Reciprocating compressor bearing bush double-wire thermocouple transient temperature measuring method

Abstract

The invention discloses a reciprocating compressor bearing bush double-wire thermocouple transient temperature measurement method, which comprises the following steps: S1, measuring the temperature of a compressor bearing bush: simultaneously acquiring actually measured transient temperature signals of two temperature measurement nodes close to each other in the compressor bearing bush through two thin-wire thermocouples with close diameters, judging whether the temperature courses of the two thin-wire thermocouples are the same or not based on the cross correlation coefficient, thereby judging whether the actually measured transient temperature is accurate or not; s2, double-wire thermocouple temperature compensation: calculating a thermocouple time constant and a time derivative of an actually measured transient temperature signal, filtering the actually measured transient temperature signal through a low-pass filter, and suppressing a high-frequency signal in the time derivative of the actually measured transient temperature signal through a Gaussian kernel convolution signal of a Gaussian smooth filter, and calculating the real transient temperature of the compressor bearing bush by combining the thermocouple time constant, the filtered actually measured transient temperature signal and the time derivative thereof. The method is high in measurement precision and good in real-time performance.

Description

Technical Field

[0001] The present invention relates to the technical field of compressors, and particularly to a method for measuring the transient temperature of a double-wire thermocouple of a bearing bush of a reciprocating compressor. Background Art

[0002] As a core dynamic device in the petrochemical industry, a reciprocating compressor has the characteristics of being flammable and explosive. Therefore, it is very necessary to perform real-time temperature detection on it. The existing temperature measurement technical solutions for reciprocating compressors mainly include:

[0003] Existing technical solution (1)

[0004] A thermoresistance temperature measurement method powered by a battery. An insertion-type PT100 thermoresistance is used to directly obtain the bearing bush temperature, and then the temperature parameter is transmitted to an external receiver by an antenna at the top of the probe.

[0005] Existing technical solution (2)

[0006] Infrared temperature measurement technology. It uses thermal radiation to measure the temperature of an object. It is a non-contact temperature measurement method that is currently widely used and has the characteristic of not damaging the compressor structure, so the safety is relatively high.

[0007] Existing technical solution (3)

[0008] Wireless temperature measurement technology based on surface acoustic wave technology. The principle of surface acoustic wave temperature measurement technology is that surface acoustic wave elements can obtain different reflection frequencies by changing their material properties and are very sensitive to the physical parameters of the environment. Therefore, surface acoustic waves can better reflect the thermal performance inside the compressor.

[0009] Among the above several traditional methods for measuring the temperature of the bearing bush of a reciprocating compressor:

[0010] (1) For the thermoresistance temperature measurement method powered by a battery, since it is battery-powered insertion temperature measurement. And the battery itself is flammable and explosive, so this temperature measurement method has great safety hazards.

[0011] (2) Although the infrared temperature measurement method is a non-contact temperature measurement method, due to the influence of dust on the surface of the compressor cylinder body and the fact that the inside of the cylinder is not exposed, its accuracy is relatively low.

[0012] (3) For the wireless temperature measurement technology based on surface acoustic wave technology, although the reflection of surface acoustic waves can more accurately reflect the temperature inside the compressor cylinder, due to its high sensitivity to the physical parameters of the environment, there is a large interference for the use scenario of a reciprocating compressor. And due to the high real-time requirement for temperature measurement inside the reciprocating compressor cylinder, this method cannot well meet its needs. Summary of the Invention

[0013] To solve the above problems, the present invention proposes a method for measuring the transient temperature of the bearing bush of a reciprocating compressor using a two-wire thermocouple, which measures the real-time temperature of the bearing bush of the compressor. The two-wire thermocouple has the characteristics of high precision, good real-time performance, and less influence from the surrounding environment, and is very suitable for the usage scenario of a reciprocating compressor. Measuring the bearing bush temperature of a reciprocating compressor using this method has the characteristics of high precision and good real-time performance, and can better guide the subsequent condition monitoring and fault diagnosis of the reciprocating compressor.

