A method and system for non-destructive monitoring of compressor cylinder pressure

Abstract

The present application belongs to the field of compressor technology, and in particular relates to a method and system for non-destructive monitoring of compressor cylinder pressure. The existing technology does not consider the strain drift problem that occurs in actual measurement, and provides a method for calculating the dynamic pressure in the cylinder under the condition of drift. The present application provides a method for non-destructive monitoring of compressor cylinder pressure, which intercepts the radial strain measurement value and the circumferential strain measurement value within a working cycle of the compressor based on the dead point signal of the compressor, and simultaneously obtains the radial drift and circumferential drift. After correcting the radial drift and circumferential drift, the oil pressure is obtained. Non-destructive measurement and reconstruction of the compressor cylinder pressure can be achieved.

Description

Technical Field

[0001] The present application belongs to the technical field of compressors, and in particular relates to a method and system for non-destructive monitoring of compressor cylinder pressure. Background Art

[0002] A compressor is a power machine that increases gas pressure. The dynamic pressure within the cylinder directly reflects the thermal processes within the cylinder and the operating status of core components. Therefore, dynamic pressure within the cylinder is a critical parameter in compressor monitoring. Traditional methods for monitoring in-cylinder pressure rely on drilling pressure holes in the cylinder to install pressure sensors. This damages the cylinder structure, affecting cylinder strength and potentially causing leakage or even explosion. Therefore, this method is not suitable for monitoring the pressure of flammable and explosive gases or high-pressure gases. Therefore, a non-destructive measurement method, reconstruction algorithm, and system for compressor in-cylinder pressure are crucial for safe and stable compressor monitoring.

[0003] Zero drift often occurs during resistance strain gauge testing. This refers to the variation in measured values caused by environmental factors such as time, temperature, and electromagnetic fields while the strain gauge is operating. Severe drift can drown out valid signals, necessitating correction for zero drift during pressure measurements.

[0004] The prior art does not consider the strain drift problem that occurs in actual measurement, and does not provide a method for calculating the dynamic pressure in the cylinder with drift considered. Summary of the Invention

[0005] 1. Technical problems to be solved

[0006] Since existing solutions do not consider the strain drift problem that actually occurs in actual measurements, and in the case of severe drift, the effective signal may even be "swamped", the present application provides a method and system for non-destructive monitoring of the compressor cylinder pressure.

[0007] 2. Technical solution

[0008] In order to achieve the above-mentioned purpose, the present application provides a method for non-destructive monitoring of the pressure in the cylinder of a compressor, which intercepts the radial strain measurement value and the circumferential strain measurement value within the working cycle according to the dead point signal of the compressor, calculates the amplitude of the radial strain measurement value and the amplitude of the circumferential strain measurement value of the working cycle according to the radial strain measurement value and the circumferential strain measurement value, obtains the ratio of the amplitude of the radial strain measurement value to the amplitude of the circumferential strain measurement value, that is, the amplitude ratio Z, and calculates the pressure of the cylinder of the compressor according to the amplitude ratio, the radial strain measurement value and the circumferential strain measurement value. A radial drift and a circumferential drift are obtained, and a corrected radial strain measurement value and a corrected circumferential strain measurement value are obtained based on the radial drift and the circumferential drift. The difference between the corrected radial strain measurement value and the corrected circumferential strain measurement value is calculated, and the cylinder surface is simplified into a circular plate model. According to the generalized Hooke's law, the boundary condition of a uniformly loaded peripheral clamped plate is introduced. A first constant term a and a second constant term b are calculated based on the structure of the measured compressor and the position of the measuring point. The dynamic pressure in the cylinder during the working cycle is calculated based on the difference, a, and b.

[0009] Another implementation manner provided by the present application is that the radial strain measurement value is the radial strain measurement value of the cylinder head, and the circumferential strain measurement value is the circumferential strain measurement value of the cylinder head.

[0010] Another implementation provided by the present application is that the radial strain measurement value after drift correction is Z times the circumferential strain measurement value after drift correction, where Z is the amplitude ratio.

