A millisecond thermocouple rise time calibration device

Abstract

The application discloses a millisecond thermocouple rise time calibration device and relates to the technical field of thermocouple calibration.The device comprises a constant-temperature constant-speed tank, an ejection system and a signal processing and collecting system; the bottom of the constant-temperature constant-speed tank is provided with an electromagnetic stirrer, and the lateral wall is provided with an electric heating ring and a thermal resistance thermometer; the ejection system comprises a guide rail, a sliding block and a compression spring, the sliding block is installed on the guide rail, a clamp is arranged on the sliding block to fix a measured thermocouple, an extension plate is further arranged on the sliding block, and a mandrel is fixedly connected to the extension plate; when the sliding block moves to the upper portion of the guide rail, the mandrel is sleeved into the compression spring, the compression spring is compressed and shortened, the positioning plate is sleeved with a handle to fix the sliding block and prevent the sliding block from moving downward; after the handle is removed, the positioning block rotates, the compressed spring generates elastic force to push the sliding block to move downward at a high speed, and the sliding block stops at a rubber buffer pad. The ejection force of the compression spring is used to throw the measured thermocouple into the medium rapidly, and the error of millisecond thermocouple rise time calibration caused by temperature step time is reduced.

Description

Technical Field

[0001] This invention relates to the field of thermocouple calibration technology, and more particularly to a millisecond-level thermocouple rise time calibration device. Background Technology

[0002] A thermocouple is a thermometer made of two conductors of different materials based on the Seebeck effect. Thermocouples have advantages such as low inertia, high accuracy, and a wide temperature measurement range, making them the most widely used and numerous thermoelectric thermometers. As a contact thermometer, when measuring the temperature of fluids that change rapidly, a thermocouple cannot immediately reflect the measured temperature; it requires a certain amount of time to reach thermal equilibrium.

[0003] The dynamic response characteristics of a thermocouple refer to the relationship between the thermocouple's output temperature and the temperature increment of the measured medium. The dynamic response characteristics are often described by using the drop test to achieve the time response caused by a step change in the input temperature. The step response time refers to the time it takes for the output to reach a specified percentage of the step change when the input undergoes a step change. The transfer function of a thermocouple can be treated as a first-order linear system, and the time required for the output to reach 63.2% of the step change is called the time constant.

[0004] In step response testing of millisecond-level fast-response thermocouples, the exact moment of the input temperature step change is often difficult to define. Rise time, for a step response, refers to the time interval from the moment the output signal reaches a specified small percentage of the step amount to the moment it first reaches a specified large percentage of the step amount. It is typically defined as the time it takes for the output signal to rise from 10% to 90% of the step amount. By not measuring the exact moment of the step change, rise time avoids the measurement errors it introduces and can more accurately describe the dynamic response characteristics of millisecond-level thermocouples.

[0005] Thermocouple dynamic response calibration, also known as step response time calibration, mainly includes: generating a stable calibration environment (stable velocity field and temperature field); subjecting the thermocouple to a temperature step excitation; and having the test system acquire the response signal of the thermocouple to the step and calculate the response time. The time required to generate the temperature step should be less than 10% of the response time of the thermocouple being calibrated for the calibration result to be valid.

[0006] A Chinese invention patent (authorization announcement number CN110617906B) discloses a dynamic response calibration device and step time measurement method for a temperature sensor, which generates a temperature step by throwing the temperature sensor under test into a constant temperature and speed water bath using a robotic arm. However, the maximum movement speed of robotic arms such as lead screw modules and linear motor modules is usually no more than 5 m / s, and the time required to generate a temperature step is relatively long. This cannot meet the technical requirements for dynamic response calibration of millisecond-level fast-response thermocouples. The inability to quickly generate a temperature step is currently a key challenge in millisecond-level thermocouple dynamic response calibration. Summary of the Invention

[0007] The purpose of this invention is to provide a millisecond-level thermocouple rise time calibration device, which solves the aforementioned technical problems.

