Thermocouple Calibration Research Articles

Nanosecond-level second-order characteristics in dynamic calibration of thin film thermocouples by short-pulse laser

In this study, we explore the dynamic response of thin-film thermocouples (TFTCs) to transient temperature changes, emphasizing their nanosecond response capabilities. Traditionally, TFTCs are modeled as first-order systems. By employing magnetron sputtering, we have prepared NiCr/NiSi TFTCs with a novel integrated lead method. A 7.6 ns short-pulse laser served as the heat source, capturing the TFTCs’ transient response with a high-speed collector at 200 M/s. Unexpectedly, the TFTCs’ response curves exhibited oscillations at high acquisition rates. Through frequency response analysis, we have established a pulse response model for the TFTCs that is highly consistent with experimental results. For the first time, we confirmed the TFTCs’ second-order dynamic characteristics. Furthermore, our findings that various substrate materials and lead methods impact the damping characteristics of TFTCs led us to conduct pulsed laser damage experiments. These experiments revealed a correlation between damping properties and the extent of damage.

Analyzing Gas Turbine Performance Through Simulation and Performance Tests: Case Study of Gas Turbine Units in Jambi, Indonesia

The purpose of this research is to analyse and compare the performance of units 1 and 2 of the gas turbine (GT) power plant based on simulation results and tests in terms of performance, to identify factors causing a decrease in gas turbine performance, and provide recommendations to improve gas turbine. The study was carried out in GT units in Jambi, Indonesia. In this location, there are two identical GT units with a capacity of 34.25 megawatts electric (MWe). The analysis was carried out using three methods, namely performance test, inspection of the measurement instruments, and simulation of the thermodynamic performance using GT-Pro software. To improve the performance of the gas turbine, it is necessary to clean the compressor blades, online compressor washing or manual deposit cleaning on the compressor blades during the overhaul, calibrate manometers, and inspect the piping line of the differential pressure of Air Inlet Filter, and also carry out inspection and calibration of the exhaust gas thermocouple on numbers 1, 2, 5, and 8 of GT Unit 2. This research not only presents practical recommendations for improving the performance of GT in Jambi, Indonesia, but also contributes to the broader field of gas turbine technology. The findings and recommendations can be applied in the power generation industry worldwide, helping to enhance the efficiency and reliability gas turbine power plants.

Large-area Fe–C eutectic fixed-points for radiation and contact thermometry

Abstract High-quality metal (carbide)–carbon eutectic materials based on high-temperature fixed points (HTFPs) are widely used in radiometry and thermometry as reference standards. HTFPs on the base of iron–carbon (Fe–C) binary eutectic alloys, with a nominal melting temperature of about 1154 °C (just above the copper freezing point of 1084.62 °C), are one of the promising candidates among the eutectic materials. To establish new HTFPs as reference metrological tools for high-temperature thermometry, their performance should be thoroughly investigated regarding reproducibility and stability. In this work, two large-area (8 mm aperture, 107 mm cavity/thermowell length) Fe–C fixed-point cells were constructed and studied in detail using a radiation thermometer and two different thermocouples (TCs). Three different furnaces were used to explore the thermal behaviors of the cells at various furnace gradients and furnace offsets. The melting temperature at the inflections point of the melting curves of the cells studied across extensive measurement campaigns demonstrated good performance with repeatability of less than 9 mK (assessed from four successive runs) and reproducibility—less than 100 mK (at different furnaces and furnace offsets). The melting temperature agreement between both cells in the same experimental conditions was better than 30 mK. In addition, the equivalence of the developed large-area cells and a small-area radiometric cell (3 mm cavity aperture, and 35 mm cavity length) were comparatively examined in the same experimental conditions. The coherence of the obtained results for the melting temperature of large-area Fe–C cells indicates the feasibility of using large-volume cells for precise calibration of both radiation thermometers and TCs.