[0011] Another implementation method provided by the present application is: one working cycle corresponds to a 360° rotation of the compressor crankshaft, and 360 sets of equations are obtained based on the radial strain measurement value after the drift correction being Z times the circumferential strain measurement value after the drift correction, and the radial drift and the circumferential drift are obtained by solving the set of equations.

[0012] Another implementation method provided by the present application is: the solution method is the least squares method.

[0013] Another embodiment provided by the present application is: the radial drift includes radial drift at each angle, and the radial drift is 360 numerical points; the circumferential drift includes circumferential drift at each angle, and the circumferential drift is 360 numerical points.

[0014] Another implementation provided by the present application is that the radial drift is temperature drift, and the circumferential drift is temperature drift.

[0015] The present application also provides a system based on the method for non-destructive monitoring of the compressor cylinder pressure, comprising a strain gauge assembly, a bridge assembly, a signal acquisition module and a signal processing module connected in sequence, wherein the signal acquisition module is connected to a proximity switch, and the proximity switch is arranged next to the coupling.

[0016] Another embodiment provided by the present application is: the strain gauge assembly includes a first strain gauge and a second strain gauge, the bridge assembly includes a first bridge and a second bridge, the first strain gauge, the first bridge, the signal acquisition module and the signal processing module are connected in sequence, and the second strain gauge, the second bridge, the signal acquisition module and the signal processing module are connected in sequence.

[0017] Another implementation provided by the present application is that the first bridge is a quarter bridge, and the second bridge is a quarter bridge.

[0018] 3. Beneficial effects

[0019] Compared with the prior art, the non-destructive monitoring method and system for compressor cylinder pressure provided by the present application have the following beneficial effects:

[0020] The non-destructive monitoring method for compressor cylinder pressure provided in this application is a strain-based non-destructive monitoring method for compressor cylinder pressure, which can correct strain drift and thus complete non-destructive measurement and reconstruction of compressor cylinder pressure.

[0021] The present application provides a non-destructive monitoring method for compressor cylinder pressure, which is a correction algorithm for strain drift and also provides a method for calculating the dynamic pressure in the cylinder taking drift into consideration.

[0022] The non-destructive monitoring method for the compressor cylinder pressure provided in this application can solve the problem of inaccurate cylinder pressure measurement due to strain drift. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Schematic diagram of the compressor cylinder pressure non-destructive monitoring system of the present application;

[0024] Figure 2 This is the principle of strain gauge layout of this application;

[0025] Figure 3 It is a stop point measurement diagram of this application;

[0026] Figure 4 is a schematic diagram of the measured signal of this application;

[0027] Figure 5 Schematic diagram of experimental results of the non-destructive monitoring method for compressor cylinder pressure of the present application;

[0028] Figure 6This is a schematic diagram for verifying the non-destructive monitoring method for compressor cylinder pressure in this application. DETAILED DESCRIPTION

[0029] Hereinafter, specific embodiments of the present application will be described in detail with reference to the accompanying drawings. Based on these detailed descriptions, those skilled in the art will be able to clearly understand the present application and implement the present application. Without violating the principles of the present application, the features of different embodiments may be combined to obtain new implementations, or certain features of certain embodiments may be substituted to obtain other preferred implementations.

[0030] The reasons for the drift are analyzed as follows: (1) Thermal strain. During the operation of the compressor, the temperature of the cylinder itself rises, causing the surface temperature of the cylinder to rise; the external ambient temperature changes, causing the surface temperature of the cylinder to change; (2) Surface heat exchange. The surface of the strain gauge is not completely insulated, so when there is air flowing on the surface, the temperature of the strain gauge will change. (In the test, the compressor air intake source is a screw air compressor, and the heat dissipation seal faces the cylinder of the compressor under test. When the heat dissipation blows, it will cause a large strain drift); (3) Instrument temperature drift. Power supply voltage instability, component parameter changes, ambient temperature changes, etc. The most important factor is temperature change, because the transistor is a temperature-sensitive device. When the temperature changes, its parameters UBE, β, and ICBQ will change, eventually causing the static operating point of the amplifier circuit to shift. In actual testing, the strain measurement value drift will be observed when the instrument is powered off and restarted before and after the test. (4) Mechanical reasons. Plastic deformation occurs in the high-voltage unit. Therefore, excluding the strain drift caused by plastic deformation, other causes can basically be classified as temperature drift caused by the object being measured or the ambient temperature and instrument drift caused by the instrument circuit.

