Temperature Measurement Technique Research Articles

Thermography and artificial intelligence in transformer fault detection

Dissolved gas analysis of insulating oil in refrigerated power transformer oil is a widespread technique for detecting incipient faults. However, this technique involves safety procedures for the collection of oil samples, laboratory response times and, in some cases, removing the transformer from operation. Removing a transformer from operation in certain situations can become very costly as there are production environments that must run uninterrupted so that stoppages such as this represent financial loss. Infrared thermography is a non-destructive temperature measurement technique commonly used to detect anomalies and predict possible faults without disrupting system operation. This paper presents studies based on the use of infrared temperature measurement to detect incipient faults in transformers through dissolved gas analysis of the insulating oil. This study’s methodology uses intelligent systems to analyse transformer face temperatures and detect incipient faults. The results obtained in this work present 86 and 83% of classification correctness using artificial neural networks and fuzzy logic, respectively.

Ex situ calibration technique for simultaneous velocity and temperature measurements inside water droplets using temperature-sensitive particles

Phosphorescence-based temperature measurements usually employ in situ calibration in macro-scale flow domains. However, the application of conventional in situ calibration in millimetre scales such as in 2 mm droplets is difficult because temperature probing using an intrusive technique such as thermocouple-based measurement can deform a droplet interface and even its integrity. Therefore, in this paper we propose an ex situ calibration technique for combined 2D fluid temperature and flow velocity measurements inside pendant droplets using thermographic phosphorescence and particle image velocimetry. This calibration technique has the potential to perform measurements not only inside droplets but also in other small-scale fluid domains that are sensitive to intrusive temperature probing. To develop this technique, the effect of local phosphorescence intensity on the phosphorescence decay constant (initial intensity effect) was studied and quantified. We observed that the phosphorescence light intensity of the first image among the decay image series affects the local decay constants as the coefficient of a half sigmoid function. This novel ex situ calibration technique was used to investigate high-spatial-resolution temperature and flow velocity distributions inside a pendant water droplet located in an air stream, and an anti-distortion algorithm was used to correct the optical distortion induced by the curved surface of the droplet. The measured temperature and velocity fields were found to be reasonable and consistent with those obtained in previous studies. The proposed technique is expected to be useful in conducting further investigations on the mechanisms of heat and mass transfers between droplets and carrier gases. Furthermore, it can potentially improve our understanding of the heat and mass exchange mechanisms within a droplet’s internal flow structures and temperature gradients.

Non-invasive Estimation of Temperature during Physiotherapeutic Ultrasound Application Using the Average Gray-Level Content of B-Mode Images: A Metrological Approach

Healing therapies that make use of ultrasound are based on raising the temperature in biological tissue. However, it is not possible to heal impaired tissue by applying a high dose of ultrasound. The temperature of the tissue is ultimately the physical quantity that has to be assessed to minimize the risk of undesired injury. Invasive temperature measurement techniques are easy to use, despite the fact that they are detrimental to human well being. Another approach to assessing a rise in tissue temperature is to derive the material's general response to temperature variations from ultrasonic parameters. In this article, a method for evaluating temperature variations is described. The method is based on the analytical study of an ultrasonic image, in which gray-level variations are correlated to the temperature variations in a tissue-mimicking material. The physical assumption is that temperature variations induce wave propagation changes modifying the backscattered ultrasound signal, which are expressed in the ultrasonographic images. For a temperature variation of about 15°C, the expanded uncertainty for a coverage probability of 0.95 was found to be 2.5°C in the heating regime and 1.9°C in the cooling regime. It is possible to use the model proposed in this article in a straightforward manner to monitor temperature variation during a physiotherapeutic ultrasound application, provided the tissue-mimicking material approach is transferred to actual biological tissue. The novelty of such approach resides in the metrology-based investigation outlined here, as well as in its ease of reproducibility.

EMPRESS: A European Project to Enhance Process Control Through Improved Temperature Measurement

A new European project called EMPRESS, funded by the EURAMET program ‘European Metrology Program for Innovation and Research,’ is described. The 3 year project, which started in the summer of 2015, is intended to substantially augment the efficiency of high-value manufacturing processes by improving temperature measurement techniques at the point of use. The project consortium has 18 partners and 5 external collaborators, from the metrology sector, high-value manufacturing, sensor manufacturing, and academia. Accurate control of temperature is key to ensuring process efficiency and product consistency and is often not achieved to the level required for modern processes. Enhanced efficiency of processes may take several forms including reduced product rejection/waste; improved energy efficiency; increased intervals between sensor recalibration/maintenance; and increased sensor reliability, i.e., reduced amount of operator intervention. Traceability of temperature measurements to the International Temperature Scale of 1990 (ITS-90) is a critical factor in establishing low measurement uncertainty and reproducible, consistent process control. Introducing such traceability in situ (i.e., within the industrial process) is a theme running through this project.

