A method for testing thermocouple performance

Abstract

This invention belongs to the field of hypersonic wind tunnel testing technology and discloses a method for testing thermocouple performance. The method includes constructing and installing a testing device; operating the testing device; and analyzing the test results. This method eliminates the need for a standard temperature source, is easy to operate, effectively reduces dependence on a standard temperature source, and allows for direct assessment of thermocouple performance consistency. By using the differential method, it solves the problems of existing thermocouple testing methods, such as reliance on a standard uniform temperature source and susceptibility to common-mode interference, thus achieving accurate assessment.

Description

Technical Field

[0001] This invention belongs to the field of hypersonic wind tunnel testing technology, specifically relating to a method for testing thermocouple performance. Background Technology

[0002] As a core sensor for temperature measurement, the accuracy of thermocouples directly impacts production safety, data quality, process control optimization, and energy management. Regular performance testing and calibration are crucial to ensuring the long-term reliability of thermocouples. However, existing thermocouple testing technologies face multiple bottlenecks in terms of principle, operability, and diagnostic depth. Specific problems include: 1. Heavy reliance on standard temperature sources, and demanding on-site implementation conditions; 2. Extremely high requirements for operational precision and synchronization; human error and system interference are significant. 3. It can only provide "static section" judgment and cannot capture "gradual performance degradation"; 4. Lack of in-depth diagnostics on whether the performance consistency of the sensor itself meets the standards.

[0003] In summary, existing thermocouple testing technologies, due to their dependence on constant temperature sources, operational complexity, limitations in application scenarios, low efficiency, and superficial diagnostic capabilities, are no longer able to meet the higher requirements of modern industry for measurement reliability, maintenance economy, and intelligent operation.

[0004] Currently, there is an urgent need to develop a method for testing thermocouple performance. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for testing thermocouple performance in order to overcome the defects of the prior art.

[0006] The thermocouple performance testing method of this invention combines the differential principle to construct a thermocouple differential pair by connecting two thermocouples in series with opposite polarities. The differential voltage signal in the circuit is extracted, and the thermoelectric potential difference between the thermocouple under test and the reference thermocouple is directly measured, thereby filtering out common-mode interference. The judgment standard is reduced from "whether the reading is accurate" to "whether the change is synchronous". It does not require a standard temperature source and avoids the problem of not being able to obtain a standard temperature source on site.

[0007] The principle of the differential method is as follows: The measuring ends of the thermocouple under test and the reference thermocouple are placed at the same temperature, but their electrical signals are connected in series with opposite polarities. Since the thermoelectric potentials generated by the two thermocouples are opposite in the circuit, according to Kirchhoff's voltage law, the thermoelectric potentials generated by the two thermocouples will cancel each other out. What is measured is no longer the absolute potential, but the differential voltage signal extracted from the circuit.

[0008] The core formula of the finite difference method principle is: Difference ΔV_diff = Measured value V_diff - Reference value V_diff0.

[0009] Ideally, if two thermocouples have identical performance and the measuring junction temperatures are the same, then the measured value V_diffc = the reference value V_diff0, and therefore the difference ΔV_diff = 0. In reality, due to differences in manufacturing tolerances and aging processes, the difference ΔV_diff will be a small and relatively stable value. When heated, if the measured thermocouple and the reference thermocouple have identical performance, their output change rates (Seebeck coefficients) are the same, and the difference ΔV_diff will remain constant. If the measured thermocouple deteriorates, its output change rate will deviate from that of the reference thermocouple, causing the difference ΔV_diff to change significantly with temperature.