[0008] To achieve the above objectives, the present invention provides the following technical solution: a millisecond-level thermocouple rise time calibration device, comprising a constant temperature and speed tank, wherein an electromagnetic stirrer is installed at the bottom of the constant temperature and speed tank, and the rotation speed of the electromagnetic stirrer is controlled by a DC motor speed controller; an electric heating coil is installed on the side wall of the constant temperature and speed tank, and a resistance temperature detector (RTD) thermometer is installed inside the constant temperature and speed tank. The RTD thermometer is L-shaped, and the temperature measuring point of the RTD thermometer is at the same height as the temperature measuring point when the thermocouple being tested is thrown into the constant temperature and speed tank at its termination position, and both are equidistant from the central axis of the constant temperature and speed tank; the RTD thermometer is electrically connected to the signal input terminal of a temperature controller, and the power output terminal of the temperature controller is connected to the electric heating coil. The heating coil is electrically connected; the temperature controller adjusts the power of the electric heating coil according to the deviation between the set temperature and the temperature measured by the resistance thermometer, so that the medium temperature is stabilized at the set value; it also includes a guide rail and a slider, the slider is mounted on the guide rail and can move linearly on the guide rail, a clamp is fixedly mounted on one side of the slider, and the thermocouple to be measured is fixedly mounted on the clamp; an extension plate is also fixedly mounted on the other side of the slider, the extension plate is provided with a spindle, a positioning plate is provided below the slider, the positioning plate is sleeved by the handle and does not rotate, so as to support the slider and prevent it from moving downward; the guide rail is provided with a lower baffle and an upper baffle, the upper baffle is provided with a compression spring, and a rubber buffer pad is fixedly mounted above the lower baffle;

[0009] It also includes a data acquisition instrument, wherein the output end of the thermocouple under test is inserted into the zero-point thermostat, and is connected to the signal amplifier via a copper wire and then to the data acquisition instrument.

[0010] The rise time of the thermocouple under test is the time it takes for its output temperature to rise from 10% to 90% of the step value; when the step time is less than 1 / 10 of the rise time of the thermocouple under test, the measurement result is valid; otherwise, the measurement result is invalid.

[0011] Preferably, when the slider moves to the upper part of the guide rail, the mandrel is fitted into the compression spring, and the compression spring is compressed.

[0012] Preferably, the medium in the constant temperature and constant speed tank is water, heat transfer oil, or molten salt.

[0013] Compared with related technologies, the millisecond-level thermocouple rise time calibration device provided by the present invention has the following beneficial effects:

[0014] This invention provides a millisecond-level thermocouple rise time calibration device. By installing an electromagnetic stirrer at the bottom of a constant temperature and speed tank, torque is transmitted through non-contact magnetic force without a drive shaft. Static seals are used instead of dynamic seals to ensure that the constant temperature and speed tank is leak-free. An electric heating coil is set on the side wall of the constant temperature and speed tank, which enhances turbulence at the side wall surface and improves the temperature uniformity inside the tank.

[0015] This invention provides a millisecond-level thermocouple rise time calibration device, which offers a rapid insertion system based on the ejection force of a compression spring. This significantly improves the insertion speed of the thermocouple under test and shortens the time for temperature step generation. Specifically, before testing, the slider is moved to the upper part of the guide rail, and the mandrel is fitted into the compression spring. The compression spring stores ejection force under compression, and a positioning plate located below the slider is fitted into the handle to prevent the slider from moving downwards. During testing, the handle is quickly removed, and the compression spring pushes the slider downwards, causing it to be thrown into the constant temperature and speed bath at high speed, thus shortening the time for temperature step generation. This device can be used for millisecond-level thermocouple rise time calibration. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the overall structure of the thermocouple under test in the initial position according to the present invention;

[0017] Figure 2 This is a schematic diagram of the overall structure of the thermocouple under test in the present invention when it is in the termination position;

[0018] Figure 3 This is a schematic diagram of the clamp structure of the present invention;

[0019] Figure 4 This is a left view of the extension plate structure of the present invention;

[0020] Figure 5 This is a left view of the positioning plate structure of the present invention;

[0021] Figure 6 This is a top view of the handle structure of the present invention.

