阅读说明：本技术 一种基于p—v图测试的往复式压缩机能效分析系统 (Reciprocating compressor energy efficiency analysis system based on P-V graph test ) 是由 余小玲 范诗怡 马海辉 吕倩 叶君超 吴伟烽 于 2020-07-16 设计创作，主要内容包括：本发明公开了一种基于p—V图测试的往复式压缩机能效分析系统,该系统包括硬件模块和软件模块,硬件模块是指压力传感器、压力变送器、温度传感器、键相传感器、互感器、数据采集卡,软件模块包括数据显示、数据处理、数据存储,此系统能够实现往复式压缩机的流量、指示功率、电机功率、效率的实时测量和分析,从而反映往复式压缩机的运行状况。本发明的有益成果有：通过测量的各级气缸的p—V图能得到压缩机流量,不必在压缩机管道上安装流量计；通过测量的各级气缸的p—V图能够反映中间各级气量的变化、各级指示功及总指示功率；基于p—V图测试的压缩机能效分析系统能够完成数据的实时处理,提高了测量效率,而且技术简便易于实现。(The invention discloses a reciprocating compressor energy efficiency analysis system based on p-V diagram test, which comprises a hardware module and a software module, wherein the hardware module refers to a pressure sensor, a pressure transmitter, a temperature sensor, a key phase sensor, a mutual inductor and a data acquisition card, the software module comprises data display, data processing and data storage, and the system can realize real-time measurement and analysis of the flow, the indication power, the motor power and the efficiency of a reciprocating compressor so as to reflect the running condition of the reciprocating compressor. The beneficial results of the invention are as follows: the flow of the compressor can be obtained through the measured p-V diagram of each stage of cylinder, and a flowmeter is not required to be arranged on a pipeline of the compressor; the change of the gas quantity of each middle stage, the indicating work of each stage and the total indicating power can be reflected through the measured p-V diagram of each stage of the cylinder; the compressor energy efficiency analysis system based on the p-V diagram test can complete real-time data processing, improves the measurement efficiency, and is simple and convenient in technology and easy to implement.)

1. A reciprocating compressor energy efficiency analysis system based on p-V diagram test is characterized by comprising:

hardware module: acquiring parameters necessary for energy efficiency analysis of the reciprocating compressor, wherein the parameters comprise each stage, exhaust pressure, each stage, exhaust temperature, pressure in each stage of cylinder, key phase signals, motor voltage and motor current;

a software module: and converting and processing the parameter signals acquired by the hardware module, and outputting a p-V diagram, flow, indication power, motor power and efficiency of the reciprocating compressor by taking the pressure in each stage of the cylinder, the key phase signal, the motor voltage and the motor current as input.

2. The p-V graph test based reciprocating compressor energy efficiency analysis system of claim 1, wherein the hardware module comprises:

a pressure sensor: the device is arranged on each stage of cylinder indicator hole of the reciprocating compressor and used for acquiring pressure values in each stage of cylinder of the reciprocating compressor;

the pressure transmitter: the device is arranged on each stage and an exhaust pipeline or a buffer tank and is used for measuring the exhaust pressure of each stage;

a temperature sensor: the device is arranged on each stage and the exhaust pipeline or the buffer tank and is used for measuring the temperature of each stage and the exhaust;

a key phase sensor: the device is arranged at a position close to a flywheel and used for acquiring a key phase signal, providing signal acquisition triggering and representing the time when a certain row of pistons of the reciprocating compressor run to an outer dead center;

mutual inductor: the device is arranged on an output line of a power supply and used for collecting the voltage and current values of a motor circuit of the reciprocating compressor;

a data acquisition unit: the device is used for connecting a pressure sensor, a pressure transmitter, a temperature sensor, a key phase sensor, a mutual inductor and a computer, and transmitting acquired signals to the computer, so that software processing is facilitated.

