A thermocouple response time measuring device and method

Abstract

The present invention discloses a thermocouple response time measuring device and method, including a constant temperature and constant speed water tank. A rotating blade is arranged in the constant temperature and constant speed water tank, and a plurality of overflow pipes are uniformly arranged on its side wall; above the constant temperature and constant speed water tank, there is a thermocouple under test driven by a robotic arm to move up and down; the output signal of the thermocouple under test passes through an ice bottle and then through a signal amplifier and is input into a digital oscilloscope; the time constant of the thermocouple under test is the time difference between the moments when its output temperature reaches 10% and 73.4% of the step quantity respectively. The overflow pipes of the measuring device of the present invention improve the flow field stability, and the signal amplifier improves the response speed of the signal processing and acquisition part. The method of calculating the response time through the time difference of different step percentages avoids the error caused by the difficult measurement of the initial moment: it provides an accurate and reliable response time measuring device and method for fast response thermocouples such as the grounded type and the exposed junction type.

Description

Technical Field

[0001] The present invention relates to the technical field of temperature sensor response time measurement, and specifically to a thermocouple response time measurement device and method. Background Technique

[0002] When a contact temperature sensor measures the temperature of a fluid with a rapidly changing temperature, it generally cannot immediately respond to the measured temperature and requires a certain amount of time to reach the thermal equilibrium state. Only when the temperature sensor reaches thermal equilibrium with the measured fluid, the temperature value reflected by the sensor is the temperature of the measured fluid. The dynamic response characteristic of the sensor refers to the relationship between the temperature of the temperature sensor and the temperature increment of the measured medium. In actual calibration, the response time is commonly used to describe the response of the temperature sensor to a step temperature. The response time refers to the time required for the output temperature of the temperature sensor to change to a certain specified percentage of the step amount of the fluid temperature when the fluid temperature undergoes a step change. The time required to reach 63.2% of the step temperature amount is called the time constant.

[0003] The dynamic response calibration of the temperature sensor, that is, the sensor response time calibration process mainly includes: generating a stable calibration working condition (stable velocity field, temperature field); making the temperature sensor receive a temperature step excitation; collecting the response signal of the sensor under calibration to the step by the test system, and calculating the response time.

[0004] Thermocouples are widely used in industrial temperature measurement due to their mature manufacturing process and low cost. Thermocouples can be classified into shell-connected type, armored type, and exposed-end type according to their structural forms. The temperature measurement point of the exposed-end thermocouple is in direct contact with the measured medium, and it has a fast response speed. The response time is a key parameter for its application.

[0005] The invention patent with the Chinese patent publication number CN110057472B provides a temperature sensor response time measurement device and method. It uses the moment when a voltage step is formed when the temperature sensor is thrown into water and contacts the water surface as the initial moment, and uses the moment when the output temperature of the temperature sensor changes to a specified percentage of the temperature step as the end moment. The time difference between the end moment and the initial moment is the response time. This method of determining the initial moment by using a voltage signal step in series with a constant temperature and constant speed water tank will interfere with the output thermal electromotive force of exposed-end and shell-connected thermocouples and cannot be used for measuring the response time of such thermocouples.

[0006] The paper (Sun Hongjian, Li Wenjun, Li Jiaqi, et al. A Thermocouple Time Constant Test System [J]. Journal of China Jiliang University, 2017, 28(2): 146-152.) captures the initial moment of the thermal response time by symmetrically welding laser transmissive photoelectric sensors on the inner wall of the top of the constant temperature bath. During the process of throwing the temperature sensor to be measured into the constant temperature bath, the optical path will be blocked, so as to capture the initial moment of the thermal response time. In the actual test process, due to the rotation of the medium in the constant temperature bath, the liquid level is concave with a lower center and higher periphery, and the optical path cannot be flush with the liquid level, so there is a deviation between the obtained initial moment and the actual moment when the temperature sensor to be measured contacts the water surface.

