CN204514392U - The digital indication flow meter of a kind of experimental teaching band piezometric tube display - Google Patents

Abstract

The utility model discloses a digital display flowmeter with pressure measuring tube display for experimental teaching, which comprises: a differential pressure flow signal generator for generating differential pressure signals; two groups of pressure measuring components, each group of pressure measuring components includes The pressure measuring cylinder, the connecting positioning tube and the pressure measuring tube; the pressure sensor used to detect the pressure difference of the compressed air in the two pressure measuring cylinders; the microcomputer digital display meter used to convert the pressure signal detected by the pressure sensor into the flow rate; The fixing bracket of Yu'an pressure measuring tube; the scale scale used to calibrate the liquid level in the pressure measuring tube. The device of the utility model comprehensively and innovatively uses the principle of fluid mechanics to solve the problem of experimental measurement and display, and combines the traditional pressure measuring tube and modern measurement technology, has high precision and high display, and can be widely used in fluid mechanics Among the experimental teaching instruments, it can stimulate students' interest in learning, inspire students' sense of innovation, is beneficial to the cultivation of innovation ability, and has a good teaching effect.

Description

A digital display flowmeter with pressure measuring tube display for experimental teaching

technical field

The utility model relates to the field of experimental measurement, in particular to a digital display flowmeter with pressure measuring tube display for experimental teaching.

Background technique

Hydraulics and Fluid Mechanics is a major professional basic course for many majors in engineering colleges. Modern hydraulics is based on the three pillars of experiment, theory and calculation. Therefore, experiment is an indispensable content in the teaching process.

Among them, the small flow, small pressure difference, and high-precision digital display flow measurement device for small pipeline water flow used in experimental teaching is currently in a blank state. Taking the small desktop hydrodynamics hydraulics teaching instrument as an example, since its diameter is usually less than 30mm and the flow rate is 5-300ml/s, the flow rate is often very small. Traditionally, the gravimetric method or the volumetric method is usually used for manual measurement. If it is equipped with conventional modern measuring instruments on the market, there are many problems in the application of experimental teaching. Take a typical differential pressure flowmeter as an example:

Most of the flow signal pressure difference generated by the differential pressure signal generator (such as Venturi, orifice plate, etc.) of the differential pressure flowmeter is only 0.1-80 cm water column, while the existing flowmeter connects the sensor through the water pipe connecting pipe. It is directly connected to the pressure measuring point of the differential pressure signal generator. The pressure of the sensor is transmitted through the water body. The sensor end is sealed with air barrier inside. The pressurized water column in the connecting pipe cannot directly act on the pressure chip of the sensor. , and because the pressure transmission channel in the sensor is very small, a large surface tension is generated on the liquid-gas interface, and its value can reach 1-5 cm water column, or even larger, so that the pressure error of the flow signal can reach more than 10%. , will cause the middle and low-end flow error to reach 10%-30%, so this type of flow meter cannot be used in teaching experimental devices with high precision requirements.

There are also non-differential pressure flowmeters such as small-diameter turbine flowmeters on the market, but at present, the flow measurement range of this type of flowmeter with an accuracy of 1%-2% or more is 70%-100% of its full scale. Less than 30% is not applicable, and the experimental flow range of commonly used small desktop hydrodynamics and hydraulics teaching instruments is just below 30%, so it cannot be selected. Therefore, there has been a blank state in the market for high-precision flowmeters for small desktop fluid mechanics teaching instruments for a long time.

At the same time, as one of the most commonly used pressure measuring instruments in hydraulic and fluid mechanics experiments, the piezometer is an essential measuring device in this type of experimental teaching instrument. In the configuration of experimental instruments in this field, according to each experimental requirement, in order to measure the pressure signals of multiple parts in the experimental pipeline or water tank at the same time, multiple piezometric tubes will be installed side by side at the same level and fixed on the pressure measuring frame. Consisting of a group of row-type multi-piezometer piezometers, this traditional piezometric device can display the pressure of each piezometric point very vividly with the height of the water column of the piezometer through the pressure transmission method, which has a good teaching effect. Of course, how to use row-type multi-piezometers to measure multiple pressure heads in the experimental pipeline is also a basic pressure measurement method that students need to master. As a differential pressure flowmeter used in teaching experiments, if the pressure signal at the 2nd end of the differential pressure flow signal generator can be converted into flow rate with high precision and displayed on the meter head, and then the pressure value can be displayed synchronously by the water column of the piezometric tube, Then it can be integrated with traditional pressure measurement tools and have a better teaching effect.

However, in order to combine the traditional row-type piezometric tube with the high-precision differential pressure flowmeter suitable for low-flow measurement as mentioned above, and integrate it into a complete set of on-site measurement and control innovative experimental equipment, there are still many problems to be solved, such as Real-time zeroing problem, automatic exhaust problem of multiple pressure measuring tubes.

Real-time zero adjustment problem: Like this kind of electric measuring instrument, it is often necessary to verify the zero point in real time. For example, after the electronic scale is weighed, the zero point can be verified by removing the weight, and the zero point of this instrument is quite stable. However, for pipe flow, the zero point is not very stable due to the influence of temperature and fluid pressure field during the experiment. When the traditional flowmeter needs to be zeroed or checked, it is often necessary to close the gate when the pipe is full of water flow, so that the water flow in the pipe is still. For the teaching experiment, it will stop the experiment operation halfway, return to the state where the experiment started, and re-run the experiment, which is very inconvenient. Therefore, it is very important to be able to zero-adjust or check the zero point in real time without shutting down the device during the experiment.

Automatic exhaust of multiple piezometric tubes: When the water column of the piezometric tube is used to measure the pressure of the pressure point, there are often bubbles or air columns in the connecting pipe between the bottom of the piezometric tube and the pressure point, which will cause the pressure of the piezometer tube to be exhausted. For this reason, the trapped air bubbles in the connecting pipe must be removed, which is called exhausting the pressure measuring tube in science. The method is to inflate and drain each piezometric tube with an ear washing ball (blowing balloon), and then use the water pressure at the measuring point to flow into the piezometric tube by itself, so that the air bubbles in the connecting thin tube are taken away with the water flow until the connecting tube and The piezometer tube is filled with continuous liquid below the liquid level. This exhaust operation is okay for a single tube, but for multi-tube manometers, especially dozens of manometers, experimenters often find it unbearable. In order to realize the automatic electronically controlled exhaust, which is convenient to operate, and at the same time for the whole experimental device to realize the function of remote network experiment facing MOOC in the future, the inventor once tried to use the air pump to carry out the method of electric exhaust to solve this problem, but it needs A small air pump is provided for each pressure measuring tube to realize the synchronous exhaust function of multiple pressure measuring tubes. This is because the pressure at the measuring point of each piezometric tube is different, and the pressure at the measuring point of some piezometric tubes is very low, even close to atmospheric pressure. The air flow from the pressure measuring port of one or several pressure measuring tubes will cause a short circuit in the gas circuit, and the pressure on the main channel of the gas circuit will drop suddenly, causing the other pressure measuring tubes to be unable to drain water, so the simultaneous exhaust will not be achieved. Effect. Therefore, if you want to use multiple tubes and one pump to exhaust, you need to design a special structure and skillfully use the principles of fluid mechanics to solve the problem.

