| 摘要 |
PROBLEM TO BE SOLVED: To continue dew-point temperature measurement without interruption during not only automatic cleaning control of a mirror surface but also dew-point temperature measurement control, thereby eliminating a need for a manual cleaning of the mirror surface or provision of an additional device for removing a condensate.SOLUTION: A dew-point meter 1 is handled as a measuring dew-point meter for initial operation, and a dew-point meter 2 is handled as an auxiliary dew-point meter for initial operation. The dew-point meters 1 and 2 are put under dew-point temperature measurement control, and dew-point temperatures of the dew-point meters 1 and 2 are respectively defined as valid and invalid. On the dew-point meter 1 whose measurement value is defined as valid, determination of the mirror surface being normal/abnormal is inhibited; while on the dew-point meter 2 whose measurement value is defined as invalid, determination of the mirror surface being normal/abnormal is permitted. In a case where the mirror surface of the dew-point meter 2 is determined to be abnormal, the dew-point meter 2 is put under automatic cleaning control, and, after the automatic cleaning control, the dew-point meter 2 is reverted to dew-point temperature measurement control and defined as valid, followed by putting the dew-point meter 1 under automatic cleaning control. Under the automatic cleaning control, condensate possibly attached to the mirror surface is removed by causing the condensate to evaporate or sublimate. |