[0022] In the diagram: 1. Constant temperature and speed bath; 2. Electromagnetic stirrer; 3. DC motor speed controller; 4. Electric heating coil; 5. Resistance thermometer; 6. Temperature controller; 7. Lower baffle; 8. Rubber buffer pad; 9. Guide rail; 10. Positioning plate; 11. Handle; 12. Slider; 13. Thermocouple under test; 14. Clamp; 15. Extension plate; 16. Mandrel; 17. Compression spring; 18. Upper baffle; 19. Zero-point thermostat; 20. Signal amplifier; 21. Data acquisition instrument; 22. Lower clamp; 23. Upper clamp. Detailed Implementation

[0023] Example

[0024] Please see Figures 1-2This invention provides a technical solution including a constant temperature and speed tank 1. An electromagnetic stirrer 2 is installed at the bottom of the constant temperature and speed tank 1. The rotation speed of the electromagnetic stirrer 2 is controlled by a DC motor speed controller 3. The rotating blades of the electromagnetic stirrer 2 drive the medium inside the constant temperature and speed tank 1 to rotate, forming a stable flow field. The electromagnetic stirrer 2 has no drive shaft; torque is transmitted through non-contact magnetic force. Static sealing replaces dynamic sealing, ensuring no leakage in the constant temperature and speed tank 1. An electric heating coil 4 is installed on the side wall of the constant temperature and speed tank 1. A resistance thermometer 5 is installed inside the constant temperature and speed tank 1. The resistance thermometer 5 is electrically connected to the signal input terminal of a temperature controller 6, and the power output terminal of the temperature controller 6 is electrically connected to the electric heating coil 4. The temperature controller 6 adjusts the power of the electric heating coil 4 according to the deviation between the set temperature and the temperature measured by the resistance thermometer 5, stabilizing the medium temperature at the set value. The electric heating coil 4, located on the side wall of the constant temperature and speed tank 1, enhances turbulence at the side wall surface and improves the temperature uniformity within the tank.

[0025] like Figure 1 , Figures 3-6 As shown, it also includes a guide rail 9 and a slider 12. The slider 12 is mounted on the guide rail 9 and can move linearly on the guide rail 9. A clamp 14 is fixedly mounted on one side of the slider 12, and the thermocouple to be tested 13 is fixedly mounted on the clamp 14. The clamp 14 includes an upper clamping plate 23 and a lower clamping plate 22, and the clamp 14 is fixed to the slider 12 by bolts.

[0026] An extension plate 15 is also fixedly installed on the other side of the slider 12, and a spindle 16 is provided on the extension plate 15; a lower baffle 7 and an upper baffle 18 are provided on the guide rail 9, a compression spring 17 is provided on the upper baffle 18, and a rubber buffer pad 8 is fixedly installed above the lower baffle 7.

[0027] When slider 12 moves to the upper part of guide rail 9, spindle 16 is fitted into compression spring 17. Compression spring 17 is compressed and stores ejection force. Positioning plate 10 is provided below slider 12. Positioning plate 10 is fitted by handle 11 and does not rotate, so as to support slider 12 and prevent it from moving downward. During testing, handle 11 is quickly removed, compression spring 17 pushes slider 12 downward, so that it is thrown into constant temperature and constant speed tank 1 at high speed, shortening the time for temperature step. In addition, when slider 12 moves downward, it overcomes the friction of guide rail 9 by its own gravity, which further increases the speed of slider 12 moving downward, shortening the time required for the tested thermocouple 13 to be thrown into constant temperature and constant speed tank 1 to generate temperature step.

[0028] It also includes a data acquisition instrument 21. The output terminal of the thermocouple under test 13 is inserted into the zero-point thermostat 19, and then connected to the signal amplifier 20 via a copper wire and then to the data acquisition instrument 21. The time delay between the signal amplifier 20 and the data acquisition instrument 21 is usually in the nanosecond range, which can be used for the processing and acquisition of the transient response signal of the thermocouple in the millisecond range.