Utility model content

The utility model provides a digital display flowmeter with pressure measuring tube display for experimental teaching, cleverly applies the basic principles of fluid mechanics, and designs a high-precision differential pressure digital display flowmeter suitable for low flow measurement in experiments , combined with the traditional row-type piezometer, well unifies the traditional measurement means and modern measurement technology, and integrates into a complete set of on-site measurement and control innovative experimental measurement device, which has excellent teaching effect.

A digital display flowmeter with a pressure measuring tube display for experimental teaching, comprising:

A differential pressure flow signal generator for generating a differential pressure signal; the differential pressure flow signal generator has two pressure measuring points;

Two sets of pressure measuring components, each set of pressure measuring components includes a pressure measuring cylinder, the lower part of each pressure measuring cylinder is provided with a water inlet, the top is provided with a connecting positioning tube, and the pressure measuring tube connected to the connecting positioning tube; the two sets of measuring tubes The pressure components are respectively connected to the two pressure measuring points of the differential pressure flow signal generator through the lower water inlets of the respective pressure measuring cylinders; the two pressure measuring points of the differential pressure flow signal generator are two output Differential pressure measuring point, one is the high end of pressure and the other is the low end of pressure;

A pressure sensor connected to the two pressure measuring cylinders in the two groups of pressure measuring cylinders for detecting the pressure difference of the compressed air in the two pressure measuring cylinders;

A microcomputer digital display head connected to the pressure sensor for converting the pressure signal detected by the pressure sensor into a flow rate;

Fixing brackets for mounting two piezometer tubes in two sets of piezometer assemblies;

The scale scale is used to uniformly calibrate the liquid level in the two pressure measuring tubes, and the zero scale of the scale scale is on the same level as the bottom surface of the connecting positioning tube in the two pressure measuring cylinders.

Below as preferred structure of the present utility model:

The digital display flowmeter with pressure measuring tube display for experimental teaching also includes: two electronically controlled ventilation valves, each electronically controlled ventilation valve includes at least three circuits, and one circuit of each electronically controlled ventilation valve is connected to a pressure measuring circuit. The cylinder is connected with compressed air, the other path of each electric control vent valve is connected with the pressure sensor, and the other path of each electric control vent valve is connected with the atmosphere.

The digital display flowmeter with a pressure measuring tube for experimental teaching also includes: an air pump communicated with the top opening of the pressure measuring tube.

The air pump communicates with the top openings of the two pressure measuring tubes through a flow divider, a damping element is connected between the flow divider and the pressure measuring tube, and an exhaust electric control ventilation valve is sealedly connected to the flow divider; The damping element is a seal, and the seal is provided with a vent hole for the flow divider and the pressure measuring tube to ventilate.

The exhaust nozzle of the air pump is in sealing connection with the flow divider.

The pressure sensor is a relative pressure sensor, and a differential pressure sensor can be used specifically.

The fixed bracket is provided with a horizontal measuring chute, and the horizontal measuring chute is provided with a slide block, and the scale scale is a ruler installed on the slide block.

The straightedge is provided with an elongated hole, and the straightedge is fixed on the slide block through screw cooperation with the elongated hole.

The water inlet of the pressure measuring cylinder is located at the bottom of the side wall of the pressure measuring cylinder.

The digital display flowmeter with piezometric tube display for experimental teaching of the utility model has 2 straight tube type piezometric tubes installed side by side vertically on the fixed bracket. The pressure tube can be placed vertically on the leveled desktop under the support of the fixed bracket. There is a horizontal measuring chute on the upper part of the fixed bracket. A slider is hung on the horizontal measuring chute, and a ruler (transparent) has a The elongated holes in the vertical direction are fixed on the slider by screws, and the slider can be moved horizontally, and the height of the water column in each piezometric tube can be measured with the same zero-elevation reference plane using a transparent ruler. At the same time, in order to keep the zero elevation level of the ruler at the same level as the bottom surface of the connected positioning tube inserted into the top of the pressure measuring cylinder, the vertical elongated hole used to connect the fixed ruler at the lower part of the slider can be used to fine-tune the upper and lower fixed positions of the ruler .

The fixed bracket is placed on a well-adjusted experimental desktop. There are two pressure measuring cylinders connected to the pressure measuring tubes on the side of the table and with zero elevation positioning. They can be made of transparent plexiglass materials and store water inside. Clearly visible, convenient for experimental observation. Moreover, the internal and external structures and sizes of the two pressure measuring cylinders are the same, and they are fixedly bonded to the same horizontal connection base plate. The height of the pressure measuring cylinder is about 1 to 3 cm higher than the horizontal plane of the zero point of the ruler. The pressure measuring cylinder can be a hollow cylinder or a polygonal hollow cylinder structure. As a row type pressure measuring cylinder, each cylinder wall can be directly vertically sealed and bonded to the same connecting bottom plate, and the connecting bottom plate can be used as the sealing bottom plate of each pressure measuring cylinder. There is a small hole on the top surface of each pressure measuring cylinder, and a connecting positioning pipe with the same outer diameter as the water inlet pipe of the water inlet at the bottom of the pressure measuring tube is vertically inserted and sealed and bonded. The water inlet pipe that communicates with the positioning pipe and the water inlet generally has a larger inner diameter of about 4mm. The connecting positioning pipe is about 1cm higher than the top surface, which is convenient for sealing the external PVC water hose, and is sealed and connected with the water inlet at the bottom of the corresponding piezometer tube to form a sealed water pipe for the piezometric tube water column. The connected positioning tube is inserted into the pressure measuring cylinder to a depth of about 1 to 3 cm, and the bottom surface is horizontal and kept on the same plane as the horizontal plane of the zero point elevation of the ruler. The lower part of the side wall of the two pressure measuring cylinders is respectively provided with a pressure measuring water inlet close to the bottom surface, and the sealable external water hose is connected to the two pressure measuring points (ie pressure measuring mouth) of the differential pressure flow signal generator. The differential pressure flow signal generator is an upper part of the experimental pipeline, and is connected with the outlet of the experimental water tank through the experimental pipeline.

