A thermal mass flowmeter suitable for interfacing with a microcomputer

The design and construction of a simple and inexpensive mass flowmeter based on a miniature bead thermistor and suitable for direct interfacing with a microcomputer or dedicated microprocessor is reported. Parameter estimation techniques are employed to derive the nonlinear relationship between the potential difference across that part of the thermistor circuit connected to the interface and the mass flowrate of air at different working pressures. It is shown that the meter is accurate generally to within 8% of the true mass flowrate provided that the temperature of the bead does not vary by more than 30K. The meter has a relatively short response time, and maximum temperature safety control can be incorporated with ease.