Time dependent and temperature dependent properties of the forward voltage characteristic of InGaN high power LEDs

Estimating the junction temperature and its dynamic behavior in dependence of various operating conditions is an important issue, since these properties influence the optical characteristics as well as the aging processes of a light-emitting diode (LED). Particularly for high-power LEDs and pulsed operation, the dynamic behavior and the resulting thermal cycles are of interest. The forward voltage method relies on the existence of a time-independent unique triple of forward-voltage, forward-current, and junction temperature. These three figures should as well uniquely define the optical output power and spectrum, as well as the loss power of the LED, which is responsible for an increase of the junction temperature. From transient FEM-simulations one may expect an increase of the temperature of the active semiconductor layer of some 1/10 K within the first 10 μs. Most of the well-established techniques for junction temperature measurement via forward voltage method evaluate the measurement data several dozens of microseconds after switching on or switching off and estimate the junction temperature by extrapolation towards the time of switching. In contrast, the authors developed a measurement procedure with the focus on the first microseconds after switching. Besides a fast data acquisition system, a precise control of the switching process is required, i.e. a precisely defined current pulse amplitude with fast rise-time and negligible transient by-effects. We start with a short description of the measurement setup and the newly developed control algorithm for the generation of short current pulses. The thermal characterization of the LED chip during the measurement procedures is accomplished by an IR thermography system and transient finite element simulations. The same experimental setup is used to investigate the optical properties of the LED in an Ulbricht-sphere. Our experiments are performed on InGaN LED chips mounted on an Al based insulated metal substrate (IMS), giving a comprehensive picture of the transient behavior of the forward voltage of this type of high power LED.

On a stochastically grain-discretised model for 2D/3D temperature mapping prediction in grinding

Excessive grinding heat might probably lead to unwanted heat damages of workpiece materials, most previous studies on grinding heat/temperature, however, assumed the wheel-workpiece contact zone as a moving band heat source, which might be not appropriate enough to capture the realistic situation in grinding. To address this, grinding temperature domain has been theoretically modeled in this paper by using a stochastically grain-discretised temperature model (SGDTM) with the consideration of grain-workpiece micro interactions (i.e. rubbing, ploughing and cutting), and the full 2D/3D temperature maps with highly-localised thermal information, even at the grain scale (i.e. with the thermal impacts induced by each individual grain), has been presented for the first time. To validate theoretical maps, a new methodological approach to capture 2D/3D temperature maps based on an array of sacrificial thermocouples have also been proposed. Experimental validation has indicated that the grinding temperature calculated by SGDTM showed a reasonable agreement with the experimental one in terms of both 1D temperature signals (i.e. the signals that are captured at a specific location within the grinding zone) and the 2D/3D temperature maps of the grinding zone, proving the feasibility and the accuracy of SGDTM. This study has also proved that, as expected, the heat fluxes are neither uniformly-distributed along the wheel width direction nor continuous along the workpiece feed direction. The proposed SGDTM and the temperature measurement technique are not only anticipated to be powerful to provide the basis for the prevention of grinding thermal damage (e.g. grinding burns, grinding annealing and rehardening), but also expected to be meaningful to enhance the existing understanding of grinding heat/temperature than using the common approach depending on the single thermocouple technique.

分光スペクトルと多変量解析を用いた放射率変動影響を受けない新放射測温技術の提案

分光スペクトルと多変量解析を用いた放射率変動影響を受けない新放射測温技術の提案

Two-Dimensional Temperature Field Distribution Reconstruction Based on Least Square Method and Radial Basis Function Approximation

The information of temperature field distribution is complex but quite important for theoretical study and industrial applications, such as burning, drying, and heating, because it can reflect the internal running state of industrial equipment, assist to develop control strategy, and ensure safety in operation. Acoustic imaging is a kind of noncontact temperature measurement technique which is able to achieve temperature field distribution reconstruction. The process of temperature field distribution reconstruction using acoustic imaging is an inverse problem and its reconstruction performance depends on reconstruction algorithm. In this paper, a modified reconstruction algorithm is investigated. Compared with other reconstruction methods of least square algorithm and radial basis function approximation, the reconstruction results indicate that the modified reconstruction algorithm occupies the best information reflection of temperature field distribution and the reconstruction accuracy is improved.

