Device and method for measuring liquid level of underground sewage pool

Abstract

According to the device and method for measuring the liquid level of the underground sewage pool, the height difference of the liquid level is formed in the vacuum measuring pipe by using the vacuum effect of physics, the differential pressure formed by the height difference of the water level is measured by using the common differential pressure transmitter, and the liquid level height of the pool is converted by measuring the differential pressure; as a common differential pressure transmitter is mature in technology, high in precision and capable of automatically calibrating measurement errors caused by different atmospheric pressure changes due to weather reasons, although the bottom of a vacuum measurement pipe is communicated with a water pool medium, water in the pipe is in a non-flowing static state due to a vacuum effect, a water isolation effect is formed, and the measurement accuracy is greatly improved. Meanwhile, the measuring pipe is large in diameter and cannot be blocked by dirty objects such as dirty oil in a sewage pool, measurement is stable, and cost is low.

Description

Technical Field

[0001] The present invention belongs to the petrochemical industry, and specifically relates to a device and method for measuring the liquid level of an underground sewage pool. Background Art

[0002] In the petrochemical industry, the level measurement of underground sewage treatment pools has always been a difficult problem that cannot be solved well. In current technology, when the pool is not deep or the pool water is highly corrosive, the most commonly used is the non-contact principle ultrasonic level meter. The ultrasonic probe is located on the pool. When it rains due to weather reasons or water vapor condenses in the air, when there are water droplets or water layers on the probe, it will cause severe attenuation of the ultrasonic wave and cannot be measured normally; when the pool is deep or the pool water is highly corrosive, current technology mostly uses non-contact principle radar level meters. When the temperature rises in summer, the water vapor on the surface of the sewage pool or the light oil component on the surface of the water volatilizes seriously, because the pool is a closed structure, an oil mist cloud or water vapor layer will form in the space on the water surface of the pool, causing severe attenuation of electromagnetic waves. Sometimes electromagnetic waves cannot penetrate the oil mist layer or water vapor layer, resulting in unstable liquid level measurement; it can be seen that when using non-contact principle ultrasonic or radar, it is greatly affected by weather reasons, and the cost of this type of instrument is also high; there is also the use of backblowing technology, using a pressure transmitter to measure the pressure of the backblowing air pipe, and the backblowing air pipe is directly inserted into the bottom of the pool, because The air volume must be very small due to the back-blowing principle, so the air outlet of the back-blowing air pipe under the liquid surface is very small. In the inspection and maintenance or accident state of the refinery or chemical plant, the sewage pool is very dirty, and a large amount of dirty oil is injected. The heavy component dirty oil is very viscous, which can easily stick to the back-blowing port. Even if it cannot be sealed, it will increase the pressure of the back-blowing air pipe, resulting in inaccurate measurement. Continuous instrument air consumption is not conducive to energy saving; there are also immersed pressure transmitters, which seal the flange pressure transmitter and sink it to the bottom of the pool with the diaphragm to measure the static pressure converted to liquid level height. However, because the water in the pool is too dirty, over time, dirty oil or dirt slowly sticks to the diaphragm, resulting in inaccurate pressure measurement. The diaphragm needs to be frequently lifted out of the water for cleaning, and the maintenance workload is large; in some chemical industries, when the sewage of the strong corrosive medium flows into the pool, the material of the measuring element in contact with the medium will be strongly corroded, and its diaphragm requires strong corrosion-resistant metal, resulting in the material of the liquid contact part being special metal or gold-plated, which increases the cost.

