Colorimetric Temperature Measurement Research Articles

A Thermopile-Based Colorimetric Temperature Measurement Method for Arbitrary Bandwidth

Colorimetric temperature measurement is an essential technique in radiometric thermometry. Traditional colorimetric methods determine temperature by comparing the ratio of radiative energies within two narrow bands at specific wavelengths, effectively mitigating the effects of the emissivity of the measured object and ambient conditions. However, these methods typically approximate integration using area calculations when calculating radiative energy. This article eliminates this approximation and calculates the radiative energy with accurate integration. Based on the principle of monotonicity, this article demonstrates for the first time that when two narrow-band infrared radiations are selected, as long as their wavelength ranges do not overlap, the ratio of radiative energies within these bands maintains a monotonic relationship with the measured temperature. This allows the temperature to be inferred from the energy ratio. Furthermore, this conclusion is extended to arbitrary widths of bands as long as their wavelength ranges do not overlap. Building on this foundation, a thermopile-based colorimetric temperature measurement method for arbitrary bandwidth is proposed. Simulation experiments validate this method, showing that the energy ratio maintains a monotonic relationship with the measured temperature as long as the infrared radiation wavelength ranges absorbed by the thermopile do not overlap. The simulation results are consistent with the mathematical proof.

Repetitive shock waves generated by a single long pulse underwater arc discharge

The electrohydraulic effect induced by underwater arc discharge is an efficient way to generate controllable, high-intensity shock waves. However, the development process of underwater arc discharge involves the complex coupling of plasma arc, gas bubble, and liquid medium, of which the evolution mechanism is not well understood. In this paper, the underwater arc discharge process at a millisecond pulse (>50 ms) was investigated by high-speed shadow imaging and colorimetric temperature measurement, and a simulation model of bubble pulsation was proposed to quantitatively estimate the state variation and energy transfer of the gas bubble. The results indicate that the whole arc discharge process can be categorized into three successive stages: short-period oscillation, long-period oscillation, and quasi-steady state. The vapor inside the bubble can reach a supercritical state (827 K and 140 MPa) at the minimum bubble radius. The simulation shows that the light radiation absorption and the heat conduct loss through metal electrodes are the two dominant factors influencing the pulsation of the bubble, and further analysis indicates that the dynamic evolution of the arc determines the bubble pulsation mode. Our findings demonstrate why and how repetitive electrohydraulic shock waves can be generated by a single long pulse underwater arc discharge, providing a low-cost way of shock wave generator based on an AC/DC high-voltage power source.

Simulation research of the influence of different representative wavelengths on colorimetric temperature measurement accuracy

Abstract Colorimetric temperature measurement can achieve greater accuracy by obtaining data on the spectral radiance at two representative wavelengths. As color CCD cameras have three pairs of color combinations, the research would explore the accuracy of these three combinations in temperature measurement by simulation research. The stimulation values of the CCD camera for the three primary colors often differ from the three primary color wavelengths specified by the CIE. Therefore, through conducting comparative temperature measurement experiments on simulated objects, the research assesses the accuracy of color temperature measurement by comparing the performance of the CIE-specified wavelengths for the three primary colors with the stimulus values of a color CCD camera. Additionally, this research would also investigate the impact of differences in representative wavelengths on the accuracy of non-grey body temperature measurements.

Study on CCD temperature measurement method without channel proportional coefficient calibration

The physical state and physicochemical properties of matter can be directly affected by high temperature process. Therefore, the measurement of high temperature is of great significance in the fields of scientific research, material processing, and equipment evaluation. However, the existing charge-coupled device (CCD) colorimetric temperature measurement technology fails to deal with the system of integral equations, and it needs to be re-calibrated to obtain the channel proportional coefficient to complete the solution. Thus, the complexity of the preparation process is increased and experimental errors inevitably occur. In this study, Lagrange theorem calculation method of CCD colorimetric temperature measurement is not considered, and a temperature solution method based on Taylor expansion of integral equations is proposed by using the same hypothesis. The theoretical error range is analyzed, and the selection method of optimal expansion wavelength and the calculation steps of actual temperature measurement are presented. The uncertainty of the system is discussed, a comparative experiment of colorimetric temperature measurement is conducted by measuring the flame temperature, and the experimental error is analyzed. To verify the accuracy of theoretical calculations, this study effectively simplifies the calibration steps of temperature measurement equipment, and provides a new idea for multi-wavelength and multi-channel two-dimensional temperature measurement.

