Industrial Platinum Resistance Thermometers Research Articles

Accurate Assessment Model for Solving Resistance-Temperature Equations of Platinum Thermometers in Range from -40 °C up to 660 °C

The missions of the thermal metrology laboratory are to maintain, disseminate, develop and realize the International Temperature Scale 1990 (ITS-90). One of the services that the laboratory has introduced is the routine calibration to all industrial sectors that covers almost all fields inside and outside Egypt. This work compares different interpolating equations of set of industrial Platinum Resistance Thermometers (IPRTs) in the temperature range from -40 °C up to 660 °C that convert the resistance of thermometer sensing element to temperature and find the optimum method in which range applicable. The used analytical methods are Callendar–van Dusen (CVD) equation and the (4th -5th) order polynomials of resistance as a function of temperature. The study splits the ranges of investigation into lower subranges, test the significant standard error and residual for each case, and give advice to the lower level calibration laboratories that does not own primary standard about the best method used. From the results it is found that the standard fit error (SFE) for 4th order polynomial on average = 30 % compared to the CVD equation, =50 % compared to the ITS-90 deviation function and = 73% compared to the 3rd order polynomial. It is preferable to used 5th order polynomial than CVD to decrease 1 point in the calibration and reduce the cost of the calibration with nearly the same accuracy if the mathematical model is applied. The study gives advice to the end user who wants to use CVD equation by selecting the best two-calibration points above 0 °C which are 100 °C and 400 °C.

EFFECTS OF VARIATION IN MEASUREMENT CHAIN ON TEMPERATURE MEASUREMENT CALIBRATION WITH RESISTANT TEMPERATURE SENSORS

Temperature is one of the most important key parameter to consider in measurement and mechanical engineering, because every measurement has to be conducted with reference to standard temperature conditions (20 °C, ISO 1). Strictly speaking, almost every measurement depends on the accuracy of the temperature measurement, which requires proper calibration. Therefore, standards list detailed criteria to fulfil temperature calibration with high precision. In fact, any calibration is only valid, if the whole measurement chain is taken into account. This would make recalibration necessary with each variation of the components in the measuring set-up (varying cable length, different measurement channel etc.), which is time-consuming or even impossible in practice. For that reason, this paper presents a practicable calibration strategy, which specifies each component individually and later combines the calibration results according to the composition of the measurement chain. This provides a fast and useful way to achieve the required accuracy of temperature measurement. The examined, exemplary measurement chain consists of an industrial platinum resistance thermometer (IPRT), cables with different lengths, an electrical amplifier and a reference temperature calibrator.

Modelling of thermal effects in a slim tin fixed-point cell

Slim fixed-point cells are an economic and suitable alternative for calibration of industrial platinum resistance thermometers, which are widely used in research and industrial applications. The most relevant disadvantage of slim cells is related with thermal effects produced by interactions between the cell and the furnace used for the realization of the fixed-points. This work presents the implementation of a two-dimensional numerical model that considers the transient heat transfer due to conduction, radiation and latent heat. The main goal was to evaluate different geometrical parameters in the design of slim fixed-point cells. Results show that thermal effects are mitigated when the annular distance between interior and exterior walls of the crucible is maximum, while the length of the cell and the thermo-well must be setup according to the temperature gradients in the furnace to avoid undesirable heat fluxes.