[0010] The thermocouple performance testing method of this embodiment includes the following steps: S10. Construct and install the detection device; S11. Construct a detection device; The testing device includes a testing tool, a temperature source, a reference thermocouple, and a thermocouple under test. The reference thermocouple and the thermocouple under test are of the same type. The testing tool is a voltage detection device with millivolt-level measurement accuracy. S12. Connect the differential circuit; Confirm the polarity of the compensating leads of the reference thermocouple and the thermocouple under test; connect the positive terminal of the compensating lead of the reference thermocouple to the negative terminal of the compensating lead of the thermocouple under test. The connection point is the common point of the entire differential circuit and also the reference terminal of the temperature measurement system; then connect the negative terminal of the compensating lead of the reference thermocouple to the negative terminal of the testing tool, and connect the positive terminal of the compensating lead of the thermocouple under test to the positive terminal of the testing tool; finally, tightly attach and bind the measuring ends of the reference thermocouple and the thermocouple under test to ensure good contact. The binding point is also the measuring end of the testing device. S13. Perform installation checks; Check each connection point to ensure it is secure and that there are no loose or disconnected connections. S20. Operate the detection device; S21. Record the baseline value; With the measuring end of the testing device at room temperature and under stable conditions, record the reference value V_diff0 of the testing tool. The reference value V_diff0 can be a positive value, a negative value, or zero that is close to 0. S22. Conduct dynamic heating tests; Heat the measuring end with a temperature source and observe the trend of the measured value V_diff until the measuring end reaches thermal equilibrium. When thermal equilibrium is reached, the measured value V_diff tends to stabilize, with fluctuations within 0.05mV. Record the measured value V_diff again. Remove the temperature source and allow it to cool naturally, observing the changes in the measured value V_diff until the measuring end returns to its initial state. S23. Obtain the measured value; During dynamic heating and natural cooling processes, the measured value V_diff was recorded in real time. S30. Analyze the test results; S31. Compare and detect values; The difference ΔV_diff = measured value V_diff - reference value V_diff0; according to the requirement of ±1% accuracy of flow field temperature in wind tunnel test, the qualified threshold of the difference ΔV_diff is set to ±0.2mV; after the test, the difference ΔV_diff is used to determine whether the thermocouple under test can be put into use. S32. Determine the condition of the thermocouple being measured; The specific judgment process is as follows: S321. The tested thermocouple is qualified; the temperature response characteristics of the tested thermocouple are close to those of the reference thermocouple. Variation of the difference ΔV_diff: During the heating and cooling process at the measuring end, the difference ΔV_diff always fluctuates within a very narrow bandwidth near the reference value V_diff0. The absolute value of the difference ΔV_diff is <0.2mV. After thermal equilibrium, it tends to stabilize and can basically return to the reference value V_diff0 after cooling. Conclusion: The tested thermocouple is qualified. The performance difference between the tested thermocouple and the reference thermocouple is within the allowable range, and the performance is acceptable. S322. The tested thermocouple is unqualified; compared with the reference thermocouple, its temperature response characteristics are significantly lower, its performance has degraded and exceeds the qualified threshold. Changes in the difference ΔV_diff: During heating, the measured value V_diff changes significantly in the negative direction, far away from the reference value V_diff0, and the change exceeds the qualified threshold. After thermal equilibrium is reached, it tends to stabilize, and after cooling, it can basically return to the reference value V_diff0. Conclusion: The tested thermocouple is unqualified; its thermoelectric conversion efficiency has decreased, and its performance is unacceptable. S323. The tested thermocouple is abnormal and unqualified: Compared with the reference thermocouple, its temperature response characteristics are significantly higher and its sensitivity is abnormally higher than that of the reference thermocouple. This may be due to changes in the material composition of the tested thermocouple, which may cause the change to exceed the qualified threshold. Changes in the difference ΔV_diff: During heating, the measured value V_diff changes significantly in the positive direction, moving far away from the reference value V_diff0, and the change exceeds the qualified threshold. After thermal equilibrium is reached, it tends to stabilize, and after cooling, it can basically return to the reference value V_diff0. Conclusion: The tested thermocouple is unqualified. Although the response result shows that it is good, it has deviated from the normal threshold, the consistency is broken, and the performance is unacceptable. S324. The tested thermocouple is unqualified; the internal materials are abnormal. The variation of the difference ΔV_diff: During heating, the measured value V_diff changes irregularly with temperature, showing jumps or sudden changes, indicating nonlinear mutations; Conclusion: The tested thermocouple is substandard, and its internal materials are abnormal; S325. The thermocouple under test is unqualified, with internal short circuit, open circuit or poor contact; During heating, if the measured value V_diff is zero and does not move at all, there may be an internal short circuit; if the measured value V_diff overflows and displays an overload OL, there may be an internal open circuit; if the measured value V_diff fluctuates wildly, there may be poor contact.

