CN114424037A - Device for calibrating high-temperature thermocouple - Google Patents
Device for calibrating high-temperature thermocouple Download PDFInfo
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- CN114424037A CN114424037A CN202080057407.1A CN202080057407A CN114424037A CN 114424037 A CN114424037 A CN 114424037A CN 202080057407 A CN202080057407 A CN 202080057407A CN 114424037 A CN114424037 A CN 114424037A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
- G01K1/00—Details of thermometers not specially adapted for particular types of thermometer
- G01K1/08—Protective devices, e.g. casings
- G01K1/12—Protective devices, e.g. casings for preventing damage due to heat overloading
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
- G01K15/00—Testing or calibrating of thermometers
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Abstract
The present invention relates to temperature measurement. The apparatus for calibrating a high temperature thermocouple comprises: a protective case made of a high melting point material and having a mounting flange; a thermocouple having a ceramic insulator; and a radiation unit. The device is placed upright, the protective casing is hermetically sealed from the working end by a plug, and has a carrier tube coaxially mounted therein, to which the hot end of the thermocouple is attached, said carrier tube being sealed at the working end by a reflector plug. The protective shell and carrier tube have holes for allowing filling with an inert gas. A protective shell containing a carrier tube and a thermal element of a thermocouple attached thereto is disposed in the working chamber of the radiant unit, which is attached to the hybrid electric heater. On the opposite side of the radiating element to its working chamber, a hole is provided for viewing the pyrometer. The present invention enables a calibration process to be performed for one or more high temperature thermocouples up to 2500 ℃.
Description
The present invention relates to the field of temperature measurement and can be used for calibration of high temperature thermoelectric converters including tungsten-rhenium thermoelectric converters, which are designed to measure the temperature of a working medium in the range of 1700 ℃ to 2500 ℃.
There are known tungsten-rhenium thermocouples (WRe thermocouples) of type a (WRe5-WRe20), in which the rhenium content in the thermoelectric elements is 5% and 20%, respectively, and tungsten-rhenium thermocouples (WRe5-WRe26), in which the rhenium content in the thermoelectric elements is 5% and 26%, respectively. Such a thermocouple has the widest measurement temperature range among the contact sensors. According to IEC60584-1:2013 standard, the upper limit of the measured temperature reaches 2300 ℃ for a C-type thermocouple, and the upper limit of the measured temperature reaches 2500 ℃ for an A-type thermocouple. However, the wide application of type a and type C thermocouples at temperatures above 1700 ℃ is limited due to the lack of reliable metering control and reliable calibration both at the manufacturing stage and during operation.
Calibration of WRe thermocouples in Russia is known according to the article "Ulanovsky A., Edler F., Fischer Y., Oleynikov P., Zaitsev P., Pokhodun A, Features of high-temperature calibration of tubular-rhenium thermal couplings// International Journal of Thermophysics, 2015, 36(2-3), p.433-443", in which calibration is performed in a horizontal furnace with graphite heaters in graphite radiation chambers mounted in the heaters. The temperature of the radiant chamber is measured by a reference pyrometer and then a WRe thermocouple, calibrated according to the measured temperature of the chamber, is immersed in the chamber. During these operations, the stability of the temperature values is maintained by the control pyrometers (feedback pyrometers) of the furnace. The calibration method in the graphite radiation chamber of the horizontal furnace has some drawbacks:
1. the calibrated thermocouple cannot be protected from graphite vapor, which can lead to distortion of the calibration curve due to shunting of the thermocouple signal.
2. Poor protection of the thermocouple forces calibration to be performed in the shortest time possible, which can lead to sudden heating and quenching of the thermocouple. This also leads to distortion of the calibration curve.
3. Calibration of a single thermocouple is not suitable for large scale sensor production due to the low productivity of expensive processes.
4. Horizontal thermocouple locations in the furnace can lead to bending of the thermoelectric elements at high temperatures and increase the risk of accidental shorting of the heater or furnace elements.
