| 摘要 |
PURPOSE:To exactly measure the physical quantity by eliminating the influence of an inter-earth voltage difference and deriving the impedance of a sensor from two detection potentials detected in accordance with two different load impedances by a physical quantity determining means. CONSTITUTION:To a signal input terminal 11 and a power supply voltage VDD, a series connecting circuit of a load resistance R1 and a transistor TR1, and a series connecting circuit of a load resistance R2 and a transistor TR2 for constituting an impedance control means are connected in parallel, respectively. Accordingly, when the TR1 is turned on and the TR2 is turned off, the resistance R1 is connected to a thermistor 1, and the potential by a resistance division of the resistance of the thermistor 1 of the power source VDD and the resistance R1 comes to a detection potential Vd. Also, when the TR1 is turned off and the TR2 is turned on, the resistance R2 is connected to the thermistor 1, and the potential by a resistance division of the resistance of the thermistor 1 of the voltage VDD and the resistance R2 comes to the potential Vd. This potential Vd is read in a 1-chip microcomputer 6 through a delaying circuit 4 and an A/D converter 5, the resistance of the thermistor 1 is calculated, a temperature is determined from the resistance, and it is displayed 8 through a driving circuit 7. |
