level. Since the suction device 15 is necessary only during the first suction, it may be attached only during the suction. If there is a water level change in the tank 10 in this state, the change is transmitted to the high pressure (negative pressure) side of the differential pressure transmitter 13 thereabove through the pressure guiding pipe 16 and appears as a pressure change. This pressure change immediately causes a change in the differential pressure from the low pressure side (usually set to atmospheric pressure), and the pressure difference changes. If the relationship between the differential pressure change value and the liquid level in the tank is set in advance, the level can be immediately known from the detected differential pressure. Actually, the change in the differential pressure is converted into an electric signal, and the level may be displayed on the indicator.
Here, in the example of FIG. 1, the case where the differential pressure is measured by filling the liquid on the high pressure side will be described. However, in the present invention, the liquid is filled on the low pressure side and a predetermined signal conversion process is performed. The same result can be obtained.

Specific data examples of the measuring apparatus in FIG. 1 are as follows: H (distance from the tip of the pressure guiding tube to the differential pressure transmitter or length of the pressure guiding tube) = 5000 mm, L (range where the instrument can be indicated) = 4000 mm The differential pressure at 0% water level is 5000 mm × 1.0 (specific gravity) = 5000 mmH ₂ O (actually −5000 mmH ₂ O due to negative pressure). span from the value 4000 mm × 1.0 (specific gravity) = from 4000mmH a ₂ O, the -5000 + 4000 = -1000mmH ₂ O. From the above, the measurement range of the measuring apparatus is −5000 to −1000 mmH ₂ O / 0 to 4 m.

  Next, FIG. 3 shows a case where the apparatus of the present invention is applied as a flow meter for a flowing water weir (water differential pressure type flow meter). For example, the waste water after being used in various processes in a factory is subjected to predetermined treatment. When discharging into a river or the sea, the weir provided in the channel immediately before that corresponds. In FIG. 3, 20 is a plate-like or wall-like triangular weir provided in the middle of the water channel or at the tip, 21 is a liquid that flows and falls in the triangular weir 20 (in this case, drainage), and 22 is upstream of the triangular weir 20. A head differential pressure type level meter 23 installed above the free surface on the side, 23 is a flow rate converter for calculating the flow rate based on the level obtained by the level meter 22. The head differential pressure type level meter 22 includes a differential pressure transmitter 24 composed of a high pressure side and a low pressure side, and a tip of the differential pressure transmitter 24 extending further downward from the high pressure side of the differential pressure transmitter 24 more than the lower edge of the triangular weir plate. The pressure guide tube 25 extends to a lower position. Although a pipe provided with a stop valve 25 is shown on the high pressure side of the differential pressure transmitter 23, a suction device (not shown) can be appropriately attached to the pipe. A combination of the water head differential pressure type level meter 22 and the flow rate converter 23 constitutes a weir flow meter. The flow rate converter 23 is composed of, for example, a general-purpose linearizer and a converter.

When measuring the flow rate, it is first necessary to measure the free surface level on the upstream side of the current triangular weir 20, and this is performed according to the same principle as shown in FIG. That is, the stop valve 25 on the high pressure side of the differential pressure transmitter 24 is opened, and an appropriate suction device is attached thereto, and drainage is sucked through the pressure guiding pipe 25 to fill the pressure guiding pipe 25 with the drainage. The high pressure side of the pressure transmitter 24 is maintained at a constant negative pressure. In this state, the differential pressure between the high pressure (negative pressure) side and the low pressure side is grasped by the head pressure upstream of the triangular weir 20, and the upstream level of the triangular weir 20 is measured based on this. Of course, in this case, the differential pressure is obtained as a negative pressure. The level thus obtained is input to the flow rate converter 23, and the flow rate Q is calculated by the following flow rate formula defined by JIS B 8302.
Q = Kh ^5/2 (m ³ / min)
K = 81.2 + 0.24 / h + (8.4 + 12 / √D) × (h / B−0.09)
The above flow rate formula applies to right-angled triangular weirs. When the weir shape is a square weir or full width weir, the flow rate Q may be calculated based on the respective flow rate formulas defined in JIS B 8302. . In the case of a square weir, Q = Kbh ^3/2 (b: width of the notched weir), and in the case of a full width weir, Q = KBh ^3/2 .