Calibration of industrial platinum resistance thermometers in thermostats (-40 °C to 420 °C)

The COOMET.T-S2 comparison is a regional comparison in which the national metrological institutes of Moldova, Georgia, Kyrgyzstan, Kazakhstan, Azerbaijan, Bosnia and Herzegovina and Turkey participate.Two standard platinum resistance thermometers (100 ohm), manufactured at VNIIM, was used as a transfer standards. National Metrology Institute (NMI) of Republic of Moldova is a pilot laboratory in this comparison.The purpose of the comparisons is to verify equivalence between the participating laboratories in the calibration of industrial platinum resistance thermometers by direct comparison in the range from minus 40 °C to 420 °C. The comparison results are used to confirm the calibration and measurement capabilities in this range.Main textTo reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCT, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Estimating Surface Temperature of a Calibration Apparatus for Contact Surface Thermometers from Its Internal Temperature Profile

A calibration apparatus for contact surface thermometers was developed. Temperature of the upper surface of a copper cube of the calibration apparatus was used as reference surface temperature, which was estimated at around $$50\,{^{\circ }}\hbox {C}$$ , $$100\,{^{\circ }}\hbox {C}$$ , and $$150\,{^{\circ }}\hbox {C}$$ by not only two conventional industrial platinum resistance thermometers (IPRTs) but also five small-sized platinum resistance thermometers (SSPRTs) calibrated based on the International Temperature Scale of 1990 (ITS-90). These thermometers were inserted horizontally into the copper cube and aligned along the center axis of the copper cube. In the case of a no-load state without anything on the upper surface, the temperature profile inside the copper cube linearly decreased from the lower part to the upper surface, which suggests that the heat conduction inside the copper cube can be regarded as a one-dimensional steady state. On the other hand, in the case of a transient state just after the contact surface thermometer was applied to the upper surface, the temperature profile became a round shape. We obtained good agreement between the curvature of the temperature profiles and the results estimated by using an error function used for a one-dimensional transient heat conduction problem. The temperature difference between the estimated temperature by linear extrapolation using two IPRTs and that by extrapolation using the error function was within $$0.2\,{^{\circ }}\hbox {C}$$ in the transient state at around $$150\,{^{\circ }}\hbox {C}$$ . Over 10 min after the contact surface thermometer was applied, the temperature profile showed a linear shape again, which indicated that linear extrapolation using two IPRTs was well for the estimation of the reference surface temperature because the heat conduction state inside the copper cube came back to the one-dimensional steady state. Difference between the surface temperature and temperature detected by the contact surface thermometer was also observed after the contact surface thermometer touched on the upper surface. The difference was over $$0.1\,{^{\circ }}\hbox {C}$$ at several minutes after the contact surface thermometer touching on the reference surface and was suppressed with passing time in the transient state and became negligible over 10 min.

Experimental Method for Determination of Self-Heating at the Point of Measurement

This paper presents a new experimental method and algorithm for the determination of self-heating of platinum resistance thermometer (PRT) when the temperature instability of medium of interest would prevent an accurate self-heating determination using standard methods. In temperature measurements performed by PRT, self-heating is one of the most common sources of error and arises from the increase in sensor temperature caused by the dissipation of electrical heat when measurement current is applied to the temperature sensing element. This increase depends mainly on the applied current and the thermal resistances between thermometer sensing element and the environment surrounding the thermometer. The method is used for determination of self-heating of a 100 $$\Omega $$ industrial PRT which is intended for measurement of air temperature inside the saturation chamber of the primary dew/frost point generator at the Laboratory for Process Measurement (HMI/FSB-LPM). Self-heating is first determined for conditions present during the comparison calibration of the thermometer, using the calibration bath. The measurements were then repeated with thermometer being placed in an air stream inside the saturation chamber. The experiment covers the temperature range between $$-65{\,}^{{\circ }}\hbox {C}$$ and $$10{\,}^{{\circ }}\hbox {C}$$ . Self-heating is determined for two different air velocities and two different vertical positions of PRT in relation to the chamber bottom.

