| 摘要 |
PURPOSE:To enable setting of a low rotational speed while preventing sudden stall by elevating the lower limit speed of a variable speed range, when the rotational speed is lower than a predetermined value, and then controlling the firing phase angle within the new variable speed range. CONSTITUTION:In an oil fan heater 5, a microcomputer 5 sets a variable speed range. The microcomputer 5 determines the rotational speed of an induction motor 2 based on the difference between the temperature detected through a temperature sensor 10 and the temperature set in a room temperature setter 9. The microcomputer 5 judges whether the rotational speed is within the variable speed range, and if it is not the rotational speed is corrected to come within the range. The microcomputer 5 further detects the rotational speed of the induction motor 2 and judges whether the detected speed is lower than a predetermined level. If it is lower than the predetermined level, lower limit speed of the variable speed range is elevated and the firing phase angle is controlled within the new range. |