Measurement of weld penetration for variable-groove weldment using dual-band imaging and neural network

For the process of gas metal arc welding, the online measurement of weld penetration has always been a research hotspot, and high-precision penetration monitoring can lay the foundation for penetration control. This study developed a novel method for measuring the weld penetration of variable-groove weldments using dual-band imaging and a neural network. First, a welding temperature field measurement system was constructed using a colour charge-coupled device (CCD), and the feasibility of using the output images from the red and green channels of the CCD for colorimetric temperature measurement was investigated. Then, a welding temperature field measuring algorithm based on a network model was investigated. Compared with the traditional temperature measurement algorithm, the proposed algorithm can measure the welding temperature field with higher precision. The distribution characteristics of the temperature field were extracted by means of the histograms of oriented gradients (HOG) algorithm. Finally, based on a back-propagation (BP) neural network, a weld penetration prediction model for variable-groove weldments was built, and the distribution features of the temperature field were used as the model input. The experimental results reveal that the proposed back bead penetration measurement method for variable-groove weldments can achieve the high-accuracy penetration measurement, which has broad application potential.

A Plasma Diagnosis Method for a Vacuum Arc Under Curved Contact

Based on the continuous spectrum theory, the plasma parameters of a vacuum arc under curved contact are diagnosed in this study. A colorimetric temperature measurement system composed of a color high-speed camera and bimodal filter is built, which is corrected by a tungsten strip lamp. According to the shape characteristics of a vacuum arc under curved contact, a calculation method of radiation intensity using curved space transformation is proposed, which reduces the error caused by the curved contact structure. Finally, the plasma parameter distributions for vacuum arcs under curved contact and butt contact are obtained, and the reason and effect on these distributions are investigated.

Thermochromic Microcapsules Containing Chiral Mesogens Enclosed by Hydrogel Shell for Colorimetric Temperature Reporters

AbstractChiral mesogens spontaneously form a cholesteric phase and show structural colors through wavelength‐selective reflection. Although chiral mesogens are pragmatic materials to build cholesteric phase due to their low toxicity, low cost, and robustness, an elaborate encapsulation technique is not reported yet. In this work, cholesteryl esters are encapsulated with a calcium‐alginate hydrogel shell using oil‐in‐water‐in‐oil double‐emulsion droplets. With capillary microfluidic devices, monodisperse double‐emulsion droplets are prepared to have a mixture of cholesteryl ester and toluene in the innermost droplets and an aqueous solution of sodium alginate and calcium‐carrying complex in the outer droplets. As toluene diffuses out from the core, cholesteryl ester forms the cholesteric phase. At the same time, calcium ions are dissociated from the complex upon chemical cues, which causes ionic crosslinking of alginate. The microcapsules show the thermochromic property as the structural color of the cholesteric core blue‐shifts along with the temperature. Therefore, the microcapsules report local temperatures with colors or reflectance spectra. As the range and sensitivity of the colorimetric temperature measurement are controllable by adjusting the composition of cholesteryl esters, a wide range of temperature can be covered by employing a proper set of compositions while maintaining high sensitivity.

Noise-Suppressed Temperature Measurement Based on Machine Learning in a Scramjet Combustor

An algorithm of noncontact portable temperature measurement sensors that can be used for scramjet combustion chamber measurement is developed. The two-wire colorimetric temperature measurement is analyzed and found unable to be applied in the scramjet combustor due to its weak noise resistance. Then the inversion capabilities of the OH (hydroxyl) radical emission spectrum database of the multilayer perceptron and the convolutional neural network are compared. Considering the influence of noise, the influence of adding different proportions of random Gaussian noise on the network prediction results is compared. After adding 5% random Gaussian noise to the convolutional neural network, the regression error of the temperature prediction in the range of 500–4000 K is less than 50 K. As a method verification, the experiment of the ground combustion chamber of the scramjet under working condition is processed. Compared with the tunable diode laser absorption spectroscopy measurement result, the measurement temperature of the convolutional neural network is about 400 K higher, and the root mean square error is close to the measurement result of tunable diode laser absorption spectroscopy.

