Cold Junction Compensation Research Articles

Research on a dedicated thin-film thermocouple testing system for transient temperature measurement

The thin-film thermocouple (TFTC) is featured on small heat capacity and rapid response speed for transient temperature measurements under narrow space and difficult installation. Consequently, we propose a novel transient temperature testing system specifically designed for TFTC. This system features signal conditioning circuits with extended bandwidth and superior transfer speeds, a cold junction compensation method that supports customizable indexing tables, and an adaptive data filtering approach that precisely balances the smoothing of steady-state data with rapid responsiveness to transient data. This approach effectively mitigating the measurement distortion of transient temperature signals and the nonlinear phenomenon in cold junction compensation for TFTC. Utilizing NiCr/NiSi TFTC, we evaluated the system’s accuracy, demonstrating a precision range of −0.5 °C–0.25 °C within 20 °C–100 °C, and a response delay under 0.1 ms. Compared to traditional thermocouple measurement systems, our system exhibits a finer time-domain resolution. Lastly, we successfully applied this system to observe the response of TFTC under the thermal load of short-pulse laser shocks, measuring a time constant of only 1.16 ms for the TFTC. This novel transient temperature testing system provides a new approach for TFTC to achieve online dynamic measurement and online calibration, and provides technical support for TFTC measurement technology towards engineering applications.

ROOT SURFACE TEMPERATURE MEASUREMENT DURING ROOT CANAL OBTURATION

Prolonged exposure to elevated temperatures exceeding 47°C, which can occur during root canal obturation, can cause damage of both dental and bone tissues. In order to study the temperature distribution on the surface of the tooth root a temperature measuring device with cold-junction compensation is proposed. For in vitro measurement of the temperature distribution on the surface of the tooth, 8 thermocouples placed in direct contact with the cementum of the tooth were used. In order to eliminate the cold-junction temperature variations, the temperature equilibration device and RTD were used. The suggested linear approximation for the thermocouples' conversion function provides a nonlinearity relative error of less than 0.05% for K-type thermocouples and 0.07% for J-type thermocouples over the temperature range from 20 to 60°C.

FPGA-based multi-channel thermocouple temperature measurement system

Aiming at the high and low temperature test requirements of spacecraft before being sent into space, this paper designs and implements a multi-channel thermocouple temperature measurement system based on FPGA.The system adopts thermocouple as temperature sensor, and ADT7310 is used as thermocouple cold junction temperature compensation, which solves the problem of thermocouple cold junction compensation better.The front end adopts AD7193, a 24-bit analog-to-digital converter with low noise, multi-channel and low power consumption, to amplify and A/D convert the signal at measuring junction of thermocouple.The control core is a field programmable logic gate array FPGA, which can better solve the problem of parallel processing of multi-channel temperature signals. At the same time, it uses the transposition method of the thermocouple standard graduation table, the interpolation look-up table algorithm and the cold junction compensation reverse look-up table algorithm, which is effective The temperature measurement accuracy of each channel is improved.The experimental results show that the system can be connected to 24 K-type or T-type thermocouple sensors, the measurement range can reach -200°C∼220°C (73.15K∼493.15K), and the relative error is less than ±0.3%F.S.

Temperature Indicators Field Calibration Method Based on an Integrated Thermostat with Cold Junction Compensation

By designing a field calibration device for temperature indicators, this paper proposed a method for field calibration of indicators based on an integrated thermostat with cold junction compensation to overcome the current problems with conventional methods, which include long duration before constant temperature at cold junction, non-portable design, low accuracy of temperature compensation. The thermostat integrated in the device can achieve rapid thermal control while remaining portable based on the miniaturized structure that the thermocouple terminals can placed in the thermostat and an algorithm for thermostat control. After error analysis and experimental verification, reliable results were obtained to prove that this method has the advantages of portability and efficiency compared with conventional methods.

Design of K Type Thermocouple Cold End Automatic Compensation Based on Single Chip Microcomputer

The K-type thermocouple is one of the most widely used temperature sensor in the industrial field, and its performance directly affects the accuracy of the sensor. As the most important measurement tools of detection technology and Instruments, the results’ accuracy of the K-type thermocouple is very important. In order to improve the compensation accuracy, this design gets improvement on the methods of cold-junction compensation. According to the great data processing capabilities of single chip microcomputer, this paper designs the K-type thermocouple cold-junction compensation circuit by using the spot potential and the algebraic sum of environmental potential as thermocouple’s standard potential.

