| 摘要 |
A liquid state detection sensor in which temperature information of a urea aqueous solution is obtained on the basis of a voltage value acquired after the start of energization of a heating resistor corresponding to a resistance value of the heating resistor (S 1 -S 6 ). Damage to the heating resistor is prevented by suspending the energization if the thus-obtained temperature is lower than or equal to the freezing point (S 7: yes and S 8 ). If the temperature is higher than the freezing point (S 7: no), a voltage value corresponding to a resistance of the heating resistor after a lapse of 700 ms (S 10 and S 11 ) and a urea concentration of the urea aqueous solution are determined from a difference DeltaV from the previously acquired voltage value. A more accurate urea concentration can be detected by making a correction using the previously obtained temperature information of the urea aqueous solution (S 13 -S 18 ).
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