A system for measuring liquid flow based on heat loss of thick film NTC thermistors

Abstract

A system for measuring flow of liquids (water) based on heat loss was formed of two thick film segmented thermistors, power supply with constant voltages RCV, 8 voltage dividers RN, acquisition card and PC with custom IWF software. The thermistors were placed in two metal or plastic housings connected in series like and filled with liquid,(water).The first thermistor Th1 is referent and measures the temperature of water incoming to the sensor, while the second thermistor Th2 is the flow sensor and it is selfheated with self current at a constant supply voltage from power source. Using the command from the PC the RCV power source generates constant voltages for powering Th2 in steps of 2V per 5°C of input water temperature increase. The self-heating current I of the Th2 thermistor is measured vs. the water flow rate Q. The water flow rate is defined from the function Q=F(I). The acquisition card measures in multiplex 8 voltages on voltage dividers: each voltage is measured 10 times per second and the computer calculates the average value for each second.

Keywords

• sensor
• flow
• temperature
• thermistors