A Novel Accuracy Validation Method of Surface Temperature Measurement by the ReFaST Pyrometer

Accuracy validation of surface temperature by optical pyrometry is always a hard task. The measurement results of pyrometers have been compared with a thermocouple that was welded or embedded on/in the tested sample in the past. However, the measurement results of the thermocouple could hardly represent the surface temperature, because thermal equilibrium is difficult to achieve between the thermocouple and tested sample when the surface temperature is above 400 °C. In our previous research, the ReFaST pyrometer has been proposed, which measures the surface temperature and emissivity simultaneously. The accuracy validation of the ReFaST pyrometer is compared with a flat-type thermocouple which is fixed on the tested sample. However, the verification method by the flat-type thermocouple still has several shortcomings and needs to be improved. In this article, a novel accuracy validation method is proposed. By inserting the ReFaST pyrometer into a blackbody furnace, multiple reflectances are formed between the reflector and the tested surface, so the tested sample and the thermocouple always maintain thermal equilibrium during the measurement. Therefore, the measurement results of the thermocouple can represent the surface temperature accurately and the uncertainty of accuracy verification is decreased. We develop the apparatus and carry out experiments. Compared with a flat-type thermocouple, the uncertainty of accuracy verification is reduced by 81% at 750 °C. The temperature difference between the ReFaST pyrometer and thermocouple is 1.76 °C on average ranging from 700 °C to 1000 °C, and the standard uncertainty is 0.69 °C. Besides, the accuracy verification method proposed in this article is suitable for any type of pyrometer, as long as the reflector with a tube is in front of the pyrometer.