CN110374857B - A diaphragm compressor oil pressure and air pressure monitoring device and method - Google Patents

Abstract

The application belongs to the technical field of compressors, and particularly relates to a device and a method for monitoring oil pressure and air pressure of a diaphragm compressor. Because the diaphragm compressor can be operated at a high pressure ratio and a wide pressure range, the highest exhaust pressure can reach 300MPa, and if a method of processing a pressure measuring hole on a cylinder body is adopted, the strength of the cylinder is influenced, and leakage can be caused, so that potential safety hazards are brought. The application provides a device for monitoring oil pressure and air pressure of a diaphragm compressor, which comprises an air cylinder and a strain gage circuit, wherein the air cylinder comprises a cylinder head; the strain gauge circuit comprises a strain gauge component and a bridge circuit which are connected with each other, and the strain gauge component is arranged on the cylinder head. By arranging the strain gauge component on the cylinder head and connecting the strain gauge component with the bridge circuit, the sensitivity of the strain gauge component is improved, and the input and the output are in a linear relation. The device is safe and reliable, has no damage to the diaphragm compressor, and can monitor the hydraulic pressure in the oil side cylinder head and the air pressure in the air side cylinder head of the diaphragm compressor particularly under the high-pressure working condition.

Description

A diaphragm compressor oil pressure and air pressure monitoring device and method

technical field

The application belongs to the technical field of compressors, and in particular relates to a device and method for monitoring oil pressure and air pressure of a diaphragm compressor.

Background technique

Diaphragm compressor is a special equipment for gas compression with no leakage in the compression chamber. Because of its good sealing performance, wide pressure range and large compression ratio, it is widely used in hydrogen refueling stations and petrochemical fields to compress and transport various high-purity gases, precious and rare gases, toxic and harmful gases and corrosive gases. . In the diaphragm compressor, the working oil in the cylinder oil chamber is pushed by the piston, and then the diaphragm is pushed back and forth in the diaphragm chamber to change the working volume of the air chamber, and no leakage is realized with the cooperation of the suction and exhaust valves. cyclical work process. In the hydraulic oil circulation system of the diaphragm compressor, the oil leakage through the hydraulic piston ring is compensated by the compensation circuit, and the oil replenishment amount is adjusted by installing an oil spill valve on the oil side cylinder head.

The oil pressure and air pressure changes of the diaphragm compressor are a comprehensive reflection of the working performance and operating status of the compressor. The oil pressure and air pressure change curves of the diaphragm compressor during the working process can reflect the piston position, the suction process time, the opening and closing of the suction valve. The closing action, the opening and closing action of the exhaust valve, the exhaust process time, the action of the oil relief valve and the oil replenishment process, so the oil pressure and air pressure change curve is the most effective tool for diagnosing the compressor failure of the diaphragm compressor. Dynamic monitoring of oil pressure is an effective method to improve the reliability and safety of equipment operation. It is also a strong demand for diaphragm compressor designers and users to ensure the monitoring of equipment operating conditions.

Due to the high operating pressure ratio and wide pressure range of the diaphragm compressor, the maximum exhaust pressure can reach 300MPa. The air pressure in the head is monitored, which not only affects the strength of the cylinder, but also may cause leakage and bring safety hazards. .

SUMMARY OF THE INVENTION

1. Technical problems to be solved

Due to the high operating pressure ratio and wide pressure range of the diaphragm compressor, the exhaust pressure can reach up to 300MPa. If the method of processing pressure measuring holes on the cylinder block is used, the hydraulic pressure and gas side in the oil side cylinder head of the diaphragm compressor Monitoring the air pressure in the cylinder head not only affects the strength of the cylinder, but also may cause leakage and bring about potential safety hazards. The present application provides a diaphragm compressor oil pressure and air pressure monitoring device and method.