[0003] Because the medium in the sewage pool is very dirty or highly corrosive, it is difficult to get a good solution when measuring the liquid level using either the non-contact principle or the contact principle, and the liquid level measurement has always been unstable. Summary of the invention

[0004] In order to solve the above problems, the present invention provides a device and method for measuring the liquid level of an underground sewage pool. The vacuum effect of physics is used to form a height difference of the liquid surface in a vacuum measuring tube, and an ordinary differential pressure transmitter is used to measure the differential pressure formed by the height difference of the water level. The liquid level height of the pool is converted by measuring the differential pressure. Because the technology of ordinary differential pressure transmitters is very mature, the accuracy can be very high. At the same time, the measurement error caused by different atmospheric pressure changes due to weather reasons can be automatically calibrated. Although the bottom of the vacuum measuring tube is connected to the water pool medium, due to the vacuum effect, the water in the tube is in a static state without flowing, forming a water isolation effect. At the same time, the measuring tube diameter is large and will not be blocked by dirt such as dirty oil in the sewage pool. The measurement is very stable and the cost is very low.

[0005] The technical solution adopted by the present invention is:

[0006] A device for measuring the liquid level of an underground sewage pool comprises a vacuum measuring tube, a measuring tube top cover, a differential pressure transmitter, a root valve, a water injection valve, a sealing pipe cap, a bottom plate, a pulley and a nylon rope; the vacuum measuring tube is arranged vertically, the bottom of the vacuum measuring tube is inserted into sewage, and the top of the vacuum measuring tube extends above the pool cover; the measuring tube top cover is fixedly connected to the top of the vacuum measuring tube to seal the top of the vacuum measuring tube; a tee is arranged on the measuring tube top cover, and the root valve and the water injection valve are respectively connected to the measuring tube top cover through the tee; the differential pressure transmitter is connected to the root valve; the sealing pipe cap is connected to the water injection valve; one side of the bottom plate is connected to the bottom of the vacuum measuring tube, and the other side of the bottom plate is connected to the nylon rope, and the nylon rope is connected to the pulley, and the bottom plate can be driven to move through the pulley to seal the bottom of the vacuum measuring tube.

[0007] The present invention provides a method for measuring the liquid level of an underground sewage pool, using the above-mentioned device for measuring the liquid level of an underground sewage pool, and comprises the following steps:

[0008] 1) When the liquid level in the sewage pool is just at the bottom of the vacuum measuring tube, open the root valve, open the bleed screw of the differential pressure transmitter, open the water injection valve, unscrew the sealing pipe cap, pull the nylon rope and fix it, cover the bottom of the vacuum measuring tube with the bottom plate, and inject water into the vacuum measuring tube through the water injection valve;

[0009] 2) After the pipe is completely filled with water, water begins to overflow from the discharge screw of the differential pressure transmitter. At this time, reduce the amount of water injection to allow the bubbles in the pipe to rise and be discharged. Close the root valve and the water injection valve, tighten the discharge screw, and tighten the sealing pipe cap to form a seal at the top of the pipe.

[0010] 3) Loosen the nylon rope, the bottom plate falls naturally due to gravity, and the bottom of the tube is opened. At this time, the top of the tube is a sealed structure. Under the weight of the water column in the tube, a vacuum is formed at the top of the tube, and the water in the tube does not flow downward. The differential pressure value at this time makes the reading of the differential pressure transmitter 0. This point is calibrated as the relative zero point of the water pool, which is also the measurement zero point;

[0011] 4) Continue to fill the pool with water until the liquid level rises to the maximum allowable level, and record the differential pressure value at this time; adjust the range of the differential pressure transmitter to the full scale with the maximum output. At this time, the full-scale online calibration of the differential pressure transmitter is completed. The output of the differential pressure transmitter is set to percentage output, or the output unit is set to millimeters of water column. At this time, the differential pressure transmitter has been calibrated online and can start measuring the pool level.

[0012] The present invention provides a method for measuring the liquid level of an underground sewage pool, which is further characterized in that a vacuum measuring tube is made of a transparent corrosion-resistant material.

[0013] The invention provides a method for measuring the liquid level of an underground sewage pool, which is further characterized in that the sealing method of the measuring tube top cover and the top end of the vacuum measuring tube is welding or glue sealing.