3. The p-V graph test based reciprocating compressor energy efficiency analysis system of claim 1, wherein the software module comprises:

a data processing module: filtering input signals, namely the pressure in each stage of cylinder, a key phase signal, motor voltage and motor current, eliminating interference, converting and calculating to obtain a required output value, wherein the output value comprises a p-V diagram, flow, indication power, motor power and efficiency of each stage of cylinder;

a data display module: the calculated output value is displayed in a visual mode in the form of images and tables;

a data storage module: on one hand, a report form of the measurement is generated, and the report form content comprises the output value obtained by calculation, the measurement time, and the information related to the measurement of the measurement personnel; on the other hand, the input values and the output values are both uploaded to a database for storage and backup.

4. The p-V graph test-based energy efficiency analysis system for reciprocating compressor according to claim 3, wherein the data processing module performs calculation to obtain the required output value by:

1) converting a pressure signal input by a pressure sensor and a key phase signal input by a key phase sensor into a pressure p and a cylinder working volume V in a cylinder of the reciprocating compressor to obtain a p-V diagram of each stage of cylinder; in addition, the rotating speed n of the reciprocating compressor can be obtained by the key phase signal;

2) obtaining intake pressure p of each stage by using pressure transmitter mounted on each stage, exhaust pipe or buffer tank_siPressure p of exhaust gas_diIntake pressure lines p of respective stages in a p-V diagram of cylinders of respective stages_sExhaust pressure line p_dInlet pressure line p_sIntersects the process line c-d-a-b of the p-V diagram at two points corresponding to the cylinder swept volume V on the abscissa₄And V₁Obtaining the intake air quantity V of each stage of the reciprocating compressor_si＝V₁-V₄Then, the intake air quantity V is adjusted_siConverting into the temperature and pressure of the first-stage inlet to obtain the flow Q_i：

Wherein Q is_iIs the flow rate, in m³/min；V₄And V₁Is the working volume of the cylinder, and the unit is m³(ii) a n is the rotating speed of the reciprocating compressor and the unit is r/min; t is_siIs the ith stage inlet temperature in K; p is a radical of_siThe pressure of the inlet air of the ith stage is Pa; z is the number of the ith working volume; the final stage air intake amount is converted to the first stage air intake state to be approximately equal to the compressor discharge air amount Q_dUnit is m³/min；

3) Calculating the area surrounded by the process line in the ith-stage cylinder P-V diagram, and obtaining the indicated power P of the ith stage of the reciprocating compressor according to the rotating speed n_ii(ii) a The process line is composed of discrete points, if the c-d-a process line has N discrete points, and symmetrically the c-b-a process line also has N discrete points, the ith level of indicating work W_ii：

Wherein, W_iiIs the ith grade indicating work, and the unit is J; p is a radical of_c-b-a(j) And p_c-d-a(k) Respectively the pressure of the jth discrete point and the kth discrete point on the c-b-a process line and the c-d-a process line, and the unit is Pa; v_c-b-a(j) And V_c-d-a(k) The working volume of the cylinder of the jth discrete point and the kth discrete point on the c-b-a process line and the c-d-a process line respectively is expressed in m³；

The ith level indicates power P_ii：

Wherein, P_iiIs the indicated power of the ith stage, and the unit is W;

the sum of the indicated powers of all the stages is the indicated power P of the compressor_i：

Wherein, P_iIs the indicated power of the compressor, and the unit is W;

4) calculating to obtain motor power P according to the input motor voltage U and motor current I_ECombined with the indicated power P_iObtaining the efficiency η of the reciprocating compressor:

P_E＝UIcosφ

wherein, P_EIs the motor power, with the unit of W; u is motor voltage and has a unit of V; i is motor current with unit of A; cos φ is the power factor.

5. The p-V graph test-based energy efficiency analysis system of reciprocating compressor as claimed in claim 4, wherein the calculation method of the rotation speed nThe formula is as follows: the key phase signal is used for indicating that a certain row of pistons of the reciprocating compressor runs to an outer dead center, a pulse is sent out at the moment, the time between two adjacent pulses is represented as the running period of the reciprocating compressor as T, and the rotating speed n of the reciprocating compressor is represented as