From patent CN 106370322 a with a priority date of 2016, 11, 24, a verification system for tungsten-rhenium thermocouples is known, which comprises a high-temperature furnace with a black body inside and a temperature control unit. The temperature control unit is part of an automated measurement system. The calibrated thermocouple is connected to the data acquisition module and the cold junction compensation device, and all data is transmitted to a common data exchange fieldbus, which is also connected to the control unit. The temperature range measured is 1500 ℃ to 2300 ℃. This patent describes the components of the WRe thermocouple calibration unit, including the vacuum system, cooling system, gas circuit, and measurement method. A block diagram of the measurements and the basic parts of the installation are given.
Closest to the claimed device in terms of technical essence is a protection tube for calibrating high temperature tungsten-rhenium thermocouples according to patent CN 102944332 a with priority date 2012 12, month 3, which protection tube provides protection for the tungsten-rhenium thermocouples during high temperature calibration in the temperature range of 1500 ℃ to 2300 ℃. The calibration process is performed within a protective tube having a separate lumen at the working end, structurally close to the black body. A tungsten-rhenium thermocouple is inserted from the upper end of a protective tube with a mounting flange and passes through an upper grating and a lower grating composed of tungsten pieces with holes for thermocouple lead-out. The thermocouple is inserted so that the working junction of the thermocouple is located within the temperature equalization zone of the protective tube. The upper flange is sealed to protect the furnace atmosphere, including the inner protective tube, from air infiltration. Before starting to heat the furnace, the protective tube is evacuated and filled with inert gas. After the furnace temperature reached the set value and stabilized, the temperature was measured by a reference pyrometer installed outside the furnace. The pyrometers were observed through quartz glass windows in the side walls of the furnace at holes in the lower part of the protective tube. Since the temperature equalization zone of the protective tube is located near the radiation aperture, the measured temperature values of the two zones are considered to be the same. The thermo-electromotive force value of the thermocouple is calibrated by the temperature measured by the reference pyrometer. Thus, the deviation of the calibrated thermocouple reading from the nominal value at the current temperature is determined. Tungsten is used as the material of the protective tube. The length of the temperature equalization zone along the axis of the tube is about 20mm and the size of the radiation chamber is 8 mm. The emissivity value of the cavity is assumed to be at least 0.98. The heating element of the furnace may be a graphite or tungsten tube. During the calibration process, the protection tube protects the thermocouple from contamination caused by evaporation and transfer of the heating element material.
The disadvantages of the thermocouple calibration described in the above patent are as follows:
1. up to three thermocouples can be calibrated per load, which greatly complicates mass production.
2. When the cavity emissivity is equal to 0.98, temperature measurements at a single wavelength with a monochromatic reference pyrometer will have additional error due to the dependence of the tungsten spectral emissivity on temperature.
3. An additional quartz glass element at the optical measuring axis will add a new component to the total measurement uncertainty of the true temperature in the chamber.
4. Due to thermal expansion of the furnace elements, the radiation chamber will be offset from the optical axis of the reference pyrometer, which will require additional adjustments of the pyrometer at each temperature level.
The present invention solves the technical problem of eliminating these drawbacks, i.e. it provides a wide range and high performance for the calibration process of high temperature thermocouples, including tungsten rhenium thermocouples, in the temperature range from 1000 ℃ to 2500 ℃.
Technical result of the invention the design features of the device provide a calibration process for three or more high temperature thermocouples, including tungsten rhenium thermocouples, at temperatures ranging from 1000 ℃ to 2500 ℃.
In order to achieve the claimed technical result, a device for calibrating a high-temperature thermocouple is proposed. The device includes: a protective tube made of refractory material with a mounting flange, a thermocouple with ceramic insulation, and a radiating block. The distinctive feature of the device is that a protective tube is hermetically sealed with a plug from the working end, and a carrier tube having a thermocouple attached thereto is coaxially mounted within the protective tube. The carrier tube is hermetically sealed to the working end by a reflector plug. The protective tube and the carrier tube have holes for filling the inner space with an inert gas. At the outlet of the protective tube, there is an insulator plug with holes through which the thermoelectric elements are led out. The assembly comprising the protective tube and the carrier tube with the thermocouple attached is placed in the working chamber of the radiant block, which is fixed inside the central zone of the electric heater with uniform temperature. On the back side of the radiant block opposite to its working chamber, there is a hole for the view of the control pyrometer of the furnace. The device has a vertical position.
