Non-contact Temperature Measurement Method Research Articles

Background radiation compensation calibration method for film cooling infrared temperature measurement based on BP neural network

The precise non-contact temperature measurement method is essential for studying gas turbine component heat transfer. While infrared thermal imaging provides high-resolution two-dimensional temperature fields, errors arise from the measurement environment's complexity, emissivity variations, and reflection radiation effects. This study utilizes BP neural networks to correct infrared radiation on gas film cooled plates. By modeling background radiation and analyzing infrared emission processes, factors influencing temperature distribution are identified. Experimental data from uncooled plate are used for network training. Experimental measurements were conducted on uncooled plates to obtain training data. A BP neural network was established based on Planck's law and the radiation transmission process to relate the mainstream temperature to the background radiation. Calibration analysis was performed based on experimental data from the cooled plate, achieving the restoration of the two-dimensional temperature field under multiple operating conditions and significantly reducing measurement errors. This method comprehensively considers the entire process of radiation transmission, thereby eliminating background radiation embedded in the infrared images. The obtained measurement results vividly depict the real temperature distribution, offered significant support for gas turbine engineering applications.

Advances in the application of non-contact temperature measurement technology for aero-engine blade.

The advancement of the aviation sector has made the temperature measurement technology for aero-engine turbine blades essential for maintaining the engine's safe and steady performance. The non-contact temperature measurement technology is a trending research focus in turbine blade temperature measurement due to its benefits of not requiring direct touch with the object being measured and its suitability for high-temperature and high-speed conditions. This paper provides a concise overview of various key non-contact temperature measurement methods for aero-engines, such as fluorescence temperature measurement, fiber-optic temperature measurement, and radiation temperature measurement. It discusses the temperature measurement principle, technical characteristics, and the current research status both domestically and internationally. Based on this, this Review further discusses the main challenges faced by the non-contact temperature measurement technology and the development trend of the future.

A novel optical thermometry strategy: Based on the combined effects of red-shift charge transfer band and thermal coupling

The non-contact temperature measurement method based on the fluorescence intensity ratio of thermally coupled energy levels has emerged as a focal point of research in recent years due to its characteristics of short response time, suitability for extreme environments, and high sensitivity. The enhancement of relative sensitivity (Sr) is a key objective in refining ratio-metric optical thermometry. However, the Sr is limited by the thermometry strategies. Regarding excitation and monitoring methods, ratio-metric temperature measurement strategies typically adopt two distinct approaches: single-excitation dual-emission (S-D), and dual-excitation single-emission (D-S). In this study, we developed a dual-excitation dual-emission (D-D) thermometry strategy that theoretically and experimentally demonstrates higher Sr and reduced temperature uncertainty (δT). This advancement was achieved by analyzing thermal coupling energy levels (TCELs) and the red-shift charge transfer band (CTB) properties. YVO4:Er3+ was selected for experimental validation due to its pronounced thermal coupling and red-shift CTB effects. The experimental results show that the Sr(D-D) equal to the sum of Sr(S-D) and Sr(D-S), and 1/δT(D-D) equal to the sum of 1/δT(S-D) and 1/δT(D-S), which well verifies the theoretical expectations. Thus, the D-D strategy emerges as a novel and effective method for ratio-metric thermometry, promising enhanced precision in temperature measurements.

Особенности расчета температуры резания при высокоскоростном фрезеровании алюминиевых сплавов без применения СОЖ

Introduction. The calculation of temperature during high-speed milling of aluminum alloys is of interest, since temperature can act as one of the main limiting factors in choosing rational milling modes. This is especially important when milling thin-walled products used in aircraft construction, since its high values can lead to local warping of the structure. It is not possible to control the temperature factor in production conditions, which makes it necessary to develop a mathematical model for calculating temperature. The purpose of the work is to develop a methodology for predicting the cutting temperature during high-speed milling of aluminum alloy workpieces for cutting conditions, in which it is not possible to use cutting fluid. Methods. This paper presents experimental studies of the cutting temperature during high-speed milling of aluminum alloy workpieces without the use of cutting fluid using non-contact temperature measurement methods. The results obtained were used to determine the coefficients substituted into formulas for calculating temperatures on the front and back surfaces of the cutting blade. Results and discussions. Based on the results of experimental tests and theoretical modeling, a temperature graph is drawn up. A comparison of experimental studies of milling of aluminum alloy D16T, with changing cutting conditions (the cutting speed changed) with theoretical data, gave a satisfactory result. The average relative error when comparing experimental data with theoretical one is 6.05 %. Based on experimental data, it can be concluded that the comparison of experimental data for measuring cutting temperatures is in satisfactory agreement with the proposed method of theoretical calculation of temperatures. The advantage of this technique is that it allows, without time-consuming and costly experimental studies, theoretically calculate (forecast) the temperatures on the front and back surfaces of the cutting blade, as well as the cutting temperature, for those narrow milling conditions, where effective heat removal from the cutting zone is impossible. It can also be used for milling aluminum alloys, the mechanical and thermophysical properties of which differ.