Deep Neural Network Based Linearization and Cold Junction Compensation of Thermocouple

In this proposed work, temperature sensors, namely, a thermocouple and thermistor were linearized using deep neural networks. The deep feedforward neural network (DFNN) technique was proposed to linearize the K-type thermocouple’s output, in the given temperature range −100 °C to 1372 °C, while nonlinearity was reduced from 2.03% to 0.002% full scale span (FSS). Deep layer recurrent neural network (DLR-NN) was used to reduce the nonlinearity of a negative temperature coefficient (NTC) thermistor from 84.63% to 0.13% FSS. The linearized thermistor was used for cold junction compensation (CJC) of the thermocouple. In both the thermocouple and thermistor, linearization was achieved in a single stage for a wide range digitally using deep neural networks alone. There were no analog pre-signal conditioning circuits, unlike the existing neural network-based linearization techniques in literature. A hardware setup of a stand-alone module for linearization was designed using the Raspberry pi microcontroller consisting of two soft modules, one for thermocouple linearization and the other for thermistor linearization. The proposed system was experimentally tested using a K-type thermocouple on a thermal calibrator in a 0 °C–300 °C range. The cold junction compensated output of the thermocouple had a maximum absolute error of 0.34 °C when ambient temperature varied from 0 °C to 40 °C. The results were satisfactory and better than the existing National Institute of Standards and Technology (NIST) standard. This linearization technique can be extended to other thermocouple types as well as other nonlinear sensors.

Development of Thin Film Thermocouple Test System for Transient Temperature Measurement

In order to achieve accurate temperature measurement in a fast temperature change environment, a set of thin film thermocouple test system for transient temperature measurement is designed and developed. The system consists of cold junction compensation and data collector. The temperature of the film thermocouple can be obtained in real time through the upper acquisition software. The hardware composition and software design of the thin film thermocouple test system are given. The data acquisition terminal and coordinator program are designed to control the temperature signal of the MAX31855 to collect the sensor, realizing the real-time transmission of temperature data between the sensor and the computer. In order to verify the actual application effect of the system, the matching, stability and reliability of the temperature acquisition system and monitoring software, the FLUKE-9144 dry calibration furnace was selected as the heat source for the temperature test. The test results show that the system has fast acquisition speed, high measurement accuracy and good temperature stability.

A synergy of voltage-to-frequency converter and continued-fraction algorithm for processing thermocouple signals

A low cost signal conditioning circuit has been devised for thermocouple temperature transducers, in which the thermocouple and the NTC thermistor for reference junction compensation have been introduced in a simple voltage-to-frequency converter circuit using LM331 IC. From the time domain parameters of the output pulse train, the reference junction temperature is obtained using the well known Steinhart-Hart equation, and the measuring junction temperature is calculated via a two-dimensional continued-fraction based algorithm. This algorithm calculates the temperature under measurement and also performs the dual task of cold junction compensation and minimization of the effects of the drifts of the signal conditioning circuit components. The performance of the system has been verified experimentally with a T-type thermocouple. The output of the voltage-to-frequency converter is acquired by a personal computer (PC) through its sound card, and the temperatures are calculated and compared with Pt-100 standard. A decent accuracy of approximately ±1.4 °C has been achieved over 45–100 °C. The possibility of replacing the PC with a microcontroller unit or field programmable gate array (FPGA) system by virtue of the simplicity of the numerical algorithm used, makes the scheme a very good choice for embedded system applications.

Thermocouple Cold End Compensation System with Programmable Function

The thermocouple is the most commonly temperature sensor used in the measurement technique. But because of the fluctuation of the ambient temperature, the cold temperature is difficult to hold invariableness. This paper proposes an improved method. There are all kinds of thermocouple compensation tables in the system. And according to the actual need, we can select the corresponding table to make the cold junction compensation. This system meets the needs of various types of thermocouples.

