| 摘要 |
PURPOSE:To reduce the scale of the facilities and to simplify the constitution of an electric heater device by unifying a temperature controller containing the combination of plural positive characteristic thermistors and a switch circuit which gives instructions to these thermistors to switch temperatures. CONSTITUTION:The relays 29E-29A of a switch circuit 28 are actuated successively in the order of lower control temperatures with command signals given from a setting circuit 31 and the positive characteristic thermistors 20E-20A of a temperature controller 12 are successively actuated to perform the temperature control of a pipeline 1 before the pipeline 1 is heated up to a prescribed temperature by an electric heater 11. If the Curie point of the thermistor 20A is set at 300 deg.C, the resistance value of the thermistor 20A is reduced as long as the temperature of the pipeline 1 is kept at <=300 deg.C. As a result, the most of the power supply voltage is applied to a heating line 15 and the pipeline 1 is heated. Then the resistance value of the thermistor 20A increases suddenly when the temperature of the pipeline 1 exceeds 300 deg.C. As a result, the power supply voltage applied to the heater 11 is reduced. In such a constitution, the facilities for detection and control of temperatures can be unified.
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