2. Technical solutions

In order to achieve the above purpose, the present application provides a diaphragm compressor oil pressure and air pressure monitoring device, including a cylinder and a strain gauge circuit;

The cylinder includes a cylinder head and an exhaust valve hole, and the exhaust valve hole is arranged on the cylinder head;

The strain gauge circuit includes an interconnected strain gauge assembly and a bridge circuit, the strain gauge assembly includes a first strain gauge group and a second strain gauge group, and the first strain gauge group is disposed on the outer surface of the cylinder head , the second strain gauge group is arranged on the bottom plane of the exhaust valve hole, the first strain gauge group is connected with the bridge circuit, and the second strain gauge group is connected with the bridge circuit .

Optionally, the first strain gauge group includes a first strain gauge and a second strain gauge, and the first strain gauge and the second strain gauge are arranged perpendicular to each other;

The second strain gauge group includes a third strain gauge and a fourth strain gauge, and the third strain gauge and the fourth strain gauge are arranged perpendicular to each other.

Optionally, the strain gauge assembly further includes a third strain gauge group and a fourth strain gauge group;

The third strain gauge group is arranged on the flange, the flange is arranged on the exhaust pipe, and the fourth strain gauge group is arranged on the flange.

Optionally, the strain gauge assembly is connected to a half-bridge circuit.

Optionally, the strain gauge assembly is connected to a full bridge circuit.

Optionally, it also includes a photoelectric sensing unit and a data acquisition unit, the photoelectric sensing unit includes a flywheel, the flywheel is correspondingly arranged with the photoelectric sensor, the data acquisition unit is connected with the strain gauge assembly, and the data The collection unit is connected with the photoelectric sensor; the data collection unit is connected with the data processing unit.

The application also provides a method for monitoring oil pressure and air pressure of a diaphragm compressor, the method comprising the following steps:

Step 1. Build a strain measurement system: select the type of strain gauge according to the size of the cylinder head, paste the selected strain gauge and connect it to the bridge, then install the photoelectric sensor at the flywheel, and configure the data acquisition unit;

Step 2, collecting signals: synchronously collect the first voltage signal and the second voltage signal output by the strain gauge circuit through the data collection unit, convert the collected first voltage signal into a first digital signal for storage, and store the collected first voltage signal. The second voltage signal is converted into a second digital signal for storage;

Step 3. Determine the start and end time of a complete cycle according to the first digital signal;

Step 4: Process the second digital signal according to the start and end time of the one complete cycle to obtain the oil pressure value and the air pressure value.

Optionally, processing the second digital signal in step 4 includes:

(1) According to the measured voltage data, calculate the strain of the working strain gauge respectively:

Among them, θ represents the crank angle, ε(θ) is the strain, e(θ) is the collected voltage signal, μ is the Poisson’s ratio, E is the elastic modulus, and K _s is the sensitivity coefficient of the strain gauge;

(2) Calculate the oil pressure:

The cylinder head is simplified as a circular plate model, and the radial stress and circumferential stress of the strain gauges on the outer surface of the cylinder head are calculated according to the measured strains. Then, according to the structure of the diaphragm compressor, the boundary of the peripheral clamped plate with uniform load is brought into it. conditions to calculate the oil pressure value;

(3) Calculate the air pressure:

According to the measured strain, the radial stress and circumferential stress of the bottom plane of the exhaust valve hole are calculated, and then the air pressure value is calculated.

Optionally, in the step 2, the first voltage signal is filtered, amplified, conditioned and A/D converted, converted into a first digital signal and transmitted to the smart terminal for processing, and the second voltage signal is filtered, Amplification, conditioning and A/D conversion are converted into a second digital signal and transmitted to the intelligent terminal for processing.

3. Beneficial effects

Compared with the prior art, the beneficial effects of the diaphragm compressor oil pressure and air pressure monitoring device and method provided by the present application are:

The diaphragm compressor oil pressure and air pressure monitoring device provided by the present application, by arranging the strain gauge assembly on the cylinder head of the gas side, and connecting the strain gauge assembly with the bridge circuit, the sensitivity of the strain gauge assembly is improved, and the input and output are in a constant state. linear relationship. Due to the non-invasive pasting of strain gauges on the air side cylinder head of the diaphragm compressor, the strain gauge assembly is set to measure the strain of the air side cylinder head, so that the oil pressure and air pressure can be measured indirectly, and the oil pressure of the diaphragm compressor can be measured safely and non-destructively. No damage to the diaphragm compressor, safe and reliable, especially under high pressure conditions, accurate monitoring of oil pressure and gas side pressure can be achieved.

