| 摘要 |
PURPOSE:To prevent thermoelectromotive force from being superposed upon voltage fluctuation to cause an error in measurement by alternating the polarities of a current applied to a sensor and canceling the thermoelectromotive force generated at a terminal of the sensor. CONSTITUTION:One terminal 132a of the 2nd contact 132 of a switch 13, one terminal 133a of the 3rd contact 133, and the negative terminal 12b of a constant current source 12 are grounded. Then when the switch 13 is operated repeatedly between 1st and 2nd stages through the operation of an arithmetic controller 16, the polarities of currents supplied to a 1st terminal 14 and a 2nd terminal 15 are alternated. Further, an amplifier 25 detects and amplifies the voltage variation between one terminal 20a of the sensor 20 and the other terminal 20b as a signal. The output of this amplifier 25 is converted by an A/D converter 26 into a digital signal, which is averaged and linearized by the controller 16, so that temperature is displayed 27. Thus, the measurement error is eliminated. |
