Fully Printed PTC Based Heat Transfer Sensor Array as Liquid Level Sensor

Liquid levels must be monitored in almost any process involving liquids. Most level sensors are mounted inside the vessel containing the liquid. Herein, a fully screen-printed level sensor is demonstrated for external use. It consists of a vertical array of 16 pixels, each comprising a voltage divider of a positive temperature coefficient (PTC) element and a shunt resistor. The self-regulating PTC elements are heated with constant voltage. Heat flow out of the PTCs dictate their resistances and enables inference about their thermal surrounding. Water in a polypropylene container changes voltage levels by (33 ± 2) % compared to air. Applications with a glass container and household oil instead of water are also successfully tested. Both liquids yield a distinctive difference in signal and the sensor determines the height of the oil/water interface as well as the surfaces of the liquid. To further demonstrate the capabilities of the sensor, segregation of a water-oil mixture, slowed by a mixing agent, is observed in real time. This work offers an adaptable and simple alternative for external level sensing.