6. The p-V diagram test-based energy efficiency analysis system of the reciprocating compressor according to claim 4, wherein the p-V diagram of each stage of the cylinder is converted in a manner that: the key phase signal represents that a certain row of the reciprocating compressor runs to an outer dead center to send out a pulse, a corresponding crank angle theta is 0 degrees at the moment, a next pulse moment corresponds to a crank angle theta is 360 degrees, crank angles corresponding to all measured data points during two pulses are uniformly distributed, and all levels of cylinder working volumes V of all data points are obtained according to the corresponding relation between the working volumes V of all levels of cylinders and the crank angles theta:

wherein, V₀Is the clearance volume in m³；D_iThe unit is the inner diameter of the ith-stage cylinder and is m; r is the crank radius in m; lambda is the crank radius connecting rod ratio and is a dimensionless constant; v₀、D_iR, λ are known constants;

the pressure signal and the key phase signal have the same sampling rate, and data acquisition is started simultaneously; the pressure p and the working volume V of the cylinder are known for all data points during a period T, and a p-V map is plotted for each cylinder.

7. The p-V diagram test-based energy efficiency analysis system for the reciprocating compressor according to claim 3, wherein the filtering in the data processing module is mainly applied to the pressure signal, so as to realize low-pass filtering and eliminate high-frequency noise in the pressure signal.

Technical Field

The invention belongs to the technical field of compressors, and particularly relates to an energy efficiency analysis system of a reciprocating compressor.

Background

The large reciprocating compressor is key equipment for chemical synthesis, natural gas gathering and transportation and other industries and is also main energy consumption equipment. With the expansion of production scale, the number and specification of reciprocating compressors are expanding, and the power of many compressors is in megawatt level. From the present compressor service behavior, many compressors all have the not meticulous problem of energy consumption management, and the energy consumption situation of compressor is unclear, may even operate under the low-efficient operating mode for a long time, causes huge energy consumption, reduces the overall efficiency of enterprise. At present, the state enters the fourteen-five stage, and energy conservation and emission reduction are important in national planning work. Therefore, the energy consumption condition of the reciprocating compressor is monitored and analyzed, and the method has important significance for improving the machine efficiency and the enterprise benefit and even promoting the green and healthy development of China.

The energy consumption of the compressor is mainly power consumption, most of the energy consumption is electric power consumption, and the water consumption and the oil consumption are small in proportion. The output of the compressor is high-pressure gas with a certain flow rate. Therefore, in order to evaluate the power consumption of the compressor, it is necessary to clarify the power consumption and flow rate parameters of the compressor. For the compressor in service, the above parameters are obtained, and the monitoring system is required to not damage the existing system of the compressor, namely the host and the pipeline system, as far as possible. However, most of the measuring devices on the market must be installed on a host machine and pipelines at present for power consumption and flow measurement, and the use of the measuring devices has great limitation because field installation conditions are not met or safety regulations do not allow the measuring devices.

Disclosure of Invention

In order to overcome the problems in the prior art, the invention aims to provide a compressor energy efficiency analysis system based on a p-V diagram test, which can realize real-time measurement and analysis of the flow, the indication power, the motor power and the efficiency of a reciprocating compressor, thereby reflecting the operation condition of the reciprocating compressor.

In order to achieve the above purpose, the solution adopted by the invention is as follows:

a reciprocating compressor energy efficiency analysis system based on p-V diagram test comprises:

hardware module: acquiring parameters necessary for energy efficiency analysis of the reciprocating compressor, wherein the parameters comprise each stage, exhaust pressure, each stage, exhaust temperature, pressure in each stage of cylinder, key phase signals, motor voltage and motor current;

a software module: and converting and processing the parameter signals acquired by the hardware module, and outputting a p-V diagram, flow, indication power, motor power and efficiency of the reciprocating compressor by taking the pressure in each stage of the cylinder, the key phase signal, the motor voltage and the motor current as input.

The hardware module includes:

a pressure sensor: the device is arranged on each stage of cylinder indicator hole of the reciprocating compressor and used for acquiring pressure values in each stage of cylinder of the reciprocating compressor;

the pressure transmitter: the device is arranged on each stage and an exhaust pipeline or a buffer tank and is used for measuring the exhaust pressure of each stage;

a temperature sensor: the device is arranged on each stage and the exhaust pipeline or the buffer tank and is used for measuring the temperature of each stage and the exhaust;

a key phase sensor: the device is arranged at a position close to a flywheel and used for acquiring a key phase signal, providing signal acquisition triggering and representing the time when a certain row of pistons of the reciprocating compressor run to an outer dead center;

mutual inductor: the device is arranged on an output line of a power supply and used for collecting the voltage and current values of a motor circuit of the reciprocating compressor;

a data acquisition unit: the device is used for connecting a pressure sensor, a pressure transmitter, a temperature sensor, a key phase sensor, a mutual inductor and a computer, and transmitting acquired signals to the computer, so that software processing is facilitated.