[0014] The technical solution adopted by the present invention is as follows:

[0015] A method for measuring the transient temperature of the bearing bush of a reciprocating compressor using a two-wire thermocouple, comprising the following steps:

[0016] S1. Measurement of the bearing bush temperature of the compressor: Simultaneously collect the measured transient temperature signals of two temperature measurement nodes with close distances in the bearing bush of the compressor through two thin-wire thermocouples with similar diameters, and judge whether the temperature histories of these two thin-wire thermocouples are the same based on the cross-correlation coefficient, so as to judge whether the measured transient temperature is accurate.

[0017] S2. Temperature compensation of the two-wire thermocouple: Calculate the time constant of the thermocouple and the time derivative of the measured transient temperature signal, filter the measured transient temperature signal through a low-pass filter, and suppress the high-frequency signals in the time derivative of the measured transient temperature signal by convolving the signal with the Gaussian kernel of the Gaussian smoothing filter. Combine the time constant of the thermocouple, the filtered measured transient temperature signal and its time derivative to calculate the true transient temperature of the bearing bush of the compressor.

[0018] Further, in step S1, the judgment of whether the temperature histories of these two thin-wire thermocouples are the same based on the cross-correlation coefficient includes: Using two thermocouples with the same wire diameter and the same node size for verification, and calculating the cross-correlation coefficient between the two. When the cross-correlation coefficient is greater than the preset value, it is considered that the difference between the temperature field and the velocity field near the two thermocouples is small enough, that is, the temperature histories of the two thin-wire thermocouples are the same.

[0019] Further, in step S1, the calculation method of the cross-correlation coefficient includes:

[0020]

[0021] In the formula: R 12 ——Cross-correlation coefficient, T′1——Fluctuation component of thermocouple T1, T′2——Fluctuation component of thermocouple T2.

[0022] Further, in step S1, the two thin-wire thermocouples are installed in the middle of the bearing bush of the compressor and are not fixed using a ceramic tube, but only supported by wires.

[0023] Further, two fine-wire thermocouples are pasted with silicone sealant. The silk thread is placed between two layers of silicone to play an insulating role. The four bottom wires are insulated by high-temperature silicone sleeves.

[0024] Further, the four wires at the bottom of the two fine-wire thermocouples are far apart from each other in pairs, and are insulated with silicone in the middle. The four bottom wires are insulated by high-temperature silicone sleeves.

[0025] Further, in step S2, the calculation method of the thermocouple time constant includes:

[0026] Express the energy balance of the thermocouple node as:

[0027]

[0028] In the formula: ρ—the average density of the thermocouple node, kg·m -3 ; c—the average specific heat capacity of the thermocouple node, kJ·(kg·K) -1 ; V—the volume of the thermocouple node, m 3 ; h—the convective heat transfer coefficient of the thermocouple node, W·m -2 ·K -1 ; A—the surface area of the thermocouple node, m 2 ; T—the measured transient temperature, K; T g —the true transient temperature, K;

[0029] Express the true transient temperature as:

[0030]

[0031] In the formula: τ is the time constant, and there is:

[0032]

[0033] Further, the calculation method of the thermocouple time constant also includes:

[0034] Express the true transient temperatures corresponding to the two fine-wire thermocouples as:

[0035]

[0036] Reduce the time-averaged difference e between the true transient temperatures T g1 and T g2 by the least squares method:

[0037]

[0038] In the formula: N is the total number of samples of each thermocouple signal, and the superscript i represents the sampled value at the time point i / f s fs is the sampling frequency; now is abbreviated as ∑, and ΔT is defined as 21 = T2 - T1, D1 = dT1 / dt and D2 = dT2 / dt, thus expanding Equation (6) to:

[0039] e = ∑(ΔT 21 ) 2 + τ1 2 (∑D1 2 ) + τ2 2 (D2 2 ) - 2τ1(∑D1ΔT 21 ) +

[0040] 2τ2(∑D2ΔT 21 ) - 2τ1τ2(∑D1D2) (7)

