A Thermal Sensor for Water Using Self-Heated NTC Thick-Film Segmented Thermistors

A simple thermal (heat loss) sensor system was designed in a small plastic tube housing using a negative thermal coefficient (NTC) thick-film thermistor as a self-heating sensor. The voltage power supply [range constant voltage (RCV)-range constant voltage] uses the measured input water temperature to select the applied voltage in steps (up and down) in order to enable operation of the sensor at optimal sensitivity for different water temperatures. The input water temperature was measured using a “cold” NTC thick-film segmented thermistor. The measured calibration curves were modeled. Additional calculated curves were interpolated between the experimental curves in fine steps to cover each temperature of input water and can be used for determining the water volume flow rate or water velocity. The realized prototype flow meter inertia, stability, repeatability, and tolerance were measured and analyzed. The proposed intelligent RCV thermal flow meter system will include a smart power supply with range-constant-voltages (auto-range), a simple acquisition card and custom designed flow meter software.