Temperature Response, Time Delay, and Hysteresis Loop of Heat Loss Flowmeter Thermistors

A heat loss flowmeter for water was made of two negative temperature coefficient (NTC) thick film thermistors Th1 and Th2 and placed in a metal housing. The first thermistor Th1 is cold and measures input water temperature <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${T} _{\text {w}}$ </tex-math></inline-formula>, and the second thermistor Th2 is self-heated at a constant voltage and measures water flow rate Q. At first temperature responses T(Q), heat loss and time delay <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${t} _{\text {d}}$ </tex-math></inline-formula> were measured and analyzed; then a temperature hysteresis loops of self-heating thermistor at switching waterflow regime was measured. The electrical responses I(Q) were measured using the flowmeter and digital acquisition card (DAC). An independent ultrasonic flowmeter was used in series with a novel heat loss flowmeter. The current values of temperature T(Q, t) of the water flow Q(t) were obtained using Steinhart-Hart equation for thermistors. Input water temperature <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${T}_{\text {w}}$ </tex-math></inline-formula> was used as a parameter (in the range of 5 °C–25 °C). The maximum thermistor power dissipation was less than 1 W. The inaccuracy of the water flow rate measurement was estimated to be less than 3%. The measuring flowmeter range of 0.003–0.3 L/s (1/2 in pipe) is suitable for measuring water consumption in households.