| 摘要 |
PROBLEM TO BE SOLVED: To provide an underwater heater which can lower the water temperature at nighttime, without causing complications in the structure and increase in the cost. SOLUTION: This underwater heater comprises a heater portion 1 having heat-generating wires; a thermostat portion 2 for feeding power to the heat-generating wires, when water temperature is lower than a set value, and for stopping the power feed, when water temperature is higher than the set value, thereby controlling the water temperature; and an optical sensor 38 for detecting the brightness of the surrounding, lowering the set water temperature in the thermostat portion 2, on the basis wherein the brightness value detected with the optical sensor 38 becomes smaller than the set value, and enhancing the set water temperature in the thermostat portion 2 to return to the original value, on the basis wherein the brightness value detected with the optical sensor 38 becomes larger than the set value. COPYRIGHT: (C)2008,JPO&INPIT
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