[0029] The medium in the constant temperature and speed bath 1 is water, heat transfer oil, or molten salt, etc. The temperature step for calibrating the rise time is determined according to the operating temperature of the thermocouple 13 being measured, and an appropriate medium is selected. When water is used as the medium, the temperature range of the constant temperature and speed bath 1 is room temperature +5℃ to 95℃. When heat transfer oil is used as the medium, the temperature range of the constant temperature and speed bath 1 is 90℃ to 300℃. When molten salt is used as the medium, the temperature range of the constant temperature and speed bath 1 is 300℃ to 550℃.

[0030] The temperature measuring point of the resistance thermometer 5 is at the same height as the temperature measuring point of the thermocouple 13 when it is dropped into the constant temperature and speed bath 1 at the termination position, and the distances of the two from the central axis of the constant temperature and speed bath 1 are equal. Since the temperature sensing element of the millisecond thermocouple is very small, the influence of thermal conduction can be ignored at a shallow insertion depth. However, the influence of thermal conduction on the error of the resistance thermometer 5 used for temperature control cannot be ignored at a shallow insertion depth. Therefore, the L-type temperature control resistance thermometer 5 is selected.

[0031] In this embodiment: the medium in the constant temperature and constant speed bath 1 is water; the temperature control resistance thermometer 5 is an industrial AA-grade high-precision Pt100 platinum resistance thermometer 5; the inner diameter of the constant temperature and constant speed bath 1 is 60cm; the step temperature ranges from room temperature (25℃) to 75℃; the power of the electric heating coil 4 is 6kW; after setting the rotation speed of the electromagnetic stirrer 2, the flow velocity at a distance of 20cm from the central axis of the constant temperature and constant speed bath 1 is measured to be 1m / s, 10cm from the water surface, using a micro Doppler flow meter; simultaneously, the flow velocity at the same radial position, 5cm from the water surface, is also measured to be 1m / s, using the micro Doppler flow meter; and the flow velocity within the constant temperature and constant speed bath 1 is measured using an L-type AA-grade platinum resistance thermometer 5. The temperature distribution is 75℃±0.1℃. The measurement results of the flow field and temperature field show that the flow field and temperature field in the constant temperature and velocity tank 1 are relatively uniform. The thermocouple 13 under test is a thin film thermocouple made by chemical vapor deposition of nickel-chromium-nickel-silicon K-type thermocouple wire. The vertical temperature field measured by the thermocouple 13 at a distance of 20cm from the central axis of the constant temperature and velocity tank 1 shows that, since the thickness of the temperature sensing element is on the order of μm, plus the ceramic bottom, the total thickness does not exceed 1mm. The output temperature of the thermocouple 13 under test basically no longer changes after the throwing depth reaches 1cm, and stabilizes at about 75℃. Therefore, the thermocouple 13 under test achieves a step temperature at a depth of 1cm in the water.

[0032] In this embodiment: the guide rail 9 has a diameter of 20mm, the slider 12 and its clamps 14, extension plate 15, and the thermocouple 13 under test have a total mass of 0.3kg, the compression spring 17 has a wire diameter of 2mm, an outer diameter of 12mm, 2 support coils, 12.5 effective coils, a free length of 48mm, a maximum compression length of 17mm, and a total of 8 compression springs 17. The core shaft 16 has a diameter of 6mm, with 2 compression springs 17 connected in series on each core shaft 16, and a spring stiffness of 13N / mm. Theoretical calculations show that the speed at which the slider 12 is pushed out when the spring reaches its free length is as high as 28m / s. The time taken for the thermocouple 13 under test to be thrown into the water at a depth of 1cm in this embodiment is measured to be 0.4ms using the electrical parameter method. Therefore, the actual average speed of the thermocouple 13 entering the water is 25m / s. The deviation between the actual water entry speed and the theoretical calculation value is mainly caused by factors such as spring parameter errors, the weight of the slider 12, and the friction of the guide rail 9.