Description of drawings

Fig. 1 is the first structural schematic diagram of the diaphragm compressor oil pressure and air pressure monitoring device of the present application;

FIG. 2 is a schematic diagram of the arrangement of strain gauges of the present application;

FIG. 3 is a schematic diagram of the connection mode of the strain gauge half-bridge of the present application;

Fig. 4 is the principle schematic diagram of the diaphragm compressor oil pressure and air pressure monitoring device of the present application;

Figure 5 is a schematic diagram of the comparison between the oil pressure measured by the sensor and the oil pressure data measured by the air side cylinder head strain gauge;

Figure 6 is a schematic diagram of the comparison between the air pressure measured by the sensor and the air pressure data measured by the air side cylinder head strain gauge;

In the figure: 1-air side cylinder head, 2-exhaust valve hole, 3-first strain gauge, 4-second strain gauge, 5-third strain gauge, 6-fourth strain gauge, 7-signal acquisition unit , 8 - flywheel, 9 - photoelectric sensor, 10 - data processing unit.

Detailed ways

Hereinafter, specific embodiments of the present application will be described in detail with reference to the accompanying drawings, from which those skilled in the art can clearly understand the present application and be able to implement the present application. Without departing from the principles of the present application, the features of the various embodiments may be combined to obtain new embodiments, or instead of certain features of certain embodiments, to obtain other preferred embodiments.

Strain gauges are components used to measure strain composed of sensitive grids and the like. The working principle of resistance strain gauge is based on the strain effect, that is, when the conductor or semiconductor material is mechanically deformed under the action of external force, its resistance value changes accordingly. This phenomenon is called "strain effect".

The quadrilateral measurement bridge circuit composed of resistors, capacitors, inductors and other components is called a bridge, and the four sides of the bridge are bridge arms. As a measurement circuit, connect a DC power supply at both ends of one diagonal line of the quadrilateral, and draw out the voltage at both ends of the other diagonal line. Using the bridge balance equation, the measured value of the known components in the bridge arm can be obtained. Component parameters (such as resistance, resistance, capacitance, inductance).

1 to 6, the present application provides a diaphragm compressor oil pressure and air pressure monitoring device, including a cylinder and a strain gauge circuit;

The cylinder includes a cylinder head 1 and an exhaust valve hole 2, and the exhaust valve hole 2 is arranged on the cylinder head 1;

The strain gage circuit includes an interconnected strain gage assembly and a bridge circuit, the strain gage assembly includes a first strain gage group and a second strain gage group, and the first strain gage group is disposed outside the cylinder head 1 The second strain gauge group is arranged on the bottom plane of the exhaust valve hole 2, the first strain gauge group is connected to the bridge circuit, and the second strain gauge group is connected to the bridge circuit connected.

The cylinder head 1 here is an air-side cylinder head or an oil-side cylinder head, and the strain gauge assembly is pasted on the air-side cylinder head or the oil-side cylinder head through an adhesive. The component attached with the strain gauge assembly is always in a certain temperature field. If the linear expansion coefficient of the strain gauge sensitive grid is not equal to the linear expansion coefficient of the construction material, when the temperature changes, due to the elongation of the sensitive grid and the component. The amount of (or compression) varies, thereby causing the sensitive grid to receive additional tension (or compression), and the resistance of the sensitive grid will change, resulting in inaccurate measurements. This phenomenon is a temperature effect.

A strain gauge assembly is a sensor whose resistance changes as a function of stress. Almost all strain gauge assemblies 2 have relatively low sensitivity, and the sensitivity can be doubled by using a bridge circuit, and the input and output are linearly related. The bridge circuit is used to detect the change of the strain gauge assembly, and it also has the advantages of extremely low current and low self-heating of the strain gauge. Therefore, bridge circuits are often used in strain gage sensor applications. Bridge circuits include quarter bridge connection, half bridge connection and full bridge connection. The wire of the strain gauge is a 25mm silver-coated copper wire (with a diameter of 0.12mm to 0.16mm). The diameter of the piston rod of different units is different, and the model of the strain gauge selected can also be different. That is to say, the strain gauge can be selected according to actual needs.