[0014] The present invention provides a method for measuring the liquid level of an underground sewage pool, which is further characterized in that: a differential pressure transmitter is arranged at the highest point of the entire measuring pipeline, the negative pressure measuring chamber of the differential pressure transmitter is connected to the root valve, the positive pressure measuring chamber is connected to the atmosphere, the positive pressure chamber is covered with a windproof net, and the differential pressure transmitter is installed on the wall of the sewage pool and fixed separately.

[0015] The invention discloses a method for measuring the liquid level of an underground sewage pool, which is further characterized in that a top of a vacuum measuring tube is fixed on a pool cover plate by a U-shaped tube clamp, and a bottom of the vacuum tube is also fixed on the pool bottom by a bracket.

[0016] The invention discloses a method for measuring the liquid level of an underground sewage pool, which is further characterized in that: the bottom plate is a corrosion-resistant organic glass plate, and its upper edge in contact with the bottom of the pipe is polished to a certain arc; a handle is arranged on the other side of the bottom plate, and a nylon rope is fixed at the end of the handle.

[0017] The invention provides a method for measuring the liquid level of an underground sewage pool, which is further characterized in that the indicating head of the differential pressure transmitter is screwed off and connected to a remote position for easy observation by a cable.

[0018] The present invention provides a method for measuring the liquid level of an underground sewage pool, which is further characterized in that: during the water injection calibration in step 1, a small colored foam float is inserted into a vacuum measuring tube, a ribbon is tied under the small float, and a very small weight is added to the bottom of the ribbon.

[0019] The present invention has the following beneficial effects:

[0020] 1. This principle is energy-saving. There is no continuous loss of energy such as instrument air caused by the back-blowing method, and no additional public engineering conditions are required.

[0021] 2. The measuring element of the differential pressure transmitter used in this principle does not come into contact with the viscous or corrosive media in the sewage, and does not even come into contact with the clean water in the vacuum measuring tube. It only comes into contact with the air. The components of the medium in the water pool have no effect on the measurement. The principle belongs to the non-contact measurement principle.

[0022] 3. This principle works as long as there is no large amount of air leakage in the pipe. It does not matter if a small amount of air seeps in. It does not require daily maintenance. According to the principles of physics, the measurement is not affected by temperature changes caused by the seasons. Whether there is a leak can be easily judged visually, and it is easy to inspect and maintain.

[0023] 4. This principle uses a differential pressure transmitter, and one end of the pressure measuring chamber is connected to the atmosphere. Changes in atmospheric pressure caused by weather conditions have no effect on the measurement. Weather conditions such as rain, snow, condensation, and water vapor evaporation in hot weather have no effect on the measurement. The measurement is stable and highly reliable.

[0024] 5. This principle does not cause any pollution, no pollutants leak out, etc., and meets any HSE requirements.

[0025] 6. The equipment consists of simple components and is easy to obtain from the market. It does not require manufacturing or processing by specialized manufacturers. Users can design and manufacture it by themselves based on the principles, with low cost.

[0026] 7. Explosion-proof treatment is very easy, and the explosion-proof technology of the transmitter is very mature.

[0027] 8. The remote meter can be set at any convenient location, making it easy to observe the liquid level on site.

[0028] 9. It can be directly connected to DCS and other control systems for observation on the operation station screen to achieve automated management.

[0029] 10. On-site calibration or maintenance is very simple. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The present invention is further described in detail below in conjunction with the structural components and functional descriptions of the drawings. The drawings and functional descriptions do not limit the scope of protection claimed by the present invention.

[0031] Figure 1 It is the measurement principle and structure diagram of the present invention.

