Gas flow rate measuring apparatus

An apparatus for measuring a gas flow rate, which includes one or a plurality of resistors arranged in a gas passage, and a gas flow rate detection circuit for outputting a gas flow rate detection signal in accordance with a gas flow rate flowing in the gas passage by detecting any one of currents flowing through the resistors and voltages generated in accordance with the currents, said apparatus comprising:

• a fixed resistor connected in series to one of the resistors;
• a first A/D converter circuit for converting an input voltage into a digital signal and outputting the digital signal by using a voltage generated in a combined resistance of the resistor and said fixed resistor as the input voltage;
• a second A/D converter circuit for converting an input voltage into a digital signal and outputting the digital signal by using a voltage generated in said fixed resistor as the input voltage;
• and
• a first digital arithmetic circuit for dividing the digital output signal from said first A/D converter circuit by the digital output signal from said second A/D converter circuit, wherein
• a digital output signal of a gas temperature signal is obtained by said first digital arithmetic circuit.

An apparatus for measuring a gas flow rate, which includes a heat resistor arranged in a gas passage;

• a first fixed resistor connected in series to the heat resistor;
• a gas temperature measuring resistor arranged in the gas passage;
• a second fixed resistor connected in series to the gas temperature measuring resistor;
• current control means for controlling a current flowing through a bridge circuit including the heat resistor, the first fixed resistor, the gas temperature measuring resistor, and the second fixed resistor;
• and a gas flow rate detection circuit for outputting a gas flow rate detection signal in accordance with a gas flow rate flowing in the gas passage based on the current flowing through the bridge circuit, said apparatus comprising:
• an A/D converter circuit for converting an input voltage into a digital signal based on a reference voltage and outputting the digital signal by using any one of a voltage at a junction of the heat resistor and the first fixed resistor and a voltage at a junction of the gas temperature measuring resistor and the second fixed resistor as the reference voltage, and using a voltage generated in a combined resistance of the gas temperature measuring resistor and the second fixed resistor as the input voltage, wherein
• a digital output signal of a gas temperature signal is obtained by said A/D converter circuit.