During the experiment, the experimental pipeline is full of water flow, and the two pressure measuring points (ie pressure measuring nozzle) of the differential pressure flow signal generator will generate a pressure difference. After connecting the pressure measuring cylinder, water will enter from the bottom side wall of the pressure measuring cylinder. The water port enters the inside of the piezometric tube. When the water level reaches the bottom level of the top connected to the positioning tube, the water level will no longer rise, and the water will enter the connected positioning tube, and then enter the piezometric tube to form a piezometric tube water column. After stabilization, slide the ruler horizontally and measure the water column height values of the two piezometric tubes respectively, which is the head pressure of the two pressure measuring points of the corresponding differential pressure flow signal generator relative to the reference horizontal plane of the zero point elevation of the ruler. A section of air column will be sealed from the horizontal plane of the bottom surface of the connecting positioning tube to the top of the pressure measuring cylinder. Since the horizontal plane of the bottom surface of the connecting positioning tube is the same plane as the horizontal plane of the zero point of the ruler, the pressure of the sealed compressed air column in this section is the pressure measuring tube The sum of head pressure and atmospheric pressure.

In order to measure the pressure of this section of sealed compressed air column, a small hole is opened on the upper part of the pressure measuring cylinder, and a thinner vent pipe (can be inserted from the top or from the upper side wall) is sealed and bonded into the bottom of the vent pipe. Don’t touch the highest water surface in the barrel. The vent tube is left about 1cm outside the pressure measuring cylinder to seal the external hollow ventilating and pressure measuring hose. In order to measure the pressure and pressure difference of the compressed air in the two pressure measuring cylinders by circuit, the two pressure measuring cylinders respectively pass through one way of ventilating and measuring hoses, and then respectively pass through an electronically controlled ventilating valve (that is, the electronically controlled three-way) and the pressure The two ends of the sensor are connected to the pressure measuring interface. Both electronically controlled air valves have 3-way air nozzles, the first way is connected with the pressure measuring cylinder vent pipe through the pressure measuring hose, the second way is connected with the atmosphere, and the third way is connected with the two pressure measuring ports of the pressure sensor respectively . When the two electronically controlled three-way valves are not energized, the first channel is connected to the third channel, and the second channel is not connected to the other two channels; The two roads are not connected.

Finally, the pressure sensor signal is transmitted and input to the microcomputer digital display meter through the traditional circuit, and the pressure difference can be displayed on the microcomputer digital display meter through the switching control combination of two electronically controlled air valves (that is, the electronically controlled three-way air valve). The digital display value of the water column height of the pressure measuring tube corresponding to the two pressure measuring points of the type flow signal generator, and the flow value of the experimental pipeline obtained by converting the pressure difference measured by the pressure sensor.

At the same time, the structural combination of two electronically controlled air valves (that is, electronically controlled three-way air valves) and a pressure measuring cylinder with a connecting positioning tube also has a very important real-time zero-adjustment function. When the pressure sensor signal is transmitted and input to the microcomputer digital display head through the traditional circuit, the traditional sensor zeroing compensation circuit is usually installed, and the existing technology can be used to realize the pressure sensor input differential pressure signal is zero, while the output voltage is not When it is zero, the compensation correction is the function of zero voltage output. The main principle of the traditional sensor zero-adjustment compensation circuit is to use the potentiometer to change the voltage value output by the sensor to the microcomputer meter, so that the negative terminal voltage of the signal received by the microcomputer digital display meter can be adjusted, so that the display value of the microcomputer digital display meter , can be adjusted to zero. In this measuring device, since the liquid-gas interface of the two pressure measuring cylinders is maintained at the same height, at any time during the experiment, the two electrically controlled gas valves (that is, the electronically controlled three-way gas valve) can be energized at the same time. In this way, the two pressure measuring ports of the pressure sensor are connected to the atmosphere at the same time, and then the real-time zeroing operation is performed by adjusting the potentiometer of the zeroing compensation circuit.

However, if the two selected pressure measuring cylinders are not connected to the positioning pipe structure, and the liquid-gas interface cannot be kept at the same height, then under the constant pressure water head of the experimental water tank, close the outflow valve of the experimental pipeline to keep the experimental pipeline full When the flow rate is zero, the two pressure measuring cylinders placed flat on the leveled table because the liquid levels in the cylinders are not equal, the input pressure difference signal transmitted by the compressed air to the pressure sensor must not be zero. At this time, the output The voltage is not zero. According to the zero adjustment operation, when the flow rate of the experimental pipeline is zero, we should adjust the potentiometer compensation in the zero adjustment compensation circuit to correct the zero voltage output to the microcomputer digital display head to display the zero value of the flow rate, but This zero-adjustment compensation operation can only be performed at the beginning of the experiment, when the experimental pipeline is full and the flow is zero, and it cannot be performed at any time during the experiment as mentioned above.

In the experimental measuring device of the above-mentioned utility model, the air column connected to the closed upper part of the bottom surface of the positioning tube in the pressure measuring cylinder is initially air atmospheric pressure, and the pressure measuring point at the two ends of the differential pressure flow signal generator (i.e. the pressure measuring point) is passed through the pressure measuring cylinder. The pressure transmitted by the piezometer (or the pressure of the water column synchronously introduced by the piezometric tube) will compress the air column in the cylinder, so that the liquid-gas interface in the cylinder rises beyond the horizontal plane of the zero point of the ruler. Although the relative error is not high (<0.2 %), but when the water column of the piezometric tube is high, such as 80cm, when the height of the initial closed air column in the piezometer is 3cm, the error is 0.22cm. This will still cause some measurement errors for real-time zeroing and actual flow measurement. In order to improve the accuracy, this error should be eliminated. At the same time, the automatic exhaust of the pressure measuring tube should be considered to eliminate the residual air bubbles that are easy to cause when the initial water enters the pressure measuring tube. , the experimental measurement device is designed with a pump and multi-tube gas filling device, the structure is as follows: a flow divider connected with the pressure measurement tube is added on the upper part of the two pressure measurement tubes, and the damping element connecting the two pressure measurement tubes and the flow divider; An air pump connected to the shunt (in this experimental device, a micro air pump can be used), and an exhaust electronically controlled air valve connected to the shunt (that is, an electronically controlled two-way air valve).

In actual implementation, a set of hydrodynamics hydraulics experimental device needs to measure the pressure of multiple points in addition to the flow of the pipeline. The number of piezometric tubes used for pressure measurement is usually 2 to 20, so the flow divider is usually For gas path connectors with more than three channels, 2 to 20 pressure measuring tubes are installed on the fixed bracket, but when implemented according to the technical solution of the utility model, only 2 to 20 pressure measuring tubes need to be connected Pressure pipe can realize the utility model purpose. In the embodiment of the utility model, there are two pressure measuring tubes, and the flow divider can adopt a three-way air path, one way is in sealing communication with the exhaust nozzle of the air pump, and two ways pass through the damping element and the top openings of the two pressure measuring tubes Seal connection.

The damping element is a seal, and the seal is provided with a vent hole for the shunt and the pressure measuring tube to ventilate. The pore size can achieve the exhaust and drainage effect of flow blocking and supercharging.

Each damping element is respectively placed in the connecting pipe between the outlet of the shunt and the top opening of the pressure measuring tube, so that the air flow can only flow into each pressure measuring tube from the damping hole.