Tungsten–Rhenium Thermocouples Calibration in Ultra-High Temperature Range

There are presented results of experimental research on calibration of tungsten–rhenium thermocouples at the temperatures exceeding the upper limit of measurements (1700 °C) of standard type B thermocouple. The research was carried out using the high-temperature installation UKT-2500 designed for practical use in production of temperature sensors based on refractory thermocouples. Available types of insulating ceramics for thermocouples have been tested in the temperature range of (1500–2500) °C. The effects of signal shunting and thermocouples stability in inert atmosphere have been investigated at upper limit of the operating temperature range. There was proved practical feasibility of the method for calibration of several contact temperature sensors (up to 10) in one run relative to radiation pyrometer readings. Its suitability for thermocouple calibration and certifying of thermocouple wires in the temperature range (1200–2200) °C was shown. Installation enables to use reference fixed-points of Me-C type to get the highest accuracy calibration of a single tungsten–rhenium thermocouple. Type A bare-wire thermocouple was calibrated in the whole measuring range from 1200 °C to 2500 °C against an accurate radiation pyrometer.

Calibration of Type S Pt/Pt–Rh alloy thermocouples and Uncertainty Estimation

Thermocouples are the most widely used thermometric sensors for different applications due to wide temperature rangeand high temperature measuring capability. They are simple temperature sensors and can be made in very small sizes toconvert heat into electricity. Additionally, they are inexpensive and one of the highly durable thermometer types. Thepurpose of this article is to perform the calibration of thermocouples with the comparison method and to calculate theexpanded uncertainty by determining the uncertainty parameters affecting the measurement

Phase transition behavior of pure Fe cells for thermocouple calibration

The fixed points adopted in the international temperature scale of 1990 have generally been used to calibrate contact thermometers, such as thermocouples, to get the highest accuracy. The fixed point for Pd is located at the upper limit range of the Pt/Rh noble metal thermocouple calibration. However, the high price of Pd itself restricts its wide use in calibration laboratories. To overcome this difficulty, this study develops an alternative fixed point having a close transition temperature to the Pd freezing temperature of 1554.8 °C. The alternative is pure Fe with a quoted melting temperature of 1538 °C. To make a thermometric cell, an alumina crucible was used to contain the molten liquid and it was found to be robust enough to last for more than 60 cycles of melting and freezing tests without any chemical and mechanical damage. Two cells were fabricated, and their melting and freezing behaviors were studied using type B thermocouples. By considering the advantage and disadvantages of melting and freezing, the melting temperature was selected as a thermometric transition point for the calibration of thermocouples because of its easy operational processes and acceptable uncertainty level. Using a reference thermocouple that had been calibrated versus a standard radiation thermometer, the average melting temperature of the two Fe cells was 1534.0 °C with an uncertainty of 1.2 °C (k = 2). From the studies, an Fe cell made in an alumina crucible can successfully replace the Pd fixed point.

Effects of Heating Temperature on the Isothermal Performance of a Potassium Concentric Annular Heat Pipe

For high-precision thermocouple calibration, the uniformity of the temperature field provided by the metal temperature equalizing block is low, and the structure of the gas-controlled heat pipe is complex. In order to improve the thermocouple calibration equipment, heat pipe technology can be used to provide the stability and uniformity of the temperature field of the equipment. The concentric annular heat pipe (CAHP) is completely placed in the heating furnace to provide a uniform temperature field, and limited studies consider this heating mode for alkali metal CAHPs. Specifically, no information is available on the effect of heating temperatures on the temperature distribution of the internal pipe of potassium CAHP. In this study, a temperature comparison based on potassium CAHP for high-precision thermocouple calibration was manufactured. The temperature stability and temperature uniformity of CAHP were measured, and the effects of heating temperature and heating mode on the isothermal performance in the metering wells of CAHP were studied. The CAHP can provide a very stable and uniform temperature field. Under uniform heating at 400 °C, the maximum temperature difference within 16 cm was 0.174 °C. After adjusting the heating mode, the maximum temperature difference was within 16 cm 0.095 °C. The CAHP can effectively reduce the influence of heating temperature fluctuation on the temperature in the metering well; the maximum temperature change rate of the metering wells affected by the heating furnace temperature was 0.0942 °C/°C.