Signal conditioning of thermocouple using intelligent technique

This paper implies using a neural network based technique for dispensation of a thermocouple signal [1]. At the stage of linearization, the thermocouple cold junction compensation and sensor transfer curve are in the same stride. For sensing the reference junction temperature a thermistor has been used and whose temperature tables are taken into consideration [2][3]. A multilayered Artificial Neural Network (ANN) has been trained using Levendberg-Marquadt algorithm [4]. For initializing the biases and weight of the ANN, to minimize measurement errors, and linearize the thermocouple by simulation methods this algorithm is as well very constructive [4]. Data of thermocouple for different material types may approach from the standard tables and must be interpolated for any readings not directly contained in these tables. The fluctuation in the hotness of the reference junction of the thermocouple have an effect on the repeatability of the thermocouple hence the reaction of the thermocouple is studied at different ambient temperatures from 0-45°C and the error due to increase in this temperature is also minimized simultaneously. As training of data increases the network becomes more capable of reducing the error close to zero. So a new technique is utilized which trains the data more and more along with increasing temperature leading to less errors than conventional or previous instances of the same program[5].

A thermometer based on diverse types thermocouples and resistance temperature detectors

A universal and low-cost temperature thermometer is realized via a special circuit, integrated circuit chip with microprocessor and analog to digital converter, and digital bus interface. Various thermocouples and resistance temperature detectors used for temperature sensing may be connected to same thermometer. A special signal condition circuitry is designed and a matching algorithm is proposed. A novel calibration method named disassembled calibration is proposed in order to enhance efficiency and flexibility for the whole system. Additionally, it presents a combination method of low order polynomial fitting and piecewise linearity for the nonlinearity calibration of the thermocouple and the resistance temperature detector. A cold junction compensation based on digital way is described. And the matching algorithm and calibration method may eliminate errors stemming from excitation voltage source and reference voltage source, and can weaken quantization error of analog to digital converter and drift of components, too. Furthermore, the 400 times oversampling is completed by sequential and equal interval sampling to upgrade accuracy of analog to digital converter from original 12 to 15 bits and to raise signal-to-noise ratio. Finally, during a long time monitoring, experiment results show that errors at each static point are less than ±0.2 °C for the thermocouple system and less than ±0.1 °C for the resistance temperature detector system.

Performance evaluation of coaxial thermocouple against platinum thin film gauge for heat flux measurement in shock tunnel

Data on surface heat flux is critical in all hypersonic missions due to the extent of risk and the penalty associated, when it is not properly accounted for. In the present study an E-type coaxial thermocouple has been designed, fabricated, validated and benchmarked against a more established platinum thin film sensor. The study proves that coaxial thermocouples used in impulse facilities do not require cold junction compensation. The comprehensive study conducted in IIT Bombay Shock Tunnel (IITB-ST) has confirmed the performance, ruggedness and reliability of the coaxial thermocouple, ascertaining it to be an effective, impulse, heat flux sensor.

Focus on sensors and detectors

Focus on sensors and detectors

An Industry Temperature Measurement Zigbee Node Design

Industry temperature measurement plays an important role in both light industries and heavy industries. This paper presents our design of an industry temperature measurement node based on a thermocouple sensor and Zigbee. The cold-junction compensation circuit and signal gain circuit were implemented in the sensor modulation board. A firmware was developed on CC2530 to control the sensor reading and packets sending. A heating and cooling experiment was carried out. The results show that our design can successfully measure the temperature in industry applications and transfer it wirelessly via Zigbee communication.

A lab-scale set up for thermal radiation experiments with cold junction compensation

The concepts of thermal radiation heat transfer are not tangible for many students. Experiments relied on various parameters can clarify the concepts of this mode of heat transfer.A lab-scale set up is described to study the thermal radiation heat transfer experiments. An electrical circuit of the thermopile sensor is designed and manufactured to provide experimental data.The validity of Inverse Square, Stefan–Boltzmann, and Kirchhoff Laws are investigated experimentally in the setup. Results indicate that, it is necessary to consider temperature shifts in the thermopile cold junction which is a potential source of error. Therefore, the output voltage, corresponding to the sensor temperature, should be noted upon each measurement.Moreover, during the experiment, thermopile characteristics which affected the recorded data are reported. Wide angle of view and spectral response of the thermopile are found to be the main source of errors.Finally, in order to decrease errors, some suggestions as the feedback of students experiments and comments, are proposed to improve both the methods and the instruments.

