Patent ID: 7591177

Claim:
A flow sensor comprising: a bypass passage; a sensor passage; and a bridge circuit including heat-generating resistance wires that constitute a part of the bridge circuit and are wound around the sensor passage, the flow sensor determining a total flow rate of a fluid that flows in a branched manner through said bypass passage and said sensor passage at a predetermined flow ratio, the total flow rate being determined by detecting, as an unbalance of said bridge circuit, heat transfer caused by said fluid flowing through the sensor passage, the total flow rate being outputted as a sensor output of the flow sensor, wherein said bypass passage includes a plurality of fine flow passages each having a cross-section defined by a substantially linear edge and a curve in contact with the substantially linear edge, and a ratio of an equivalent hydraulic diameter (d) of the fine flow passages to a common logarithm of a length (T) of the fine flow passages is 0.27 or less.