| 摘要 |
PURPOSE: To correctly detect a stagnant state generated when the flowing direction is reversed by detecting temperatures on the right and left of the flowing direction of a heat-generating band, a heating temperature of the heat-generating band and a heating outside temperature in the periphery of the heat-generating band, and comparing the temperature with preliminarily stored related data. CONSTITUTION: In a flow direction-judging means 24 of a flow direction-detecting part 20, related data stored in a related data memory means 21 are compared with a first temperature difference and a second temperature difference calculated by a first temperature difference-calculating means 22 and a second temperature-calculating means 23, thereby to judge whether the flow is directed forward or rearward or is stagnant. For instance, when the second temperature differenceΔT2 is larger than a predetermined value, the flow is judged to be stagnant irrespective of the first temperature differenceΔT1. When the flow direction is reversed minutely moving in the forward direction Fa or the backward direction Fb, that is, when the flow is stagnant, the stagnant state is not detected correctly only by detecting the sign of the first temperature differenceΔT1. However, if the relation to the second temperature differenceΔT2 is employed, the stagnant state can be correctly detected.
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