The first strain gauge group is arranged on the outer surface of the cylinder head 1, that is, the working sheet group is pasted on the outer surface of the cylinder head on the gas side. When the diaphragm is not in contact with the cylinder head on the gas side, the oil pressure and air pressure have an accompanying relationship, which is almost the same. Therefore, at this time Since the strain of cylinder head 1 caused by air pressure is consistent with the strain of cylinder head 1 caused by oil pressure, when the diaphragm contacts the cylinder head on the gas side, the pressure of the oil measurement will be directly applied to the cylinder head on the gas side through the diaphragm, so it can be The first strain gauge group attached to the cylinder head 1 on the air side monitors the oil pressure in the cylinder.

The air pressure in the cylinder is monitored through the second strain gauge group pasted at the bottom plane of the exhaust valve hole 2, that is, the work piece group.

The position where the strain gauge is attached to the cylinder head on the gas side is: the front of the cylinder head on the gas side, along the extension line connecting the center of the suction valve hole and the exhaust valve hole, and paste it in the half-surface area without the suction valve hole;

The strain gauge on the air side cylinder head or the oil side cylinder head measures the oil pressure, and the strain gauge on the exhaust valve hole measures the air pressure.

Further, the first strain gauge group includes a first strain gauge 3 and a second strain gauge 4, and the first strain gauge 3 and the second strain gauge 4 are arranged perpendicular to each other;

The second strain gauge group includes a third strain gauge 5 and a fourth strain gauge 6, and the third strain gauge 5 and the fourth strain gauge 6 are arranged perpendicular to each other.

Two mutually perpendicular working sheets are used, and these working sheets are connected to the half-bridge circuit, and the working sheets are all connected with one bridge arm of the half-bridge circuit.

Further, the strain gauge assembly further includes a third strain gauge group and a fourth strain gauge group;

The third strain gauge group is arranged on the flange, the flange is arranged on the exhaust pipe, and the fourth strain gauge group is arranged on the flange.

The first strain gauge is pasted radially along the outer surface of the cylinder head on the gas side, the second strain gauge is pasted along the circumferential direction of the outer surface of the gas side cylinder head; the third strain gauge is pasted radially along the bottom plane of the exhaust valve hole 2, and the fourth strain gauge Glue along the circumference of the bottom plane of the exhaust valve hole 2;

In this scheme, two working sheets are vertically arranged on the outer surface of the cylinder head 1 on the gas side, two working sheets are vertically arranged on the bottom plane of the exhaust valve hole 2, and four compensating sheets are arranged on the flange of the exhaust pipe. The fifth strain gauge group and the sixth strain gauge group eliminate the influence of the temperature of the wire on the measurement results by pasting the compensation sheet. The compensation sheet can also be set in other places that can ensure that the temperature of the compensation sheet is close to the temperature of the cylinder head and is not stressed. place.

Paste two strain gauges at two positions (outer surface of cylinder head 1 and bottom surface of exhaust valve hole 2) respectively, these four are working gauges, used to measure the circumferential and radial strain at the bonding position (because it is a circular flat plate) , so there are circumferential and radial strains), and the oil pressure and air pressure can be calculated according to the radial and circumferential strains. When the working piece is pasted on the cylinder body, when the bottom surface of the cylinder head 1 and the exhaust valve hole 2 is deformed, the strain gauge attached here will also be stretched, so the resistance of the working piece will change, and the resistance change will cause the bridge The output voltage of the circuit changes.

Further, the strain gauge assembly is connected to the half-bridge circuit. The bridge circuit is constructed by the half-bridge method to increase the output of the strain gauge and eliminate the temperature influence of the wire. As shown in the half-bridge method in Figure 3, the working sheet and the temperature compensation sheet are respectively connected to two adjacent bridge arms, and the other two bridge arms are connected to fixed resistors.

