Innovative Low-Temperature Calibration System for Infrared Thermometers in Frozen Food Industry: Effects of Measurement Distance and Temperature Uniformity

Dhonluck Manop¹Salisa Wangtong²Worasit Palkawong Na Ayuthaya³Narudom Noulkhow⁴Panya Khaenamkaew^1*

• ¹Department of Basic Science and Physical Education, Faculty of Science at Si Racha, Kasetsart University, Si Racha Campus, Si Racha, Thailand
• ²Department of Nautical Science and Maritime Logistics, Faculty of International Maritime Studies,, Kasetsart University, Si Racha Campus, Si Racha, Thailand
• ³Department of Resources and Environment, Faculty of Science at Si Racha, Kasetsart University, Si Racha Campus, Si Racha, Thailand
• ⁴Policy and Strategy Department, National Institute of Metrology (Thailand), Phatumthani, Thailand

The calibration of infrared thermometers (IRTs) in the frozen food industry is hindered by condensation on temperature reference sources in subzero environments, resulting in measurement errors and uncertainty. This study investigated a novel closed-cylinder pneumatic calibration system designed to eliminate condensation using a controlled argon gas purge. The effects were systematically evaluated of gas pressure, flow rate, and measurement distance (tube length) on calibration accuracy. At −15 °C, the introduction of argon at 2 kg/cm² and 25 L/min effectively prevented ice formation on the calibration target. The system was tested using tube lengths of 30 cm, 50 cm, and 100 cm, yielding expanded uncertainties ranging from 0.62 °C to 0.74 °C across all temperature set points. The shortest tube length (30 cm) provided the highest precision with minimal correction required, while 50 cm offered a reliable alternative with slightly increased uncertainty. In contrast, 100 cm introduced greater variability due to the increased spot size and spatial nonuniformity. Based on the results, the sealed calibration system enabled accurate and reproducible IRT calibration under subzero conditions, particularly at shorter distances. This solution should be especially relevant for applications in frozen food logistics, where precision temperature monitoring is essential for product safety and quality assurance.