[0007] During the test process of the response time of the grounded and exposed junction thermocouples, it is difficult to accurately measure the initial moment, resulting in a large measurement error of the response time, which is a difficult problem encountered in the measurement of the response time of such temperature sensors. Summary of the Invention

[0008] In view of the deficiencies of the prior art, the present invention provides a thermocouple response time measurement device and method, which have the advantages of accurate measurement and rapid response.

[0009] To achieve the above object, the present invention provides the following technical solution: A thermocouple response time measurement method, the method is carried out by using a thermocouple response time measurement device, the thermocouple response time measurement device includes a constant temperature and constant speed water bath, and a plurality of overflow pipes are uniformly arranged on the side wall of the constant temperature and constant speed water bath. The overflow pipes are respectively communicated with the top and bottom of the side wall of the constant temperature and constant speed water bath through an overflow inlet and a communication hole. The diameter of the communication hole is significantly smaller than the diameter of the overflow inlet. A rotating blade is arranged in the constant temperature and constant speed water bath, and the position of the rotating blade is higher than the position of the communication hole;

[0010] Above the constant temperature and constant speed water bath, there is a thermocouple to be measured driven by a robotic arm to move up and down. The extension wire of the thermocouple to be measured is inserted into an ice bottle. The output end of the ice bottle is electrically connected to the input end of a signal amplifier, and the output end of the signal amplifier is electrically connected to the input end of a digital oscilloscope;

[0011] The measuring end of the thermocouple to be measured faces the air outlet of a set fan;

[0012] The method includes the following steps:

[0013] S1. Turn on the constant temperature and constant speed water bath, set the temperature and flow rate, and make the water temperature and flow rate stable at the set values; fix the thermocouple to be measured on the slider;

[0014] S2. Turn on the fan, robotic arm, signal amplifier and digital oscilloscope;

[0015] S3. The digital oscilloscope starts to collect and store signals, and starts the robotic arm to throw the thermocouple to be measured into the water;

[0016] S4. Read the time differences at different step percentages on the response curve of the digital oscilloscope. That is, the moment when the output temperature of the thermocouple under test reaches 10% of the step temperature is the initial moment of the response time, and the moment when the output temperature reaches 73.4% of the step temperature is the termination moment of the response time. The time difference between the termination moment and the initial moment is the time constant of the thermocouple under test;

[0017] S5. Perform at least 3 measurements, and the deviation between the 3 measurement results and the mean value is less than 10%. Otherwise, repeat the operation until the requirements are met;

[0018] S6. After the measurement is completed, remove the thermocouple under test and turn off the power supply.

[0019] As a preferred technical solution of the present invention, the robotic arm includes a slider and a guide rail. The thermocouple under test is detachably installed on the slider, and the slider is slidably arranged on the guide rail.

[0020] As a preferred technical solution of the present invention, the response time of the combination of the signal amplifier and the digital oscilloscope is less than 10% of the response time of the thermocouple under test; the time resolution of the combination of the signal amplifier and the digital oscilloscope is less than 1% of the response time of the thermocouple under test.

[0021] Compared with the prior art, the present invention provides a device and method for measuring the response time of a thermocouple, having the following beneficial effects:

[0022] 1. In this thermocouple response time measurement device, by providing an overflow pipe on the constant temperature and constant speed water tank, it avoids water overflowing outside the constant temperature and constant speed water tank due to rotation. An overflow inlet is provided at the top of the side wall of the constant temperature and constant speed water tank, which can effectively control the liquid level height. The communication hole between the overflow pipe and the constant temperature and constant speed water tank is located below the rotating blade, avoiding disturbing the rotating flow field. The design that the diameter of the communication hole is significantly smaller than the diameter of the overflow inlet can ensure a large overflow inflow volume and effectively reduce the disturbance to the rotating flow field.