Fabrication of a mini multi-fixed-point cell for the calibration of industrial platinum resistance thermometers

A mini multi-fixed-point cell (length 118 mm, diameter 33 mm) containing three materials (In–Zn eutectic (mass fraction 3.8% Zn), Sn and Pb) in a single crucible was designed and fabricated for the easy and economical fixed-point calibration of industrial platinum resistance thermometers (IPRTs) for use in industrial temperature measurements. The melting and freezing behaviors of the metals were investigated and the phase transition temperatures were determined using a commercial dry-block calibrator. Results showed that the melting plateaus are generally easy to realize and are reproducible, flatter and of longer duration. On the other hand, the freezing process is generally difficult, especially for Sn, due to the high supercooling required to initiate freezing. The observed melting temperatures at optimum set conditions were 143.11 °C (In–Zn), 231.70 °C (Sn) and 327.15 °C (Pb) with expanded uncertainties (k = 2) of 0.12 °C, 0.10 °C and 0.13 °C, respectively. This multi-fixed-point cell can be treated as a sole reference temperature-generating system. Based on the results, the realization of melting points of the mini multi-fixed-point cell can be recommended for the direct calibration of IPRTs in industrial applications without the need for a reference thermometer.

Hysteresis and Instability in Some IPRT Sensors Within Temperature Ranges Extending from $$-196\,^{\circ }\hbox {C}$$ - 196 ∘ C to $$150\,^{\circ }\hbox {C}$$ 150 ∘ C

Industrial platinum resistance thermometer (IPRT) sensors or probes suffer from some instability on cycling over significant ranges of temperature and, specifically, from hysteresis in which the resistance tends to follow different paths for increasing temperatures compared with decreasing temperatures. The effect is well known, and cases of quite large hysteresis have been reported in the literature. Therefore, in establishing calibration and measurement capabilities for IPRT calibrations it is important to include an assessment of the performance which can be expected of a ‘typical good’ IPRT and to include this in the overall uncertainty which the laboratory can expect to achieve in such calibrations, even though the effect itself is outside the laboratory’s control. This paper presents results which have been obtained in cycling IPRT probes from four sources within various temperature ranges of current interest at NPL, between $$-196\,^{\circ }\hbox {C}$$ and $$150\,^{\circ }\hbox {C}$$ , to see what levels of hysteresis may be expected. The cycles were carried out quite quickly in order to detect the hysteresis before it was mitigated by relaxation effects, but the time dependence was not itself studied. In most cases, hysteresis was $${<}0.0025\,^{\circ }\hbox {C}$$ between $$0\,^{\circ }\hbox {C}$$ and $$100\,^{\circ }\hbox {C}$$ , and $${<}0.0035\,^{\circ }\hbox {C}$$ when the range extended down to $$-80\,^{\circ }\hbox {C}$$ or up to $$150\,^{\circ }\hbox {C}$$ . Greater instability occurred when the sensors were cooled to $$-196\,^{\circ }\hbox {C}$$ .

Onsite Calibration of a Precision IPRT Based on Gallium and Gallium-Based Small-Size Eutectic Points

Onsite thermometer calibration with temperature scale transfer technology based on fixed points can effectively improve the level of industrial temperature measurement and calibration. The present work performs an onsite calibration of a precision industrial platinum resistance thermometer near room temperature. The calibration is based on a series of small-size eutectic points, including Ga–In (\(15.7 \,{^{\circ }}\hbox {C}\)), Ga–Sn (\(20.5 \,{^{\circ }} \hbox {C}\)), Ga–Zn (\(25.2 \,{^{\circ }} \hbox {C}\)), and a Ga fixed point (\(29.7 \,{^{\circ }} \hbox {C}\)), developed in a portable multi-point automatic realization apparatus. The temperature plateaus of the Ga–In, Ga–Sn, and Ga–Zn eutectic points and the Ga fixed point last for longer than 2 h, and their reproducibility was better than 5 mK. The device is suitable for calibrating non-detachable temperature sensors in advanced environmental laboratories and industrial fields.