[0041] In order to obtain the minimum value of the time-averaged difference e, by additionally supplementing a condition, making the partial derivatives of the time-averaged difference e with respect to the time constants τ1 and τ2 equal to 0, thus obtaining the time constants of the two fine-wire thermocouples respectively:

[0042]

[0043] Furthermore, the Gaussian kernel of the Gaussian smoothing filter is defined as:

[0044] g(t) = exp(-λt 2 ) (9)

[0045] where: λ - smoothing factor, used to set the cut-off frequency;

[0046] Equation (9) is used to calculate the convolution of the original signal, and then each data in the original signal is replaced by the weighted average of a data segment centered on that data; by adjusting the smoothing factor λ, the high-frequency part in the original signal will be averaged or reduced within the selected data segment length; the smaller the smoothing factor λ, the smoother, but the lower the cut-off frequency;

[0047] If the temperature signal is represented by T(t), then the filtered signal is represented as:

[0048]

[0049] Furthermore, the calculation method of the time derivative of the measured transient temperature signal includes: using the commutative law of convolution to calculate the time derivative of the measured transient temperature signal:

[0050]

[0051] where: dg(t) / dt = -2λt exp(-λt 2)。

[0052] The beneficial effects of the present invention are as follows:

[0053] The present invention uses a two-wire thermocouple to measure the real-time temperature of the compressor bearing bush. Since the two-wire thermocouple uses two thin thermocouple probes with similar diameters to measure transient temperature, when the temperature measurement nodes of these two thin thermocouples are close enough, it can be considered that they experience the same temperature history, equivalent to two thermocouples measuring temperature simultaneously. Therefore, the accuracy is well guaranteed.

[0054] The two-wire thermocouple has the characteristics of high accuracy, good real-time performance, and less influence from the surrounding environment, and is very suitable for the use scenario of reciprocating compressors. Using this method to measure the bearing bush temperature of reciprocating compressors has the characteristics of high accuracy and good real-time performance, and can better guide the subsequent condition monitoring and fault diagnosis of reciprocating compressors. Brief Description of the Drawings

[0055] Figure 1 Flow chart of the transient temperature measurement method of the two-wire thermocouple for the bearing bush of the reciprocating compressor in the embodiment of the present invention.

[0056] Figure 2 Schematic diagram of the two-wire thermocouple probe in the embodiment of the present invention.

[0057] Figure 3 Schematic diagram of the dimensions of the two-wire thermocouple probe in the embodiment of the present invention.

[0058] Figure 4 One of the installation schematic diagrams of the two-wire thermocouple probe in the embodiment of the present invention.

[0059] Figure 5 Another installation schematic diagram of the two-wire thermocouple probe in the embodiment of the present invention. Detailed Embodiments

[0060] In order to have a clearer understanding of the technical features, objectives, and effects of the present invention, the specific embodiments of the present invention are now described. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention, that is, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative efforts belong to the scope of protection of the present invention.

[0061] This embodiment provides a transient temperature measurement method for the bearing bush of a reciprocating compressor with a two-wire thermocouple. As Figure 1 shown, it includes the following steps:

[0062] S1. Compressor bearing temperature measurement: Simultaneously collect the measured transient temperature signals of two temperature measurement nodes close to each other in the compressor bearing through two thin-wire thermocouples with similar diameters. Based on the cross-correlation coefficient, determine whether the temperature histories of these two thin-wire thermocouples are the same, so as to judge whether the measured transient temperature is accurate;

[0063] S2. Temperature compensation for double-wire thermocouple: Calculate the time constant of the thermocouple and the time derivative of the measured transient temperature signal. Filter the measured transient temperature signal through a low-pass filter, and suppress the high-frequency signals in the time derivative of the measured transient temperature signal by convolving the signal with the Gaussian kernel of the Gaussian smoothing filter. Combine the time constant of the thermocouple, the filtered measured transient temperature signal and its time derivative to calculate the true transient temperature of the compressor bearing.

