| 摘要 |
PURPOSE:To enhance measuring accuracy to a large extent by making the output, when a fluid is not flowed, constant regardless of temp., by controlling a first heat generating element so that the temp. of a flow speed detection element is raised by a definite value with respect to circumferential temp. in such a state that the fluid is not flowed. CONSTITUTION:The voltage between the base emitters of a transistor changes linearily with respect to temp. In order to keep the difference between the temp. o a flow speed detection element 13, when a fluid is not flowed, and circumferential temp. constant, it is necessary that the current Ih1 flowed to a transistor 11 for generating heat has relation of Ih1=CT+D. This CD is calculated experimentally. If resistors R6, R7, R4Vr are properly set, the difference between the temp. of the flow detection element 13 and circumferential temp. can be always kept constant even if circumferential temp. changes. By this method, the generation of heat by the first heat generating transistor 111 on the flow speed detection element 13 is controlled by a first drive circuit containing operational amplifiers 152, 153 and no current is flowed to a second heat generating transistor 112 for detecting a flow speed.
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