[0023] 2. In this thermocouple response time measurement device, by applying a forced convection fan to the measurement end of the thermocouple under test, it ensures the consistency and stability of the measurement end and the room temperature before the thermocouple under test is thrown into the water, and reduces the interference of the hot steam in the constant temperature and constant speed water tank on the initial temperature of the response time test of the thermocouple under test. The extension wire of the thermocouple under test is inserted into an ice bottle, reducing the temperature measurement error of the thermocouple under test and being able to reduce the uncertainty caused by the temperature error during the measurement of its response time.

[0024] 3. In this thermocouple response time measurement device, by using a signal amplifier to amplify the thermal electromotive force of the thermocouple under test, it reduces the time delay caused by using a temperature transmitter in the traditional technology and improves the ability of the device to measure fast-response bare-ended and grounded thermocouples.

[0025] 4. The above measures of the thermocouple response time measuring device ensure the safety of the device, the stability of the flow field, accurate temperature measurement, rapid response, and improve the measurement accuracy and energy level of the response time.

[0026] 5. The thermocouple response time measurement method calculates the response time of the measured thermocouple by using the time difference of different step percentages, avoids the error caused by the confirmation at time zero, improves the measurement accuracy of the response time, and does not require additional devices, reducing the equipment investment and operation and maintenance costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a schematic diagram of the overall structure of the present invention;

[0028] Figure 2 is a flowchart of the measurement method of the present invention;

[0029] Figure 3 is a schematic diagram of the thermocouple response time measurement curve and the corresponding points of different step percentages of the present invention.

[0030] In the figure: 1. Constant temperature and constant speed water tank; 2. Overflow pipe; 3. Overflow inlet; 4. Communication hole; 5. Rotating blade; 6. Measured thermocouple; 7. Slide block; 8. Guide rail; 9. Robot arm; 10. Extension wire; 11. Ice bottle; 12. Signal amplifier; 13. Digital oscilloscope; 14. Fan. DETAILED DESCRIPTION OF THE EMBODIMENTS Embodiment

[0031] Please refer to Figure 1 , a thermocouple response time measuring device, including a constant temperature and constant speed water tank 1. A rotating blade 5 is arranged in the constant temperature and constant speed water tank 1. The rotating blade 5 is driven by an external variable frequency motor to rotate. Different rotation speeds can form flow fields with different rotation speeds in the constant temperature and constant speed water tank 1;

[0032] In this embodiment, the temperature of the constant temperature and constant speed water tank 1 is measured by a common platinum thermal resistance, heated by an electric heating rod, and forms a closed-loop control by a PID temperature controller;

[0033] A plurality of overflow pipes 2 (in this embodiment, 1-8 overflow pipes 2 can be arranged) are uniformly arranged on the side wall of the constant temperature and constant speed water tank 1. The overflow pipes 2 are respectively communicated with the top and bottom of the side wall of the constant temperature and constant speed water tank 1 through an overflow inlet 3 and a communication hole 4. The diameter of the communication port 4 is significantly smaller than the diameter of the overflow inlet 3. The rotating position of the rotating blade 5 is higher than the opening position of the communication hole 4;

[0034] By setting an overflow pipe 2 on the constant temperature and constant speed water tank 1, it is avoided that water overflows outside the constant temperature and constant speed water tank 1 due to rotation. An overflow inlet 3 is arranged at the top of the side wall of the constant temperature and constant speed water tank 1, which can effectively control the liquid level height. The communication port 4 between the overflow pipe 2 and the constant temperature and constant speed water tank 1 is located below the rotating blade 5, avoiding disturbing the rotating flow field. In this embodiment, the diameter of the communication port 4 is significantly smaller than the diameter of the overflow inlet 3, which can not only ensure a large overflow inflow volume but also effectively reduce the disturbance to the rotating flow field.