[0064] The transient temperature measurement method of the double-wire thermocouple in this embodiment is specifically described as follows.

[0065] I. Fabrication of double-wire thermocouple probe

[0066] It can be seen from the gas state equation that two state parameters are required to determine the state of the working fluid in the compressor. Among the most important state parameters such as temperature, density, and enthalpy, the easiest and most economical one to use is to measure the transient temperature of the working fluid with a thin-wire thermocouple. However, when using a thin-wire thermocouple alone to measure the transient temperature, the flow velocity of the working fluid near the measurement point is additionally required to compensate for the measured transient temperature, and the corresponding relationship between the flow velocity and the time constant needs to be measured separately before the measurement.

[0067] Therefore, this embodiment provides a more convenient method, that is, to measure the transient temperature by using a double-wire thermocouple probe, as Figure 2 shown. This method means using two thin-wire thermocouples with similar diameters to simultaneously measure the transient temperature near a certain measurement point. When the distance between the temperature measurement nodes of these two thin-wire thermocouples is close enough, it can be considered that the temperature histories they experience are the same. Of course, for whether the temperature histories experienced by the two thin-wire thermocouples are the same, two thermocouples with the same wire diameter and the same node size can be used for verification, and their cross-correlation coefficient can be calculated. Generally, when the cross-correlation coefficient is greater than 0.99, it is considered that their temperature histories are the same. Regarding the distance between the two temperature measurement nodes, it should not be too far to prevent the difference in their temperature histories from being too large, nor too close to prevent the two nodes from possibly colliding with each other in the turbulent airflow, resulting in signal interference or even breakage of the thin wire.

[0068] Preferably, Figure 2 the typical dimensions of the double-wire thermocouple probe in Figure 3 are as Figure 3The four-hole corundum ceramic tube used has a diameter of 3 mm and a pore diameter of 0.6 mm, which can play the roles of both thermal insulation and electrical insulation. The thin wires used for the thermocouple are made of NiCr / NiSi, and the diameters of the two groups of thin wires are 18 μm and 35 μm respectively. To reduce the time constant of the thermocouple and increase its response speed, the node diameter of the thermocouple must be as small as possible. Therefore, after multiple weldings, thermocouples with node diameters of 18 μm and 35 μm were selected to fabricate the double-wire thermocouple probe. At the same time, to increase the rigidity of the thermocouple, the wire diameter used is 0.5 mm, which can be regarded as a support. The gap between the support and the hole is sealed and fixed using cyanoacrylate adhesive. It is generally considered that when the ratio of the length of the thermocouple to the wire diameter is greater than 200, the heat conduction between the thermocouple node and the support can be ignored. Therefore, to reduce the axial heat conduction of the thermocouple thin wire, the total length of the thermocouple is about 16 mm, and the length between the node and the support is about 8 mm. To conveniently control the distance between the two nodes to ensure that their temperature histories are as similar as possible, the two thermocouples are arranged to form an X shape in space, and first, three of the four thermocouples are welded to the corresponding supports. By changing the position of the last solder joint, the distance between the two nodes can be accurately controlled, and the crossover and contact of the two thermocouples in space can be minimized.

[0069] To verify whether the temperature fields and velocity fields at the two thermocouple nodes in the double-wire thermocouple probe are approximately the same, the cross-correlation coefficient can be used for verification. By setting two identical thermocouples with a diameter of 18 μm in the double-wire thermocouple in Figure 3 and using the fluctuating components output by these two thermocouples to calculate the cross-correlation coefficient, which is defined as follows:

[0070]

[0071] In the formula: R 12 —— cross-correlation coefficient, T′1 —— the fluctuating component of thermocouple T1, T′2 —— the fluctuating component of thermocouple T2.

[0072] The calculated cross-correlation coefficient R 12 is 0.997. Generally, it is considered that when the cross-correlation coefficient is greater than 0.99, the difference between the temperature fields and velocity fields near the two thermocouples is small enough to be ignored.