Correlation Between Insulation Resistance and Temperature Measurement Error in Type K and Type N Mineral Insulated, Metal Sheathed Thermocouples

Mineral insulated, metal sheathed (MI) Type K and Type N thermocouples are widely used in industry for process monitoring and control. One factor that limits their accuracy is the dramatic decrease in the insulation resistance at temperatures above about 600 °C which results in temperature measurement errors due to electrical shunting. In this work the insulation resistance of a cohort of representative MI thermocouples was characterised at temperatures up to 1160 °C, with simultaneous measurements of the error in indicated temperature by in situ comparison with a reference Type R thermocouple. Intriguingly, there appears to be a systematic relationship between the insulation resistance and the error in the indicated temperature. At a given temperature, as the insulation resistance decreases, there is a corresponding increasingly negative error in the temperature measurement. Although the measurements have a relatively large uncertainty (up to about 1 °C in temperature error and up to about 10 % in insulation resistance measurement), the trend is apparent at all temperatures above 600 °C, which suggests that it is real. Furthermore, the correlation disappears at temperatures below about 600 °C, which is consistent with the well-established diminution of insulation resistance breakdown effects below that temperature. This raises the intriguing possibility of using the as-new MI thermocouple calibration as an indicator of insulation resistance breakdown: large deviations of the electromotive force (emf) in the negative direction could indicate a correspondingly low insulation resistance.

Calibration of the ITER outer vessel steady-state magnetic sensors

The outer vessel steady-state magnetic field sensors (OVSS), a subsystem of the ITER magnetic diagnostics, consists of 60 units that will be installed on the vacuum vessel outer shell. Each OVSS unit features a pair of Hall sensors with a sensing layer made of bismuth and an onboard thermocouple. Prior to the installation of the sensors on ITER, OVSS will be subject to the complex calibration process designed to satisfy the ITER requirement for the measurement accuracy of 4 mT (2σ) in the range of the magnetic field from 0 to 2.5 T.The calibration process includes the calibration of the onboard thermocouple, sensor controller calibration, measurement of tilt of each Hall sensor with respect to the OVSS housing, and the measurement of the sensitivity of Hall sensors as a function of temperature and magnetic field for the range of ITER-relevant magnetic fields and temperatures. The expected calibration error projected to the magnetic field measurement of 2.5 mT will allow to meet the required measurement accuracy.

Push-rod dilatometer calibration and thermal expansion coefficient measurement of standard material

The linear thermal expansion coefficient (LTEC) is a very important thermal property in the field of length standard, precision engineering and novel material science. There are several methods in measuring the LTEC of a material and the push-rod type is a one of the frequently used method. In this work, the calibration and the measurement procedures of the SRM 736 which is a certified material provided from NIST are carried out with push-rod type dilatometer (Dil402, NETZSCH) and the results are presented in the temperature range from 300°C to 500°C. The calibration of thermocouple and a linear variable differential transformer (LVDT) sensor have been performed with the melting point of the pure metals and the calibration device consisting of the rod and micrometer provided from the NETZSH.

Melting and freezing behavior of pure Ni cells in alumina crucibles with different internal structures

Two pure Ni cells for thermocouple calibration were fabricated in alumina crucibles with different internal structures to investigate their melting and freezing behaviors. One of the produced crucibles had a smooth surface, and the other was made with internal circular grooves. The melting and freezing processes of each cell were investigated in 10 melting/freezing cycles using a type B thermocouple calibrated with a standard radiation thermometer. The reproducibility of the melting point was better than that of the freezing point by a factor of more than 2, regardless of the internal shape of the crucible. The freezing temperature gradually decreased with the degree of supercooling, and the slope was observed to be about −0.08 °C. It was found that in terms of reproducibility and easiness of realization the melting point was better than the freezing point for use as a fixed temperature point. Therefore, it is proposed to use the melting point as a fixed point for thermocouple calibration. Regarding the difference in internal structure of the crucible, it was observed that a cell with circular grooves was slightly better in terms of reproducibility of melting and freezing points, but it was still unclear whether this was due to the grooves formed inside the cells, and, thus, additional research is needed. The average melting temperature and uncertainty of the Ni cells fabricated in this study was evaluated as (1454.1 ± 0.9) °C.