Under normal measurement conditions, the opening at the top of the pressure measuring tube must be open to the atmosphere. For this reason, an exhaust electric control vent valve connected to it is provided on the shunt (specifically, a normally open type electronically controlled two vent valve can be used). Through the conventional control circuit When the air pump is working, it is powered on and off at the same time, and it is automatically turned on when the air pump stops at the same time.

From the above, when the power is turned on, the air pump is turned on, and the exhaust electric control vent valve (normally open type electric control two-ventilation valve) is closed, and the two pipes of the pressure measuring tube can be exhausted and reset at the same time. Due to the current-limiting and supercharging effect of the damping element, two or more pressure measuring tubes can be exhausted synchronously by using a micro air pump, even when some pressure measuring ends of the pressure measuring tubes are open to the atmosphere. It is capable of draining and exhausting the pressure-measuring tubes in which there is still pressurized liquid in a single tube. In this experimental device, the electronically controlled exhaust can eliminate the trapped air bubbles in the piezometric tubes and also has a reset function, that is, during the actual exhaust operation, it is necessary to wait for all the water columns in the piezometric tubes to be discharged into each piezometric tube, and The liquid-gas interface in each cylinder is depressed by the compressed air blown by the air pump, just after it is separated from the horizontal plane of the bottom surface of the connecting positioning pipe in each cylinder, and after the reset effect is achieved, the air pump and the ventilation valve are powered off. At this time, the upper part of each pressure measuring cylinder is no longer the air column of the initial atmospheric pressure, but the compressed air column blown in by the air pump. After the air pump is stopped and the ventilation valve is opened, the upper part of the pressure measuring cylinder is opened again to communicate with the outside atmosphere. However, due to the current-limiting and supercharging effect of the damping element, the liquid level in the pressure measuring cylinder rises and the compressed air in the upper part of the cylinder is squeezed out through the damping hole of the damping element of the pressure measuring tube. When the liquid level in the pressure measuring cylinder rises to the level of the bottom surface connected with the positioning tube in the cylinder, the pressure of the closed compressed air column in the upper part of each pressure measuring cylinder is equal to the pressure difference flow signal generator in the corresponding experimental pipeline The head pressure + atmospheric pressure transmitted from the two measurement points. Afterwards, the water column in the corresponding piezometric tube rises to the height of the water column pressure of the same size, and the compressed air in the upper part of the two piezometer tubes has been compressed before closing and has achieved gas-liquid pressure balance, so it will not be compressed again to make the liquid The air interface rises, resulting in an error with the zero elevation level of the ruler. In this way, through the ingenious exhaust reset design and operation, the system error caused by the compression of the initial atmospheric pressure air column in the pressure measuring cylinder can be accurately eliminated, and the experimental accuracy can be improved.

In the above-mentioned embodiment, during specific application, the size of the damping hole (that is, the air hole) of the damping element needs to be determined according to which hydrodynamics hydraulic experimental device the measuring device is used in, and according to the number of row-type piezometric tubes, the main ventilation tube measures Press the water head to decide. For example, if it is integrated and applied in an experimental device with 6 piezometric tubes, the utility model only needs to connect 6 piezometric tubes and use 2 piezometric tubes to realize the purpose of the utility model. The piezometer water head of 1~6 is generally within 1 meter. If 5 of the piezometer tubes are directly connected to the atmosphere, and the other piezometer tube gives a pressurized head of 1 meter of water column, then it is necessary to exclude the piezometer in this piezometer tube. Pressurized water, then the air pressure it provides must be more than 1 meter, that is to say the air pressure that the air pump loses to the main ventilation pipe should be greater than 1 meter of water column. According to the experiment, the size of the damping hole (ie, the vent hole) of the damping element is determined so that the pressure on the main channel passes through the damping hole of each tube to limit the flow and pressurize to meet this requirement, so as to realize the exhaust function of one pump and multiple tubes.

An experimental measurement method adopts the digital display flowmeter with a piezometer tube display for the experimental teaching, and includes the following steps:

(1) The liquid in the differential pressure flow signal generator is full of pipe flow, the liquid enters the pressure measuring cylinder and the pressure measuring tube from the two pressure measuring points of the differential pressure flow signal, and the liquid flow is stopped to make the differential pressure flow signal generator The flow rate of the inner liquid full pipe flow is zero;

(2) Start the air pump and close the exhaust electric control ventilation valve, exhaust and reset the two pressure measuring tubes at the same time, so that the liquid-gas interface in the two pressure measuring tubes is separated from the bottom surface of the connecting positioning tube in the tube, and turn off the air pump And open the air circuit of the exhaust electric control ventilation valve, so that the water level in the pressure measuring tube rises stably, observe whether the water columns in the two pressure measuring tubes are at the same height, and observe whether there are still air bubbles in the pressure measuring tube and the hose connected to the pressure measuring cylinder , if the height is inconsistent or/and there are air bubbles attached, then repeat step (2), if the height is the same and no air bubbles are attached, then go to step (3);

(3) The pressure sensor is initially zeroed through the compensation circuit, and the two measurement ports of the pressure sensor are simultaneously connected to the atmosphere to realize real-time zeroing;

(4) After the zero adjustment is completed, start the experiment to make the liquid flow in the differential pressure flow signal generator, and adjust the flow according to the needs of the experiment. After each flow adjustment is stable, repeat the exhaust reset operation of step (2) to eliminate the After the error caused by the change of air compression in the upper part of the pressure measuring cylinder, the pressure at the two ends of the differential pressure flow signal generator can be measured synchronously through two pressure measuring tubes, and the differential pressure flow signal can be measured through the microcomputer head. Generator terminal pressure and flow data.

The described experimental measurement method also includes step (5): when controlling the two electronically controlled ventilating valves to not vent to the atmosphere, the microcomputer meter head will display the flow value converted from the pressure sensor output differential pressure signal; control the two electrically controlled ventilating valves wherein When one is connected to the atmosphere and the other is not connected to the atmosphere, the microcomputer meter will display the pressure value of the end connected to the one of the two electronically controlled ventilation valves that is not connected to the atmosphere on the differential pressure flow signal generator.

Compared with the prior art, the utility model has the following advantages:

The digital display flowmeter with piezometric tube display used in the experimental teaching of the utility model is equipped with two liquid-gas conversion pressure measuring cylinders (referred to as pressure measuring cylinders) that can control the equal height of the liquid level, and the differential pressure flow signal generator and the The pressure sensor is directly transmitted by the liquid in the positioning tube through the liquid-gas conversion double cylinder, which is converted into a gas medium, and the pressure is transmitted to the pressure sensor, which avoids the liquid being directly in contact with the pressure sensor airtight connection tube. There is an almost 10% level of pressure error caused by the surface tension of the liquid caused by small air bubbles that are difficult to empty, so that the accuracy of small flow measurement can be increased from 10% to more than 1%, and it fills the benchtop small hydrodynamic hydraulics experimental instrument High-precision digital display flow meter blank. At the same time, the corrosion of the pressure sensor caused by the long-term contact between the liquid and the pressure sensor is avoided, and the service life and long-term use accuracy of the pressure sensor are improved.

