| 摘要 |
PURPOSE:To improve the accuracy of sensing frosted condition by a method wherein a variation in electric current caused by a variation in voltage is corrected in response to a characteristics of a motor. CONSTITUTION:Variation in electric current of an axial blower installed in a cooling unit is sensed by a current sensor 1 as frosting is advanced, and a voltage is sensed by a voltage sensor 2. These sensed values, reference current and reference voltage under non-frosted condition stored in a memory part 3 are compared by a comparator and calculator 4 so as to produce a defrosting start signal when they are reached to such a rate as determined by a rate setting unit 6. At this time, in order to prevent erroneous operation for the variation in voltage, the electric current is corrected by a function of the voltage to show an approximate value. That is, I=aV<3>+bV<2>+cV+D can be applied to make an approximate value, the coefficients (a), (b) and (c) are fed from the coefficient of correction setting unit 7 so as to perform a correction.
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