Patent ID: 8051708

Claim:
A temperature measuring circuit in a flowmeter, comprising: first and second resistor-type temperature sensors which are provided at first and second measuring positions in the flowmeter and form a serial connection state when one ends of the sensors are connected to each other; a first electric wire which includes a line-to-line resistor and is connected to another end of the first resistor-type temperature sensor; a voltage reference connected to the first electric wire through a power supply resistor; a second electric wire which includes a line-to-line resistor and is connected to the one ends of the first and second resistor-type temperature sensors; a third electric wire which includes a line-to-line resistor and is connected to another end of the second resistor-type temperature sensor; a reference resistor in which one end thereof is connected to the third electric wire and another end side thereof is grounded; a switching device that is connected to both of the second electric wire and the third electric wire and turns those electric wires to a conductive state or a non-conductive state; a multiplexer that selects any one of the first electric wire, the second electric wire, the third electric wire, and the grounded side of the reference resistor; an A/D converter that performs A/D conversion on divided voltages selected by the multiplexer; and an arithmetic operation/control device that controls the switching device and receives a signal from the A/D converter, wherein the arithmetic operation/control device determines a value of the line-to-line resistor by subtracting a resistance value determined as a product of a voltage ratio based on the divided voltages and a value of the reference resistor in the non-conductive state between the second electric wire and the third electric wire from a resistance value determined as a product of a voltage ratio based on the divided voltages and a value of the reference resistor in the conductive state therebetween.