[0011] Furthermore, the testing tool is a millivolt-level multimeter.

[0012] Furthermore, the temperature source is a hot air gun with a temperature of 300°C or higher, and the heating temperature of the temperature source is within the range of the reference thermocouple and the thermocouple being measured.

[0013] Furthermore, the ambient temperature range at the location of the reference end does not fluctuate by more than ±1℃.

[0014] Furthermore, both the reference thermocouple and the thermocouple under test are type K nickel-chromium / nickel-silicon thermocouples; the positive electrode of the type K nickel-chromium / nickel-silicon thermocouple is a nickel-chromium alloy containing 90% nickel and 10% chromium, and the negative electrode is a nickel-silicon alloy containing 95% nickel and 5% silicon.

[0015] Furthermore, the reference thermocouple is a thermocouple that meets user standards, is known to be in good condition, and has not experienced any attenuation in temperature response sensitivity.

[0016] The thermocouple performance testing method of the present invention has the following characteristics: 1. It eliminates the need to know the actual temperature value of the temperature source, avoiding the difficulty of obtaining a standard temperature source on-site, effectively reducing dependence on constant temperature sources, and lowering the difficulty and cost of testing; 2. Differential circuit design is used to suppress common-mode interference and improve test accuracy; 3. It focuses more on the "stability" of the measured value V_diff rather than the specific "standard" value of the temperature source. Therefore, it does not have high precision requirements for the test equipment. Only a voltage detection device with millivolt-level measurement accuracy is required. 4. The detection device is easy to connect and operate, and is compatible with various thermocouples including K-type, T-type, and S-type, as well as various scenarios, and can be widely applied; 5. The testing method can determine the dynamic response capability of the thermocouple under test, which is more in line with the actual use scenarios of thermocouples.

[0017] In summary, the thermocouple performance testing method of the present invention does not require a standard temperature source, is easy to operate, effectively reduces the dependence on a standard temperature source, and can intuitively judge the consistency of thermocouple performance. By using the differential method, it solves the problems of existing thermocouple testing relying on a standard uniform temperature source and being susceptible to common-mode interference, thus achieving accurate judgment. Attached Figure Description

[0018] The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this disclosure. It is obvious that the drawings described below are merely some embodiments of this disclosure, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort. Furthermore, the same reference numerals denote the same parts throughout the drawings.

[0019] Figure 1 This is a flowchart of the thermocouple performance testing method of the present invention; Figure 2 This is a circuit connection diagram of the detection device used in the thermocouple performance testing method of the present invention.

[0020] Table 1 shows the test results of the five sets of examples.

[0021] 1. Reference end; 2. Measuring end; 3. Reference thermocouple; 4. Thermocouple under test. Detailed Implementation

