| 摘要 |
<p>PROBLEM TO BE SOLVED: To prevent a flammable fluid to be inspected from being fired and exploded while protecting a flow sensor against aging by preventing the ambient temperature of the heating element in a thermal flow sensor from rising unduly. SOLUTION: The flow sensor comprises a heating element 112 and a temperature-sensitive body 104-1 for flow rate detection disposed to be effected by the heating element 112 and a passage for conducting fluid to be inspected is formed such that heat is transmitted from the heating element 112 to the fluid to be inspected and absorbed thereby. A bridge circuit 104 is formed including the temperature-sensitive body 104-1 for flow rate detection and a temperature-sensitive body 104-2 for temperature detection and the output therefrom is inputted through a differential amplifier circuit 106 and an integrating circuit 108 to the base of a transistor 110 in order to control current supply thereto from a power supply. Current supply to the transistor 110, and thereby to the heating element 112, is controlled such that the temperature sensing results of the temperature-sensitive body 104-1, i.e., the output from the bridge circuit 104, matches a target level. Flow rate of the fluid to be inspected is detected based on the voltage being applied to the heating element 112.</p> |