The software module comprises:

a data processing module: filtering input signals, namely the pressure in each stage of cylinder, a key phase signal, motor voltage and motor current, eliminating interference, converting and calculating to obtain a required output value, wherein the output value comprises a p-V diagram, flow, indication power, motor power and efficiency of each stage of cylinder;

a data display module: the calculated output value is displayed in a visual mode in the form of images and tables;

a data storage module: on one hand, a report form of the measurement is generated, and the report form content comprises the output value obtained by calculation, the measurement time, and the information related to the measurement of the measurement personnel; on the other hand, the input values and the output values are both uploaded to a database for storage and backup.

The method for calculating by the data processing module to obtain the required output value comprises the following steps:

1) converting a pressure signal input by a pressure sensor and a key phase signal input by a key phase sensor into a pressure p and a cylinder working volume V in a cylinder of the reciprocating compressor to obtain a p-V diagram of each stage of cylinder; in addition, the rotating speed n of the reciprocating compressor can be obtained by the key phase signal;

2) obtaining intake pressure p of each stage by using pressure transmitter mounted on each stage, exhaust pipe or buffer tank_siPressure p of exhaust gas_diIntake pressure lines p of respective stages in a p-V diagram of cylinders of respective stages_sExhaust pressure line p_dInlet pressure line p_sIntersects the process line c-d-a-b of the p-V diagram at two points corresponding to the cylinder swept volume V on the abscissa₄And V₁Obtaining the intake air quantity V of each stage of the reciprocating compressor_si＝V₁-V₄Then, the intake air quantity V is adjusted_siConverting into the temperature and pressure of the first-stage inlet to obtain the flow Q_i：

Wherein Q is_iIs the flow rate, in m³/min；V₄And V₁Is the working volume of the cylinder, and the unit is m³(ii) a n is the rotating speed of the reciprocating compressor and the unit is r/min; t is_siIs the ith stage inlet temperature in K; p is a radical of_siThe pressure of the inlet air of the ith stage is Pa; z is the number of the ith working volume; the final stage air intake amount is converted to the first stage air intake state to be approximately equal to the compressor discharge air amount Q_dUnit is m³/min；

3) Calculating the area surrounded by the process line in the ith-stage cylinder P-V diagram, and obtaining the indicated power P of the ith stage of the reciprocating compressor according to the rotating speed n_ii(ii) a The process line is composed of discrete points, if the c-d-a process line has N discrete points, and symmetrically the c-b-a process line also has N discrete points, the ith level of indicating work W_ii：

Wherein, W_iiIs the ith grade indicating work, and the unit is J; p is a radical of_c-b-a(j) And p_c-d-a(k) Respectively the pressure of the jth discrete point and the kth discrete point on the c-b-a process line and the c-d-a process line, and the unit is Pa; v_c-b-a(j) And V_c-d-a(k) The working volume of the cylinder of the jth discrete point and the kth discrete point on the c-b-a process line and the c-d-a process line respectively is expressed in m³；

The ith level indicates power P_ii：

Wherein, P_iiIs the indicated power of the ith stage, and the unit is W;

the sum of the indicated powers of all the stages is the indicated power P of the compressor_i：

Wherein, P_iIs the indicated power of the compressor, and the unit is W;

4) calculating to obtain motor power P according to the input motor voltage U and motor current I_ECombined with the indicated power P_iObtaining the efficiency η of the reciprocating compressor:

P_E＝UI cosφ

wherein, P_EIs the motor power, with the unit of W; u is motor voltage and has a unit of V; i is motor current with unit of A; cos φ is the power factor.