The essence of the solution is illustrated by the following description and the accompanying drawings.
Fig. 1 shows an apparatus for high temperature thermocouple calibration, wherein:
1. a working junction of a thermocouple;
2. a thermocouple wire;
3. a thermocouple ceramic insulator;
4. carrying a pipe;
5. a reflector plug;
6. protecting the tube;
7. protecting the pipe plug;
8. installing a flange;
9. an insulator plug;
10. a hole for an inert gas;
11. a radiating block;
12. a working cavity of the radiating block;
13. a tubular electric heater consisting of a graphite annular stack;
14. a pyrometer view port.
Figure 1 shows the device positioned vertically within the electric heater. The working junction 1 of the thermocouple is fixed to the carrier tube 4. The working end of the carrier tube (view B) is sealed by a reflector plug 5, which reflector plug 5 has a profiled surface that scatters radiation within the tube. The thermocouple wires 2 are placed in a ceramic insulator 3.
The length of the carrier tube 4 is not less than 50 times the value of the inner diameter of the carrier tube. This makes the radiation cavity parameters as close as possible to those of the black body. The carrier tube 4 with the thermoelectric element 2 attached thereto is inserted into the protective tube 6. The protective tube 6 is hermetically sealed with the working end (view B) by means of a plug 7. The protective tube 6 is centered together with the carrier tube 4 and in the working volume of the furnace above the mounting flange 8. The protective tube 6 and the carrier tube 4 are electrically isolated from each other. The outlet opening (fig. a) between the protective tube 6 and the carrier tube 4 is closed by an insulator plug 9, through which insulator plug 9 the thermocouple wires 2 are led out. In the upper part of the protective tube 6 and the carrier tube 4 there are holes 10 for filling the inner volume with inert gas. There is no inert gas flow near the working junction 1 of the thermocouple that can cool the working junction 1. The protective tube 6 with the thermoelectric element 2 is inserted into the working chamber 12 of the radiant block 11, which is fixed between the ring elements of the hybrid electric heater 13 in the furnace zone with uniform temperature. The protective tube 6 is not allowed to come into contact with the wall or bottom of the cavity 12 of the radiating mass 11. The depth of the cavity is not less than twice the diameter of the protective tube 6. The radiating mass 11 serves as an additional element for equalizing the temperature field in the vicinity of the working junction 1 of the thermocouple being calibrated. On the back side of the radiation block 11 opposite the working chamber 12, there is a hole 14 for observing the replica pyrometer thereon.
The design of the proposed device for calibrating high-temperature thermocouples enables the following results to be achieved:
1. for high temperature thermocouples, including tungsten-rhenium thermocouples, the full range and high performance of expensive calibration processes is achieved;
2. a protective tube made of refractory material, hermetically sealed from the working end, protects the thermocouple wires from contamination by vapors of other materials present at high temperatures;
3. the presence of a carrier tube in the device makes it possible to place more than three thermocouples on the carrier tube and to fix the working junctions of the thermocouples in the homogeneous temperature zone of the furnace and close to the reflector plug, on which the reference pyrometers are observed;
4. the carrier tube with the reflector plug enables the measurement of axial and azimuthal inhomogeneities of the temperature field within the measurement zone;
5. a reflector plug with a profiled surface scatters radiation within the carrier tube to bring it closer to the parameters of the black body;
6. eliminating rapid heating and quenching of the calibrated thermocouple;
7. the vertical arrangement of the thermocouple and the protective tube eliminates the risk of accidental short-circuiting of the heater or furnace element;
8. the radiation cavity of the carrier tube is not displaced relative to the optical axis of the reference pyrometer;
9. there is no intermediate element between the lens of the reference pyrometer and the radiation chamber of the carrier tube along the optical measuring axis;
10. by means of the radiation block, the blackbody parameter is approached, the expansion of the uniform temperature zone is realized, which is necessary for the thermocouple calibration;
11. an aperture at the back side of the radiation block opposite the working chamber enables the use of a replica radiation pyrometer that controls the temperature values of the measurement zone;
12. the device enables the unit that achieves the reference melting point of the metal carbide eutectic "M-C" to be installed in the cavity of the radiating block. A set of such fusion (fixation) points within a calibration range, for example: Pd-C (1492 ℃ C.); Rh-C (1657 ℃ C.); Pt-C (1738 ℃ C.); cr (chromium) component3C2-C (1827 ℃); Ru-C (1953 deg.C); Ir-C or Y-C (2290 ℃ C.); Re-C (2474 ℃ C) -enables a single thermocouple, such as a tungsten-rhenium thermocouple, to be calibrated with high accuracy of no more than 1 Kelvin.