[0031] See also Figures 1 to 6The present application provides a method for nondestructive monitoring of compressor cylinder pressure. The method comprises intercepting radial strain measurement values and circumferential strain measurement values within a working cycle based on a dead-point signal of the compressor. The amplitudes of the radial strain measurement values and the circumferential strain measurement values for the working cycle are calculated based on the radial strain measurement values and the circumferential strain measurement values. The ratio of the amplitude of the radial strain measurement value to the amplitude of the circumferential strain measurement value, i.e., the amplitude ratio Z, is obtained. The radial drift and the circumferential drift are calculated based on the amplitude ratio, the radial strain measurement values, and the circumferential strain measurement values. The radial drift and the circumferential drift are obtained based on the radial drift and the circumferential drift. The difference between the corrected radial strain measurement value and the corrected circumferential strain measurement value is calculated. The cylinder surface is simplified as a circular plate model. According to the generalized Hooke's law, the boundary condition of a uniformly loaded peripheral clamped plate is introduced. A first constant term a and a second constant term b are calculated based on the structure of the compressor under test and the location of the measuring points. The dynamic pressure in the cylinder within the working cycle is calculated based on the difference, a, and b.

[0032] The cylinder surface is simplified into a circular plate model. According to the generalized Hooke's law, the boundary conditions of the uniformly distributed load and the surrounding clamped plate are used to calculate the strain ε after considering the drift correction. rM (i), ε θM The relationship between (i) and pressure p(i):

[0033]

[0034] Extract the pressure term and obtain the difference ε between the dynamic pressure in the cylinder and the calculated correction. M (i) The relationship:

[0035]

[0036] This formula is derived from the relationship between strain and pressure after considering drift correction.

[0037] Where: a and b are constants, which are only related to the structure of the compressor being tested and the position of the measuring point. The calculation formulas are: t-plate thickness; μ-material Poisson's ratio; E-material elastic modulus; r-strain gauge bonding radius, R cyl - radius of cylinder head, p - pressure in cylinder.

[0038] Based on the above formula, the oil pressure in the cylinder can be obtained.

[0039] Furthermore, the radial strain measurement value is a radial strain measurement value of the cylinder head, and the circumferential strain measurement value is a circumferential strain measurement value of the cylinder head.

[0040] Measure the radial strain ε at a certain position of the cylinder head rT and circumferential strain ε θT The two strain gauges are connected to the 1 / 4 bridge respectively to measure the radial strain and circumferential strain.

[0041] Furthermore, the radial strain measurement value after the drift correction is Z times the circumferential strain measurement value after the drift correction, where Z is the amplitude ratio.

[0042] The signal between two adjacent dead point signals is the signal of one working cycle of the compressor. The radial strain ε within one cycle is intercepted respectively. rT and circumferential strain ε θT Calculate the radial strain amplitude Z of one cycle respectively r and the circumferential strain amplitude Z θ (Amplitude is the maximum value minus the minimum value), set Z to the amplitude ratio

[0043] According to the material property Poisson's ratio: while the material produces elongation (or shortening) deformation along the load direction, it also produces shortening (or elongation) deformation in the direction perpendicular to the load.

[0044] Since the measurement positions are perpendicular to each other, the value of Z will be very close to the Poisson's ratio (material property) of the material. The cylinder material (metal) of the compressor is less affected by temperature, so the Z value is relatively stable.