[0033] In this embodiment, the rise time of the thermocouple 13 from a 10% to a 90% temperature jump was measured three times, and the values ​​were 5.8ms, 6.7ms, and 6.1ms, respectively. The average value was 6.2ms. The maximum deviation between the three measurement results and the average value was 8.1%, which is less than 10%, indicating that the measurement results are reliable. The temperature jump time of 0.4ms is less than 1 / 10 of the rise time of the thermocouple 13 (6.2ms), which meets the technical requirements of the measurement process.

[0034] By configuring a longer or thicker compression spring 17, the present invention can achieve a faster insertion speed of the thermocouple 13 under test, a shorter temperature step time, and meet the calibration requirements for a faster thermocouple rise time.

[0035] This invention can also be used for the calibration of the rise time of the fast-response resistance thermometer 5. It requires replacing the zero-point thermostat 19 and the signal amplifier 20 with a Wheatstone bridge. The Wheatstone bridge is a commonly used measuring device for the resistance thermometer 5, which will not be described in detail in the embodiments.

[0036] This invention provides a rapid throwing system based on the ejection force of a compression spring 17, which greatly improves the throwing speed of the thermocouple 13 under test and shortens the time for generating a temperature step: it can be used for the calibration of the rise time of millisecond-level temperature sensors.

Claims

1. A millisecond thermocouple rise time calibration device, characterized by: It comprises a constant-temperature constant-speed tank (1), the constant-temperature constant-speed tank (1) is provided with an electromagnetic stirrer (2) at the bottom, the rotating speed of the electromagnetic stirrer (2) is controlled by a DC motor speed regulator (3), the constant-temperature constant-speed tank (1) is provided with an electric heating ring (4) on the side wall, the constant-temperature constant-speed tank (1) is provided with a thermal resistance thermometer (5), the thermal resistance thermometer (5) is L-shaped, the temperature measuring point of the thermal resistance thermometer (5) and the temperature measuring point of the measured thermocouple (13) are at the same height when the measured thermocouple (13) is thrown into the constant-temperature constant-speed tank (1) and stop at the position, and the distance of the two from the central axis of the constant-temperature constant-speed tank (1) is equal, the thermal resistance thermometer (5) is electrically connected with the signal input end of a temperature controller (6), the power output end of the temperature controller (6) is electrically connected with the electric heating ring (4), the temperature controller (6) adjusts the power of the electric heating ring (4) according to the deviation between the set temperature and the temperature measured by the thermal resistance thermometer (5), so that the medium temperature is stabilized at the set value. It also comprises a guide rail (9) and a sliding block (12), the sliding block (12) is installed on the guide rail (9) and can move linearly on the guide rail (9), a clamp (14) is fixedly installed on one side of the sliding block (12), and the measured thermocouple (13) is fixedly installed on the clamp (14), an extension plate (15) is also fixedly installed on the other side of the sliding block (12), the extension plate (15) is provided with a mandrel (16), a positioning plate (10) is arranged below the sliding block (12), the positioning plate (10) is not rotated by being sleeved with a handle (11) to support the sliding block (12) from moving downward, the guide rail (9) is provided with a lower baffle (7) and an upper baffle (18), the upper baffle (18) is provided with a compression spring (17), and a rubber buffer gasket (8) is fixedly installed above the lower baffle (7). It also comprises a data acquisition instrument (21), the output end of the measured thermocouple (13) is inserted into a zero-temperature controller (19), connected with a signal amplifier (20) through copper wires and then connected with the data acquisition instrument (21). The rising time of the measured thermocouple (13) is the time for the output temperature to reach 10% to 90% of the step amount, when the step time is less than 1 / 10 of the rising time of the measured thermocouple (13), the measurement result is valid, otherwise the measurement result is invalid. When the sliding block (12) moves to the upper part of the guide rail (9), the mandrel (16) is sleeved into the compression spring (17), and the compression spring (17) is compressed and shortened.

2. A millisecond thermocouple rise time calibration device as claimed in claim 1, characterized in that: The medium in the constant-temperature constant-speed tank (1) is water, heat-conducting oil or molten salt, etc.

3. A millisecond thermocouple rise time calibration device as claimed in claim 1, characterized in that: ​

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