Analysis and optimization of a thermal sensor system for measuring water flow

A simple thermal sensor system was designed for measuring water flow in the water mains using the heat loss principle with a NTC thick film segmented thermistor as a self-heating sensor. Thick film segmented thermistors were screen printed on alumina substrate. NTC thermistor paste was formed of very fine Cu0.2Ni0.5Zn1.0Mn1.3O4 powder obtained by a combined mechanical activation/thermal treatment process, an organic vehicle and glass frit. The thermal sensor system was analyzed in the static and dynamic regime. A range constant voltage power supply was defined in the range 9-19 V for input water temperatures of 30-2 °C, maintaining a supply voltage in steps of 2 V for a change in 5 °C of input water temperature. This enables optimal operating power, i.e. heat generation on the self-heating thermistor. Measured calibration curves for different input water temperatures and input water flow rates were modeled, enabling interpolation of additional calculated curves to cover a wide range of input water temperatures.