| 摘要 |
PROBLEM TO BE SOLVED: To provide a liquid state detection sensor capable of achieving a high speed of feedback control for stabilizing the power to be supplied to a heating resistor, and enhancing detection accuracy of a liquid state such as a concentration of a specific component in liquid. SOLUTION: Concerning the heating resistor 114 for detecting a urea concentration in urea aqueous solution, a closed loop circuit is constituted through the ground by connecting a power source part 390, the heating resistor 114, an MOS-FET 350 and a current detection resistance 360 together in this order. A gate voltage of the MOS-FET 350 is controlled by an operation amplifier 370, and the control is performed by comparison between a potential S appearing on one end of the current detection resistance 360 and a potential T of a reference power source 380, and thereby a constant-current circuit is formed. Since the current detection resistance 360 is grounded, a differential amplifying circuit for detecting a potential difference between both ends of the current detection resistance 360 is not required, and the speed of the feedback control to the MOS-FET 350 by the operation amplifier 370 can be heightened. COPYRIGHT: (C)2009,JPO&INPIT
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