Innovative application of the principle of fluid mechanics, the design of the Unicom positioning tube in the pressure measuring cylinder, can not only transmit the pressure of the pressure measuring point to the pressure sensor through the sealed air circuit, convenient and direct electrical measurement to obtain the relative atmospheric pressure relative to zero elevation, but also through The pressure of the sealed waterway is transmitted to the traditional piezometric tube to form a piezometric tube water column. While the microcomputer digital display head displays the flow rate, it can also vividly display the two ends of the differential pressure flow signal generator synchronously with the two piezometric tube water columns. The pressure transmitted by the pressure measuring nozzle is matched with the application of traditional differential pressure flowmeters such as Venturi and orifice plates that have been written in textbooks for a long time in the past century. The digital display flowmeter with pressure measuring tube display is used in this experimental teaching. Very suitable for experimental teaching use.

By making the bottom surface of the connecting positioning tube on the top of the piezometric tube be at the same level as the zero point of the piezometric tube scale, the zero point of the pressure difference relative to the atmospheric pressure measured by the pressure sensor and the zero point of the elevation where the piezometric tube scale is suspended (the reference zero point of the piezometric tube head) can be automatically determined Elevation) equal zero position, which solves the problem that it is difficult to unify the reference zero point when the traditional pressure measuring tube is equipped with a digital display pressure gauge, and also solves the problem of how to accurately maintain the equal height of the liquid level between the two pressure measuring cylinders. It also lays the foundation for the system to be able to real-time zero adjustment and exhaust reset to improve measurement accuracy.

After using the liquid-gas conversion pressure measuring cylinder, the air circuit on-off switching system is cleverly applied to the electronically controlled micro-air valve. Through circuit switching, a pressure sensor can realize the water head and flow pressure difference of 2 sets of pressure measuring tubes. At the same time, it cooperates with a pump and multi-pipe air filling device to realize the function of real-time zero adjustment of the system during the experiment, and through the special experimental operation method of exhaust reset, the upper air compression in the pressure measuring cylinder can be completely eliminated. The pressure measurement error caused by the rise of the liquid level.

In the one-pump multi-pipe air filling device, the principle of flow-limiting pressurization of damping holes in fluid mechanics is innovatively used, which saves the cumbersome operation of exhausting and draining each piezometric tube with ear washing balls, and uses less air pumps. , simple structure, convenient operation, good exhaust effect, and also facilitates the operation of electronically controlled exhaust reset. It is not only suitable for this flow measurement device, but also especially suitable for automatic control exhaust of row-type manometers with more tubes.

As a flow measuring instrument for fluid mechanics experiment teaching, the utility model comprehensively and innovatively utilizes various principles of fluid mechanics to solve experimental measurement problems, can stimulate students' interest in learning, inspire students' innovation consciousness, and is beneficial to cultivating innovation ability. It has a good teaching effect.

Description of drawings

Fig. 1 is a schematic structural view of a digital display flowmeter with piezo tube display for experimental teaching of the present invention.

Detailed ways

As shown in Figure 1, it is a digital display flowmeter with a pressure measuring tube display for experimental teaching of the present invention, including: a differential pressure flow signal generator 29 for generating a differential pressure signal, a differential pressure flow signal generator 29 There are two pressure measurement points on the generator 29; two sets of pressure measurement components, each group of pressure measurement components includes a pressure measurement cylinder 11, each pressure measurement cylinder 11 is provided with a water inlet 12 at the bottom, and a connecting positioning pipe 10 at the top , the pressure measuring tube 2 connected with the communication positioning pipe 10; two groups of pressure measuring components are respectively connected to the two pressure measuring points of the differential pressure flow signal generator 29 through the water inlet 12 of the lower part of the pressure measuring cylinder 11 respectively; The two pressure measuring cylinders 11 in the pressure measuring assembly are connected, and are used to detect the pressure sensor 19 of the compressed air pressure difference in the two pressure measuring cylinders 11. The pressure sensor 19 can specifically adopt a differential pressure sensor; it is connected with the pressure sensor 19 for A microcomputer digital display meter 23 that converts the pressure signal detected by the pressure sensor 19 into a flow rate; a fixing bracket 1 for installing two pressure measuring tubes 2 in two sets of pressure measuring components; and a unified calibration for the two pressure measuring tubes 2 The scale scale of the inner liquid level, the zero scale of the scale scale is on the same level as the bottom surface of the communication positioning tube 10 in the two pressure measuring cylinders 11 . The water inlet of the pressure measuring cylinder 11 is located at the bottom of the side wall of the pressure measuring cylinder 11 .

The digital display flowmeter with pressure measuring tube display for experimental teaching also includes: two electronically controlled ventilation valves, that is, an electronically controlled three-way valve 17 and an electronically controlled three-way valve 18, each electronically controlled ventilation valve includes at least three One way of each electrically controlled ventilation valve communicates with the compressed air in a pressure measuring cylinder 11, the other way of each electrically controlled ventilation valve is connected with the pressure sensor 19, and each electrically controlled ventilation valve also has one way connected with the atmosphere.

The digital display flowmeter with pressure measuring tube display for experimental teaching also includes: an air pump 43 communicated with the top opening of the pressure measuring tube 2 . The air pump 43 communicates with the top openings of the two pressure measuring tubes 2 through the flow divider 41, the damping element 42 is connected between the flow divider 41 and the pressure measuring tube 2, and the electric control two ventilation valves 44 (i.e. exhaust Pneumatic electric control ventilation valve); the damping element 42 is a seal, and the seal is provided with a vent hole for the shunt 41 and the pressure measuring tube 2 to ventilate. The exhaust nozzle of the air pump 43 is in sealing connection with the flow divider 41 .

The fixed support 1 is provided with a horizontal measuring chute 8, and the horizontal measuring chute 8 is provided with a slide block 5, and the scale scale is a ruler 3 installed on the slide block 5. The ruler 3 is provided with an elongated hole 7, and the ruler 3 is fixed on the slider 5 through the cooperation of the screw 6 and the elongated hole 7.