Approach to multispectral thermometry with Planck formula and hybrid metaheuristic optimization algorithm.

Accurate temperature measurement has significant implications for product quality, industrial process control, and scientific research. As a non-contact temperature measurement method with broad application prospects, multispectral thermometry still poses significant challenges in data processing. Currently, most multispectral thermometry methods use the Wien approximation equation to construct the objective function. However, the use of the Wien approximation equation is conditional and generally applicable only to low temperatures or short wavelengths. In this paper, what we believe is a new data processing model of multispectral thermometry is established based on the Planck formula; Additionally, a feasible region constraint method is proposed to constrain the emissivity range; By utilizing a hybrid metaheuristic optimization algorithm based on differential evolution (DE) and multi-population genetic (MPG) algorithms, the simulation results of six different models and experimental results of silicon carbide demonstrate that the proposed algorithm achieves an average relative error in temperature measurement within 0.42% and a random relative error within 0.79%. The average computation time for each temperature inversion is approximately 0.26 seconds. The accuracy and efficiency of the algorithm ensure that it can be applied to real-time temperature measurement in industrial field.

Research on accurate non-contact temperature measurement method for telescope mirror.

Non-contact temperature measurement for a solar telescope mirror is critical for improving the mirror seeing and thermal deformation of solar telescopes, a long-standing challenge in astronomy. This challenge arises from the telescope mirror's inherent weak thermal radiation, often overwhelmed by reflected background radiations due to its high reflectivity. In this work, an infrared mirror thermometer (IMT) is equipped with a thermally-modulated reflector, and a measurement method based on an equation for extracting mirror radiation (EEMR) has been developed for probing the accurate radiation and temperature of the telescope mirror. Using this approach, we can extract the mirror radiation from the instrumental background radiation via the EEMR. This reflector has been designed to amplify the mirror radiation signal incident on the infrared sensor of IMT, while inhibiting the radiation noise from the ambient environment. In addition, we also propose a set of evaluation methods for IMT performance based on EEMR. The results reveal that the temperature measurement accuracy of IMT to the solar telescope mirror using this measurement method can be achieved better than ±0.15°C.

Errors of non-contact temperature measurement

In recent years, there is a trend of improving the performance and efficiency of all existing measuring instruments due to a leap in technology. Almost every industry uses a variety of technologies that apply temperature control. Temperature of a heated body can be estimated by measuring the parameters of its thermal radiation, which are electromagnetic waves of different lengths. Temperature measurement is necessary for comfortable automatic control and management of production processes. The use of non-contact means makes it possible to measure the temperature of, firstly, moving objects, secondly, objects in inaccessible places, thirdly, to avoid damage to the measuring instruments when controlling large temperatures. High speed, the possibility of measuring temperature without disconnecting the object from the technological process, ensuring personnel safety, temperature measurement up to 3000 °C – these are the advantages of non-contact temperature measurement method. To obtain reliable values when measuring thermophysical quantities it is necessary to know the processes occurring in interaction of the measuring device or sensor with the object of measurement. These processes affect the magnitude of the measurement error, that is, magnitude of the result deviation from the true value of the measured parameter. This paper describes the errors of non-contact temperature measurement of pyrometers, namely total radiation pyrometer, partial radiation pyrometer, spectral ratio pyrometer, as well as shows the results of comparative calculations between them. Expressions for the evaluation of methodical errors of total radiation, partial radiation and spectral ratio pyrometers are given, as well as the results of comparative calculations of errors are shown.