Direct numerical simulation of the passive heat transfer in a turbulent flow with particle

Turbulent non-isothermal fully developed channel flow with solid particles was investigated through Direct Numerical Simulation combined with the point-particle approach. The focus was on the interactions between discrete and continuous phase and their effect on the velocity and the temperature of the particles. It has been found that low momentum inertia particles have a mean temperature similar to the fluid temperature and this effect is almost independent of particle thermal inertia. For particles with larger momentum, the inertia thermal effect is more complex, particle temperature in the near-wall and buffer region is significantly lower than the fluid temperature. The difference between the fluid mean temperature and particle mean temperature increases along with the momentum response time. This may have important consequences on the chemical reactions, technological processes and on the accuracy of temperature measurement techniques based on seeding particle.

Relationship between nano-architectured Ti1−x Cu x thin film and electrical resistivity for resistance temperature detectors

Ti1−x Cu x thin films were produced by the glancing angle deposition technique (GLAD) for resistance temperature measurements. The deposition angle was fixed at α = 0° to growth columnar structures and α = 45° to growth zigzag structures. The Ti-to-Cu atomic concentration was tuned from 0 to 100 at.% of Cu in order to optimize the temperature coefficient of resistance (TCR) value. Increasing the amount of Cu in the Ti1−x Cu x thin films, the electrical conductivity was gradually changed from 4.35 to 7.87 × 105 Ω−1 m−1. After thermal “stabilization,” the zigzag structures of Ti1−x Cu x films induce strong variation of the thermosensitive response of the materials and exhibited a reversible resistivity versus temperature between 35 and 200 °C. The results reveal that the microstructure has an evident influence on the overall response of the films, leading to values of TCR of 8.73 × 10−3 °C−1 for pure copper films and of 4.38 × 10−3 °C−1 for a films of composition Ti0.49Cu0.51. These values are very close to the ones reported for the bulk platinum (3.93 × 10−3 °C−1), which is known to be one of the best material available for these kind of temperature-related applications. The non-existence of hysteresis in the electrical response of consecutive heating and cooling steps indicates the viability of these nanostructured zigzag materials to be used as thermosensitive sensors.

Embedded thermocouple wall temperature measurement technique for scraped surface heat exchangers

Heating and cooling processes involving viscous fluids, crystallization processes or with fouling tendency require often the employment of scraped surface heat exchangers to enhance the heat transfer. In these cases, obtaining the heat transfer coefficient is complex due to the difficulty of measuring the wall temperature. The present work introduces an innovative measurement technique to retrieve the scraped wall temperature based on embedded thermocouples, welded directly into the wall plate. The thermocouple wires were introduced into a knockout and welded with a filler material. Once welded, the entire set was calibrated in a cold room at controlled temperature. A total of 26 T-type thermocouples were welded to a stainless steel wall substrate, tested later in a rotating scraped surface heat exchanger employed in the ice slurry production. The thermocouples presented a variance of 0.3°C and an accuracy after calibration of 0.2°C. The deviation between the scraped wall temperature and the thermocouple measurement was assessed by 2D numerical simulations of the transient heat conduction across the wall substrate. The influence of the wall substrate thickness, thermocouple location and scraping velocity has been considered.

Influence of phase transitions on green fluorescence intensity ratio in Er3+ doped K0.5Na0.5NbO3 ceramic.

The fluorescence intensity ratio (FIR) method is a non-contact temperature (T) measurement technique based on thermally coupled levels of rare earth ions in a doped host. Green fluorescence originating from 2H11/2 and 4S3/2 states of Er3+ doped K0.5Na0.5NbO3 (KNN) ceramic are studied in the temperature range of 300 K to 720 K. The fluorescence intensities change dramatically around phase transition points where the crystal symmetry changes, inducing deviation of the FIR from Boltzmann's law. The temperature determined by the FIR method deviates from thermocouple measurements by 7 K at the orthorhombic to tetragonal phase transition (TO-T) point and 13 K at the Curie point (TC). This finding gives guidance for developing fluorescent T sensors with ferroelectrics and may also provide a fluorescent method to detect phase transitions in ferroelectric materials.