The digital display flowmeter with piezometric tube display for experimental teaching of the utility model has 2 straight tube type piezometric tubes 2 installed vertically side by side on the fixed bracket 1, the top opening of the piezometric tube 2 is open to the atmosphere, and the bottom surface has an inlet. The nozzle 4 and the pressure measuring tube 2 can be placed vertically on the leveled desktop 25 under the support of the fixed bracket 1. There is a horizontal measurement chute 8 on the upper part of the fixed bracket 1, and a slider 5 is suspended on the horizontal measurement chute 8. , the top of a ruler 3 (transparent) has a vertically elongated hole 7, which is fixed on the slider 5 by screws 6, and the transparent ruler 3 can be used with the same zero-elevation reference plane by moving the slider 5 horizontally. , measure the height of the water column in each piezometric tube 2. Simultaneously in order to keep the zero elevation horizontal plane 26 of the ruler on the same level as the bottom surface of the connected positioning tube 10 inserted into the top of the pressure measuring cylinder 11, the vertical elongated hole 7 that can be used to connect the fixed ruler 3 through the bottom of the slide block 5 can be fine-tuned The up and down fixed position of ruler 3.

The fixed bracket 1 is placed on a leveled experimental desktop 25, and two pressure measuring cylinders 11 with zero elevation positioning correspondingly connected to the pressure measuring tube 2 are arranged on the edge of the table top, which can be made of transparent plexiglass material , the internal water storage is clearly visible, which is convenient for experimental observation. Moreover, the two pressure measuring cylinders 11 have the same internal and external structure and size, and are fixedly bonded on the same horizontal connection base plate 14 . The height of the pressure measuring cylinder 11 is about 1 to 3 cm higher than the horizontal plane at the zero point of the ruler 3 . The pressure measuring cylinder 11 can be a hollow cylinder or a polygonal hollow cylinder structure. As a row type pressure measuring cylinder, each cylinder wall can be directly vertically sealed and bonded to the same connecting bottom plate 14, so that the connecting bottom plate 14 can be used as a seal for each pressure measuring cylinder 11. bottom plate. Each pressure measuring cylinder 11 top surface has a small hole, vertically inserted and sealed and bonded with a connected positioning tube 10 with the same outer diameter as the water inlet pipe of the water inlet 4 at the bottom of the pressure measuring tube 2 . The water inlet pipe that communicates with the positioning pipe 10 and the water inlet 4 has a relatively large internal diameter of about 4mm. The connecting positioning pipe 10 is about 1 cm higher than the top surface, which is convenient for sealing the external PVC water hose 9, and is sealed and communicated with the water inlet 4 at the bottom of the corresponding piezometric tube 2 to form a sealed water piping for the piezometric tube 2 water column. The connecting positioning pipe 10 is inserted into the pressure measuring cylinder 11 to a depth of about 1-3 cm, and the bottom surface is horizontal, and is kept on the same plane as the horizontal plane 26 at the zero elevation of the ruler 3 . Two pressure measuring cylinders 11 are provided with a pressure measuring water inlet 12 near the bottom of the side wall bottom, and the sealable outer connection water hose 28 is connected to two pressure measuring points of the differential pressure flow signal generator 29 . The differential pressure flow signal generator 29 is a flow measuring pipe section capable of generating a differential pressure signal, specifically using traditional flow pressure measurement experiment pipe sections such as Venturi, orifice plate or nozzle, which is also a part of the experimental pipeline 30, and passes through the experimental pipeline 30 It is connected with the outlet of the experimental water tank 33. The two pressure measurement points on the differential pressure flow signal generator 29 are respectively set at the high pressure point and the low pressure point of the traditional differential pressure pressure measurement experiment pipe section, and two small holes are opened below the two points of the pipe wall to insert two stainless steel hollow pipes. The pipe can be used as the connecting port leading out of the pressure measuring point. An overflow plate 34 is provided in the experimental water tank 33. The overflow plate 34 divides the experimental water tank 33 into a water inlet working area and an overflow area. The bottom of the water inlet working area is provided with The bottom of the water inlet and overflow area is provided with a water outlet, and water is fed through the water inlet of the experimental water tank 33 to form an overflow liquid level 35 to provide constant-pressure water supply for the experimental pipeline 30 .

During the experiment, the experimental pipeline 30 is filled with full pipe water flow, and the two pressure measuring points of the differential pressure flow signal generator 29 will generate a pressure difference. After entering the inside of the pressure measuring tube 11, when the water level reaches the bottom horizontal surface 26 of the top connecting positioning tube 10, the water level will no longer rise, and the water will enter the connecting positioning tube 10, and then enter the piezometric tube 2 to form a piezometric tube water column 27. After the water column height of the piezometric tube is stable, slide the ruler 3 horizontally, and measure the water column height values of the two tubes respectively, which is the water head pressure of the two pressure measuring nozzles corresponding to the differential pressure flow signal generator 29 relative to the zero point elevation reference level 26 of the ruler 3 . A section of air column will be sealed from the bottom horizontal plane 26 of the connecting positioning tube 10 of the pressure measuring cylinder 11 to its top. Since the horizontal plane 26 of the bottom surface of the communicating positioning tube 10 is on the same plane as the horizontal plane 26 of the zero point of the ruler, this section seals the compressed air column The pressure is the sum of the head pressure in the piezometer tube and the atmospheric pressure.

In order to measure the pressure of this section of sealed compressed air column, a small hole is opened on the upper part of the pressure measuring cylinder 11, and a stainless steel vent pipe 13 with an inner diameter of 2mm is inserted into it by sealing and bonding (it can be inserted from the top or from the upper side wall), The bottom surface of the vent pipe 13 should not touch the highest water surface in the bucket, and the vent pipe 13 can be sealed and externally connected to the hollow ventilating pressure measuring hose 15 about 1 cm outside the pressure measuring cylinder 11. In order to measure the pressure and pressure difference of the compressed air in the two pressure measuring cylinders by circuit, the two pressure measuring cylinders 11 respectively pass through one way of ventilation pressure measuring hose 15, and then pass through an electronically controlled three-way valve 17 and an electronically controlled three-way valve respectively. The vent valve 18 is connected to a pressure sensor 19 . Both the electronically controlled three-way air valve 17 and the electronically controlled three-way air valve 18 have three air nozzles, the first of which is connected to the pressure measuring hose 15, the second is connected to the atmosphere, and the third is respectively connected to the pressure measuring interface 20 of the pressure sensor 19. It communicates with the pressure measuring port 21. When the electric control three-way air valve 17 and the electric control three-way air valve 18 are not powered on, the first road is connected to the third road, and the second road is not connected to the other two roads; when the power is on, the second road is connected to the third road , the first road is not connected to the other two roads.

Finally, the signal of the pressure sensor 19 is transmitted and input to the microcomputer digital display meter 23 through the traditional circuit, and the differential pressure flow signal generator can be displayed on the microcomputer digital display meter 23 through the switching control combination of the electronically controlled three-way valve 17 The digital display value of the water column height of the pressure measuring tube corresponding to the two pressure measuring nozzles of 29, and the experimental pipeline flow value converted from the pressure difference measured by the pressure sensor 19.