[0045] Furthermore, one working cycle corresponds to a 360° rotation of the compressor crankshaft, and 360 sets of equations are obtained based on the radial strain measurement value after the drift correction being Z times the circumferential strain measurement value after the drift correction. The radial drift and the circumferential drift are obtained by solving the set of equations.

[0046] Furthermore, the solution method is the least squares method.

[0047] Furthermore, the radial drift includes radial drift at each angle, and the radial drift is 360 numerical points. The circumferential drift includes circumferential drift at each angle, and the circumferential drift is 360 numerical points.

[0048] Furthermore, the radial drift is temperature drift, and the circumferential drift is temperature drift.

[0049] Specifically, drift correction calculation. The compressor crankshaft rotates 360 degrees, which corresponds to one rotation cycle. Each degree has one strain, and 360 strain values form a dynamic curve of one cycle. Assume that the radial drift ε r0 (i) and circumferential drift ε θ0 (i) Radial test value ε rT (i) and circumferential test value ε θT(i) Strain measurement value ε after drift correction rM (i) and the circumferential strain measurement ε θM (i), where i=0, 1, 2, ..., 359.

[0050] Drift-corrected radial strain measurement ε rM (i) = ε rT (i)-ε r0 (i)

[0051] Drift-corrected circumferential strain measurement ε θM (i) = ε θT (i)-ε θ0 (i)

[0052] Drift-corrected radial strain measurement ε rM (i) and the drift-corrected circumferential strain measurement ε θM (i) The following relationship is satisfied: rM (i) = Zε θM (i).

[0053] The compressor crankshaft rotates 360 degrees, which corresponds to one rotation cycle. One strain is generated per degree, and 360 strain values form a dynamic curve of one cycle. Therefore, the 360 equations to be solved are:

[0054]

[0055] Solve the above equations using the least squares method to obtain the radial drift ε corresponding to each angle in one cycle. r0 (i) and circumferential drift ε θ0 (i) Then, the drift-corrected strain measurement value ε is obtained. rM (i) and the circumferential strain measurement ε θM (i), and calculate the difference between the two after correction.

[0056] The present application also provides a system for the non-destructive monitoring method of the compressor cylinder pressure, comprising a strain gauge assembly, a bridge assembly, a signal acquisition module and a signal processing module connected in sequence, wherein the signal acquisition module is connected to a proximity switch, and the proximity switch is arranged next to the coupling.

[0057] Specifically, a proximity switch is mounted on a metal frame next to the coupling. When the piston is at top dead center, a specific nut is installed on the coupling directly opposite the sensor. During compressor operation, when the piston reaches top dead center, the sensor and the specific nut intersect, and the proximity switch outputs a 10V pulse signal. This pulse signal indicates that the piston is at top dead center. The proximity switch is positioned directly opposite the coupling, mounted on the metal frame opposite it. When the piston reaches top dead center, the sensor intersects the specific nut (installed on the coupling). The interval between these two pulse signals represents one cycle of compressor operation, from which the oil pressure signal for that cycle can be derived.

[0058] The proximity switch acts as a dead center sensor and is used to determine the moment when the piston reaches the top dead center position.

[0059] Furthermore, the strain gauge assembly includes a first strain gauge and a second strain gauge, the bridge assembly includes a first bridge and a second bridge, the first strain gauge, the first bridge, the signal acquisition module 1 and the signal processing module 2 are connected in sequence, and the second strain gauge, the second bridge, the signal acquisition module 1 and the signal processing module 2 are connected in sequence.

[0060] The signal processing module here is a smart terminal such as a computer or tablet computer.

[0061] Furthermore, the first bridge is a quarter bridge, and the second bridge is a quarter bridge. Only the quarter bridge is selected here because the algorithm considers the strain in each direction separately as the accurate value + drift value.

[0062] like Figure 6 As shown in the figure, after drift correction, the suction pressure is 0.8MPa and the exhaust pressure is 1.1MPa, which is consistent with the pressure gauge measurement result.

