| 摘要 |
PURPOSE:To prevent malfunctions and to improve reliability with a safety device by using a current transformer to detect the energization of a heater. CONSTITUTION:The detection signal received from a current transformer CT is detected as the both-end voltage (a) of a resistance R1 and the output (e) is obtained via a detecting part 51, a rectifying part 52 and a comparing part 53. In a normal state of the output waveform (e), a transistor (TR) Q2 of a selecting part 54 is turned on and off by an AC/DC converting part 55. Thus a triac TR is driven with control via a phototriac PT. Then a TR Q1 is turned on when the voltage value (f) rises up to the level of the Zener voltage ZD1 in an abnormal state of the waveform (e). Thus both TRs Q3 and Q4 are turned on and keep their self-hlding actions. As a result, a TR Q5 is turned off to open the contact point of a relay RL. Then the supply of an AC power supply is cut and a protection state is secured.
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