[0073] II. Installation of the double-wire thermocouple probe

[0074] When the thermocouple is used to measure the transient temperature of the gas working medium in the bearing shell, it is easily affected by the radiant heat of the inner wall surface of the working chamber, the piston surface, and the cylinder head, resulting in inaccurate measurement results. Multiple tests have shown that the influence is minimized when the double-wire thermocouple is installed in the middle of the bearing shell. Therefore, the installation schematic diagram of the double-wire thermocouple probe is asFigure 4 and Figure 5 as shown

[0075] Install a two-wire thermocouple probe in the middle of the bearing bush, without using a ceramic tube for fixation, and only use wires for support, as Figure 4 shown. Use kafuter K-704 silicone sealant for pasting. The silk thread is placed between two layers of silicone to play an insulating role. The four wires at the bottom are insulated by using Huazhong 2751 high-temperature silicone sleeves for wire encapsulation.

[0076] It can also be as Figure 5 shown, making the four wires far apart from each other in pairs, using silicone for insulation in the middle, and the four wires at the bottom are also insulated by using Huazhong 2751 high-temperature silicone sleeves for wire encapsulation. The two-wire thermocouple probe protrudes about 4 mm from the surface of the air valve.

[0077] III. Thermocouple time constant

[0078] Generally, when the heat conduction and radiation heat loss at the thermocouple junction can be ignored, the energy balance at the thermocouple junction can be expressed as:

[0079]

[0080] In the formula: ρ—the average density of the thermocouple junction, kg·m -3 ; c—the average specific heat capacity of the thermocouple junction, kJ·(kg·K) -1 ; V—the volume of the thermocouple junction, m 3 ; h—the convective heat transfer coefficient of the thermocouple junction, W·m -2 ·K -1 ; A—the surface area of the thermocouple junction, m 2 ; T—the measured transient temperature, K; T g —the true transient temperature, K;

[0081] Express the true transient temperature as:

[0082]

[0083] In the formula: τ is the time constant, and there is:

[0084]

[0085] IV. Temperature compensation of the two-wire thermocouple

[0086] The measurement of transient temperature by a two-wire thermocouple essentially utilizes two fine-wire thermocouples with similar time constants. Therefore, the positions of the temperature-sensing junctions of these two thermocouples must be as close as possible to ensure that the temperature fields and velocity fields in their vicinity can be considered the same. According to the formula, the true temperature measured by the two-wire thermocouple probe can be expressed as:

[0087]

[0088] Considering the difference between the true transient temperature T g1 and T g2 , the least squares method can be used to reduce this time-averaged difference, that is During the experiment, the continuous temperature signal in time is discretized when converted into digital quantity by the acquisition card. The frequency of this discretization is the sampling frequency, f s . At this time, the time-averaged difference e can be expressed as:

[0089]

[0090] In the formula: N is the total number of samples of each thermocouple signal, and the superscript i represents the sampling value at the time point i / f s . For convenience, is abbreviated as ∑, and ΔT 21 =T2 - T1, D1 = dT1 / dt and D2 = dT2 / dt are defined, so as to expand formula (6) to:

[0091] e = ∑(ΔT 21 ) 2 +τ1 2 (∑D1 2 )+τ 22 (D2 2 )-2τ1(∑D1ΔT 21 )+

[0092] 2τ2(∑D2ΔT 21 )-2τ1τ2(∑D1D2) (7)

[0093] In order to obtain the minimum value of the time-averaged difference e, by adding an additional condition, the partial derivatives of the time-averaged difference e with respect to the time constants τ1 and τ2 are made equal to 0, so as to obtain the respective time constants of the two fine-wire thermocouples:

[0094]

[0095] However, it can be seen from the formula that the calculation of the time constant first requires the calculation of the time derivative of the actually measured temperature of the thermocouple, resulting in the measurement noise being amplified proportionally with the noise frequency. Therefore, even if there is no error in the estimation of the time constant, the compensated temperature contains the amplified noise. Therefore, it is necessary to limit the bandwidth of the temperature signal and the time derivative of the temperature signal.