  As described above, in the present invention, the differential pressure transmitter that is normally used based on the detection of the positive pressure is used for the detection of the negative pressure. It became possible to install a differential pressure transmitter in a place that did not exist. In actual operation, following the detection of the level of the tank and the detection of the level / flow rate of the weir, the present invention may be utilized by appropriately connecting a level control, a flow control system or an alarm system via electrical means. .

In FIG. 3, when H ₁ = 2000 mm, H ₂ = 500 mm, and h = 110 mm, the differential pressure at the upper limit level of the right angle triangular weir is −2000 + 610 = −1390 mmH ₂ O, and the differential pressure at the lower limit level of the right angle triangular weir is − 2000 + 500 = −1500 mmH ₂ O, and the measurement range is −1500 to −1390 mmH ₂ O. Fill the pressure guiding tube (15A) with the measuring liquid, change the differential pressure with the head pressure, measure the weir liquid level, convert it into a flow rate with a linearizer and a converter, and record it as an electrical signal. Recorded. As a level measurement, the measurement work could be performed with an accuracy of ± 1 mm without being affected by external factors (steam, bubbles, wind).
On the other hand, when measuring the level and flow rate of a weir with the same right-angle triangular weir with a conventional ultrasonic flowmeter, it is easily affected by external factors, and the measurement accuracy is at most ± 10 mm. Was about 4 to 5 times the differential pressure transmitter. Further, periodic calibration is impossible with an ultrasonic flowmeter, but calibration is possible with a differential pressure transmitter employed in the present invention, and traceability can be established.

  By utilizing the principle of the present invention described above, it becomes possible to easily apply the measurement when the level of various liquids is difficult to measure using a differential pressure transmitter based on positive pressure.

It is a schematic explanatory drawing which shows the example which applied this invention to the liquid level measurement in a water storage tank. It is explanatory drawing which shows the outline | summary of the conventional differential pressure type liquid level gauge for measuring the liquid level in an open type tank. It is explanatory drawing which shows the outline | summary of the apparatus at the time of applying this invention to the flow measurement of a triangular weir.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Open type tank 2 Differential pressure transmitter 3 Liquid in tank 4 Pressure guiding pipe 10 Tank main body 11 Liquid 12, 22 Water seal type differential pressure level meter 13, 24 Differential pressure transmitter 14, 25 Stop valve 15 Suction device 16, 25 Pressure tube 20 Triangular weir 21 Drainage 23 Flow rate converter

Claims (4)

  A device for measuring a liquid level in a tank that contains a liquid, and a differential pressure transmitter is installed on the upper side of the liquid, and is guided from the high pressure side of the differential pressure transmitter to the bottom of the tank. A pressure tube is provided, and the pressure guide tube is filled with liquid in the tank to maintain the high pressure side or the low pressure side of the differential pressure transmitter at a negative pressure. A level measuring device characterized by grasping as a change and obtaining a liquid level in the tank based on the differential pressure.   2. The level according to claim 1, wherein the tank for storing the liquid is a sealed or open water storage tank for storing domestic water or industrial water, and the water level in the water storage tank is measured by a differential pressure transmitter and a pressure guiding pipe. measuring device.   In a device that measures the flow rate of a weir provided in a waterway, reservoir, or reservoir, a differential pressure transmitter is installed above the upstream side of the weir, and water in the weir is passed from the high pressure side of the differential pressure transmitter. A pressure guiding pipe extending beyond the lowest limit of the liquid level of the weir is placed, and the high pressure side or the low pressure side of the differential pressure transmitter is maintained at a negative pressure by filling the pressure guiding pipe with the liquid in the weir. It is characterized by grasping the pressure change due to the water level change as the differential pressure change in the differential pressure transmitter, obtaining the weir upstream head based on this differential pressure, and automatically calculating the weir flow rate based on the obtained water head Weir flow measurement device.   4. The in-weir flow rate measuring device according to claim 3, wherein the water channel is a drainage channel that flows into a river or the sea.

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