The calculation mode of the rotating speed n is as follows: the key phase signal is used for indicating that a certain row of pistons of the reciprocating compressor runs to an outer dead center, a pulse is sent out at the moment, the time between two adjacent pulses is represented as the running period of the reciprocating compressor as T, and the rotating speed n of the reciprocating compressor is represented as

The conversion mode of the p-V diagram of each stage of cylinder is as follows: the key phase signal represents that a certain row of the reciprocating compressor runs to an outer dead center to send out a pulse, a corresponding crank angle theta is 0 degrees at the moment, a next pulse moment corresponds to a crank angle theta is 360 degrees, crank angles corresponding to all measured data points during two pulses are uniformly distributed, and all levels of cylinder working volumes V of all data points are obtained according to the corresponding relation between the working volumes V of all levels of cylinders and the crank angles theta:

wherein, V₀Is the clearance volume in m³；D_iThe unit is the inner diameter of the ith-stage cylinder and is m; r is the crank radius in m; lambda is the crank radius connecting rod ratio and is a dimensionless constant; v₀、D_iR, λ are known constants;

the pressure signal and the key phase signal have the same sampling rate, and data acquisition is started simultaneously; the pressure p and the working volume V of the cylinder are known for all data points during a period T, and a p-V map is plotted for each cylinder.

The filtering in the data processing module is mainly applied to the pressure signal, so that low-pass filtering is realized, and high-frequency noise in the pressure signal is eliminated.

The invention provides a compressor energy efficiency analysis system based on a p-V diagram test. And the real-time measurement of the p-V diagram of the compressor is carried out by utilizing the indicator hole on the compressor cylinder, and the real-time power consumption and flow calculation are carried out, so that the real-time energy consumption condition of the compressor is analyzed. The method does not need to install a flowmeter on the pipeline, does not damage the main engine and the pipeline of the compressor at all, and can comprehensively analyze the efficiency and the running condition of the compressor.

Compared with the prior art of measuring the flow of the compressor by the flowmeter and then carrying out energy efficiency analysis, the invention at least has the following beneficial effects:

1) the invention measures the flow of the compressor by measuring the p-V diagram of each stage of cylinder without installing a flowmeter on the pipeline of the compressor, which is very convenient for the in-service compressor which has an indicator hole on the cylinder and is inconvenient for changing the pipeline on site.

2) The invention measures the p-V diagram of each stage of cylinder, and further can calculate the air input of each stage, and can determine the change of each stage of air quantity. The flowmeter is generally only arranged on an air inlet pipeline or a final stage exhaust pipeline of the compressor, and can only measure one-stage air inlet quantity or final stage exhaust quantity, and the change of middle gas quantities at various stages is unclear.

3) The invention measures the p-V diagram of each stage of cylinder, and then calculates to obtain each stage of indication power and total indication power. The traditional measuring method can only measure the power of the motor. The invention can measure the indicated power and the motor power, thereby obtaining the efficiency of the compressor.

4) The measured p-V maps of the cylinders at each stage of the present invention are not only used for the purpose of compressor energy efficiency analysis as described herein, but subsequent upgrades can be used for compressor fault diagnosis.

5) The energy efficiency analysis system adopted by the invention is realized based on hardware and software, can complete real-time processing of data, has high calculation precision, greatly reduces subsequent processing time, improves measurement efficiency and reduces manpower and material resources. Meanwhile, the measurement parameters are stored in the forms of reports and databases, so that the subsequent research and the query of historical data are facilitated;

drawings

FIG. 1 is a schematic structural diagram of a compressor energy efficiency analysis system based on a p-V diagram test in the invention.

FIG. 2 is a schematic diagram of the operation of the hardware module in the compressor energy efficiency analysis system based on the p-V diagram test in the invention.

FIG. 3 is a schematic diagram of the operation of software modules in the compressor energy efficiency analysis system based on p-V diagram test according to the present invention.

FIG. 4 is a schematic diagram of a compressor energy efficiency analysis system based on a p-V diagram test according to the present invention.

Figure 5 is a p-V diagram of the i-th stage cylinder of the reciprocating compressor of the present invention.

Detailed Description

The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.

