Design of a scanning thermocouple inhomogeneity

Inhomogeneities are known to develop within thermoelements exposed to elevated temperatures, resulting in temperature measurement errors and reduced energy efficiency. During process, it is important to determine how much the inhomogeneities affect the measurement result. Thermoelectric inhomogeneity is important factor of the calibration for budget uncertainty calculation. It is normally assessed by gradual, insertion of a thermocouple into a furnace or liquid bath. But, the length that can be scanned by using this equipment typically limited. It need an equipment to scan more length of wire thermocouple to see characteristic of thermocouple. This paper described development design double gradient method for measurements of inhomogeneities in type K and T thermocouples with various diameter and temperature scanning using hot air that can produce heating process up to 600 °C with some sensor to detection real temperature output from hot air source. Therefore, an equipment with a short, movable heating zone to scan along the thermocouple while both the measuring and reference junctions using ice bath are kept at 0 °C. The design of the equipment system was focused on measuring the stability of hot air and controlling the movement of the stepper motor control using a microcontroller. Interpretation of the measurement results and calculation of inhomogeneity using movable heating zone of type K and T thermocouples of the uncertainty budget is presented.