Temperature measurement technology

Miniaturized fixed-point cells integrated into thermometers enable, for the first time, direct in-situ calibration of thermometers with a direct connection to the ITS-90 during the process.  Research in this field over the past 20 years has marked a significant step toward more practical and industrially viable fixed-point calibrations. Throughout Germany, the Institute for Process Measurement and Sensor Technology is the only research institution with comprehensive expertise in this field, which forms the basis of the concept. In collaboration with an industrial partner, this expertise was subsequently expanded enabling continuous single-point calibration of a thermometer directly in the process using a reference material integrated into the thermometer, whose Curie temperature T_C = 118 °C provides the reference temperature for the calibration.

References:

• BERNHARD, F.; BOGUHN, D.; AUGUSTIN, S.; MAMMEN, H.; DONIN, A.: Field Experience with Self-Calibrating Thermocouples in Power Plant Applications. In: Temperatur 2003. Berlin: VdI-Verlag, 2003, pp. 259–266
• BERNHARD, F.; AUGUSTIN, S.; MAMMEN, H.: Application of Self-Calibrating Thermometers with Miniature Fixed-Point Cells in a Temperature Range from 300 °C to 650 °C. In: TEMPMEKO 2004. Dubrovnik, 2004
• SCHALLES, M.; VRDOLJAK, P.: In-situ Calibration of Thermometers in the Process. In: Sensors and Measurement Systems / 19th Symposium on Sensors and Measurement Systems, 2018 Nuremberg. - Berlin: VDE Verlag GmbH, 2018, pp. 219–222

Various test facilities have been set up at the institute to investigate the static and dynamic behavior of contact thermometers in accordance with applicable standards and guidelines. These facilities are used, on the one hand, to compare the characteristics of different thermometer designs and, on the other hand, to validate the results obtained through numerical methods. The dependence of the characteristic values on temperature-dependent material properties as well as on various medium, installation, and environmental conditions is determined both theoretically through numerical calculations and experimentally. The results of this research have been incorporated into various standards and guidelines (e.g., VDI/VDE GMA Guideline 3522, “Dynamic Behavior of Contact Thermometers”). The test facilities are available for measurements as part of our service offerings.

References:

• AUGUSTIN, S.; FROEHLICH, T.: Temperature dependence of dynamic parameters of contact thermometers. In: Sensors. MDPI, Vol. 19 (2019), DOI: 10.3390/s19102299
• AUGUSTIN, S.; FROEHLICH, T.; SCHALLES, M.; KRUMMECK, S.: Bilateral comparison for determining the dynamic characteristic values of contact thermometers in fluids. In: Journal of Sensors and Sensor Systems. Vol. 7, 2018, pp. 331–337
• AUGUSTIN, S.; FROEHLICH, T.: Dynamic Behavior of Contact Thermometers Taking into Account the Temperature Dependence of Material Data—Extension of VDI/VDE Guideline 3522. In: Technisches Messen. Vol. 83, 2016, 7–8, pp. 402–409
• AUGUSTIN, S.; BERNHARD, F.: Numerical calculation of static and dynamic parameters of industrial temperature sensors. In: Measurement / International Measurement Confederation. Elsevier Science, Vol. 17, 1996, No. 4, pp. 217–228

When measuring surface temperature by contact using probe or tube-contact thermometers, different factors affecting the thermometers’ static and dynamic characteristics must be taken into account compared to measurements in fluids (e.g., contact force, surface roughness, etc.). For this reason, special calibration facilities were developed and set up in cooperation with various partners from industry and the PTB for the calibration and determination of thermal measurement errors.

The same applies to the development of various calibration stations for radiation thermometers and heat flux sensors. In some cases, the triple-fixed-point cells developed at the institute were used, which enable direct traceability of the calibration to the International Temperature Scale ITS-90.  

At the institute, the various factors influencing measurements with surface thermometers and heat flux sensors were identified, and their contributions to the corresponding measurement uncertainty budgets were comprehensively determined experimentally. This work formed an important basis for the development of new guideline documents in this field.

References:

• BERNHARD, F.; AUGUSTIN, S.; MAMMEN, H.; SOMMER, K.-D.; TEGELER, E.; WAGNER, M.; DEMISCH, U.; TRAGESER, P.: Calibration of contacting sensors for temperature measurements on surfaces. In: Proceedings of TEMPMEKO '99, the 7th International Symposium on Temperature and Thermal Measurement in Industry and Science; June 1999, Delft, pp. 257–262
• SCHALLES, M.: Triple-fixed-point blackbody for the calibration of radiation thermometers, Technical University of Ilmenau, doctoral dissertation, 2009
• SCHALLES, M.; BERNHARD, F.: Triple-fixed-point blackbody for the calibration of radiation thermometers. In: Int. Journal of Thermophysics 28 (2007), No. 6, pp. 2049–2058
• HOHMANN, M.; MARIN, S.; SCHALLES, M.; FROEHLICH, T.: Dry block calibrator with improved temperature field and integrated fixed-point cells. In: International Journal of Thermophysics. Vol. 38 (2017), 2, Article 17, 10 pp. total, DOI: 10.1007/s10765-016-2155-9
• HOHMANN, M.; MARIN, S.; SCHALLES, M.; FROEHLICH, T.: Dry block calibrator with improved temperature field and integrated fixed-point cells. In: International Journal of Thermophysics. Vol. 38 (2017), 2, Article 17, 10 pp. total, DOI: 10.1007/s10765-016-2155-9
• HOHMANN, M.: Implementation of a block calibrator with heat flux sensors and integrated fixed-point cells, Technical University of Ilmenau, doctoral dissertation, 2016
• PUFKE, M.: Metrological Investigation of Contact Thermometers. Ilmenau University of Technology, doctoral dissertation, 2019
• PUFKE, M.; FROEHLICH, T.: Factors Affecting Measurements with Contact Thermometers. In: Technisches Messen. Vol. 86, 2019, 1, pp. 67–71
• KUEHNEL, P.: Calibration radiators for thermal imaging cameras. Ilmenau University of Technology, Master’s thesis, 2019

Thermal modeling is important in virtually all research in the field of thermometry, as well as in the development of precision measuring instruments in which temperature is a source of measurement error. Both analytical and FEM-based solution methods are used in static and dynamic thermal calculations, as well as in coupled calculations.

The simulated systems are optimized with respect to their static and dynamic thermal properties. To this end, parameters derived from the geometry and material properties are generated and varied using stochastic calculations. Simulated results are validated against measurements obtained using various test setups. Stochastic methods, including the Monte Carlo method, are later used to calculate measurement uncertainties.

References:

• MARIN, S.; FROEHLICH, T.: Approach for Determining the Uncertainty and Predictive Capability of an FEM Simulation Model of a Small Multi-Fixed-Point Cell for Calibrating Contact Thermometers. In: Technisches Messen. Vol. 85, 2018, 1, pp. 86–94
• WEIS, H. S.; AUGUSTIN, S.: Simulation of thermal behavior in high-precision measurement instruments. In: International Journal of Thermophysics 29 (2008), No. 3, pp. 1184–1192
• FRÖHLICH, T.: Temperature Compensation of Precision Measuring Instruments, Technical University of Ilmenau, Habilitation, 2006
• AUGUSTIN, S.; BERNHARD, F.: Numerical calculation of static and dynamic parameters of industrial temperature sensors. In: Measurement / International Measurement Confederation. Elsevier Science, Vol. 17, 1996, No. 4, pp. 217–228