| 摘要 |
PURPOSE:To effectively control the firing angle of a thyristor without any influence to the controlling operation of the firing angle even if the operation of a counter stops temporarily at the data setting time by alternately switching and employing two counters having the same counting function. CONSTITUTION:The output voltage from a thermocouple 6 provided in an electric furnace 2 is corrected at the reference temperature by a reference temperature correcting circuit 7 and is applied to an isolation amplifier (IP) 8. The output of the IP is inputted through an operational amplifier 10 to an A/D converter 11, and is fed as a digital data D1 to a CPU12. The CPU12 calculates the PID from the actual furnace temperature and the set temperaure, and calculates the power necessary for heating to set the prescribed set temperature. The calculated result of the CPU12 is outputted as the number of pulses corresponding to the prescribed firing angle, and the pulses corresponding to the firing angle are counted by the counter 31 or 32, thereby controlling the conduction of a thyristor 4. |
