| 摘要 |
<p>PROBLEM TO BE SOLVED: To provide a flow sensor that is seldom affected by variations in the resistance value of each temperature-measuring resistor. SOLUTION: The flow sensor 1 includes a heating element 2 placed in a flow passage, a first temperature-measuring element 3 placed on the upstream side from the heating element 2 within the flow passage, and a second temperature-measuring element 4 placed on the downstream side from the heating element 2. A heating device 5 has a current source 6 supplying a constant current I 2 to the heating element 2 to heat the same. The non-inverted input terminal and inverted input terminal of a temperature measuring circuit (differential amplifier) 7 are connected, respectively, to (d) and (e) points at both of the terminals of the heating element 2 to detect the voltage between the terminals of the heating element 2 to detect the temperature of the heating element 2. The first temperature-measuring element 3 and the second temperature- measuring element 4 are connected in series with each other, and a constant current I 1 is supplied thereto by a constant current source 9. A voltage difference detecting device 10 includes a comparator 11 detecting the voltage between the terminals of the first temperature-measuring element 3, a comparator 12 detecting the voltage between the terminals of the second temperature-measuring element 4, and a comparator 13 comparing the output voltage of the comparators 11, 12.</p> |
