| 摘要 |
A heating resistor flow rate measuring instrument includes a sub-passage (3) disposed in a main passage (4). A heating resistor (1) and a thermally sensitive resistor (2) are disposed in the sub-passage (3). The sub-passage (3) comprises a first sub-passage having an upstream-side opening face substantially perpendicular to the forward direction of a fluid flow and a downstream-side opening face substantially parallel to the direction opposite to the forward fluid flow, and a second sub-passage having an upstream-side opening face substantially parallel to the forward direction of the fluid flow and a downstream-side opening face substantially perpendicular to the direction opposite to the forward fluid flow. The heating resistor (1) is disposed in the first sub-passage, and the thermally sensitive resistor (2) is disposed in the second sub-passage. The heating resistor (1) is heated to a temperature about 100° C.-300° C. higher than a fluid temperature Ta. The thermally sensitive resistor (2) is heated higher than the fluid temperature Ta by about {fraction (1/10 to ½ of the temperature to which the heating resistor (1) is heated. When the fluid flows in the forward direction, the heating resistor (1) outputs a value depending on the flow rate of the fluid. When the fluid flows in the opposite direction, the thermally sensitive resistor (2) is cooled to a temperature lower than that resulting when the fluid flows in the forward direction, and an electric current flowing through the heating resistor (1) is decreased. As a result, even when a pulsation occurs in the fluid, a precise flow rate can be measured because not only a plus effect caused by a backward flow is eliminated, but also a value corresponding to the backward flow is subtracted.
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