Patent ID: 8844350
Filing Date: 2014-09-30
Classification: G01F

Abstract:
1. A flow quantity measuring apparatus comprising: a sensor chip that has a circuit board, which includes a thin wall portion, wherein a wall thickness of the thin wall portion, which is measured in a direction perpendicular to a plane of the circuit board, is smaller than that of an adjacent area of the circuit board that is adjacent to the thin wall portion; a heat generating resistor that is placed on the thin wall portion, wherein the heat generating resistor generates heat when a heating electric current flows through the heat generating resistor; first and second upstream-side temperature sensitive resistors that are placed on the thin wall portion and are located on an upstream side of the heat generating resistor in a flow direction of fluid, wherein a resistance value of each of the first and second upstream-side temperature sensitive resistors is variable depending on a temperature; and first and second downstream-side temperature sensitive resistors that are placed on the thin wall portion and are located on a downstream side of the heat generating resistor in the flow direction of the fluid, wherein a resistance value of each of the first and second downstream-side temperature sensitive resistors is variable depending on a temperature, wherein: the first upstream-side temperature sensitive resistor and the first downstream-side temperature sensitive resistor are connected with each other in series to form a first series circuit; the second downstream-side temperature sensitive resistor and the second upstream-side temperature sensitive resistor are connected with each other in series to form a second series circuit; the first series circuit and the second series circuit are connected with each other in parallel to form a bridge circuit; the first upstream-side temperature sensitive resistor and the first downstream-side temperature sensitive resistor have a generally identical characteristic with respect to a change in the resistance value thereof relative to the temperature; the second downstream-side temperature sensitive resistor and the second upstream-side temperature sensitive resistor have a generally identical characteristic with respect to a change in the resistance value thereof relative to the temperature; the bridge circuit includes a first conductive line, through which a midpoint electric potential of the first series circuit is outputted, and a second conductive line, through which a midpoint electric potential of the second series circuit is outputted; the first series circuit includes a first connection, which is located at a midpoint between the first upstream-side temperature sensitive resistor and the first downstream-side temperature sensitive resistor and is connected with the first conductive line; the second series circuit includes a second connection, which is located at a midpoint between the second downstream-side temperature sensitive resistor and the second upstream-side temperature sensitive resistor and is connected with the second conductive line; the first connection and the second connection are placed on the sensor chip and are located on a center line of the heat generating resistor, which extends in a direction generally perpendicular to the flow direction of the fluid; and the first conductive line and the second conductive line are branched from the first series circuit and the second series circuit, respectively, on the sensor chip.