Patent ID: 7650784

Claim:
A thermal type flow measuring apparatus comprising: a fixed temperature difference bridge circuit for controlling current flowing through a heat generating resistor at which the heating of the heat generating resistor is controlled so as to have a fixed temperature difference relative to the ambient temperature; wherein a flow rate of a fluid is detected by using a resistor which is arranged near the heat generating resistor; wherein the bridge circuit consists of a first serially connected circuit in which a first temperature sensitive resistor and a second temperature sensitive resistor are connected in series and a second serially connected circuit in which a third temperature sensitive resistor and a fourth temperature sensitive resistor are connected in series, and the first serially connected circuit and the second serially connected circuit are connected in parallel by connecting one end of the first temperature sensitive resistor and one end of the third temperature sensitive resistor, and connecting one end of the second temperature sensitive resistor and one end of the fourth temperature sensitive resistor; wherein the first, second, third and fourth temperature sensitive resistors are formed on a semiconductor base plate, and the first temperature sensitive resistor is formed on a diaphragm formed in the semiconductor base plate; wherein the first, second, third and fourth temperature sensitive resistors have the same resistance-temperature coefficient; and the second temperature sensitive resistor and the fourth temperature sensitive resistor are arranged close to each other in order that the second temperature sensitive resistor and the fourth temperature sensitive resistor are held at the same temperature, or the third temperature sensitive resistor and the fourth temperature sensitive resistor are arranged close to each other in order that the third temperature sensitive resistor and the fourth temperature sensitive resistor are held at the same temperature.