[0022] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0023] Example: Figure 1 As shown, the thermocouple performance testing method of this embodiment includes the following steps: S10. Construct and install the detection device; S11. Construct a detection device; like Figure 2 As shown, the testing device includes a testing tool, a temperature source, a reference thermocouple 3, and a thermocouple under test 4. The reference thermocouple 3 and the thermocouple under test 4 are of the same type. The testing tool is a voltage detection device with millivolt-level measurement accuracy. S12. Connect the differential circuit; Confirm the polarity of the compensating leads of the reference thermocouple 3 and the thermocouple under test 4; connect the positive terminal of the compensating lead of the reference thermocouple 3 to the negative terminal of the compensating lead of the thermocouple under test 4. The connection point is the common point of the entire differential circuit and also the reference terminal 1 of the temperature measurement system; then connect the negative terminal of the compensating lead of the reference thermocouple 3 to the negative terminal of the testing tool, and connect the positive terminal of the compensating lead of the thermocouple under test 4 to the positive terminal of the testing tool; finally, tightly attach and bind the measuring ends of the reference thermocouple 3 and the thermocouple under test 4 to ensure good contact. The binding point is also the measuring terminal 2 of the testing device. S13. Perform installation checks; Check each connection point to ensure it is secure and that there are no loose or disconnected connections. S20. Operate the detection device; S21. Record the baseline value; With the measuring end 2 of the detection device at room temperature and stable, record the reference value V_diff0 of the test tool. The reference value V_diff0 can be a positive value, a negative value, or zero that is close to 0. S22. Conduct dynamic heating tests; Heat measuring end 2 with a temperature source and observe the trend of the measured value V_diff until measuring end 2 reaches thermal equilibrium. When thermal equilibrium is reached, the measured value V_diff tends to stabilize, with fluctuations within 0.05mV. Record the measured value V_diff again. Remove the temperature source and allow it to cool naturally. Observe the changes in the measured value V_diff until measuring end 2 returns to its initial state. S23. Obtain the measured value; During dynamic heating and natural cooling processes, the measured value V_diff was recorded in real time. S30. Analyze the test results; S31. Compare and detect values; The difference ΔV_diff = measured value V_diff - reference value V_diff0; according to the requirement of ±1% accuracy of flow field temperature in wind tunnel test, the qualified threshold of difference ΔV_diff is set to ±0.2mV; after the test, the difference ΔV_diff is used to determine whether the tested thermocouple 4 can be put into use. S32. Determine the state of the thermocouple being tested (4); As shown in Table 1, the specific judgment process is as follows: S321. The tested thermocouple 4 is qualified; the temperature response characteristics of the tested thermocouple 4 and the reference thermocouple 3 are close. Variation of the difference ΔV_diff: During the heating and cooling process of measuring end 2, the difference ΔV_diff always fluctuates within a very narrow bandwidth near the reference value V_diff0. The absolute value of the difference ΔV_diff is <0.2mV. After thermal equilibrium, it tends to stabilize and can basically return to the reference value V_diff0 after cooling. Conclusion: The tested thermocouple 4 is qualified. The performance difference between the tested thermocouple 4 and the reference thermocouple 3 is within the allowable range, and the performance is acceptable. S322. The tested thermocouple 4 is unqualified; compared with the reference thermocouple 3, its temperature response characteristics are significantly lower, its performance has degraded and exceeds the qualified threshold. Changes in the difference ΔV_diff: During heating, the measured value V_diff changes significantly in the negative direction, far away from the reference value V_diff0, and the change exceeds the qualified threshold. After thermal equilibrium is reached, it tends to stabilize, and after cooling, it can basically return to the reference value V_diff0. Conclusion: Thermocouple 4 tested is unqualified. The thermoelectric conversion efficiency of thermocouple 4 has decreased, and its performance is unacceptable. S323. Tested thermocouple 4 is abnormal and unqualified: Compared with the reference thermocouple 3, its temperature response characteristics are significantly higher and its sensitivity is abnormally higher than that of the reference thermocouple 3. It is possible that the material composition of the tested thermocouple 4 has changed, causing the change to exceed the qualified threshold. Changes in the difference ΔV_diff: During heating, the measured value V_diff changes significantly in the positive direction, moving far away from the reference value V_diff0, and the change exceeds the qualified threshold. After thermal equilibrium is reached, it tends to stabilize, and after cooling, it can basically return to the reference value V_diff0. Conclusion: Thermocouple 4 tested is unqualified. Although the response result shows that it is good, it has deviated from the normal threshold, the consistency is broken, and the performance is unacceptable. S324. The tested thermocouple 4 is unqualified; its internal material is abnormal. The variation of the difference ΔV_diff: During heating, the measured value V_diff changes irregularly with temperature, showing jumps or sudden changes, indicating nonlinear mutations; Conclusion: Thermocouple 4 tested was unqualified, and its internal materials were abnormal; S325. The tested thermocouple 4 is unqualified, with internal short circuit, open circuit or poor contact; During heating, if the measured value V_diff is zero and does not move at all, there may be an internal short circuit; if the measured value V_diff overflows and displays an overload OL, there may be an internal open circuit; if the measured value V_diff fluctuates wildly, there may be poor contact.