[0032] The accompanying drawings indicate: 1-vacuum measuring tube, 2-pool cover, 3-sewage, 4-bottom of measuring tube, 5-top cover of measuring tube, 6-differential pressure transmitter, 7-root valve, 8-water injection valve, 9-sealing pipe cap, 10-bottom plate, 11-pulley, 12-nylon rope. DETAILED DESCRIPTION

[0033] The present invention will be described in detail below in conjunction with the accompanying drawings:

[0034] Overall assembly instructions:

[0035] like Figure 1 As shown, a highly transparent and corrosion-resistant organic glass tube is prepared as a vacuum measuring tube 1, with a diameter of DN100, which can be adjusted. The size of the tube diameter is preferably such that the lower opening is not easily blocked by the dirty oil or sludge in the sewage 3. The length is such that the lower end of the tube is 100 to 200 mm above the bottom of the pool, and the upper end is about 500 mm above the pool cover 2 for easy maintenance. Generally, the height of the pool is within 10 meters, and the length of the measuring tube cannot exceed the range of the absolute vacuum allowable water column of 10 meters. The strength and thickness of the tube should be able to resist vacuum without breaking, and be suitable for U-shaped pipe clamp fixation, which is related to the depth of the pool.

[0036] The bottom 4 of the measuring tube is designed to be open, and the top cover 5 of the measuring tube is sealed with a plexiglass sealing cover. The sealing method can be welding or glue sealing. The center of the cover is equipped with a PVC tee. The smaller the diameter of the tee, the better, preferably 1 / 2", and the total length is about 150mm. The top of the tee is equipped with a PVC small ball valve as a root valve 7, and the side is equipped with a PVC small ball valve as a water injection valve 8. A short section of PVC pipe about 150mm long is equipped after the water injection valve 8, and a threaded joint is added at the end with a threaded sealing pipe cap 9 for sealing. The top of the root valve 7 is equipped with a mounting piece according to the connection type of the differential pressure transmitter, and the top is connected to the differential pressure transmitter. The negative pressure measuring chamber of the pressure transmitter 6 and the positive pressure measuring chamber are connected to the atmosphere. The positive pressure chamber is covered with a windproof net. The differential pressure transmitter is installed on the side of the pool wall and fixed separately. The differential pressure transmitter is located at the highest point of the entire measuring pipeline. The vacuum measuring tube 1 is installed on the side of the pool wall for easy maintenance and observation. A hole is opened on the pool cover 2, and the vacuum measuring tube is extended out of the cover about half a meter. The top of the vacuum measuring tube 1 is fixed on the cover with a U-shaped pipe clamp, and the bottom of the tube is also fixed with a bracket on the bottom of the pool. During installation, according to the measurement principle, it is not necessary to ensure strict verticality, as long as it is relatively vertical, and the installation is simple.

[0037] A loose-leaf bottom plate 10 is fixed at the bottom of the measuring tube. The bottom plate 10 is a heavier and thicker corrosion-resistant organic glass plate. The upper edge of the bottom plate in contact with the bottom of the tube can be properly polished to a certain arc to facilitate relative sealing with the lower edge of the vacuum measuring tube 1. A handle can be made on the other side of the bottom plate, which can be made longer. A nylon rope is fixed at the end of the handle. By using the lever effect, when the nylon rope 12 is pulled through the fixed pulley 11 above, a very small force can be used to form a large upward support force at the bottom of the tube to resist the gravity of the water in the tube.

[0038] How to use and principle description:

[0039] 1) When the liquid level in the pool is just at the bottom 4 of the vacuum measuring tube, open the root valve 7, open the bleed screw of the differential pressure transmitter, open the water injection valve 8, unscrew the sealing cap 9, pull the nylon rope 12 and fix it, and cover the bottom 4 of the vacuum measuring tube with the bottom plate 10. It is not necessary to seal it in a strict sense. Just cover the bottom of the tube and ensure that the water injection speed is faster than the water leakage speed. The strength of the nylon rope 12 is required to bear the weight of the tube filled with water. Pull a water pipe from nearby to the sealing cap 9 to start filling the vacuum measuring tube 1 with water.

[0040] 2) At this time, you can visually observe that the water level in the pipe continues to rise until the pipe is completely filled and begins to overflow from the discharge screw of the negative pressure chamber of the differential pressure transmitter. Slowly reduce the amount of water injected to allow the bubbles in the pipe to rise and be discharged. Quickly close the root valve 7 and the water injection valve 8, tighten the discharge screw, and tightly tighten the sealing pipe cap 9 to form a seal at the top of the pipe.

