Effect of palm oil temperature on thermal losses of PTC sensor designed for overfill protection using current-voltage characteristic

Abstract

Characteristic of positive temperature coefficient (PTC) sensor can be described using current-voltage curve which depends on thermal properties of medium. The PTC sensor for overfilling protection designed for palm oil (CPO) container cannot identify the medium liquid with high temperature and high viscosity due to the overlapping of current voltage curve. For this case, a signal of worst-case alarm is generated. This paper presents the effect of CPO temperature on thermal losses of the PTC sensor represented by thermal resistance factor between the sensor and the medium surrounding it. A type of EPCOS B59050D1100 PTC sensor was characterized in two mediums; CPO and still air, to simulate “full” and “empty” status. The sensor responds was then observed through the current-voltage curve at different temperature from 300 K to 360 K. The thermal resistance were then obtained from the modeling of current voltage curve, resulting the values of 125 K/W for CPO and 343 K/W for still air with 63.5% in difference between both mediums. Using proposed two points method, the effect of medium temperature on thermal resistance can be eliminated and reduced, where the Rw variation is less than 3.15% for palm oil and 4.5% for still air. This result is within the normal operation tolerance below 5% and can be used safely to determine the status whether the sensor is in still air or in palm oil medium.