Remote sensing of human skin temperature by AI speckle pattern analysis

Analysis of dynamic differential speckle patterns, scattered from human tissues illuminated by a laser beam, has been found by many researchers to be applicable for noncontact sensing of various biomedical parameters. The COVID-19 global pandemic brought the need for massive rapid-remote detection of a fever in closed public spaces. The existing non-contact temperature measurement methods have a significant tradeoff between the measurement distance and accuracy. This paper aims to prove the feasibility of an accurate temperature measurement system based on speckle patterns analysis, enabling the sensing of human temperature from an extended distance greater than allowed by the existing methods. In this study, we used speckle patterns analysis combined with artificial intelligence (AI) methods for human temperature extraction, starting with fever/no fever binary classification and continuing with temperature measurement at higher resolution.

Radiation temperature measuring method with high dynamic range via fast double-exposure image fusion

The CCD (Charge-coupled device) image sensor can invert the surface temperature of the object by collecting the radiation signal of the high-temperature object. It is a non-contact temperature measurement method, which has the characteristics of fast response without affecting the surface distribution of the tested object. Due to the restriction of the development level of CCD, the exposure tolerance of imaging is low. As a result, the temperature field measurement range is low. In order to solve the problem of low exposure tolerance caused by dark current and saturation in CCD, this paper proposes a radiation temperature measuring method with high dynamic range via fast double-exposure image fusion technology, and a high temperature field measurement system based on LabVIEW and visible light industrial camera is developed. The method proposed in this study is suitable for the stationary objects in temperature range from 750 to 1200 ℃. By correcting the non-impulse response of the sensor, the temperature measurement error is better than 2%. By fusing two images with different exposure duration, the dynamic temperature measurement range is increased to 59.2%, which significantly improves the adaptability of the CCD in the measurement of high temperature field.

Dynamic Group Difference Coding Based on Thermal Infrared Face Image for Fever Screening

Recently, noncontact temperature measurement methods based on infrared face perception have received widely attentions since fever screening plays an important role in the early prediction of respiratory infections, such as SARS, H1N1, and COVID-19. However, the performance of these methods always significantly degrades when facing the changes of environment. Thus, the majority of these methods leverage the block-body and sensors to reduce the influence of environment changes. It is a pity that the increased instrument complexity leads to higher costs and failure rate. To address the aforementioned issues, this article presents a novel fever screening method, named dynamic group difference coding (DGDC), which is based on the analysis about the influencing factors. The key idea of DGDC is to compute the temperature differences between the target person and the recently passed crowd (dynamic group). Specifically, we develop the face temperature encoder (FTE) to describe the face temperature and thus construct the difference matrix of the embedding feature between the target person and the dynamic group. Multilayer perceptions (MLP) are employed to capture the intrinsic information by characterizing the difference matrix in vertical and horizontal directions, respectively. Finally, we provide a dataset of thermal infrared face (TIF) images and conduct extensive experiments to demonstrate the advantages of the proposed method over the competing methods.

Intelligent Compensation Method of Infrared Temperature Measurement for Multiple Interference Factors

Infrared thermography is a widely used noncontact temperature measurement method. However, the infrared temperature measurement result is susceptible to interference factors. To overcome the infrared temperature measurement errors caused by the simultaneous influence of multiple interference factors, this article takes the measuring distance and dust as specific interference factors and proposes an intelligent compensation method for the infrared temperature measurement errors caused by the measuring distance and dust. First, the influence of the measuring distance and dust is analyzed from the perspective of the infrared temperature measurement principle. Second, a weighted ensemble stacked denoising autoencoder (WE-SDAE) is proposed and used to construct an intelligent compensation model. Then, the measuring distance, dust transmittance, and measured temperature are used as the input of the compensation model to estimate the errors caused by the measuring distance and dust. Finally, the estimated error is used to compensate for the original infrared temperature measurement results under multifactor interference. Experimental results in two cases show that the proposed method is effective in compensating for the infrared temperature measurement errors caused by the measuring distance and dust, which is beneficial to ensure the accuracy of the infrared thermal imager in complex temperature measurement scenarios.