Research on 2D Temperature Field Measurement Method of Mg/CO2 Combustion Flame Based on Color CCD

A new Mg/CO2 powder rocket propulsion system is proposed for Mars exploration. Accurate measurement of Mg/CO2 combustion flame temperature field has important reference value for understanding the combustion characteristics and operating conditions. In this paper, the two dimensional temperature field of the Mg/CO2 combustion flame is obtained by building a Mg/CO2 combustion device and colorimetric temperature measurement system based on the color charge coupled device (CCD). The influence of magnesium powder particle size, premixed Reynolds number, and CO2/Mg oxygen fuel ratio on the flame temperature of Mg/CO2 combustion are discussed. The results show that the maximum temperature of Mg/CO2 combustion flame under different working conditions is between 2500K and 2900K, and it increases with the increase of magnesium powder particle size, premixed Reynolds number, and oxygen-fuel ratio.

Visualization of Arc Energy Distribution Based on CCD Image Sensor

With the advancement of computer and sensor technology, visualization research has been more and more widely used in the industrial field, especially for arc plasma research of high energy fields. During the electrical breaking process, the DC arc energy distribution directly affects the working performance of the switchgear. A single voltage and current monitoring method is difficult to characterize the complex energy evolution process of the arc. Therefore, the visualization of the arc energy distribution is particularly important. In this paper, the arc energy distribution of the arc combustion process is visualized as the main research content. The arc characteristic detection platform is built, and the voltage, current, contact displacement value and arc image between the contacts are synchronously collected. According to the spectral characteristics of the color CCD image sensor, the colorimetric temperature measurement formula with calibration coefficient is derived to establish the relationship between the pixel and the arc temperature. The acquired arc image is processed by matlab image processing technology to visualize the two-dimensional energy distribution characteristics of the arc in the horizontal projection direction during the breaking process.

Removal of optical crosstalk caused by light source for synchronous measurement of temperature and deformation

Synchronous measurement of temperature and the deformation field can be achieved through reasonable assignment of R, G, and B channels of a CCD camera in a high-temperature environment. The R and G channels are used for colorimetric temperature measurement, and the B channel is adopted for deformation measurement. However, the external blue compensation light source may cause crosstalk of the R and G channels, leading to inaccurate measurement. To eliminate such an interference phenomenon, we first use the function relationship between the illumination of the object surface and the exposure time to calibrate the camera parameters at room temperature, thus removing the initial gray level of the R and G channels in the high-temperature image. This contributes to improving the low-temperature measurement accuracy for the temperature field, with a calculation error of <5 % . In contrast, an experiment shows that the temperature deviation of the low-temperature region calculated using the uncorrected image is up to hundreds of degrees. Then, the radiation intensity of channel B is removed using the temperature balance relationship, which increases the calculation accuracy by 15% in comparison to the uncorrected result. The algorithm is validated by the heating experiment of C/SiC material with an oxy-acetylene flame. The results suggest that the proposed improved algorithm is of great significance for the evaluation of materials at high temperatures.

Hump weld bead monitoring based on transient temperature field of molten pool

The molten pool images of GMAW (Gas Metal-Arc Welding) was acquired during the base time period using a self-built system for measuring the transient temperature field of molten pool. The transient temperature field of the molten pool of GMAW at different welding speeds was calculated based on the principle of colorimetric temperature measurement. When analyzing the temperature distribution at the middle and tail region of the molten pool in the process of hump bead formation under high speed GMAW, it was found that the temperature distribution of the molten pool is uneven perpendicular to the welding direction, and this law does not accord with the time when the hump appears in the image, and the accuracy rate accorded with the law was also counted. Through this rule, the welding robot can adjust and control the process in time before the appearance of hump, and the prediction of hump before bead formation under GMAW is preliminarily realized.