As shown in fig. 1, the present invention relates to a reciprocating compressor energy efficiency analysis system based on p-V diagram test, including:

hardware module: acquiring parameters necessary for energy efficiency analysis of the reciprocating compressor, wherein the parameters comprise each stage, exhaust pressure, each stage, exhaust temperature, pressure in each stage of cylinder, key phase signals, motor voltage and motor current;

a software module: and converting and processing the parameter signals acquired by the hardware module, and outputting a p-V diagram, flow, indication power, motor power and efficiency of the reciprocating compressor by taking the pressure in each stage of the cylinder, the key phase signal, the motor voltage and the motor current as input.

As shown in fig. 2, the hardware module includes:

a pressure sensor: the device is arranged on each stage of cylinder indicator hole of the reciprocating compressor and used for acquiring pressure values in each stage of cylinder of the reciprocating compressor;

the pressure transmitter: the device is arranged on each stage and an exhaust pipeline or a buffer tank and is used for measuring the exhaust pressure of each stage;

a temperature sensor: the device is arranged on each stage and the exhaust pipeline or the buffer tank and is used for measuring the temperature of each stage and the exhaust;

a key phase sensor: the device is arranged at a position close to a flywheel and used for acquiring a key phase signal, providing signal acquisition triggering and representing the time when a certain row of pistons of the reciprocating compressor run to an outer dead center;

mutual inductor: the device is arranged on an output line of a power supply and used for collecting the voltage and current values of a motor circuit of the reciprocating compressor;

a data acquisition unit: the device is used for connecting a pressure sensor, a pressure transmitter, a temperature sensor, a key phase sensor, a mutual inductor and a computer, and transmitting acquired signals to the computer, so that software processing is facilitated.

As shown in fig. 3, the software module includes:

a data processing module: filtering input signals, namely the pressure in each stage of cylinder, a key phase signal, motor voltage and motor current, eliminating interference, converting and calculating to obtain a required output value, wherein the output value comprises a p-V diagram, flow, indication power, motor power and efficiency of each stage of cylinder;

a data display module: the calculated output value is displayed in a visual mode in the form of images and tables;

a data storage module: on one hand, a report form of the measurement is generated, and the report form content comprises the output value obtained by calculation, the measurement time, and the information related to the measurement of the measurement personnel; on the other hand, the input values and the output values are both uploaded to a database for storage and backup.

The principle of the compressor energy efficiency analysis system based on the p-V diagram test is shown in FIG. 4, and specifically comprises the following steps:

1) obtaining a key phase signal through a key phase sensor arranged at a position close to a flywheel, representing that a certain row of pistons of the reciprocating compressor rotates to an outer stop point, sending a pulse at the moment, representing the time between two adjacent pulses as the operation period of the reciprocating compressor is T, and then reciprocating pressureThe rotational speed n of the compressor is

2) Obtaining pressure p in a cylinder through a pressure sensor arranged on a power indicator hole of the cylinder of the reciprocating compressor, wherein the pressure sensor and a key phase sensor have the same sampling rate, and simultaneously start to collect data, when the key phase sensor sends out a pulse, a certain row of pistons of the reciprocating compressor are represented to rotate to an outer dead center, the pressure p in the cylinder starts to be recorded, at the moment, a crank angle theta corresponding to the reciprocating compressor is 0 degrees, a crank angle theta corresponding to the next pulse moment is 360 degrees, crank angles corresponding to all measured data points during two pulses are uniformly distributed, and all levels of cylinder working volume values V of all data points are obtained according to the corresponding relation between the i-th level of cylinder working volume V and the crank angle theta:

wherein, V₀Is the clearance volume in m³；D_iThe unit is the inner diameter of the ith-stage cylinder and is m; r is the crank radius in m; lambda is the crank radius connecting rod ratio and is a dimensionless constant; v₀、D_iR, λ are known constants.

In the above, the pressure p in the cylinder and the working volume V of the cylinder of all data points in one period T of the reciprocating compressor are completely recorded, so that a p-V diagram of the i-th-stage cylinder is visualized on a software platform, as shown in fig. 5, c-d is a gas expansion process line in the actual cycle of the reciprocating compressor, d-a is a gas inlet process line in the actual cycle of the reciprocating compressor, a-b is a gas compression process line in the actual cycle of the reciprocating compressor, and b-c is a gas exhaust process line in the actual cycle of the reciprocating compressor; points 1, 2, 3, 4 are the inlet pressure lines p of the respective stages_sAnd an exhaust pressure line p_dThe intersection with each process line.