Acoustic Tomography Temperature Reconstruction Based on Virtual Observation and Residual Network

High-quality measurement of temperature distribution information is of great significance for industrial production. As a typical non-contact temperature measurement method, acoustic tomography (AT) can obtain temperature distribution through reconstruction algorithms. To improve the reconstruction quality, a two-stage algorithm based on virtual observation (VO) and residual network (ResNet) was proposed. This algorithm combines the advantages of VO and ResNet. Aiming at total least squares, the VO method was adopted to reconstruct the ultrasonic time-of-flight (TOF) to obtain the temperature distribution under a coarse grid. Then, ResNet was built to predict the temperature distribution under the refined grid, and the dual-input model was used to improve the network generalization ability. At the same time, the sub-pixel convolution layer was introduced to reduce the network computing dimension, which improves the computing efficiency and the reconstruction quality. The numerical simulation of typical temperature field models was carried out, and the reconstruction results show that the average relative error and root mean square error are less than 0.86% and 1.21%, respectively. The noise immunity and reconstruction spatial resolution are better than traditional algorithms and the previous two-stage algorithm.

A multispectral thermometry based on multi-objective constraint optimization

Multispectral thermometry is a widely used non-contact temperature measurement method. How to obtain accurate target temperature under the unknown spectral emissivity is a difficult problem to be solved in this field. The emissivity assumption model method commonly used cannot be widely applied to the temperature measurement of various materials. Therefore, a multispectral thermometry based on multi-objective constraint optimization is proposed, which can accurately solve the true temperature and spectral emissivity without any prior knowledge of emissivity. In this method, the multi-objective function is established according to the radiation equations. The new emissivity constraint conditions are set for the objective function, and a mixed penalty function method is used to solve the constraint optimization problem. The simulation experiment results show that the relative error of temperature measurement for the method is less than 1%, and the average running time is less than 0.1 s, which prove the feasibility and reliability of the proposed method.

Temperature non-uniformity detection on dPCR chips and temperature sensor calibration.

A microfluidic-based digital polymerase chain reaction (dPCR) chip requires precise temperature control as well as uniform temperature distribution to ensure PCR efficiency. However, measuring local temperature and its distribution over thousands of μL/nL-volume samples with minimum disturbance is challenging. Here, we present a method of non-contact localized temperature measurement for determination of the non-uniformity of temperature distribution over a dPCR chip. We filled the dPCR chip with a PCR solution containing amplified DNA fragments with a known melting temperature (TM). We then captured fluorescent images of the chip when it was heated from 70 to 99 °C, plotted the fluorescence intensity of each partition as a function of temperature, and calculated measured TM values from each partition. Finally, we created a 3-D map of the dPCR chip with the measured TM as the parameter. Even when the actual TM of the PCR solution was constant, the measured TM value varied between locations due to temperature non-uniformity in the dPCR chip. The method described here thereby characterized the distribution of temperature non-uniformity using a PCR solution with known TM as a temperature sensor. Among the non-contact temperature measurement methods, the proposed TM-based method can determine the temperature distribution within the chip, instead of only at the chip surface. The method also does not suffer from the undesirable photobleaching effect of fluorescein-based temperature measurement method. Temperature determination over the dPCR chip based on TM allowed us to calibrate the temperature sensor and improve the dPCR configuration and precision. This method is also suitable for determining the temperature uniformity of other microarray systems where there is no physical access to the system and thus direct temperature measurement is not possible.

Uncertainty of Thermographic Temperature Measurement with an Additional close-up Lens

Abstract The thermographic temperature measurement is burdened with uncertainty. This non-contact temperature measurement method makes it possible to measure the temperature of the electrical device under load. When the observed object is small (a few square millimeters) the spatial resolution of the thermographic cameras is often insufficient. In this case, the use of the additional macro lens is needed. After using an additional lens, the uncertainty of the thermographic measurement is different from the uncertainty of thermographic measurement without an additional lens. The values of the uncertainty contributions depend on the conditions during the measurement and the used methodology. The authors constructed an uncertainty budget of thermographic temperature measurement with an additional macro lens, based on EA-4/02 (European Accreditation publications). The uncertainty contributions were also calculated. On the basis of the calculated values of the uncertainty contributions, it was determined which factor had the greatest impact on the value of the thermographic temperature measurement with an additional lens.

