| 摘要 |
<p><P>PROBLEM TO BE SOLVED: To provide a thermal flowmeter that enables flow measurement with high accuracy by using one flow sensor with low power consumption in a wide flow rate measuring range. <P>SOLUTION: The flow sensor is provided with a first and a second temperature detecting sensor element with a heater element between them in a fluid conducting direction, and an ambient temperature detecting sensor element detecting ambient temperature thereof. A first heater control means maintains the heater temperature of the heater element at a fixed temperature degree higher than the ambient temperature to measure the flow rate with low consumption. A second heater control means maintains the mean value of detected temperatures measured by the first and second temperature detecting sensor elements at a fixed temperature degree higher than the ambient temperature to improve the flow rate measurement in a high flow area and expand the flow rate measuring range in response to the change of the ambient temperature. Then a switch means alternatively uses the first or second heater control means in response to the flow rate of the fluid, and then a flow rate measuring means measures the flow rate of the fluid from the difference between the detected temperatures of the first and second temperature detecting sensors. <P>COPYRIGHT: (C)2003,JPO</p> |