[0063] The drift in this measurement is caused by temperature drift. During compressor operation, from the cold state at startup to the hot state during operation, the compressed gas generates compressor heat, causing the compressor cylinder wall to continuously rise. This changing temperature causes drift in the strain measurement.

[0064] Although the present application has been described above with reference to specific embodiments, it should be understood by those skilled in the art that many modifications may be made to the configurations and details disclosed herein within the principles and scope of the present application. The scope of protection of the present application is determined by the appended claims, and the claims are intended to cover all modifications encompassed by the literal meaning or scope of equivalents of the technical features in the claims.

Claims

1. A method for non-destructive monitoring of compressor cylinder pressure, characterized by: According to the dead point signal of a working cycle of the compressor, radial strain measurement values and circumferential strain measurement values within the working cycle are intercepted. Based on the radial strain measurement values and the circumferential strain measurement values, the amplitudes of the radial strain measurement values and the circumferential strain measurement values for the working cycle are calculated to obtain the ratio of the amplitude of the radial strain measurement value to the amplitude of the circumferential strain measurement value, i.e., the amplitude ratio Z. Radial drift and circumferential drift are calculated based on the amplitude ratio, the radial strain measurement values, and the circumferential strain measurement values. Corrected radial strain measurement values and corrected circumferential strain measurement values are obtained based on the radial drift and the circumferential drift. The difference between the corrected radial strain measurement value and the corrected circumferential strain measurement value is calculated. The cylinder surface is simplified as a circular plate model. According to the generalized Hooke's law, the boundary conditions of a uniformly loaded peripheral clamped plate are substituted. A first constant term a and a second constant term b are calculated based on the structure of the measured compressor and the measurement point locations. The dynamic pressure in the cylinder within the working cycle is calculated based on the difference, a, and b.

2. The method for non-destructive monitoring of compressor cylinder pressure according to claim 1, characterized in that: The radial strain measurement value is a radial strain measurement value of the cylinder head, and the circumferential strain measurement value is a circumferential strain measurement value of the cylinder head.

3. The method for non-destructive monitoring of compressor cylinder pressure according to claim 1 or 2, characterized in that: The drift-corrected radial strain measurement value is Z times the drift-corrected circumferential strain measurement value, where Z is the amplitude ratio.

4. The method for non-destructive monitoring of compressor cylinder pressure according to claim 3, wherein: One working cycle corresponds to a 360° rotation of the compressor crankshaft. 360 equation groups are obtained based on the radial strain measurement value after the drift correction being Z times the circumferential strain measurement value after the drift correction. The radial drift and the circumferential drift are obtained by solving the equation groups.

5. The method for non-destructive monitoring of compressor cylinder pressure according to claim 4, characterized in that: The solution method is the least squares method.

6. The method for non-destructive monitoring of compressor cylinder pressure according to claim 4, characterized in that: The radial drift includes radial drift at each angle, and the radial drift is 360 numerical points. The circumferential drift includes circumferential drift at each angle, and the circumferential drift is 360 numerical points.

7. The method for non-destructive monitoring of compressor cylinder pressure according to claim 6, characterized in that: The radial drift is temperature drift, and the circumferential drift is temperature drift.

8. A system according to the method for non-destructive monitoring of compressor cylinder pressure according to any one of claims 1 to 7, characterized in that: The invention comprises a strain gauge assembly, a bridge assembly, a signal acquisition module and a signal processing module which are connected in sequence. The signal acquisition module is connected to a proximity switch which is arranged beside a coupling.

9. The system according to claim 8, wherein: The strain gauge assembly includes a first strain gauge and a second strain gauge, and the bridge assembly includes a first bridge and a second bridge. The first strain gauge, the first bridge, the signal acquisition module, and the signal processing module are connected in sequence, and the second strain gauge, the second bridge, the signal acquisition module, and the signal processing module are connected in sequence.

10. The system according to claim 9, wherein: The first bridge is a quarter bridge, and the second bridge is a quarter bridge.

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