Final report on APMP supplementary comparison of industrial platinum resistance thermometer for range -50 °C to 400 °C. (APMP.T-S6)

The National Metrology Laboratory, Malaysia (NML-SIRIM) had coordinated the Supplementary Comparison of Industrial Platinum Resistance Thermometer (IPRT) started from July 2009 until April 2011 together with the National Measurement Institute of Australia (NMIA) and Korea Research Institute of Standards and Science (KRISS). This comparison was opened to all APMP members and 16 participants had taken part in order to consolidate or improve their calibration and measurement capabilities (CMCs). Three units of artefacts 100-ohm IPRT belonging to NML-SIRIM, NMIA and KRISS were used and three loops of measurement were run in parallel to shorten the circulation time. The stability of artefacts was monitored with initial and final ice point measurement by each laboratory. The participants need to perform measurement at temperature points (0,-50,-30, 0, 100, 200, 300, 400,0) °C. All submitted data were compiled and adjusted at nominal temperature and by using the linkage from NMIA and KRISS as reference value for all three loops , the temperature deviation from participants from different loops can be compared. The approach of Birge Ratio for final exclusion comprised all the excluded results from the analysis of each loop and the measurement performance for each participant were summarized by the En number value.Main textTo reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCT, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Interpolating equation of industrial platinum resistance thermometers in the temperature range between 0 °C and 500 °C

This paper compares four interpolation equations for the calibration of 18 industrial platinum resistance thermometers (IPRTs) in the temperature range between 0 °C and 500 °C. They are the quadratic Callendar–van Dusen (CVD) equation, the deviation function specified in the International Temperature Scale of 1990 (ITS-90), and the third- and fourth-order polynomials of resistance as a function of temperature. It was found that when the upper limit of the calibration range was higher than 240 °C, the third- and fourth-order polynomials resulted in a smaller standard error-of-fit than either the CVD equation or ITS-90 deviation function did, and of the latter two functions, the ITS-90 deviation function worked better. When the upper limit of the temperature range was 500 °C, the fourth-order polynomials showed distinctly better performance than the others. The standard error-of-fit for the fourth-order polynomial in the temperature range between 0 °C and 500 °C was on average ≈1/3 compared to the CVD equation, ≈1/2 compared to the ITS-90 deviation function and ≈70% compared to the third-order polynomial. When the upper limit was 100 °C, the difference among the four equations was insignificant. Consideration is briefly given to using interpolation as specified in the ITS-90 but with additional check points, and also to the use of the CVD equation below 0 °C.

Final report on SIM.T-S5: comparison of the calibration of 100 Ω platinum resistance thermometers

An International Comparison on industrial Platinum Resistance Thermometers (PRTs) among the National Metrology Institutes (NMIs) of Spain, Panama, Honduras, El Salvador, Costa Rica and Nicaragua began in 2013 and was successfully completed in 2014. Two PRTs were circulated (hand carried) and compared in the range from -38.8 °C up to 250 °C. The Centro Español de Metrología (Spanish NMI), CEM, acted as the pilot laboratory providing the reference value of the comparison.The thermometers have shown an acceptable behavior throughout the comparison, therefore the results can be considered valid for comparing the measurement capabilities of the participant laboratories. The equivalence between the participant laboratories in the calibration of platinum resistance thermometers by comparison in the range from -38,8 °C up to 250 °C has been demonstrated in almost all cases.This report presents the results of this comparison and provides detailed information of the measurements performed by the participating laboratories.Main text.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCT, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Temperature Dependence of IPRT and SPRT Self-Heating: Does Working with $${{\varvec{W}}}$$ W Really Help?