[0041] 3) Loosen the nylon rope 12, the bottom plate 10 falls naturally due to gravity, and the bottom of the tube is opened. At this time, because the top of the tube is a completely sealed structure, a vacuum is formed at the top of the tube under the weight of the water column in the tube, and the water in the tube does not flow downward. At this time, the reading of the differential pressure transmitter is: differential pressure value = positive pressure chamber measurement value - negative pressure chamber measurement value = 0 - (- (L-H1) = L-H1 millimeter of water column (mmH2O).

[0042] L- The distance between the differential pressure transmitter discharge screw and the pool bottom. (This value can be obtained by actual measurement on site).

[0043] H-water pool liquid level, when calibrated to zero point, H=H1.

[0044] H1- The height of the bottom 4 of the vacuum measuring tube from the bottom of the pool (this value can be obtained by actual measurement on site).

[0045] The magnitude of the differential pressure value measured at this time is not important, because this value needs to be shifted. Shifting this value makes the reading of the differential pressure transmitter 6 0, which is calibrated as the relative zero point of the water pool and also the measurement zero point.

[0046] 4) Continue to fill the pool with water. When the liquid level rises to the maximum allowable level H=H2, the differential pressure value is calculated as:

[0047] Differential pressure value = 0-(LH) = -L+H2.

[0048] At this time, the size of the differential pressure value is not important. Adjust the range of the differential pressure transmitter 6 to the full scale with the maximum output. At this time, the full-scale online calibration of the differential pressure transmitter is completed. Because the liquid level rises, the differential pressure signal will gradually decrease. The direction of the signal displayed in the DCS is opposite to the actual measurement. The output at the lowest point is the largest and the output at the highest point is the smallest. Therefore, the signal needs to be reversed in the DCS to linearize the measured value and the output at the lowest point H1 is the smallest and the output at the highest point H2 is the largest. Then set the output of the differential pressure transmitter to a percentage output, or set the output unit to millimeters of water column. At this time, the differential pressure transmitter 6 has been calibrated online and can start measuring the pool level.

[0049] 5) If Figure 1 As shown, when the sewage in the pool is at any liquid level H,

[0050] When the differential pressure transmitter 6 reading is a percentage, the measurement of the differential pressure transmitter is a linear output, so the differential pressure transmitter 6 measurement value reading is:

[0051] Measurement value% = (H-H1) / (H2-H1)*100%

[0052] The actual height of the pool can also be converted in DCS as:

[0053] Actual liquid level height = measured value%*(H2-H1)+H1

[0054] When the differential pressure transmitter reading is set to mmH2O,

[0055] Transmitter reading mmH20 = H-H1

[0056] The actual height of the pool can be converted in DCS as:

[0057] Real liquid level H = measured value mmH2O + H1

[0058] Because the accuracy of ordinary differential pressure transmitters is generally less than or equal to ±0.075%, when the maximum height of the water pool is 10 meters, the maximum calculated error is 7.5mm. When the medium in the pool is basically water and the density does not change much with the seasons throughout the year, the error can fully meet the measurement requirements.

[0059] Because the top of the vacuum measuring tube 1 is a fully enclosed vacuum structure, the water column in the vacuum measuring tube 1 forms a vacuum at the top of the tube under the action of gravity, sealing the entire tube water in the tube. The water in the tube is always static and does not flow, but the bottom is not sealed and is connected to the pool water at the bottom. The liquid can transmit pressure in any direction without changing. The differential pressure transmitter 6 can measure the change in vacuum degree caused by the change in the pool liquid level. Even when the pool water level is lower than the bottom of the vacuum measuring tube 4, as long as the total length from the bottom of the tube to the negative pressure chamber of the differential pressure transmitter is less than 10 meters, the bottom of the tube may even be exposed to the atmosphere for a short time, and the water in the tube will not flow out.