Further, the strain gauge assembly is connected to a full bridge circuit.

There are three methods for pasting strain gauges: quarter bridge, half bridge and full bridge, all of which are reasonable. For quarter bridge, only 2 strain gages are connected to the half bridge connection, and 4 strain gages are connected to the full bridge.

Further, it also includes a photoelectric sensing unit and a data acquisition unit 7, the photoelectric sensing unit includes a flywheel 8, the flywheel 8 is correspondingly arranged with the photoelectric sensor 9, and the data acquisition unit 7 is connected with the strain gauge assembly , the data acquisition unit 7 is connected with the photoelectric sensor 9 ; the data acquisition unit 7 is connected with the data processing unit 10 .

There are many detection methods for the piston dead point signal. Hall type and photoelectric sensors are commonly used in compressor technology. The sending end of the sensor is generally arranged on the flywheel 8. The photoelectric sensor 9 is generally reflective. Precise positioning is required, that is, rotating the flywheel 8 so that the piston is at the inner and outer dead centers respectively, and then aligning the probe with the signalling point (magnetic steel, iron block or reflective strip).

The flywheel 8 rotates around the vertical axis of the axis, and the crank finds the position where the piston moves to the top dead center as the reference for the phase reference. At this time, make a mark on any position of the flywheel 8, and install a light spot sensor on the frame to make it Alignment marks. Under normal circumstances, the photoelectric sensor 9 collects a stable signal, and when the mark is transferred to the photoelectric sensor 9, an impact signal appears, which is used as the starting position of the cycle, and there is a cycle between every two consecutive impact signals.

The photoelectric sensing unit is to obtain a periodic signal to judge a complete cycle. A photoelectric sensor 9 is installed at the flywheel 8, and the initial value 0 of the crank angle θ of the compressor is determined by the obtained outer dead center signal; the analog signal output by the photoelectric sensor 9 is converted into the final digital signal required by the data acquisition unit 7 and stored for subsequent use. analysis and processing.

The data acquisition used here are the strain acquisition cards NI9237, NI9205 and acquisition chassis cDAQ-9185 of National Instruments (NI) Co., Ltd. The data acquisition is carried out by writing LabVIEW programs.

The data processing unit is an intelligent terminal. The smart terminal here refers to a device that can calculate and analyze data, such as a computer. In addition to storing data, the computer also runs a data acquisition program to control the sampling and display of signals, such as setting parameters such as sampling frequency and sample storage length. The data acquisition system realizes a series of functions of signal filtering, amplification, conditioning and A/D conversion. The computer displays the collected photoelectric sensor 9 dead point signal and the output voltage signal of the strain gauge circuit. The display can be monitored in real time.

The data acquisition unit 7 includes an acquisition card and a signal conditioning module. Set the data sampling frequency and the corresponding acquisition channel.

The data acquisition unit 7 realizes a series of functions of signal filtering, amplification, conditioning and A/D conversion.

The application also provides a method for monitoring oil pressure and air pressure of a diaphragm compressor, the method comprising the following steps:

Step 1. Build a strain measurement system: select the type of strain gauge according to the size of the cylinder head, paste the selected strain gauge and connect it to the bridge, then install the photoelectric sensor at the flywheel, and configure the data acquisition unit;

Step 2, collecting signals: synchronously collect the first voltage signal and the second voltage signal output by the strain gauge circuit through the data collection unit, convert the collected first voltage signal into a first digital signal for storage, and store the collected first voltage signal. The second voltage signal is converted into a second digital signal for storage;

Step 3. Determine the start and end time of a complete cycle according to the first digital signal;

Step 4: Process the second digital signal according to the start and end time of the one complete cycle to obtain the oil pressure value and the air pressure value.