[0035] Above the constant temperature and constant speed water tank 1, a measured thermocouple 6 driven by a robotic arm 9 to move up and down is movably arranged. In this embodiment, the robotic arm 9 includes a slider 7 and a guide rail 8. The measured thermocouple 6 is detachably installed on the slider 7. The slider 7 is slidably arranged on the guide rail 8. The slider 7 can be driven to move up and down by the cooperation of a motor and a lead screw, or can also be driven to move up and down by a cylinder, which can be set according to actual needs, and can realize the throwing of the measured temperature sensor 6 into the water.

[0036] In this embodiment, the extension wire 10 of the measured thermocouple 6 is inserted into the ice bottle 11, reducing the temperature measurement error of the measured thermocouple and being able to reduce the uncertainty caused by temperature error during the measurement of its response time.

[0037] The output end of the ice bottle 11 is electrically connected to the input end of the signal amplifier 12, and the output end of the signal amplifier 12 is electrically connected to the input end of the digital oscilloscope 13. The combined response time of the signal amplifier 12 and the digital oscilloscope 13 is less than 10% of the thermal response time of the measured thermocouple 6, and the time resolution of the combination of the signal amplifier 12 and the digital oscilloscope 13 is less than 1% of the thermal response time of the measured temperature sensor 6. By using the signal amplifier 12 to amplify the thermal electromotive force of the measured thermocouple, the time delay caused by using a temperature transmitter in the traditional technology is reduced. In this embodiment, the response time of the digital oscilloscope 13 is in the nanosecond level, which can fully meet the measurement requirements of the response time of fast-response thermocouples: improving the ability of the device to measure fast-response exposed-junction and grounded-junction thermocouples.

[0038] It further includes a fan 14. The measuring end of the measured temperature sensor 6 faces the air outlet of the fan 14, ensuring the consistency and stability of the measuring end with the room temperature before the measured thermocouple 6 is thrown into the water, and reducing the interference of the hot steam in the constant temperature and constant speed water tank 1 to the initial temperature of the response time test of the measured thermocouple 6.

[0039] The above measures in this embodiment ensure the safety, stable flow field, accurate temperature measurement, and rapid response of the device, improving the measurement accuracy and energy level of the response time.

[0040] As Figure 2 shown, this embodiment also provides a method for measuring the response time of a thermocouple. The specific steps are as follows:

[0041] Step 1: Turn on the constant temperature and constant speed water tank 1, set the temperature and flow rate, and stabilize the water temperature and flow rate at the set values; fix the thermocouple under test 6 on the slider 7;

[0042] Step 2: Turn on the fan 14, the robotic arm 9, the signal amplifier 12, and the digital oscilloscope 13;

[0043] Step 3: The digital oscilloscope 13 starts to collect and store signals, and starts the robotic arm 9 to throw the thermocouple under test into the water;

[0044] Step 4: Read the time differences at different step percentages on the response curve of the digital oscilloscope 13. That is, the moment when the output temperature of the thermocouple under test 6 reaches 10% of the step temperature amount is the initial moment of the thermal response time, and the moment when the output temperature reaches 73.4% of the step temperature amount is the termination moment of the thermal response time. The time difference between the termination moment and the initial moment is the time constant of the thermocouple under test 6;

[0045] Step 5: Perform at least 3 measurements, and the deviation between the 3 measurement results and the average value is less than 10%. Otherwise, repeat the operation until the requirements are met;

[0046] Step 6: After the measurement is completed, remove the thermocouple under test 6 and turn off the power supply.