[0060] According to this principle, since the water column in the tube is injected with clean water at the beginning of the calibration zero point, a water seal is formed in the tube under the action of vacuum, and the diaphragm of the differential pressure transmitter is installed at the top of the tube. After the seal is formed, the diaphragm does not contact the medium in the measuring tube. After the seal is formed at the top of the calibration zero point, there will be a very small amount of residual gas at the top at the moment the nylon rope is loosened. The little bit of gas remaining in the tube will form a very strong vacuum gas column. According to the principles of physics, the pressure transmission of gas and liquid remains unchanged in all directions, so the vacuum inside the vacuum measuring tube is still accurately transmitted to the negative pressure chamber to convert the liquid level height. The less residual gas in the tube, the smaller the impact of ambient temperature changes on the measurement, because the expansion or contraction of the gas brings about a very small change in the height of the liquid column in the tube. Because the bottom of the liquid column in the tube is connected to the pool water, as long as the vacuum at the top remains unchanged, the expansion or contraction of its volume does not affect the height of the liquid column. Even if a small amount of corrosive medium from the sewage pool enters the pipe due to the long-term diffusion of molecules, its concentration is very limited. Even if dirty oil enters the measuring tube, it floats above the vacuum measuring tube 1 due to its density less than that of air. Because the differential pressure transmitter 6 is installed at the highest point of the measuring pipeline system, the dirty oil is always below the diaphragm and cannot contact the diaphragm of the differential pressure transmitter 6. The diaphragm is not in contact with liquid, and the material does not need to be special or there is a possibility of sticking. The differential pressure transmitter works stably.

[0061] The intrinsic safety explosion-proof technology of the differential pressure transmitter is very mature, so the transmitter installed in the explosion-proof area on the top of the dirty oil pool can fully meet the intrinsic safety requirements of the explosion-proof area.

[0062] The connection between differential pressure transmitter and control systems such as DCS is very mature. The liquid level can be easily displayed on the control system screen, which can realize intelligent operation.

[0063] Compared with non-contact instruments, differential pressure transmitters are very common, inexpensive, highly localized, and easy to obtain spare parts.

[0064] Because the pool has a strong odor, the indicating head of the differential pressure transmitter can be unscrewed and connected with a cable to a remote location for easy observation, which greatly facilitates the observation of the liquid level during inspections.

[0065] Because a transparent plexiglass tube is selected, during the initial calibration and water injection, several colored foam small floats can be stuffed into the vacuum measuring tube 1, and a long red ribbon is tied under the small float, and a very small weight is added to the bottom of the ribbon. According to the principles of physics, solids in the liquid do not affect the transmission of pressure, and the red ribbon in the tube can be easily observed visually from a long distance. When it is found that the position of the small float is not at the top of the tube, it means that there is an air leak in the tube at this time, and the tube needs to be refilled with water and the seal needs to be checked. The nylon rope 12 can be tightened, water can be refilled into the tube, and a vacuum can be re-formed at the top. The nylon rope 12 can be loosened to restore the connection between the bottom and the pool water. Maintenance and repair are very convenient. As long as the tube is fully closed, basically no maintenance and repair are required. It doesn’t matter if the water in the tube starts to get dirty, and it does not affect normal measurement and use.

Claims

1. A device for measuring the liquid level of an underground sewage pool, characterized in that It includes a vacuum measuring tube, a measuring tube top cover, a differential pressure transmitter, a root valve, a water injection valve, a sealing pipe cap, a bottom plate, a pulley and a nylon rope; the vacuum measuring tube is vertically arranged, the bottom of the vacuum measuring tube is inserted into the sewage, and the top of the vacuum measuring tube extends above the pool cover; the measuring tube top cover is fixedly connected to the top of the vacuum measuring tube to seal the top of the vacuum measuring tube; a tee is arranged on the measuring tube top cover, and the root valve and the water injection valve are respectively connected to the measuring tube top cover through the tee; the differential pressure transmitter is connected to the root valve; the sealing pipe cap is connected to the water injection valve; one side of the bottom plate is connected to the bottom of the vacuum measuring tube, and the other side of the bottom plate is connected to the nylon rope, and the nylon rope is connected to the pulley, and the nylon rope can be pulled to drive the bottom plate to move through the pulley to seal the bottom of the vacuum measuring tube.