Further, processing the second digital signal in step 4 includes:

(1) According to the measured voltage data, calculate the strain of the working strain gauge respectively:

Among them, θ represents the crank angle (0～360°), ε(θ) is the strain, e(θ) is the collected voltage signal, μ is the Poisson’s ratio, E is the elastic modulus, and K _s is the sensitivity coefficient of the strain gauge ; Here first calculate the strain of 4 working sheets;

(2) Calculate the oil pressure:

The cylinder head is simplified as a circular plate model, and the radial stress and circumferential stress of the strain gauges on the outer surface of the cylinder head are calculated according to the measured strains. Then, according to the structure of the diaphragm compressor, the boundary of the peripheral clamped plate with uniform load is brought into it. conditions to calculate the oil pressure value;

(3) Calculate the air pressure:

According to the measured strain, the radial stress and circumferential stress of the bottom plane of the exhaust valve hole are calculated, and then the air pressure value is calculated.

Further, in the step 1, the first voltage signal is filtered, amplified, conditioned and A/D converted, converted into a first digital signal and transmitted to the smart terminal for processing, and the second voltage signal is filtered and amplified. , conditioning and A/D conversion, converted into a second digital signal and transmitted to the intelligent terminal for processing.

The specific process of data acquisition is that the analog signal output by the strain gauge and photoelectric sensor is converted into the final digital signal required by the data acquisition system and stored in the computer hard disk for subsequent analysis and processing.

When calculating, use a computer to calculate according to the formula, and the realization method can be software programming or excel.

According to the collected data, the formula can be used to calculate. The computer is used here, and the LabVIEW program is written to do the calculation.

In this application, strain gauges are used to monitor the strain on the surface of the air-side cylinder head 1 of the diaphragm compressor and the platform on the bottom surface of the exhaust valve hole 2, including eight strain gauges, four working sheets, and four compensation sheets. On the outer surface of the cylinder head 1 on the air side, the working strain gauges Rw1 and Rw2 are pasted, wherein Rw1 is pasted in the radial direction, and Rw2 is pasted in the circumferential direction. On the bottom platform of the exhaust valve hole 2 of the air side cylinder head, the working strain gauges Rw3 and Rw4 are pasted, wherein Rw3 is pasted in the radial direction, and Rw4 is pasted in the circumferential direction. For the compensation sheet: eliminate the influence of temperature on the measurement results by pasting the compensation sheet, and paste the compensation sheet on the flange of the exhaust pipe (or other places that can ensure that the temperature at the compensation sheet is close to the temperature of the cylinder head and is not stressed ). The bridge circuit is constructed by the half-bridge method to increase the output of the strain gauge and eliminate the temperature influence of the wire.

The diaphragm compressor oil pressure monitoring device provided by the present application, by arranging the strain gauge assembly on the cylinder head of the gas side, and connecting the strain gauge assembly with the bridge circuit, the sensitivity of the strain gauge assembly is improved, and the input and output are in a linear relationship . Due to the non-invasive pasting of strain gauges on the air side cylinder head of the diaphragm compressor, the strain gauge assembly is set to measure the air side cylinder head strain, so that the oil pressure and air pressure can be indirectly measured, and the oil pressure and air pressure of the diaphragm compressor can be measured safely and non-destructively. air pressure. The method is safe and reliable, has no damage to the diaphragm compressor, and can achieve accurate monitoring of oil-side pressure and gas-side pressure especially under high-pressure working conditions.

The "first, second..." in this application is only to distinguish the strain gauges, and their structures are all the same.

Although the present application has been described above with reference to specific embodiments, it will be understood by those skilled in the art that many modifications may be made in configuration and detail disclosed herein within the spirit and scope of the present disclosure. The scope of protection of the present application is to be determined by the appended claims, and the claims are intended to cover all modifications encompassed by the literal meaning or scope of equivalents to the technical features in the claims.

