| 摘要 |
PROBLEM TO BE SOLVED: To provide an electric floor-heating apparatus, in which a breaker does not open a circuit to an overcurrent, and a harmonic noise, as is seen in a phase control, is not produced, when a floor heating is conducted in a comparatively spacious room. SOLUTION: A plurality of time sequence duty-cycle, in which ON-OFF are repeated, are formed by combining constant ON-time and sets of OFF-time different from each other. In each of the time sequences, timing for switching-on is shifted by a predetermined time to form groups of time sequences. In an analogous fashion, a plurality of groups of time sequences are created, which are classified by the length of OFF-time. Those groups are arranged in decreasing order of OFF-time. Current passing through heating units in ON-time at an arbitrarily selected group of time sequences are summed up. When the sum total exceeds a predetermined value, the control step returns in succession from a selected group to a group of sequences of longer OFF-time, until the value becomes lower than the predetermined time. After elapse of a predetermined time, while it is confirmed that a lower value current flows in the previously selected group of tie sequences, the step returns in succession to the initial group of time sequences.
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