[0024] Furthermore, the testing tool is a millivolt-level multimeter.

[0025] Furthermore, the temperature source is a hot air gun with a temperature of 300°C or higher, and the heating temperature of the temperature source is within the range of the reference thermocouple 3 and the thermocouple under test 4.

[0026] Furthermore, the ambient temperature range at the location of the reference terminal 1 does not fluctuate by more than ±1℃.

[0027] Furthermore, both the reference thermocouple 3 and the thermocouple under test 4 are K-type nickel-chromium-nickel-silicon thermocouples; the positive electrode of the K-type nickel-chromium-nickel-silicon thermocouple is a nickel-chromium alloy containing 90% nickel and 10% chromium, and the negative electrode is a nickel-silicon alloy containing 95% nickel and 5% silicon.

[0028] Furthermore, the reference thermocouple 3 is a thermocouple that meets user standards, is known to be in good condition, and has not experienced any attenuation in temperature response sensitivity.

[0029] In this embodiment, the multimeter is set to the mV range. The measuring end 2 is slowly and evenly heated with a hot air gun. The changing trend of the multimeter reading, i.e. the measured value V_diff, is observed and recorded. Heating is stopped when the temperature of the hot air gun reaches 300°C. The natural change in the temperature of the measuring end 2 is observed. If the fluctuation of the multimeter reading is within 0.05mV, it is determined that the measuring end 2 has reached thermal equilibrium.

[0030] Table 1

[0031] Although the embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. For those skilled in the art, all features disclosed in the present invention, or all steps in all methods or processes disclosed, except for mutually exclusive features and / or steps, can be combined in any way without departing from the principles of the present invention. The present invention is not limited to the specific details and illustrations shown and described herein.