At the same time, the structural combination of the electronically controlled three-way air valves 17, 18 and the pressure measuring cylinder 11 connected with the positioning tube 10 also has a very important real-time zero-adjustment function. When the pressure sensor 19 signal is transmitted and input to the microcomputer digital display gauge 23 through a traditional circuit, a traditional sensor zeroing compensation circuit is usually provided, and the existing technology can be used to realize that the pressure sensor 19 input differential pressure signal is zero, and When the output voltage is not zero, the function of compensation correction is zero voltage output. The main principle of the traditional sensor zeroing compensation circuit is to use the potentiometer to change the voltage value output by the sensor to the microcomputer digital display meter 23, so that the negative terminal voltage of the signal received by the microcomputer digital display meter 23 can be adjusted, so that the microcomputer digital display meter The display value of head 23 can be adjusted to zero. In this measuring device, since the liquid-gas interface of the two pressure measuring cylinders 11 is maintained at the same height, at any time during the experiment, the electronically controlled three-way valve 17, 18 can be connected to the circuit at the same time, so that The two pressure measuring ports of the pressure sensor 19 are communicated with the atmosphere at the same time, and then the real-time zeroing operation is performed by adjusting the potentiometer of the zeroing compensation circuit.

However, if the two pressure measuring cylinders 11 selected do not communicate with the positioning pipe 10 structure, and the liquid-gas interface cannot be kept at the same height, then under the constant pressure head of the experimental water tank 33, the outflow valve of the experimental pipeline 30 is closed to maintain When the experimental pipeline 30 is full and the flow rate is zero, two pressure-measuring cylinders 11 placed flat on the leveled desktop 25 will transmit the pressure to the input pressure difference signal of the pressure sensor 19 because the liquid levels in the cylinders are not equal. It is definitely not zero, and the output voltage is not zero at this time. According to the zero adjustment operation, when the flow rate of the experimental pipeline is zero, we should adjust the potentiometer compensation in the zero adjustment compensation circuit to correct the zero voltage output to the microcomputer digital display meter. 23, to display the zero value of the flow rate, but this zero-adjustment compensation operation can only be performed at the beginning of the experiment, when the experimental pipeline 30 is full of zero flow, and cannot be performed at any time during the experiment. Real-time zero-adjustment operation as mentioned above.

In the above-mentioned experimental measurement device, the air column connected to the bottom surface of the positioning tube 10 in the pressure measuring cylinder 11 is initially at the air atmospheric pressure, and the pressure measuring cylinder 11 is transmitted through the pressure difference flow signal generator 29 at the two ends of the pressure measuring nozzle. The coming pressure (or the pressure of the water column synchronously introduced by the piezometric tube 2) will compress the air column in the cylinder, so that the liquid-gas interface in the cylinder rises beyond the horizontal plane 26 of the zero point of the ruler. Although this error is not high (<0.2% ), but when the water column of the piezometric tube 2 is relatively high, such as 80cm, when the height of the initial enclosed air column in the piezometric cylinder 11 is 3cm, the error is 0.22cm. This will still cause some measurement errors for real-time zeroing and actual flow measurement. In order to improve the accuracy, this error should be eliminated. At the same time, the automatic exhaust of the pressure measuring tube 2 should be considered to eliminate the pressure caused by the initial water intake in the pressure measuring tube 2. When the experimental measurement device is implemented, a multi-pipe air filling device with one pump is added, and the structure is as follows: a splitter 41 connected to the pressure measurement tube is added to the top of the two pressure measurement tubes 2, and the two pressure measurement tubes are connected. The damping element 42 of the tube 2 and the flow divider 41 ; the air pump 43 connected to the flow divider 41 (in this experimental device, a micro air pump can be used), and the electronically controlled two-way valve 44 connected to the flow divider 41 .

In actual implementation, a set of hydrodynamics hydraulics experimental equipment needs to measure the pressure of multiple points in addition to the flow of the pipeline. The number of piezometric tubes used for pressure measurement is usually 2 to 20, so the flow divider 41 is usually It is a gas path connector with more than three channels. In this example, there are two pressure measuring tubes 2, and the flow divider 41 can adopt an air circuit tee, one of which is in sealing communication with the exhaust nozzle of the air pump 43, and two paths pass through the damping element 42 and the two pressure measuring tubes 2. The top opening is sealed and communicated.

The damping element 42 is a seal, and the seal is provided with a vent hole for the flow divider 41 and the pressure measuring tube 2 to ventilate. Micropores, the size of which can achieve the exhaust and drainage effect of blocking flow and supercharging.

Each damping element 42 is respectively placed in the connecting pipe between the outlet of the flow divider 41 and the top opening of the pressure measuring tube 2, so that the air flow can only flow into each pressure measuring tube 2 from the damping hole.

Under normal measurement conditions, the top opening of the pressure measuring tube 2 must be open to the atmosphere. For this reason, an electronically controlled two-vent valve 44 communicated with it is provided on the flow divider 41, connected through a conventional control circuit, and it is energized at the same time when the air pump 43 is working. Closed, when the air pump 43 stops, the power is automatically turned on simultaneously.

From the above, when energized, the air pump 43 is opened, and the two electronically controlled vent valves 44 are closed, so that 2 pipes of the piezometric tube 2 can be exhausted and reset simultaneously. Due to the current-limiting and supercharging effect of the damping element 42, two or more piezometric tubes 2 can be exhausted synchronously by using a micro air pump 43, even if some pressure-measuring ends of the piezometric tubes 2 are open to the atmosphere Under certain circumstances, it is also possible to drain and exhaust the pressure measuring tubes that still have pressurized liquid in a single tube. In this experimental device, the electronically controlled exhaust has a reset function while eliminating the trapped air bubbles in the piezometric tubes, that is, during the actual exhaust operation, it is necessary to wait until all the water columns in the piezometric tubes 2 are completely discharged into the piezometric tubes 11 , and the liquid-gas interface in each cylinder is pressed down by the compressed air blown in by the air pump 43, and just separated from the horizontal plane of the bottom surface of the connecting positioning pipe in each cylinder, after the reset effect is achieved, then the air pump 43 and the second electric control valve 44 are powered off . At this time, the upper part of each pressure measuring cylinder 11 is no longer an air column of initial atmospheric pressure, but a compressed air column blown in by the air pump, the air pump 43 is stopped, and after the electronically controlled second ventilation valve 44 is opened, the pressure measuring cylinder is reopened 11, the upper part of the gas path communicates with the outside atmosphere, but also due to the flow-limiting and supercharging effect of the damping element 42, the liquid level in the pressure measuring cylinder 11 rises, and the compressed air in the upper part of the cylinder passes through the damping hole of the damping element 42 of the pressure measuring tube 2. While pressing out, it will automatically achieve pressure balance with the compressed air in the upper part of the cylinder. When the liquid level in the pressure measuring cylinder 11 rises to the bottom level 26 connected with the positioning tube 10 in the cylinder, the closed compressed air in the upper part of each pressure measuring cylinder 11 will The column pressure is equal to the head pressure+atmospheric pressure transmitted from each pressure measuring point of the differential pressure flow signal generator 29 in the corresponding experimental pipeline. Thereafter, the water column in the corresponding piezometric tube 2 rises back to the height of the water column pressure of the same size, and the compressed air in the upper part of the two piezometric cylinders 11 will not be compressed because it has been compressed before closing and has achieved gas-liquid pressure balance. The liquid-gas interface rises, resulting in an error with the zero-point elevation level of the ruler. In this way, through the ingenious exhaust reset design and operation, the system error caused by the compression of the initial atmospheric pressure air column in the pressure measuring cylinder can be accurately eliminated, and the experimental accuracy can be improved.