Understanding time-temperature characteristics in microwave cladding

Microwave cladding is an emerging surface modification technique. Temperature control is the key issue in any surface modification technique. In microwave cladding, non-contact temperature measurement methods are widely used; however, these methods report only the surface temperature of the susceptor. In the present study, a modified B-type thermocouple was used to measure the real time-temperature distribution while developing Ni-based clad. Formation of clad has been discussed with respect of time-temperature distribution. Effect of microwave power on heating profile was also investigated.

Non-contact temperature measurement method for dynamic rating of overhead power lines.

The increase in energy efficiency of power systems and the development of smart grids are strongly based on new and more accurate ways of monitoring. In overhead power line systems, the focus is on monitoring weather conditions and the main line parameters, such as the current and temperature of the conductor. Current and temperature are linked by the Joule heating effect and ampacity, which is the maximum amount of electrical current a conductor can continuously carry before sustaining deterioration given the dynamic environmental conditions. Conductor temperature is also related to another critical parameter for overhead power lines: their maximum allowable sag. These two parameters, ampacity and sag, give an idea of the importance of conductor temperature dynamic monitoring. There are several contact temperature methods on the market; however, they are expensive and challenging to implement owing to the complexity of electronic devices working in a high voltage environment related to the maintenance and life span of the instrumentation. This paper presents a novel method to estimate the temperature of overhead power lines using a non-contact infrared system. From the comparison between contact and non-contact temperature measurement methods a correction function was obtained to infer the temperature of the conductor from the infrared measurements. This option has several advantages in comparison with the current methods as it is a cheap and passive system that foregoes the need to attach electronic components to the power line, thus simplifying the maintenance and improving the safety of the operations.

On the thermal sensitivity and resolution of a YSZ:Er3+/YSZ:Eu3+ fluorescent thermal history sensor

This paper deals with the problem of thermal history analysis of high temperature components for applications such as furnaces, nuclear reactors and jet engines. It focuses on fluorescent thermal history sensors, which exhibit permanent changes in their luminescence properties when exposed to high temperature. These changes can then be quantitatively evaluated to determine the temperature of exposure from a previous thermal event. The main objective of this paper is to investigate the thermal sensitivity and the thermal resolution of a yttria-stabilized zirconia (YSZ) Er3+-doped phosphor produced by a sol-gel route and combined with a thermal history insensitive YSZ:Eu3+ reference, which was selected for its high sensitivity to thermal history above 1173 K. In particular, the interest of this YSZ:Er3+/YSZ:Eu3+ sensor is discussed in the view of the physical properties of sol-gel deposited YSZ coatings, the selection of an appropriate excitation wavelength and the practical measurement of coatings fluorescence properties. The sensitivity and the resolution of two thermal history measurement fluorescence methods, based on intensity ratios and lifetime analysis, were determined and compared. A comparison is also made with standard non-contact temperature measurement methods such as infrared thermography and thermochromic paints.

The effect of surface observation angle on accuracy of non-contact temperature measurement method

Thermal control by IR devices is a fairly difficult task, because it depends on a large number of external factors. The greatest error of contactless temperature measurement method is unknown or variable emissivity of the surface of the object. This is due to the fact that the ability of the object to emit infrared radiation can vary because it is depended on the material, properties of the surface, observation direction, and in the case of some materials – on temperature. Technological audit was conducted to identify the variation characteristics of emissivity coefficient in terms of thermal control. The aim of audit was to determine the effect of observation angle on the emissivity coefficient. Using thermal imager and auxiliary equipment it was found that with the measurement error is increased with increase of observation angle and may reach 50 %. The authors conducted a series of experiments confirming the effect of observation angle on accuracy of temperature measurement, and proposed dependencies allowing to reduce the value of absolute error of measurement using IR devices to several degrees that in relative form less than 1 %. Research results will improve the accuracy of temperature measurement by taking into account an effect of observation angle on emissivity coefficient of the object, normalize image thermograms for different sections of the object, as well as the select possible defective areas on the thermogram to determine the uniformity of thermal field.

A noncontact temperature measurement method in polymerase chain reaction reactors

A new noncontact method for measuring temperatures of liquids, which is based on the fluorescent probes, is proposed. The method is intended for measuring temperatures of reaction media in reactors of devices for polymerase chain reactions in real time and can be used for determining dynamic temperature parameters.