3) The pressure transmitter and the temperature sensor which are arranged on each stage, the exhaust pipeline or the buffer tank are used for obtaining each stageAir pressure p_siPressure p of exhaust gas_diAnd the intake air temperature T_si. By using the obtained p-V diagram of the i-th stage cylinder, the corresponding stage air inlet pressure line p is drawn in the diagram_sInlet pressure line p_sIntersects the process line c-d-a-b at two points corresponding to the cylinder swept volume V of the abscissa₄And V₁Obtaining the intake air quantity V of each stage of the reciprocating compressor_si＝V₁-V₄Then, the intake air quantity V is adjusted_siConverting into the temperature and pressure of the first-stage inlet to obtain the flow Q_i：

Wherein Q is_iIs the flow rate, in m³/min；V₄And V₁Is the working volume of the cylinder, and the unit is m³(ii) a n is the rotating speed of the reciprocating compressor and the unit is r/min; t is_siIs the ith stage inlet temperature in K; p is a radical of_siThe pressure of the inlet air of the ith stage is Pa; z is the number of the ith working volume; the final stage air intake amount is converted to the first stage air intake state to be approximately equal to the compressor discharge air amount Q_dUnit is m³/min；

And calculating the area surrounded by the process line in the p-V diagram of the i-th stage cylinder to obtain the indicated work of the i-th stage of the reciprocating compressor. The process line is composed of discrete points, N discrete points are not arranged on the c-d-a process line, symmetrically, N discrete points are also arranged on the c-b-a process line, and the ith level indicating work W_ii：

Wherein, W_iiIs the ith grade indicating work, and the unit is J; p is a radical of_c-b-a(j) And p_c-d-a(k) Respectively the pressure of the jth discrete point and the kth discrete point on the c-b-a process line and the c-d-a process line, and the unit is Pa; v_c-b-a(j) And V_c-d-a(k) The working volume of the cylinder of the jth discrete point and the kth discrete point on the c-b-a process line and the c-d-a process line respectively is expressed in m³；

The ith level indicates power P_ii：

Wherein, P_iiIs the indicated power of the ith stage, and the unit is W;

the sum of the indicated powers of all the stages is the indicated power P of the compressor_i：

Wherein, P_iIs the indicated power of the compressor, and the unit is W;

4) calculating to obtain motor power P according to the input motor voltage U and motor current I_ECombined with the indicated power P_iObtaining the efficiency η of the reciprocating compressor:

P_E＝UIcosφ

wherein, P_EIs the motor power, with the unit of W; u is motor voltage and has a unit of V; i is motor current with unit of A; cos φ is the power factor.

Based on the principle, the collected data is transmitted to a LabVIEW platform in a computer through a data acquisition card, and the collected data is processed, displayed and stored through programming in the LabVIEW platform:

LabVIEW is a graphical software development integration environment which is wide in application, rapid in development and powerful in function at present. LabVIEW adopts a structural block diagram of a graphic mode to form a program code, and can provide convenience for data acquisition, instrument control, measurement analysis and the like, so that LabVIEW can help scientists and engineers to improve efficiency by reducing development time of an application system and project preparation cost.

Therefore, the invention takes the pressure, the key phase signal, the motor voltage and the current in the cylinder, which are acquired by the hardware platform, as the software platform, realizes data processing by programming, and outputs a p-V diagram, flow, indicating power, motor power and efficiency, thereby improving the measurement efficiency and reducing the manpower and material resources.

In addition, the output data gives certain feedback to the operator in the form of EXCEL report forms, so that the current running condition of the reciprocating compressor can be known conveniently, and the measurement data can be stored conveniently. On the other hand, the input data and the output data are uploaded to the SQL Server database for centralized storage and management, so that historical data can be conveniently inquired, and the follow-up research is facilitated.

This detailed description is merely a preferred example of the invention and is not intended to limit the invention. All other embodiments which can be obtained by a person skilled in the art by means of modification, substitution, improvement, etc. without departing from the principle of the invention and without making innovations should be considered as within the technical scope protected by the present invention.