Claims

1. A method for testing thermocouple performance, characterized in that, The thermocouple performance testing method includes the following steps: S10. Construct and install the detection device; S11. Construct a detection device; The testing device includes a testing tool, a temperature source, a reference thermocouple (3) and a thermocouple under test (4), wherein the reference thermocouple (3) and the thermocouple under test (4) are of the same type; the testing tool is a voltage detection device with millivolt-level measurement accuracy; S12. Connect the differential circuit; Confirm the polarity of the compensating wires of the reference thermocouple (3) and the thermocouple under test (4); connect the positive terminal of the compensating wire of the reference thermocouple (3) to the negative terminal of the compensating wire of the thermocouple under test (4). The connection point is the common point of the entire differential circuit and also the reference end (1) of the temperature measurement system; then connect the negative terminal of the compensating wire of the reference thermocouple (3) to the negative terminal of the test tool, and connect the positive terminal of the compensating wire of the thermocouple under test (4) to the positive terminal of the test tool; finally, tightly attach and bind the measuring ends of the reference thermocouple (3) and the thermocouple under test (4) to ensure good contact. The binding point is also the measuring end (2) of the detection device. S13. Perform installation checks; Check each connection point to ensure it is secure and that there are no loose or disconnected connections. S20. Operate the detection device; S21. Record the baseline value; Under the condition that the measuring end (2) of the detection device is at room temperature and stable, record the reference value V_diff0 of the test tool. The reference value V_diff0 is a positive value, a negative value or zero that is close to 0. S22. Conduct dynamic heating tests; Heat the measuring end (2) with a temperature source and observe the trend of the measured value V_diff until the measuring end (2) reaches thermal equilibrium. When thermal equilibrium is reached, the measured value V_diff tends to stabilize and the fluctuation range is within 0.05mV. Record the measured value V_diff again. Remove the temperature source and allow it to cool down naturally. Observe the change of the measured value V_diff until the measuring end (2) returns to its initial state. S23. Obtain the measured value; During dynamic heating and natural cooling processes, the measured value V_diff was recorded in real time. S30. Analyze the test results; S31. Compare and detect values; The difference ΔV_diff = measured value V_diff - reference value V_diff0; according to the requirement of ±1% accuracy of wind tunnel test flow field temperature, the qualified threshold of difference ΔV_diff is set to ±0.2mV; after the test, the difference ΔV_diff is used to determine whether the thermocouple (4) under test can be put into use; S32. Determine the state of the thermocouple (4) being tested; The specific judgment process is as follows: S321. The tested thermocouple (4) is qualified; the temperature response characteristics of the tested thermocouple (4) and the reference thermocouple (3) are close; The variation of the difference ΔV_diff: During the heating and cooling process of the measuring end (2), the difference ΔV_diff always fluctuates within a very narrow bandwidth near the reference value V_diff0. The absolute value of the difference ΔV_diff is <0.2mV. After thermal equilibrium, it tends to stabilize and can basically return to the reference value V_diff0 after cooling. Conclusion: The tested thermocouple (4) is qualified. The performance difference between the tested thermocouple (4) and the reference thermocouple (3) is within the allowable range and the performance is acceptable. S322. The tested thermocouple (4) is unqualified; compared with the reference thermocouple (3), its temperature response characteristics are significantly lower, its performance degrades and exceeds the qualified threshold. Changes in the difference ΔV_diff: During heating, the measured value V_diff changes significantly in the negative direction, far away from the reference value V_diff0, and the change exceeds the qualified threshold. After thermal equilibrium is reached, it tends to stabilize, and after cooling, it can basically return to the reference value V_diff0. Conclusion: The tested thermocouple (4) is unqualified. The thermoelectric conversion efficiency of the tested thermocouple (4) has decreased and its performance is unacceptable. S323. The tested thermocouple (4) is abnormal and unqualified: Compared with the reference thermocouple (3), its temperature response characteristics are significantly higher and its sensitivity is abnormally higher than that of the reference thermocouple (3). It is possible that the material composition of the tested thermocouple (4) has changed, resulting in the change exceeding the qualified threshold. Changes in the difference ΔV_diff: During heating, the measured value V_diff changes significantly in the positive direction, moving far away from the reference value V_diff0, and the change exceeds the qualified threshold. After thermal equilibrium is reached, it tends to stabilize, and after cooling, it can basically return to the reference value V_diff0. Conclusion: The tested thermocouple (4) is unqualified. Although the response result shows that it is good, it has deviated from the normal threshold, the consistency is destroyed, and the performance is unacceptable. S324. The tested thermocouple (4) is unqualified, and its internal material is abnormal; The variation of the difference ΔV_diff: During heating, the measured value V_diff changes irregularly with temperature, showing jumps or sudden changes, indicating nonlinear mutations; Conclusion: The tested thermocouple (4) is unqualified, and its internal materials are abnormal; S325. The thermocouple under test (4) is unqualified, with internal short circuit, open circuit or poor contact; During heating, if the measured value V_diff is zero and does not move at all, there may be an internal short circuit; if the measured value V_diff overflows and displays an overload OL, there may be an internal open circuit; if the measured value V_diff fluctuates wildly, there may be poor contact.

2. The thermocouple performance testing method according to claim 1, characterized in that, The testing tool mentioned is a millivolt-level multimeter.

3. The thermocouple performance testing method according to claim 1, characterized in that, The temperature source is a hot air gun with a temperature of 300°C or higher, and the heating temperature of the temperature source is within the range of the reference thermocouple (3) and the thermocouple under test (4).

4. The thermocouple performance testing method according to claim 1, characterized in that, The ambient temperature range at the location of the reference end (1) shall not exceed ±1℃.

5. The thermocouple performance testing method according to claim 1, characterized in that, The reference thermocouple (3) and the thermocouple under test (4) are both K-type nickel-chromium-nickel-silicon thermocouples; the positive electrode of the K-type nickel-chromium-nickel-silicon thermocouple is a nickel-chromium alloy containing 90% nickel and 10% chromium, and the negative electrode is a nickel-silicon alloy containing 95% nickel and 5% silicon.

6. The thermocouple performance testing method according to claim 1, characterized in that, The reference thermocouple (3) is a thermocouple that meets the user's usage standards and is known to be in good condition, and has not experienced any temperature response sensitivity decay.

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