2. The device for measuring the liquid level of an underground sewage pool according to claim 1, characterized in that: The sealing method of the measuring tube top cover and the top end of the vacuum measuring tube is welding or adhesive sealing.

3. The device for measuring the liquid level of an underground sewage pool according to claim 1, characterized in that: The top of the vacuum measuring tube is fixed on the pool cover by a U-shaped tube clamp, and the bottom of the vacuum measuring tube is also fixed on the pool bottom by a bracket.

4. A method for measuring the liquid level of an underground sewage pool, using the underground sewage pool liquid level measuring device according to claim 1, characterized in that The following steps are involved: 1) When the liquid level in the sewage pool is just at the bottom of the vacuum measuring tube, open the root valve, open the bleed screw of the differential pressure transmitter, open the water injection valve, unscrew the sealing pipe cap, pull the nylon rope and fix it, cover the bottom of the vacuum measuring tube with the bottom plate, and inject water into the vacuum measuring tube through the water injection valve; 2) After the pipe is completely filled with water, water begins to overflow from the discharge screw of the differential pressure transmitter. At this time, reduce the amount of water injection to allow the bubbles in the pipe to rise and be discharged. Close the root valve and the water injection valve, tighten the discharge screw, and tighten the sealing pipe cap to form a seal at the top of the pipe. 3) Loosen the nylon rope, the bottom plate falls naturally due to gravity, and the bottom of the tube is opened. At this time, the top of the tube is a sealed structure. Under the weight of the water column in the tube, a vacuum is formed at the top of the tube, and the water in the tube does not flow downward. The differential pressure value at this time makes the reading of the differential pressure transmitter 0. This point is calibrated as the relative zero point of the water pool, which is also the measurement zero point; 4) Continue to fill the pool with water until the liquid level rises to the maximum allowable level, and record the differential pressure value at this time; adjust the range of the differential pressure transmitter to the full scale with the maximum output. At this time, the full-scale online calibration of the differential pressure transmitter is completed. The output of the differential pressure transmitter is set to percentage output, or the output unit is set to millimeters of water column. At this time, the differential pressure transmitter has been calibrated online and can start measuring the pool level.

5. The method for measuring the liquid level of an underground sewage pool according to claim 4, characterized in that: The vacuum measuring tube is made of transparent corrosion-resistant material.

6. The method for measuring the liquid level of an underground sewage pool according to claim 4, characterized in that: The differential pressure transmitter is arranged at the highest point of the entire measuring pipeline. The negative pressure measuring chamber of the differential pressure transmitter is connected to the root valve, and the positive pressure measuring chamber is connected to the atmosphere. The positive pressure chamber is covered with a windproof net. The differential pressure transmitter is installed on the wall of the sewage pool and fixed separately.

7. The method for measuring the liquid level of an underground sewage pool according to claim 4, characterized in that: The bottom plate is a corrosion-resistant organic glass plate, and the upper edge of the bottom plate in contact with the bottom of the tube is polished to a certain arc; a handle is arranged on the other side of the bottom plate, and a nylon rope is fixed at the end of the handle.

8. The method for measuring the liquid level of an underground sewage pool according to claim 4, characterized in that: Unscrew the indicating head of the differential pressure transmitter and connect it with a cable to a remote location for easy observation.

9. The method for measuring the liquid level of an underground sewage pool according to claim 4, characterized in that: Step 1) When calibrating the water injection, insert a small colored foam float into the vacuum measuring tube, tie a ribbon under the small float, and add a small weight at the bottom of the ribbon.

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