Claims (8)

1. A diaphragm compressor oil pressure and air pressure monitoring device, characterized in that: comprise a cylinder and a strain gauge circuit; The cylinder comprises a cylinder head (1) and an exhaust valve hole (2), and the exhaust valve hole (2) is arranged on the cylinder head (1); The strain gauge circuit includes an interconnected strain gauge assembly and a bridge circuit, the strain gauge assembly includes a first strain gauge group and a second strain gauge group, and the first strain gauge group is disposed on the cylinder head (1). ) outer surface, the second strain gauge group is arranged on the bottom plane of the exhaust valve hole (2), the first strain gauge group is connected to the bridge circuit, and the second strain gauge group is connected to the The bridge circuit is connected; it also includes a photoelectric sensing unit and a data acquisition unit (7), the photoelectric sensing unit includes a flywheel (8), the flywheel (8) is correspondingly arranged with the photoelectric sensor (9), and the The data acquisition unit (7) is connected with the strain gauge assembly, the data acquisition unit (7) is connected with the photoelectric sensor (9); the data acquisition unit (7) is connected with the data processing unit (10) connect. 2. The oil pressure and air pressure monitoring device for a diaphragm compressor according to claim 1, wherein the first strain gauge group comprises a first strain gauge (3) and a second strain gauge (4), and the first strain gauge group comprises a first strain gauge (3) and a second strain gauge (4). A strain gauge (3) and the second strain gauge (4) are arranged perpendicular to each other; The second strain gauge group includes a third strain gauge (5) and a fourth strain gauge (6), and the third strain gauge (5) and the fourth strain gauge (6) are arranged perpendicular to each other. 3. The oil pressure and air pressure monitoring device of a diaphragm compressor according to claim 1, wherein the strain gauge assembly further comprises a third strain gauge group and a fourth strain gauge group; The third strain gauge group is arranged on the flange, the flange is arranged on the exhaust pipe, and the fourth strain gauge group is arranged on the flange. 4 . The oil pressure and air pressure monitoring device of a diaphragm compressor according to claim 1 , wherein the bridge circuit comprises a half bridge circuit, and the strain gauge assembly is connected to the half bridge circuit. 5 . 5 . The oil pressure and air pressure monitoring device of a diaphragm compressor according to claim 1 , wherein the bridge circuit comprises a full bridge circuit, and the strain gauge assembly is connected to the full bridge circuit. 6 . 6. A method for monitoring oil pressure and air pressure of a diaphragm compressor, wherein the method comprises the steps: Step 1. Build a strain measurement system: select the type of strain gauge according to the size of the cylinder head, paste the selected strain gauge and connect it to the bridge, then install the photoelectric sensor at the flywheel, and configure the data acquisition unit; Step 2, collecting signals: synchronously collect the first voltage signal and the second voltage signal output by the strain gauge circuit through the data collection unit, convert the collected first voltage signal into a first digital signal for storage, and store the collected first voltage signal. The second voltage signal is converted into a second digital signal for storage; Step 3. Determine the start and end time of a complete cycle according to the first digital signal; Step 4: Process the second digital signal according to the start and end time of the one complete cycle to obtain the oil pressure value and the air pressure value. 7. The method for monitoring oil pressure and air pressure of a diaphragm compressor according to claim 6, wherein the processing of the second digital signal in the step 4 comprises: (1) According to the measured voltage data, calculate the strain of the working strain gauge respectively:

Among them, θ represents the crank angle, ε(θ) is the strain, e(θ) is the collected voltage signal, μ is the Poisson’s ratio, E is the elastic modulus, and K _s is the sensitivity coefficient of the strain gauge; (2) Calculate the oil pressure: The cylinder head is simplified as a circular plate model, and the radial stress and circumferential stress of the strain gauge on the outer surface of the cylinder head are calculated according to the measured strain, and then the boundary of the peripheral clamped plate with uniform load is brought into the diaphragm compressor structure. conditions to calculate the oil pressure value; (3) Calculate the air pressure: According to the measured strain, the radial stress and circumferential stress of the bottom plane of the exhaust valve hole are calculated, and then the air pressure value is calculated. 8 . The method for monitoring oil pressure and air pressure of a diaphragm compressor according to claim 7 , wherein the first voltage signal in the step 2 is converted into the first voltage signal after filtering, amplifying, conditioning and A/D conversion. 9 . The digital signal is transmitted to the intelligent terminal for processing, and the second voltage signal is filtered, amplified, conditioned and A/D converted, converted into a second digital signal and transmitted to the intelligent terminal for processing.

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