A Combined Rotational Raman–Rayleigh Lidar for Atmospheric Temperature Measurements Over 5–80 km With Self-Calibration

A combined lidar system on the basis of conventional Rayleigh lidar has been extended by two rotational Raman (RR) channels for nocturnal atmospheric temperature measurements from 5 to 80 km over Wuhan, China (30.5°N, 114.5°E). An overlapping altitude range of about 10 km is obtained with the RR-technique temperatures reaching upward to 40 km and the Rayleigh-integration-technique temperatures above 30 km. Temperature values obtained by two different mechanisms match nicely in the overlapping area. By using a data-merge method, complete temperature profiles covering widely from 5 to 80 km are obtained for the observation of the thermal structure and perturbations from the troposphere up to the mesosphere. Based on the overlapping-region (30–40 km) data obtained from this combined RR–Rayleigh lidar system and Rayleigh-integration-technique temperatures initialized with model data at an upper height (90 km), we develop a self-calibration method for the determination of the system-dependent constants for RR temperature retrieval. Compared with the conventional radiosonde calibration method, the self-calibration obtained in the overlap region of both lidar temperature measurement techniques can be extrapolated to the lower temperatures in the tropopause region by using the simpler two-constant calibration function. With this new calibration method, the combined lidar system can perform independent and accurate atmospheric temperature measurements when a coincident (in time and space) radiosonde is not available, as it is often the case. This combined RR–Rayleigh lidar thus has the potential for long-term studies of atmospheric thermal structure and associate perturbations.

Junction temperature measurement of alternating current light-emitting-diode by threshold voltage method

Junction temperature of alternating current light-emitting-diode (AC-LED) has a significant effect on its stable light output and lifetime. The threshold voltage measurement is employed to characterize the junction temperature of AC-LED, due to its excellent merits in high efficiency and accuracy. The threshold voltage is measured when the driving current of an AC-LED rises to a reference on-set value from the zero-crossing node. Based on multiple measurements of threshold voltage at different temperatures, a linear relationship was uncovered between the threshold voltage and the junction temperature of AC-LED with the correlating factor of temperature sensitive parameter (TSP). Thereby, we can calculate the junction temperature with the TSP and threshold voltage once the AC-LED stays at thermal equilibrium state. The accuracy of the proposed junction temperature measurement technique was found to be ±3.2°C for the reference current of 1 mA. It is concluded that the method of threshold voltage is accurate and simple to implement, making it highly suitable for measuring the junction temperature of AC-LED in industry.

Air flow temperature measurements using infrared thermography

Accuracy of two infrared thermography techniques for air flow temperature measurements is evaluated for a benchmark test case of natural convection over a horizontal heated plate. The first technique, which can be called infrared thermography of optically thin media, involves observation of a distant screen with known temperature through the investigated air flow. It allows obtaining 2D temperature fields averaged along line-of-sight, like quantitative schlieren or interferometry techniques, using only software supplied with infrared camera. The second technique employs solid targets installed within the air flow. Temperature distributions, obtained with both methods, are compared to each other, to measurements using background oriented schlieren technique, to thermocouple measurements and to results of 2D and 3D numerical simulations. It is shown that solid target apparent temperature is affected by radiative heat exchange with environment, in this particular case with the heated plate. Simultaneous use of three kinds of targets with special treatment is proposed to take this effect into account. Infrared thermography of optically thin media is shown to be simple and reliable non-intrusive technique for air flow temperature measurements with random error increasing with transmissivity of the flow under study.

Conventional and novel body temperature measurement during rest and exercise induced hyperthermia

Despite technological advances in thermal sensory equipment, few core temperature (TCORE) measurement techniques have met the established validity criteria in exercise science. Additionally, there is debate as to what method serves as the most practically viable, yet upholds the proposed measurement accuracy. This study assessed the accuracy of current and novel TCORE measurement techniques in comparison to rectal temperature (TREC) as a reference standard. Fifteen well-trained subjects (11 male, 4 female) completed 60min of exercise at an intensity equating to the lactate threshold; measured via a discontinuous exercise test. TREC was significantly elevated from resting values (37.2±0.3°C) at the end of moderate intensity exercise (39.6±0.04°C; P=0.001). Intestinal telemetric pill (TPILL) temperature and temporal artery temperature (TTEM) did not differ significantly from TREC at rest or during exercise (P>0.05). However, aural canal temperature (TAUR) and thermal imaging temperature (TIMA) were both significantly lower than TREC (P<0.05). Bland Altman analysis revealed only TPILL was within acceptable limits of agreement (mean bias; 0.04°C), while TTEM, TAUR and TIMA demonstrated mean bias values outside of the acceptable range (>0.27°C). Against TREC, these results support the use of TPILL over all other techniques as a valid measure of TCORE at rest and during exercise induced hyperthermia. Novel findings illustrate that TIMA (when measured at the inner eye canthus) shows poor agreement to TREC during rest and exercise, which is similar to other ‘surface’ measures.