In summary, the experimental measurement method of a digital display flowmeter with piezometric tube display for experimental teaching of the present invention is as follows:

(1) When the liquid level in the test water tank 33 is at an elevation of 35 degrees of the overflow liquid level, there is a constant pressure test water head, and the test pipeline 30 is kept full to flow out, and the water in the test pipeline 30 will pass through the differential pressure flow signal on the pipeline to generate The pressure measuring points at the two ends of the device 29 enter the pressure measuring cylinder 11 and the pressure measuring tube 2 respectively. At this time, close the outlet valve of the experimental pipeline 30 to keep the full pipe flow rate in the experimental pipeline 30 as zero.

(2) energize the electric pump 43 and the second electronically controlled vent valve 44, exhaust and reset the two pressure measuring tubes 2 at the same time, so that the liquid-gas interface in the two pressure measuring cylinders 11 is separated from the bottom surface of the communicating positioning tube 10 in the cylinder , immediately cut off the electric pump 43 and the second electric control vent valve 44, open the gas path of the electric control second vent valve 44, so that the water level in the piezometric tube 2 rises stably, observe whether the water columns in the two piezometer tubes 2 are at the same height, and measure the pressure Check whether there are air bubbles attached in the tube 2 and the hose connected to the pressure measuring cylinder 11. If so, repeat step (2) to exhaust and reset the operation. Generally, the air bubbles can be removed after 1 or 2 times, and the pressure measurement is completed at the same time. The compressed air in the barrel 11 inflates and resets. Until, the water columns in the two piezometric tubes 2 have the same height, and there is no air bubbles attached in the piezometric tubes 2 and in the flexible pipes connected with the piezometric cylinder 11, the step (3) can be entered;

(3) At this time, the microcomputer digital display gauge 23 should show zero, and when it is not zero, the initial zeroing operation can be performed by adjusting the compensation circuit of the pressure sensor 19. At the same time, control the electric control three-way valve 17 and 18 to be energized at the same time, and the two pressure measuring ports of the pressure sensor 19 are both connected to the atmosphere at the same time, and the pressure difference is zero, that is, the system is set to the real-time zeroing state. If the initial zeroing operation has been performed, Then it can be verified that the microcomputer digital display meter head 23 should be displayed as zero equally.

(4) Open the outlet valve of the test pipeline 30, and adjust the flow in the test pipeline according to the needs of the experiment. After the flow is adjusted to stabilize each time, repeat the exhaust reset operation of step (2) to eliminate the pressure measuring cylinder 11 After the error caused by the change of the inner upper air compression, the pressure at the two ends of the differential pressure flow signal generator 29 can be measured synchronously through the two pressure measuring tubes 2, and the data can be measured by the microcomputer gauge head.

(5) When the electronically controlled three-way valves 17 and 18 are not energized, the microcomputer digital display head 23 will display the flow value converted from the pressure sensor 19 output differential pressure signal; When the valve 18 is not energized, the microcomputer meter 23 will display the pressure value at one end of the differential pressure flow signal generator 29; when the electronically controlled three-way air valve 17 is not energized, and when the electronically controlled three-way air valve 18 is energized, the microcomputer meter 23 will display The pressure value at the other end of the differential pressure flow signal generator 29.

Claims (8)

1. A digital display flowmeter with a piezometric tube display for experimental teaching, characterized in that it comprises: A differential pressure flow signal generator for generating a differential pressure signal, the differential pressure flow signal generator has two pressure measuring points; Two sets of pressure measuring components, each set of pressure measuring components includes a pressure measuring cylinder, the lower part of each pressure measuring cylinder is provided with a water inlet, the top is provided with a connecting positioning tube, and the pressure measuring tube connected to the connecting positioning tube; the two sets of measuring tubes The pressure components are respectively connected to the two pressure measuring points of the differential pressure flow signal generator through the lower water inlets of the respective pressure measuring cylinders; A pressure sensor connected to the two pressure measuring cylinders in the two groups of pressure measuring cylinders for detecting the pressure difference of the compressed air in the two pressure measuring cylinders; A microcomputer digital display head connected to the pressure sensor for converting the pressure signal detected by the pressure sensor into a flow rate; Fixing brackets for mounting two piezometer tubes in two sets of piezometer assemblies; The scale scale is used to uniformly calibrate the liquid level in the two pressure measuring tubes, and the zero scale of the scale scale is on the same level as the bottom surface of the connecting positioning tube in the two pressure measuring cylinders. 2. The digital display flowmeter with piezometric tube display for experimental teaching according to claim 1, further comprising: two electronically controlled ventilating valves, each electrically controlled ventilating valve comprising at least three circuits, each One path of the electric control ventilation valve is connected with the compressed air in a pressure measuring cylinder, the other path of each electric control ventilation valve is connected with the pressure sensor, and the other path of each electric control ventilation valve is connected with the atmosphere. 3 . The digital display flowmeter with piezometric tube display for experimental teaching according to claim 2 , further comprising: an air pump communicated with the top opening of the piezo tube. 4 . 4. The digital display flowmeter with piezometric tube display for experimental teaching according to claim 3, characterized in that, said air pump communicates with the top openings of two piezo tubes through a flow divider, and said flow divider A damping element is connected to the pressure measuring tube, and an exhaust electronically controlled ventilation valve is sealed and connected to the flow divider; The damping element is a seal, and the seal is provided with a vent hole for the flow divider and the pressure measuring tube to ventilate. 5 . The digital display flowmeter with piezometric tube display for experimental teaching according to claim 4 , wherein the exhaust nozzle of the air pump is in sealing connection with the flow divider. 6 . 6. The digital display flowmeter with a piezometric tube display for experimental teaching according to claim 1, wherein said fixed support is provided with a horizontal measurement chute, and the horizontal measurement chute is provided with a slide block, so that The scale scale described above is a straightedge installed on the slide block. 7. The digital display flowmeter with piezometric tube display for experimental teaching according to claim 6, characterized in that, said ruler is provided with an elongated hole, and the ruler cooperates with the elongated hole through a screw fixed on the slider. 8 . The digital display flowmeter with piezometric tube display for experimental teaching according to claim 1 , wherein the water inlet of the piezometric cylinder is located at the bottom of the side wall of the piezometric cylinder.