Search

In the framework of the HiTeMS project of the European Metrology Research Pogramme (EMRP) a new multi-wavelength device for measurement of high temperatures in industrial applications was developed at INRIM. The apparatus takes advantage of the ultra-violet operation with working wavelengths from 350 nm up, which reduces the possible errors connected with the multi-wavelength approach. The instrument has been characterised in terms of optical and electronic behaviour and some laboratory trials were carried out to verify the reliability of the multi-wavelength approach. The true temperature of a blackbody source at 1300 °C with optical windows of unknown spectral transmittance interposed has been defined. By applying an approach that allows a result to be accepted when a threshold limit is reached, it was found that, when an acceptable result can be obtained, errors are comprised within less than 1% of the temperature of the source. Three others single-band thermometers, at 508 nm, 650 nm and an IR broadband 0.8–1.1 μm, were also used to the purpose of a comparison. It has been found that, when the multi-wavelength approach is applicable, it provides generally better or in few cases, at worst similar results of corrected single-wavelength thermometers.

A precision infrared thermometer was constructed and was used to study an absolute calibration technique between the freezing points of tin (232°C) and copper (1085°C). This technique is based onto a calibration of the thermometer at four freezing points (Sn, Zn, Al and Cu) and on the assumption of an empirical equation to relate the output signal of the thermometer to temperature. It was found that the thermometer can be calibrated in terms of ITS-90 temperatures with an uncertainty at a 99% confidence level of ±0.04°C. This paper reports on the past achievements as well as on the developments under way that are aimed to a simplification of the design and operation of the thermometer. These developments include the replacement of the Si PbS detector previously used with an InGaAs photodiode and the design of a much simpler optical system.

Cylindrical blackbody cavities are analysed in view of their use as transfer sources for comparing pyrometers. Attention is given to the effect of temperature gradients on the comparison accuracy. It is shown that temperature gradients have a limited effect even when the working wavelengths of the pyrometers to be compared are largely different.