Colorimetric Temperature Measurement Method Considering Influence of Ambient Temperature

Colorimetric temperature measurement has important applications in industrial production. However, it’s usually applied to high temperature measurement because it lacks accuracy in medium-low temperature measurement. Aimed at improving the low accuracy of traditional colorimetric temperature measurement method in medium-low temperature measurement, this paper pays attention to the influence of ambient temperature on colorimetric temperature measurement method, especially focusing on the influence of ambient temperature on the measured target and the non-refrigerated infrared detector, and improves the traditional method by considering the influence of ambient temperature. Experimental results show that in the experimental temperature range, the relative error of the method proposed in this paper is less than 1.2%, while the relative error of traditional method is less than 4.0%. So this method can significantly improve the precision of temperature measurement especially in medium-low temperature measurement.

Temperature Measurement System of Roller Kiln Based on Colorimetry

In order to overcome the shortcomings of the traditional temperature measurement method which can only acquire the single point temperature or local temperature in the production process of roller kiln, In this paper, according to the principle of colorimetric temperature measurement, using the method of image preprocessing, designed a temperature measurement system based on CCD image sensor. The system can monitor and measurement the internal temperature of the roller kiln, and can obtain the global distribution of temperature field. According to the standard value method ,the system is calibrated using a blackbody furnace, to increase the detection precision and accuracy of temperature.The experimental results show that the system has high accuracy, can real-time reflect the global temperature field distribution of the roller kiln ,and the system has the great potential of industrial application.

Colorimetric Temperature Measurement Algorithm Based on Multi-Sensor Data Fusion

Wavelength and other factors have a deep influence on temperature measurement system based on CCD image sensor. Deviations between measurement values sometimes are large. In order to reduce error, the temperature outputs in different wavelength combinations do have multi-sensor correlation properties in point of colorimetric temperature measurement system view. The colorimetric temperature measurement algorithm based on real-time adaptive weighted is put forward by such performance index that minimum of standard deviation. According to measured value of each sensor, we will find out the corresponding weights in adaptive manner. And discuss the statistical properties of the estimated standard deviation. Estimation unbiasedness is proved. The algorithm has the following advantages .A much smaller amount of calculation, without any a priori knowledge, only relying on the output of each sensor. All of these make temperature estimation be optimal, measurement accuracy and the real-time performance of the system are improved. Theoretical analysis and experimental results show that the colorimetric temperature measurement algorithm based on the real-time adaptive weighted improves obviously when comparing with the traditional means algorithm in measurement accuracy.

Design and Implementation of a Soft-Measuring System for High-Temperature Field Based on Color CCD Image Sensor

The soft-measuring system consists of an optical lens, a color CCD camera, an image acquisition card, a computer and associated measuring software based on colorimetric temperature measurement. Using the system, the temperature distribution of a high-temperature field can be measured and then displayed on the screen. A method of adjusting the intensity of light is developed to expand the range of the measuring temperature of the system, and the calibration experiments through blackbody furnace are adopted to calibrate the soft-measuring system. The errors of the measurement caused by the non-ideal spectrum response of CCD image sensor are corrected. Multi-spectral segmenting is applied on the image of the high-temperature field, thus various high-temperature noises in the color image can be reduced or even eliminated. The experiment indicates the soft-measuring instrumentation meets the high-temperature detecting requirements of industrial production due to its high accuracy and reliability.

On-line Temperature Measurement System for Carbonization Chamber Wall of Coke Oven

The basic principle of radiation pyrometer and colorimetric pyrometer are introduced first. Then the design of a colorimetric fiber-optic temperature measurement system used for temperature measurement in the carbonization chamber of coke oven is described in detail. The use of double-clad silica fiber solves the problem of high ambient temperature. The system is consisted by STC12C5A60S2 single-chip microcomputer as the core and AD converter MAX195. The colorimetric temperature measurement can eliminate the background interference and the measuring precision and stability are greatly enhanced. Temperature measurement system is satisfied with the demand of scene. It is shown that this system is available.

Online Temperature Detecting System in Hot Machining Process

A kind of optical fiber radiation pyrometer based on the theory of color comparison temperature measurement is designed in order to get the precise temperature on the appearance of work pieces during the process of plasma hot machining. In this article, the advantage of temperature measurement by optical fiber, the building of mathematic module for colorimetric temperature measurement, the application of key technology during the process of system building and the methods of reducing the interference is described in detail. The data calibrated and tested in blackbody furnace is given out. The results show that the precision of temperature measurement could reach to 0.5%. It is repetitiveness is well enough.