Patent ID: 8069718

Claim:
A thermal flowmeter having a thin film part formed on a substrate and a heater resistor disposed on the thin film part for measuring the flow rate of a fluid flow, said flowmeter comprising: a first temperature difference sensor disposed upstream of the heater resistor in the flow direction of the fluid; a second temperature difference sensor disposed downstream of the heater resistor in said flow direction; a first heating temperature sensor disposed on the thin film part of the flowmeter upstream of the first temperature difference sensor; a second heating temperature sensor disposed on the thin film part of the flowmeter downstream of the second temperature difference sensor; a heating control device that controls the heating current supplied to the heater resistor based on the temperature change of the first and second heating temperature sensors, so that the average temperature of the first and second heating temperature sensors settles to a value that exceeds the temperature of said fluid by a predetermined amount; and detection means for measuring the flow rate of the fluid according to the difference between the temperatures detected by the first and second temperature difference sensors.