Towards on-chip time-resolved thermal mapping with micro-/nanosensor arrays

In recent years, thin-film thermocouple (TFTC) array emerged as a versatile candidate in micro-/nanoscale local temperature sensing for its high resolution, passive working mode, and easy fabrication. However, some key issues need to be taken into consideration before real instrumentation and industrial applications of TFTC array. In this work, we will demonstrate that TFTC array can be highly scalable from micrometers to nanometers and that there are potential applications of TFTC array in integrated circuits, including time-resolvable two-dimensional thermal mapping and tracing the heat source of a device. Some potential problems and relevant solutions from a view of industrial applications will be discussed in terms of material selection, multiplexer reading, pattern designing, and cold-junction compensation. We show that the TFTC array is a powerful tool for research fields such as chip thermal management, lab-on-a-chip, and other novel electrical, optical, or thermal devices.

Ceramic thin film thermocouples for SiC-based ceramic matrix composites

Conductive ceramic thin film thermocouples were investigated for application to silicon carbide fiber reinforced silicon carbide ceramic matrix composite (SiC/SiC CMC) components. High temperature conductive oxides based on indium and zinc oxides were selected for testing to high temperatures in air. Sample oxide films were first sputtered-deposited on alumina substrates then on SiC/SiC CMC sample disks. Operational issues such as cold junction compensation to a 0°C reference, resistivity and thermopower variations are discussed. Results show that zinc oxides have an extremely high resistance and thus increased complexity for use as a thermocouple, but thermocouples using indium oxides can achieve a strong, nearly linear response to high temperatures.

Design and development of a high precision thermocouple based smart industrial thermometer with on line linearisation and data logging feature

Design and development of a high precision thermometer for industrial application is described in this paper. A class-1 grade K-type Thermocouple is considered for this purpose. The conditioned signal is linearised using a 9th order polynomial based on National Institute of Standards and Technology (NIST) data with the help of a 12-bit analog-to-digital converter and a 8-bit microcontroller. The cold junction compensation is achieved using a serial synchronous temperature to digital converter. The linearised data is transmitted for remote monitoring and logging via RS232C. The system is calibrated with 20 calibration point from 0 °C to 200 °C with a low cost calibration setup. The precision index of the system is also calculated.

A Critical Look at Type T Thermocouples in Low-Temperature Measurement Applications

Type T thermocouples are commonly used in industrial measurement applications due to their accuracy relative to other thermocouple types, low cost, and the ready availability of measurement equipment. Type T thermocouples are very effective when used in differential measurements, as there is no cold junction compensation necessary for the connections to the measurement equipment. Type T’s published accuracy specifications result in its frequent use in low-temperature applications. An examination of over 250 samples from a number of manufacturers has been completed for this investigation. Samples were compared to a standard platinum resistance thermometer (SPRT) at the LN2 boiling point along with four other standardized measurement points using a characterized ice point reference, low-thermal EMF scanner, and an 8.5 digit multimeter, and the data were compiled and analyzed. The test points were approximately −196 °C, −75 °C, 0 °C, + 100 °C, and + 200 °C. These data show an anomaly in the conformance to the reference functions where the reference functions meet at zero. Additionally, in the temperature region between −100 °C and −200 °C, a positive offset of up to 5.4 °C exists between the reference function equations published in the United States in ASTM E230-06 for the nitrogen point and the measured response of the actual wire. This paper also examines the historical and technological reasons for this anomaly in the US reference function. The study concludes that Type T thermocouples typically do not conform to the ASTM E230-06 published reference function describing their performance when used to measure temperature in the range of −100 °C to −200 °C.

The Calibration and Use of Thermocouple Simulators

Abstract:Thermocouple simulators and calibrators have greatly simplified thermometer calibration. Their use will be contrasted with historical calibration methods. The paper details the three critical calibration parameters: DC voltage gain, cold junction calibration, and implementation of the thermocouple curves. The implementation of cold junction compensation internal to a thermometer or a thermocouple simulator is described. An uncertainty analysis is presented for a specific thermocouple simulator that is part of a multicalibrator based on the guidance of the recently updated European Association of National Metrology Institutes (EURAMET) calibration guides EURAMET/cg-08/v.01 and EURAMET/cg-11/v.01. Finally, an explanation is given for reporting measured values of 30,000 °C on calibration certificates for the example calibrator.