[0047] In this embodiment, by calculating the response time of the thermocouple under test 6 using the time differences at different step percentages, the error caused by the confirmation of the 0 moment is avoided, the measurement accuracy of the response time is improved, and no additional devices are required, reducing the equipment investment and operation and maintenance costs;

[0048] In this embodiment, the inner diameter of the constant temperature and constant speed water tank 1 is 60 cm, the rotational speed of the rotating blade 5 is 38.2 r / min, the linear velocity at a radius of 25 cm is 1 m / s. The thermocouple under test 6 is vertically thrown into the water at this radius. The downward movement speed of the slider 7 is set to 2 m / s, the ambient temperature is 25 °C, the water temperature is set to 75 °C, the thermocouple under test 6 is a K-type bare-ended thermocouple with an outer diameter of 6 mm. In the range of 25 °C to 75 °C, it can be approximately considered that the thermal electromotive force of the thermocouple is linearly related to the temperature. The output signal of the thermocouple measured on the digital oscilloscope 13 is as Figure 3 shown;

[0049] Figure 3Among them, time 0 represents the moment when the digital oscilloscope 13 starts to collect data. The initial value of the output signal of the thermocouple is 3.0V, the termination value is 3.5V, and the step amount is 0.5V. The time constant of the thermocouple refers to the response time required when its output changes to 63.2% of this step amount. The initial moment of the time constant is the moment when the step occurs, and the termination moment is the moment when the thermocouple output changes to 63.2% of the step. However, the definition of the initial moment is difficult to operate in the existing technology. As introduced in the background technology, the electrical parameter method will interfere with the output thermal electromotive force of the butt - shell type and exposed - end type thermocouples, and the optical path method cannot be flush with the concave liquid surface, resulting in a large error in the confirmation of the initial moment. In addition, due to the thermal inertia of the measured thermocouple 6, after it is thrown into water, its output thermal electromotive force will not rise immediately but has a certain hysteresis. Therefore, taking the moment when its output thermal electromotive force starts to rise as the initial moment will also cause a large error.

[0050] The present invention proposes a method for calculating the response time of the measured thermocouple 6 by using the time difference of different step percentages. Figure 3 , P1 represents the voltage value when the thermocouple output changes to 10% of the step, that is, 3.050V, and the corresponding moment T1 is 0.704s; P2 represents the voltage value when the thermocouple output changes to 73.4% of the step, that is, 3.367V, and the corresponding moment T2 is 1.506s. The difference between T2 and T1 is equal to 0.802s, that is, the time constant of the measured K - type exposed - end thermocouple is 0.802s;

[0051] To verify the measurement error of this embodiment, by measuring the structural dimensions and material thermal physical property parameters of the measured thermocouple 6, a three - dimensional numerical simulation model of the measured thermocouple 6 is established. The calculation results show that the time constant of the measured thermocouple is 0.799s. Therefore, the measurement error of this embodiment is 0.4%, indicating that the measurement method provided by the present invention can accurately measure the response time of the measured thermocouple 6.

[0052] The working principle and usage process of the present invention:

[0053] By setting an overflow pipe 2 on the constant - temperature and constant - speed water tank 1, it is avoided that water overflows outside the constant - temperature and constant - speed water tank 1 due to rotation. By setting an overflow inlet 3 at the top of the side wall of the constant - temperature and constant - speed water tank 1, the liquid level height can be effectively controlled. The communication hole 4 between the overflow pipe 2 and the constant - temperature and constant - speed water tank 1 is located below the rotating blade 5, avoiding disturbing the rotating flow field. The design that the diameter of the communication hole 4 is significantly smaller than the diameter of the overflow inlet 3 can ensure a large overflow inflow volume and effectively reduce the disturbance to the rotating flow field;

[0054] By applying a forced convection fan 14 to the measurement end of the thermocouple 6 under test, the consistency and stability between the measurement end of the thermocouple 6 under test and the room temperature are ensured before it is thrown into the water, and the interference of the hot steam in the constant temperature and constant speed water tank 1 to the initial temperature of the response time test of the thermocouple 6 under test is reduced. The extension wire 10 of the thermocouple 6 under test is inserted into the ice bottle 11, reducing the temperature measurement error of the thermocouple 6 under test and being able to reduce the uncertainty caused by the temperature error during the measurement of its response time;

