Patent ID: 6843123

Claim:
A flow rate sensor comprising: a sensor pipe arranged in parallel to a bypass of a fluid passage; a resistor group spirally wound around the sensor pipe and consisting of an even number of resistors having a resistance value changing according to the temperature and connected in series in the longitudinal direction of the sensor pipe; a reference resistor group consisting of a plurality of reference resistors connected in series to one another and connected in parallel to the aforementioned resistor group; a constant current source for flowing a constant current to the resistor group and the reference resistor group; a first differential circuit for detecting a potential difference between a connection point between the reference resistors and a connection point between the resistors; and a flow rate decision unit for deciding a flow rate of a fluid flowing in the fluid passage according to the potential difference output from the first differential circuit; the flow rate sensor further comprising: at least one bypass circuit having switch means for selectively shortcircuiting a part of the even number of resistors so as to perform bypassing; at least one flow rate range increasing differential circuit for detecting a potential difference between the bypass circuit and the connection point between the reference resistors; and a second flow rate decision unit for detecting the flow rate of the fluid flowing in the fluid passage according to the potential difference output from the flow rate range increasing differential circuit.