Electric field dependence of optical phonon frequencies in wurtzite GaN observed in GaN high electron mobility transistors

Due to the high dissipated power densities in gallium nitride (GaN) high electron mobility transistors (HEMTs), temperature measurement techniques with high spatial resolution, such as micro-Raman thermography, are critical for ensuring device reliability. However, accurately determining the temperature rise in the ON state of a transistor from shifts in the Raman peak positions requires careful decoupling of the simultaneous effects of temperature, stress, strain, and electric field on the optical phonon frequencies. Although it is well-known that the vertical electric field in the GaN epilayers can shift the Raman peak positions through the strain and/or stress induced by the inverse piezoelectric (IPE) effect, previous studies have not shown quantitative agreement between the strain and/or stress components derived from micro-Raman measurements and those predicted by electro-mechanical models. We attribute this discrepancy to the fact that previous studies have not considered the impact of the electric field on the optical phonon frequencies of wurtzite GaN apart from the IPE effect, which results from changes in the atomic coordinates within the crystal basis and in the electronic configuration. Using density functional theory, we calculated the zone center E2 (high), A1 (LO), and E2 (low) modes to shift by −1.39 cm−1/(MV/cm), 2.16 cm−1/(MV/cm), and −0.36 cm−1/(MV/cm), respectively, due to an electric field component along the c-axis, which are an order of magnitude larger than the shifts associated with the IPE effect. Then, we measured changes in the E2 (high) and A1 (LO) Raman peak positions with ≈1 μm spatial resolution in GaN HEMTs biased in the pinched OFF state and showed good agreement between the strain, stress, and electric field components derived from the measurements and our 3D electro-mechanical model. This study helps to explain the reason the pinched OFF state is a suitable reference for removing the contributions of the electric field and the IPE-induced stress from the temperature rise in the ON state and suggests that the IPE-induced stress in the GaN buffer is an order of magnitude smaller than previously believed. Our analysis and experimental results support previous theoretical studies discussing the electric field dependence of optical phonon frequencies apart from the IPE effect and suggest that this is a general phenomenon occurring in all wurtzite and zincblende crystals. The total electric field dependence of the optical phonon frequencies in piezoelectric crystals is a critical consideration in accurately characterizing the stress, strain, electric field, and temperature distributions in microelectronic devices via micro-Raman spectroscopy.

Development of a spectroscopic technique for simultaneous magnetic field, electron density, and temperature measurements in ICF-relevant plasmas.

Spectroscopic techniques in the visible range are often used in plasma experiments to measure B-field induced Zeeman splitting, electron densities via Stark broadening, and temperatures from Doppler broadening. However, when electron densities and temperatures are sufficiently high, the broadening of the Stark and Doppler components can dominate the emission spectra and obscure the Zeeman component. In this research, we are developing a time-resolved multi-axial technique for measuring the Zeeman, Stark, and Doppler broadened line emission of dense magnetized plasmas for Z-pinch and Dense Plasma Focus (DPF) accelerators. The line emission is used to calculate the electron densities, temperatures, and B-fields. In parallel, we are developing a line-shape modeling code that incorporates the broadening effects due to Stark, Doppler, and Zeeman effects for dense magnetized plasma. This manuscript presents the details of the experimental setup and line shape code, along with the results obtained from an Al iii doublet at the University of Nevada, Reno at Nevada Terawatt Facility. Future tests are planned to further evaluate the technique and modeling on other material wire array, gas puff, and DPF platforms.

Temperature and heat flux measurement techniques for aeroengine fire test: a review

This review is made of studies whereby some types of fire test measuring instrument were compared based on their mode of operation, sensing ability, temperature resistance and their calibration mode used for aero-engine applications. The study discusses issues affecting temperature and heat flux measurement, methods of measurement, calibration and uncertainties that occur in the fire test. It is found that the temperature and heat flux measurements of the flame from the standard burner need to be corrected and taken into account for radiation heat loss. Methods for temperature and heat flux measurements, as well as uncertainties analysis, were also discussed.

Simultaneous distributed measurement of the strain and temperature for a four-point bending test using polarization-maintaining fiber Bragg grating interrogated by optical frequency domain reflectometry

Abstract We demonstrate a simultaneous distributed strain and temperature measurement technique with the spatial resolution of 1 mm using fiber Bragg gratings inscribed in a polarization-maintaining and absorption-reducing fiber (PANDA-FBGs) and optical frequency domain reflectometry (OFDR). We conduct four-point bending tests in an environmental chamber. Using high birefringent PANDA-FBGs that are manufactured specifically for the simultaneous measurements, the uniform temperature distributions and the typical strain distribution profiles of the four-point bending tests were successfully obtained. The measurement errors of strain were from −31 μe to 19 μe, and of temperature were from −0.9 °C to 1.3 °C. The spatial standard deviation was 7.5 μe and 0.9 °C. We also discussed the effect of the residual strain of the sensor-bonding procedures and the data averaging.