Laser based method for dynamic calibration of thermocouples

In dynamic temperature measurement, thermocouple sensors are widely used in harsh environments, and their dynamic characteristics directly affect the accuracy of dynamic temperature measurement. When the dynamic characteristics do not meet the requirements of dynamic test, dynamic errors will occur. In order to obtain the dynamic characteristics, it is necessary to calibrate the thermocouple dynamically. In this paper, a dynamic calibration system for the thermocouple was built. In the system, a high power laser was used to generate pulse temperature excitation. In order to realize the uniform heating, the laser beam homogenization system based on microlens array was studied and added to the dynamic calibration system. The homogenization system was designed and simulated, and the uniformity of the laser spot was measured after homogenization. A K-type butt-welded thermocouple was dynamically calibrated by using the dynamic calibration system. The dynamic mathematical model of the thermocouple was obtained by the system identification method, and the dynamic characteristics of the thermocouple were analyzed.

Calibration of thermocouples from 419,527 °C (freezing point of Zn) up to 1492 °C (melting point of the Pd-C eutectic), by the temperature fixed point and comparison methods

This report present the results of the EURAMET inter-comparison carried out to compare the calibration of thermocouples from 419,527 °C (freezing point of Zn) up to 1492 °C (melting point of the Pd-C eutectic). This inter-comparison is intended to be used to support the calibration and measurement capabilities (CMCs) of the participants in the calibration of thermocouples.The comparison was organized in three loops with nineteen participating laboratories and it allowed the performance of the measurement either in fixed points and/or by comparison. The method used to analyse the results of the comparison was the generalized weighted mean that takes into account the full covariance matrix that includes correlations between the participants which have similar traceability sources and between measurements performed by the same laboratory (i.e. the pilots that performed measurements at the beginning and at the end of each loop and the measurements performed by the same laboratory in fixed points and by comparison at the same calibration point).Main textTo reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCT, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Temperature assignment of a Co–C eutectic fixed-point cell for thermocouple calibration

The Co–C eutectic fixed point has been popular for thermocouple calibration since 2010. In this study, the ITS-90 temperature of a Co–C eutectic fixed-point cell intended for thermocouple calibration of noble thermocouples was measured using a radiation thermometer and a group of Pt/Pd and PtRh10%-Pt thermocouples. Satisfactory consistency was observed for measurements using both methods.

Correction of inertance of temperature sensing devices in high-speed flow

The influence of the thermocouple calibration method on the reconstruction of the real temperature in impulse wind tunnel with operation duration of up to 100 ms is presented. It is shown that in an impulse set-up allow obtaining a stepwise thermal load with long temperature plateau which enough to determination of instrumental function, necessary for temperature reconstruction. To this aim, the developed technique, based on the application of the solution of the convolution integral equation, was used. It was included the information on the instrumental function, which was obtained from the calibration measurements. In the deconvolution procedure, the signal was first smoothed by splines, the convolution kernel was extracted by the differentiation of smoothed function, and regularization was performed by Kaczmarz algorithm with relaxation parameter. A comparison is made of the temperature reconstruction in the regular mode of hot shot wind tunnel with two different methods for measuring the response of thermocouples to the temperature step: measurement behind the shock wave front and rapid immersion in aluminum melt. It is found that the use of the instrumental function obtained in a wind tunnel allows one to more reliably determine the position of the temperature maximum in real experiment, which corresponds to the physical structure of the flow.

Reducing Uncertainty in a Type J Thermocouple Calibration Process

Thermocouples are used in many manufacturing processes in order to read the actual temperature of the product. Calibration of thermocouples is critical wherever they are used. However, the uncertainties must be considered and the factors that affect the uncertainty value must be regarded during the calibration of thermocouples. In this study, design of experiments by Taguchi method has been performed in order to reduce uncertainty during calibration of Type J thermocouples. Within the scope of this study, parameters which are assumed to effect temperature oscillations have been determined and necessary experiments have been conducted using temperature well and proper inserts. The parameters were selected as insert material, thermocouple immersion depth and type. It can be concluded that the immersion type has the highest effect, whereas “immersion depth” has minimum effect on the uncertainty value. As a result of the study, a value for parameters which results in best possible temperature uniformity of the well is achieved.