Platinum resistance thermometers (PRTs) are capable of providing reliable measurements at the millikelvin level, and are widely used in both industry and research applications. However, the intrinsic thermal noise associated with their resistance requires the use of a measurement current of typically around a milliampere to determine their resistance. Unfortunately, this same current also dissipates heat into the thermometer element, causing the well-known “self-heating” effect of typically a few millikelvins. Performing measurements in terms of the ratio to the resistance at the ice point provides some level of cancelation of this error around this temperature: If the thermal resistance between the sensor and environment were constant, this cancelation would work over a much wider temperature range. However, there is little evidence on the effectiveness of this strategy in practice. This paper reports on an extensive set of systematic measurements of the self-heating of six standard platinum resistance thermometers (SPRTs) and six industrial platinum resistance thermometers (IPRTs) of different designs, as a function of temperature, over the range from $$-190~^{\circ }\mathrm{C}$$ to $$420\,^{\circ }\mathrm{C}$$ , in a range of intercomparison baths and blocks. The measurements show that PRT self-heating varies from being almost constant with temperature to being nearly proportional to temperature. The assumption of a roughly temperature-independent thermal resistance is thus not justified in general. The results allow estimation of appropriate uncertainty terms for SPRT and IPRT self-heating for the two scenarios of “working in $$R$$ ” and “working in $$W$$ .”

Calibration of Industrial Platinum Resistance Thermometers up to $$700\,^{\circ }\mathrm{C}$$ 700 ∘ C

Industrial grade platinum resistance thermometers were calibrated in the temperature range from $$200\,^{\circ }\mathrm{C}$$ to $$700\,^{\circ }\mathrm{C}$$ . Both wire-wound and thin-film sensor-based thermometers were investigated. The purpose of the study was to investigate thermometers which could be used in future coal power plants. The calibrations were performed in a vertical cesium heat-pipe furnace and in a horizontal and vertical sodium heat-pipe furnace. The reference thermometer was a standard platinum resistance thermometer calibrated at fixed points up to the aluminum point. In addition to calibration, various thermal tests including immersion measurements and thermal-cycling tests were performed. The stability of the sensors was determined by monitoring the ice-point resistance. Possible contamination of the sensors was determined by measuring the resistance ratio $$R(30\,^{\circ }\mathrm{C})/R(10\,^{\circ }\mathrm{C})$$ several times during the measurement period. The calibration curves were compared with the ICE 60751 standard and International Temperature Scale 1990 (ITS-90) reference functions. Considerable changes were found in all tested thermometers. The wire-wound sensors were more stable than the thin-film sensors.

고정밀 백금저항온도계를 이용한 교정기관의 온도교정능력 수행평가

Calibration capabilities for thermometer calibration by comparison method were assessed using high-precision industrial platinum resistance thermometers (IPRT). It was found in the performance assessment that out of 31 laboratories who participated, 28 laboratories resulted magnitude of En number less than 1 at every calibration points they submitted results in the range from 50 to <TEX>$500^{\circ}C$</TEX>. The results of about 75% of the laboratories showed the difference from the assigned values less than 1/10 of the tolerance level of the class B IPRT. This indicates that the participating calibration laboratories performed with satisfactory level that was enough to calibrate IPRTs to significant precision. The sensors used in this work were manufactured and chosen by the criteria of long-term instability less than 4 mK and hysteresis less than 8 mK in the temperature range used in this work. Furthermore, the change in the resistance of the sensors in the calibration temperature range were less than the uncertainty of the calibration, 25 mK (k=2).

Modelling the calibration of the industrial platinum-resistance thermometers according to GUM

According to the Guide to the Expression of Uncertainty in Measurement (GUM, JCGM 100: 2008), the calibration process and its uncertainty evaluation should be expressed in terms of mathematical function(s) of input quantities. However, in practice, expressing measurement or calibration in a way that is fully compliant with GUM might be unrealistic and require a clear definition of the calibration process itself. Depending on the applied cali- bration process, different modelling equations with various complexities can be written. In this paper, four different approaches are given to model the calibration process of industrial platinum-resistance thermometers.