[0055] By using a signal amplifier 12 to amplify the thermal electromotive force of the thermocouple 6 under test, the time delay caused by using a temperature transmitter in the traditional technology is reduced, and the ability of the device to measure fast-response bare-ended and grounded thermocouples is improved. The above measures ensure the safety of the device, stable flow field, accurate temperature measurement, rapid response, and improve the measurement accuracy and energy level of the response time;

[0056] By using the time difference of different step percentages to calculate the response time of the thermocouple 6 under test, the error caused by the confirmation at time 0 is avoided, the measurement accuracy of the thermal response time is improved, and no additional devices are required, reducing the equipment investment and operation and maintenance costs;

[0057] In industry, sometimes it is necessary to measure the response time when the output temperature of the temperature sensor changes to 50% of the step amount of the fluid temperature. At this time, a step percentage different from that of this embodiment needs to be selected to calculate the corresponding response time. The response time measurement method based on different step percentages disclosed in the present invention can also be used for the response time test of resistance temperature sensors.

Claims

1. A method for measuring the response time of a thermocouple, characterized in that: the method is carried out by using a thermocouple response time measuring device, the thermocouple response time measuring device includes a constant temperature and constant speed water tank (1), a plurality of overflow pipes (2) are uniformly arranged on the side wall of the constant temperature and constant speed water tank (1), the overflow pipes (2) are respectively communicated with the top and bottom of the side wall of the constant temperature and constant speed water tank (1) through an overflow inlet (3) and a communication hole (4), the diameter of the communication hole (4) is significantly smaller than the diameter of the overflow inlet (3), a rotating blade (5) is arranged in the constant temperature and constant speed water tank (1), and the position of the rotating blade (5) is higher than the position of the communication hole (4); above the constant temperature and constant speed water tank (1), there is a thermocouple under test (6) driven by a robotic arm (9) to move up and down, the extension wire (10) of the thermocouple under test (6) is inserted into an ice bottle (11), the output end of the ice bottle (11) is electrically connected to the input end of a signal amplifier (12), and the output end of the signal amplifier (12) is electrically connected to the input end of a digital oscilloscope (13); the measuring end of the thermocouple under test (6) faces the air outlet of a fan (14) arranged opposite; the method includes the following steps: S1. Turn on the constant temperature and constant speed water tank (1), set the temperature and flow rate, and make the water temperature and flow rate stable at the set values; fix the thermocouple under test (6) on a slider (7); S2. Turn on the fan (14), the robotic arm (9), the signal amplifier (12) and the digital oscilloscope (13); S3. The digital oscilloscope (13) starts to collect and store signals, and starts the robotic arm (9) to throw the thermocouple under test into the water; S4. Read the time difference at different step percentages on the response curve on the digital oscilloscope (13), that is, the moment when the output temperature of the thermocouple under test (6) reaches 10% of the step temperature amount is the initial moment of the response time, the moment when the output temperature reaches 73.4% of the step temperature amount is the termination moment of the response time, and the time difference between the termination moment and the initial moment is the time constant of the thermocouple under test (6); S5. Perform at least 3 measurements, and the deviation between the 3 measurement results and the mean value is less than 10%, otherwise repeat the operation until the requirements are met; S6. After the measurement is completed, remove the thermocouple under test (6) and turn off the power supply.

2. A method for measuring the response time of a thermocouple according to claim 1, characterized in that: the robotic arm (9) includes a slider (7) and a guide rail (8), the thermocouple under test (6) is detachably installed on the slider (7), and the slider (7) is slidably arranged on the guide rail (8).

3. A method for measuring the response time of a thermocouple according to claim 1, characterized in that: the response time of the combination of the signal amplifier (12) and the digital oscilloscope (13) is less than 10% of the response time of the thermocouple under test (6); the time resolution of the combination of the signal amplifier (12) and the digital oscilloscope (13) is less than 1% of the response time of the thermocouple under test (6).

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