The thermopower of NiCr- and PtRh-alloys – a new view

Abstract For the interpretation of the Seebeck coefficient S ( T ) S(T) of transition metal alloys where one or both of the alloy partners develop a spin moment, so far spincluster models in connection with the standard Boltzmann-Fermi theory S ( T ) ∼ T S(T)\sim T have been adopted. However, this interpretation suffers from some obvious inconsistencies, in particular with NiCr-alloys. In this contribution we try to alleviate these inconsistencies by implementing the recently proposed correlated electron thermopower terms which appear in the framework of Fermi-Boltzmann statistics when it is applied to Stoner-Slater intraatomic exchange (J) split electronic states. For both NiCr- and PtRh-alloys we recover the typical electron correlation term of the thermoelectric power, S D {S_{D}} , while former inconsistencies can be removed. As NiCr and PtRh-alloys are often used in high temperature sensing because of their stability, this new interpretation of the thermoelectric power may help to develop a better calibration and compositional choice of alloy-based thermocouples.

Report on the comparison of the calibration of noble metal thermocouples from 419 ºC up to 1100 ºC (EURAMET.T-S5)

An International Comparison on the calibration of noble metal thermocouples from 419 °C up to 1100 °C has been carried out among the National Metrology Institutes (NMIs) of Spain, FYR Macedonia and Chile. Measurements were performed from March 2016 to June 2017. One type R thermocouple circulated between the participants that was calibrated by using fixed points or by comparison, depending of the capabilities of the laboratories. The Centro Español de Metrología (Spanish NMI), CEM, acted as the pilot laboratory providing the reference value of the comparison.The thermocouple shown an acceptable behavior throughout the comparison, with no critical deterioration of its homogeneity and a maximum drift lower than 2 μV in the worst case. The results of the comparison were quite satisfactory. The three institutes are compatible with a coverage factor k= 2 in all the calibration points and in the case of aluminum and zinc they are even compatible for a coverage factor k = 1.This report presents the results of this comparison and provides detailed information of the measurements performed by the participating laboratories.Main textTo reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCT, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Influence of Cr-Content on the thermoelectric and mechanical properties of NiCr thin film thermocouples synthesized on thermally sprayed Al2O3

Ni/Ni-Cr thin film thermocouples were deposited by means of DC magnetron sputtering for the application in plastic extrusion dies. In order to ensure the application of the thermocouples on complex surfaces, a thermally sprayed Al2O3 layer was used between the substrate and the thin films for thermal insulation and electrical isolation. The study includes the deposition, characterization, calibration, and validation of thin film thermocouples. The influence of the composition (10 at.-%, 20 at.-% and 30 at.-% Cr) was analyzed concerning mechanical and electrical properties. It was found out that the electrical resistance increases with the temperature and the Cr-content due to a decreasing crystallite size. By means of a scratch-tester and nanoindentation, a higher scratch load and hardness were observed for larger Cr-contents on the thermally sprayed Al2O3 coating. Despite the composition, the influence of the size as well as the thickness of the thermocouples were analyzed regarding the Seebeck coefficient. Independent from the size and Cr-content, all thermocouples feature a comparable Seebeck coefficient of about 40 μV/K. This high coefficient is similar to that of wire thermocouples, showing a low number of defects in the thin films. The ceramic coating features a thermal insulation of about 20 °C at 200 °C, allowing a more accurate measurement of the ambient medium.

Calibration of Thermocouple by Comparison against Standard Radiation Thermometer in a Blackbody Comparator

A set-up to calibrate thermocouple up to 1500 °C by comparison against radiation thermometer is recently established in Research Center for Metrology – LIPI (RCM – LIPI). A blackbody cavity, made of silicon carbide, is put in a single-zone-controller furnace as a comparator block. A radiation thermometer standard (worked at λ = 650 nm) is employed to determine the reference temperature of the calibration. In this work, a type B thermocouple is calibrated in the range of 1000 – 1500 °C. The expanded uncertainty (k = 2) is evaluated to be 2.4 °C at 1500 °C. The uncertainty due to inhomogeneity of the thermocouple contributes more than 50% (1.4 °C) of the total uncertainty.