Fig. 2 shows a measurement scheme for calibrating a high temperature thermocouple from radiation pyrometer readings, and all auxiliary devices are indicated in the scheme.
The measurement during the calibration process is performed as follows. After the thermocouple calibration device was installed in the furnace, heating was started to the first calibration point. The temperature of the radiating mass is controlled by a replica pyrometer, which replica pyrometer reading is transmitted to a temperature measuring unit, and which replica pyrometer can also be used to control heating. The radiant surface temperature of the reflector plug of the device carrier tube is measured by a reference pyrometer. This temperature is the true value of the temperature of the working junction of the thermocouple located near the radiating surface of the reflector plug. A check is also made for the temperature of the radiating mass measured by the replica pyrometer. Thus, the temperature of the working chamber near the working junction of the thermocouple can be controlled from both sides. All current data is displayed in real time on the personal computer screen and can be saved to a separate calibration file. The free end of the thermocouple was connected to a copper wire and the contact point was immersed in a dewar vessel with de-icing to achieve a temperature of the thermocouple cold junction equal to 0 ℃. The thermo-electromotive force of each thermocouple was measured by a precision millivolt meter and stored in a calibration file. The measured value of the thermo-electromotive force of the thermocouple is adjusted to the temperature value measured by the reference pyrometer. All measurements were performed at a steady oven temperature with a drift of no more than 0.5 degrees per minute. The furnace is then heated to the next set calibration point. Thus, the thermocouple is calibrated within the operating temperature range.
The maximum calibration temperature achievable is determined only by the properties of the ceramic insulator of the thermocouple.
The proposed invention thus eliminates the drawbacks of the devices described above, namely:
1. providing protection of the calibrated thermocouple from the heater material vapor.
2. So that more than three thermocouples can be calibrated simultaneously to ensure mass production of the temperature sensor.
3. Quenching and quenching of the calibrated thermocouple is eliminated.
4. The vertical arrangement of the thermocouple and the protective tube eliminates the risk of accidental short-circuiting of the heater or furnace element.
5. The radiation chamber is not displaced with respect to the optical axis of the reference pyrometer.
6. The optical measurement scheme has no intervening elements between the pyrometer lens and the radiation chamber, which eliminates one component of measurement uncertainty.
Thus, the set of these design features achieves a specified technical result including the possibility of calibrating more than three thermocouples at specified points in the temperature range from 1000 ℃ to 2500 ℃ simultaneously.
Example of high temperature thermocouple calibration
As a device reproducing the full range of operating temperatures of 1000 ℃ to 2500 ℃ (type a tungsten rhenium thermocouple), high temperature furnace BB3500YY was chosen. Overall dimensions of the working space of the furnace: 47mm in diameter and 500mm in height. The maximum operating temperature of the vertical furnace with the graphite heater was 3500 ℃, protective gas-argon, and water cooling of the furnace unit.
The working junctions of the ten thermocouples were fixed to a carrier tube near the radiant surface of the reflector plug, which was placed coaxially inside a protective tungsten tube hermetically sealed from the working end. The calibration device (all components) is immersed in the working chamber of the graphite radiant block located within the temperature equalization zone of the furnace. The size of the homogeneous zone is predetermined. The temperature of the radiant block is controlled by a replica pyrometer on the opposite side of the furnace (from the bottom).
