Digital temperature compensation of a thermistor flowmeter
The temperature compensation of a thermistor flowmeter is accomplished digitally, thus simplifying the compensation problem by replacing required hardware with software. The resistance-temperature curve of the thermistor is a least-squares fit to a logarithmic function whose coefficients are stored in computer memory. Signals representing the temperature of the heated thermistor and the ambient temperature are digitised and converted to temperature values based on the stored resistance-temperature curve. In this case the signals are obtained from a single thermistor switched between the high and low overheat modes. The thermistor temperature T, the ambient temperature Ta, and the electrical power input are used to form the dissipation factor (K=P/(T-Ta)) which calibrates the flowmeter when plotted against velocity. Results from calibration experiments on a thermistor flowmeter designed for use in human coronary arteries are presented to demonstrate the viability of the method.