[0096] In this embodiment, a low-pass filter is used to filter the temperature signal, while a Gaussian smoothing filter is used for the time derivative of the temperature signal. The Gaussian smoothing filter suppresses high-frequency signals by convolving the signal with a Gaussian kernel, and the Gaussian kernel is defined as:

[0097] g(t) = exp(-λt 2 ) (9)

[0098] In the formula: λ - smoothing factor, used to set the cut-off frequency.

[0099] Generally, the Gaussian smoothing filter is a linear smoothing filter, and formula (9) is used to calculate the convolution of the original signal. Then each data in the signal is replaced by the weighted average of a data segment centered on this data. By adjusting the smoothing factor λ, the high-frequency part in the signal will be averaged or reduced within the selected data segment length. The smaller the λ value, the smoother it is, but the lower the cut-off frequency.

[0100] If the temperature signal is represented by T(t), the filtered signal can be expressed as:

[0101]

[0102] The time derivative of the actually measured transient temperature signal can be calculated using the commutative law of convolution as follows:

[0103]

[0104] In the formula: dg(t) / dt = -2λt exp(-λt 2 ).

[0105] To sum up, this method uses a two-wire thermocouple to measure the real-time temperature of the compressor bearing bush. The two-wire thermocouple has the characteristics of high precision, good real-time performance, and less influence from the surrounding environment, and is very suitable for the use scenario of reciprocating compressors. Using this method to measure the bearing bush temperature of reciprocating compressors has the characteristics of high precision and good real-time performance, and can better guide the subsequent condition monitoring and fault diagnosis of reciprocating compressors.

[0106] The above are only the preferred embodiments of the present invention. It should be understood that the present invention is not limited to the forms disclosed herein, should not be regarded as excluding other embodiments, but can be used in various other combinations, modifications and environments, and can be changed within the scope of the concept described herein through the above teachings or the technology or knowledge in related fields. And any changes and modifications made by those skilled in the art without departing from the spirit and scope of the present invention shall fall within the protection scope of the appended claims of the present invention.

Claims

1. A transient temperature measurement method for a double-wire thermocouple of a reciprocating compressor bearing shell, characterized in that It includes the following steps: S1. Measurement of the temperature of the compressor bearing: Simultaneously collect the measured transient temperature signals of two temperature measurement nodes with close distances in the compressor bearing through two thin-wire thermocouples with similar diameters. Based on the cross-correlation coefficient, judge whether the temperature histories of the two thin-wire thermocouples are the same, so as to judge whether the measured transient temperature is accurate; S2. Temperature compensation of the two-wire thermocouple: Calculate the time constant of the thermocouple and the time derivative of the measured transient temperature signal. Filter the measured transient temperature signal through a low-pass filter, and suppress the high-frequency signals in the time derivative of the measured transient temperature signal by convolving the signal with the Gaussian kernel of the Gaussian smoothing filter. Combine the time constant of the thermocouple, the filtered measured transient temperature signal and its time derivative to calculate the true transient temperature of the compressor bearing.

2. The transient temperature measurement method of the double-wire thermocouple for the reciprocating compressor bearing bush according to claim 1, characterized in that In step S1, the judgment of whether the temperature histories of the two thin-wire thermocouples are the same based on the cross-correlation coefficient includes: Using two thermocouples with the same wire diameter and the same junction size for verification, and calculating the cross-correlation coefficient between the two. When the cross-correlation coefficient is greater than the preset value, it is considered that the difference between the temperature field and the velocity field near the two thermocouples is small enough, that is, the temperature histories of the two thin-wire thermocouples are the same.

3. The transient temperature measurement method of the reciprocating compressor bearing shell double-wire thermocouple according to claim 1, characterized in that In step S1, the calculation method of the cross-correlation coefficient includes: Where: R 12 —— Cross-correlation coefficient, T′1—— Fluctuation component of thermocouple T1, T′2—— Fluctuation component of thermocouple T2.