The length of the carrier tube is not less than 50 times of the value of the inner diameter of the carrier tube, so that the radiation cavity is as close to a black body as possible. Holes have been opened in the upper cooling part of the protective tube and the carrier tube wall to fill the inner volume with inert gas (argon). The calibration temperature is determined by the readings of the reference pyrometer and the replica pyrometer. The temperature value is adjusted to the value of the thermal electromotive force of the calibrated thermocouple. Based on the measurements, a separate calibration curve is determined for each thermocouple. An example of a calibration table for one of the thermocouples is shown in table 1.
Thus, ten tungsten-rhenium thermocouples were calibrated simultaneously over a temperature range of 1000 ℃ to 2500 ℃. The results confirm the technical result claimed.
TABLE 1
Calibration results for type A thermocouple series No. 01
And (4) conclusion: thermocouple type a sequence number 01 that was calibrated corresponds to the second precision class of gorstr 8.585-2001.
Claims (2)
1. An apparatus for high temperature thermocouple calibration, comprising: protection tube made of refractory material with mounting flange, thermocouple with ceramic insulator, and radiation block, characterized in that: the device is placed vertically, the protective tube is hermetically closed with a working end by means of a plug, a load tube is mounted coaxially inside the protective tube, with thermocouples and working junctions fixed to the tube, the load tube is hermetically sealed with the working end by means of a reflector plug, the protective tube and the load tube have holes for filling with inert gas, the protective tube and the load tube with attached thermoelectric elements are placed in the working chamber of the radiant block, the radiant block is fixed to a composite electric heater, and there are holes for pyrometer observation at the back side of the radiant block opposite to the working chamber of the block.
2. The device according to claim 1, characterized in that the insulator plug is placed at the outlet of the protective tube, through which insulator plug the thermoelectric element is led out.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| RU2019144999 | 2019-12-30 | ||
| RU2019144999A RU2720819C1 (en) | 2019-12-30 | 2019-12-30 | Device for calibration of high-temperature thermocouples |
| PCT/RU2020/050140 WO2021137731A1 (en) | 2019-12-30 | 2020-06-30 | Device for calibrating high-temperature thermocouples |
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| Publication Number | Publication Date |
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| CN114424037A true CN114424037A (en) | 2022-04-29 |
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| CN202080057407.1A Pending CN114424037A (en) | 2019-12-30 | 2020-06-30 | Device for calibrating high-temperature thermocouple |
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| CN (1) | CN114424037A (en) |
| RU (1) | RU2720819C1 (en) |
| WO (1) | WO2021137731A1 (en) |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| SU1700394A1 (en) * | 1988-11-14 | 1991-12-23 | Московский институт стали и сплавов | Temperature sensor with a built-in calibrator |
| US6473708B1 (en) * | 1999-12-20 | 2002-10-29 | Bechtel Bwxt Idaho, Llc | Device and method for self-verifying temperature measurement and control |
| RU2325622C1 (en) * | 2007-03-22 | 2008-05-27 | Общество с ограниченной ответственностью "Производственная компания "ТЕСЕЙ" | Technique of controlling authenticity of readings of thermoelectric converter during operation |
| CN104180928B (en) * | 2014-09-04 | 2017-07-11 | 北京三原兆兴科技有限公司 | A kind of sealed thermostat |
| CN104535224B (en) * | 2015-01-26 | 2017-06-30 | 中国航空工业集团公司北京长城计量测试技术研究所 | A kind of pyrometer couple assay furnace calandria |
| JP6992553B2 (en) * | 2018-01-31 | 2022-01-13 | 株式会社デンソー | Temperature sensor and temperature measuring device |
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2019
- 2019-12-30 RU RU2019144999A patent/RU2720819C1/en active
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2020
- 2020-06-30 CN CN202080057407.1A patent/CN114424037A/en active Pending
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| RU2720819C1 (en) | 2020-05-13 |
| WO2021137731A1 (en) | 2021-07-08 |
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