Final report on SIM.T-S2: Comparison of the calibration of 100 Ω platinum resistance thermometers

An International Comparison on industrial platinum resistance thermometers (PRTs) among the National Metrology Institutes (NMIs) of Spain, Mexico and the Andean Countries (Bolivia, Colombia, Ecuador, Peru and Venezuela) began in 2004 and was successfully completed in 2005. Two PRTs were circulated (hand-carried) and compared from −40 °C up to 250 °C. The Centro Español de Metrología (Spanish NMI), CEM, was the pilot laboratory and the Centro Nacional de Metrología (Mexican NMI), CENAM, was the co-pilot laboratory.This report presents the results of this comparison and provides detailed information of the measurements performed by the participating laboratories.Main text.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by SIM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

산업용 백금저항온도계를 위한 향상된 내삽식

We propose an improved interpolating equation to express temperature-resistance characteristics for modern industrial platinum resistance thermometers (PRTs). Callendar-van Dusen equation which has been widely used for platinum resistance thermometer fails to fully describe temperature characteristics of high quality PRTs and leaves systematic residual when the calibration point include temperatures above <TEX>$300^{\circ}C$</TEX>. Expanding Callendar-van Dusen to higher-order polynomial drastically improves the uncertainty of the fitting even with reduced degrees of freedom of the fitting. We found that in the fourth-order polynomial fitting, the third-order and fourth-order coefficients have a strong correlation. Using the correlation, we suggest an improved interpolating equation in the form of fourth-order polynomial, but with three fitting parameters. Applying this interpolating equation reduced the uncertainty of the fitting to 32 % of that resulted from the traditional Callendar-van Dusen. This improvement was better than that from a simple third-order polynomial despite that the degrees of the freedom of the fitting was the same.

Low-Cost Ratiometric Front-End for Industrial PRT Applications

Cost, size, speed, and measurement range limitations make the resistance bridge not always suitable for temperature measurements with platinum resistance thermometers (PRTs) in industrial applications. However, high-accuracy resistance thermometer systems are often needed in many industrial applications, where measurement performances comparable to resistance bridges are often needed at a lower cost and size. A tiny, portable, ratiometric front-end exploiting a 24-bit analog-to-digital converter (ADC) with Σ Δ modulator is described. It was designed to measure the resistance ratio between a 100 Ω industrial PRT (IPRT) and a reference resistor with repeatability to within a few parts in 106. Its small size makes it ideal for integration in the stem-handle assembly of a thermometric probe, enabling an early transmission of measurement data in digital form. The ADC-based system design, development, and performance testing are discussed. The system was investigated in the resistance ratio range from about 4 × 10−3 to 5 × 10−2. Furthermore, a comparison between the system performance and a commercial AC resistance bridge was carried out and the results reported in this paper. An accurate thermometer for industrial applications resulted from the above developments. The compactness of the devices enabled an implementation of the ‘smart sensor’ concept in the measurement chain, where the front-end electronics was placed inside the IPRT handle together with an integrated memory to hold device identification, calibration coefficients, and the associated uncertainty. All data are transmitted to the readout module and are available to the user at a 5 Hz update rate for further analysis.

Thermal Hysteresis in Thin-Film Platinum Resistance Thermometers

Thin-film platinum resistance thermometers (PRTs) are generally manufactured using the deposition of a thin platinum film on an alumina substrate and a laser-trimming method. Because of the strong adhesion between the platinum thin film and the alumina substrate, the PRTs inevitably have strain over the operating temperature range. This causes anomalies and instabilities in the resistance versus temperature characteristics (R–T). The most prominent and observable effect of thermally induced strain is the thermal hysteresis in the R–T characteristics. Thermal hysteresis is one of the main uncertainty factors in the calibration of industrial platinum resistance thermometers in laboratories. The thermal hysteresis for 30 thin-film PRTs was measured in the range of 0 °C to 500 °C in 100 °C steps. The thermal hysteresis was measured repeatedly using the same process, and the hysteresis decreased drastically with the repeated measurements. The thermal hysteresis was distributed from 16 mK to 156 mK for all sensors, and the lowest hysteresis was 1 mK to 11 mK in the test temperature range.