Comparison of the Reference Surface Temperature Apparatus at NMIs by comparison of Transfer Surface Temperature Standards
The aim of this comparison is to find the unknown systematic deviations and to work out a common used method for uncertainty budget.
Investigations led for laboratories to a better approach of surface temperature measurements using contact sensors and improvements in the calibration methods and procedures.
Bilateral comparisons carried out in this field between PTB and OMH, and between BNM-LNE and OMH showed a good general consistency of the results and have met industrial need.
The technical co-operation activities will consist of exchange of experience and comparison concerning the development of the basic apparatus, requirements and procedures for traceability, influence of thermophysical properties of surfaces, impact on thermal conditions effect.
Two types of surface sensors with instruments will be circulated and calibrated simultaneously in the temperature range between 50 °C and 300 °C, performing measurements at nominally 50 °C, 75 °C, 100 °C, 200 °C and 300 °C. The reference surface will be directed horizontally, the sensor will be applied vertically. The thickness of the reference surface should be at least 10 mm. The calibration could be done on targets with previously polished surfaces, with different thermal conductivity: aluminium and stainless steel. The sensors will be applied manually to the wall and are proposed to be calibrated also immersed in liquid bath before the contct with the reference surface. For a given laboratory, the time allowed for calibration is one month, including the travelling between tow laboratories. Greater collaboration between laboratories should, however, shed more light on the various sources of error and uncertainties linked with the calibration of surface sensors.
Final Report 2004-03-22
The starting date of the measurements was on 01.12.2001.
The first international comparison on surface temperature measurements has been performed within the EUROMET frame. The main objective with this exercise was to compare different types of contact sensors on different surface temperature measurement apparatus, on the basis of previous bilateral comparisons carried out in this field between PTB and OMH, and between BNM-LNE and OMH.
Nine European laboratories and the South-African laboratory CSIR-NML took part in the comparison. Two types of surface sensors with indicators were circulated and calibrated simultaneously in the temperature range between (50 ÷ 300)°C. The sensors were applied on heat-plates with different thermal conductivity: aluminium, copper and stainless-steel.
An analysis of the sources of uncertainty related to the calibration of surface sensors was drawn from the budgets submitted by the participants. The uncertainty consists of three main components: sources of uncertainty associated with the temperature in a well inside the reference block, with the temperature of the reference surface determined by extrapolation and with the temperature of the surface sensor. In the general part of the uncertainty evaluation “classical” uncertainty contributions were taken into account: stability, homogeneity and drift of the standard used inside the well of the reference block, reproducibility and resolution of the surface sensor, etc. The largest contributions to the uncertainty were pointed out.
Specific uncertainty contributions have been identified and studied: operator effect, influence of the reference target material, influence of ambient conditions, etc. The uncertainty budget does not take into account uncertainties arising from surface oxidation and influence of material thickness. To analyse the influence of the apparatus on the measurement results, a model test with a lowered surface was made.
In spite of the diversity of the calibration procedures and of the characteristics of each apparatus, the measurement results are strikingly close to one another. This project has shown that the participating National Metrology Institutes are able to calibrate sensors for surface temperature with adequate accuracy and the deviations among the NMIs are within the estimated uncertainties.
The detailed final report was delivered to each participant.