4. The transient temperature measurement method of the reciprocating compressor bearing shell dual-line thermocouple according to claim 1, characterized in that In step S1, the two thin-wire thermocouples are installed in the middle of the compressor bearing, without using a ceramic tube for fixation, and only supported by wires.

5. The transient temperature measurement method for the double-wire thermocouple of the reciprocating compressor bearing bush according to claim 4, characterized in that The two thin-wire thermocouples are pasted with silicone sealant. The silk thread is placed between two layers of silicone to play an insulating role. The four wires at the bottom are insulated by high-temperature silicone sleeves for wire encapsulation.

6. The transient temperature measurement method for the double-wire thermocouple of the reciprocating compressor bearing bush according to claim 4, characterized in that, The four wires at the bottom of the two thin-wire thermocouples are far apart from each other, insulated by silicone in the middle, and the four wires at the bottom are insulated by high-temperature silicone sleeves for wire encapsulation.

7. The transient temperature measurement method for the double-wire thermocouple of the reciprocating compressor bearing bush according to claim 1, characterized in that In step S2, the calculation method of the thermocouple time constant includes: Express the energy balance of the thermocouple junction as: Where: ρ——average density of thermocouple nodes, kg·m -3 ; c——average specific heat capacity of thermocouple nodes, kJ·(kg·K) -1 ; V——volume of thermocouple nodes, m 3 ; h——convective heat transfer coefficient of thermocouple nodes, W·m -2 ·K -1 ; A——surface area of thermocouple nodes, m 2 ; T——measured transient temperature, K; T g ——true transient temperature, K; Express the true transient temperature as: In the formula: τ is the time constant, and there is:

8. The transient temperature measurement method of the double-line thermocouple for the reciprocating compressor bearing bush according to claim 7, characterized in that, The calculation method of the thermocouple time constant also includes: Express the true transient temperatures corresponding to the two thin-wire thermocouples as: Reduce the time-averaged difference e between the true transient temperature T g1 and T g2 by the least squares method: Where: N is the total number of samples for each thermocouple signal, and the superscript i represents the sampled value at the time point i / f s and f s is the sampling frequency; now is abbreviated as ∑, and ΔT 21 is defined as T2 / T1, D1 = dT1 / dt, and D2 = dT2 / dt, so as to expand Equation (6) to: e = ∑(ΔT 21 ) 2 + τ1 2 (∑D1 2 ) + τ2 2 (∑D2 2 ) - 2τ1(∑D1ΔT 21 ) + 2τ2(∑D2ΔT 21 ) - 2τ1τ2∑D1D2) (7) In order to obtain the minimum value of the time-averaged difference e, by adding an additional condition, make the partial derivatives of the time-averaged difference e with respect to the time constants τ1 and τ2 equal to 0, so as to obtain the respective time constants of the two thin-wire thermocouples:

9. The transient temperature measurement method of the reciprocating compressor bearing double-line thermocouple according to claim 8, characterized in that, The Gaussian kernel of the Gaussian smoothing filter is defined as: g(t) = exp(-λt 2 ) (9) In the formula: λ - the smoothing factor, used to set the cut-off frequency; Formula (9) is used to calculate the convolution of the original signal, and then each data in the original signal is replaced by the weighted average of a data segment centered on this data; by adjusting the smoothing factor λ, the high-frequency part in the original signal will be averaged or reduced within the selected data segment length; the smaller the smoothing factor λ, the smoother it is, but the lower the cut-off frequency; If the temperature signal is represented by T(t), the filtered signal is represented as:

10. The transient temperature measurement method for the double-wire thermocouple of the reciprocating compressor bearing shell according to claim 9, characterized in that, The calculation method of the time derivative of the measured transient temperature signal includes: Using the commutative law of convolution to calculate the time derivative of the measured transient temperature signal: where: dg(t) / dt = -2λt exp(-λt 2 ).

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